Multiplexing https://store.theartofservice.com/the-multiplexing-toolkit.html.

Multiplexing

4G Multiplexing and access schemes
The Migration to 4G standards incorporates elements of many early technologies and many solutions use code (a cypher), frequency or time as the basis of multiplexing the spectrum more efficiently. While Spectrum is considered finite, Cooper's Law has shown that we have developed more efficient ways of using spectrum just as the Moore's law has shown our ability to increase processing.

Recently, new access schemes like Orthogonal FDMA (OFDMA), Single Carrier FDMA (SC-FDMA), Interleaved FDMA, and Multi-carrier CDMA (MC-CDMA) are gaining more importance for the next generation systems

WiMax is using OFDMA in the downlink and in the uplink

The other important advantage of the above-mentioned access techniques is that they require less complexity for equalization at the receiver. This is an added advantage especially in the MIMO environments since the spatial multiplexing transmission of MIMO systems inherently require high complexity equalization at the receiver.

In addition to improvements in these multiplexing systems, improved modulation techniques are being used. Whereas earlier standards largely used Phase-shift keying, more efficient systems such as 64QAM are being proposed for use with the 3GPP Long Term Evolution standards.

Code division multiple access Code division multiplexing (Synchronous CDMA)
Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings

Code division multiple access Code division multiplexing (Synchronous CDMA)
Each user in synchronous CDMA uses a code orthogonal to the others' codes to modulate their signal

Multiplexing In telephony, George Owen Squier is credited with the development of telephone carrier multiplexing in 1910.

Multiplexing The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the high-level communication channel into several low-level logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, can extract the original channels on the receiver side.

Multiplexing A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX).

Multiplexing Inverse multiplexing (IMUX) has the opposite aim as multiplexing, namely to break one data stream into several streams, transfer them simultaneously over several communication channels, and recreate the original data stream.

Multiplexing - Types of multiplexing
Multiplexing technologies may be divided into several types, all of which have significant variations: space-division multiplexing (SDM), frequency-division multiplexing (FDM), time-division multiplexing (TDM), and code division multiplexing (CDM).

Multiple variable bit rate digital bit streams may be transferred efficiently over a single fixed bandwidth channel by means of statistical multiplexing, for example packet mode communication. Packet mode communication is an asynchronous mode time-domain multiplexing which resembles time-division multiplexing.

Digital bit streams can be transferred over an analog channel by means of code-division multiplexing (CDM) techniques such as frequency-hopping spread spectrum (FHSS) and direct-sequence spread spectrum (DSSS).

In wireless communications, multiplexing can also be accomplished through alternating polarization (horizontal/vertical or clockwise/counterclockwise) on each adjacent channel and satellite, or through phased multi-antenna array combined with a multiple-input multiple-output communications (MIMO) scheme.

Multiplexing - Space-division multiplexing
Wired space-division multiplexing is typically not considered as multiplexing.

Multiplexing - Space-division multiplexing
These techniques may also be utilized for space diversity (improved robustness to fading) or beamforming (improved selectivity) rather than multiplexing.

Multiplexing - Frequency-division multiplexing
Frequency-division multiplexing (FDM) is inherently an analog technology. FDM achieves the combining of several signals into one medium by sending signals in several distinct frequency ranges over a single medium.

One of FDM's most common applications is the old traditional radio and television broadcasting from terrestrial, mobile or satellite stations, using the natural atmosphere of Earth, or the cable television. Only one cable reaches a customer's residential area, but the service provider can send multiple television channels or signals simultaneously over that cable to all subscribers without interference. Receivers must tune to the appropriate frequency (channel) to access the desired signal.

A variant technology, called wavelength-division multiplexing (WDM) is used in optical communications.

Multiplexing - Time-division multiplexing
Time-division multiplexing (TDM) is a digital (or in rare cases, analog) technology. TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver. If done sufficiently quickly, the receiving devices will not detect that some of the circuit time was used to serve another logical communication path.

Multiplexing - Time-division multiplexing
Consider an application requiring four terminals at an airport to reach a central computer. Each terminal communicated at 2400 bit/s, so rather than acquire four individual circuits to carry such a low-speed transmission, the airline has installed a pair of multiplexers. A pair of 9600 bit/s modems and one dedicated analog communications circuit from the airport ticket desk back to the airline data center are also installed.

Multiplexing - Polarization-division multiplexing

Multiplexing - Polarization-division multiplexing
Polarization-division multiplexing uses the polarization of electromagnetic radiation to separate orthogonal channels. It is in practical use in both radio and optical communications, particularly in 100 Gbit/s per channel fiber optic transmission systems.

Multiplexing - Orbital angular momentum multiplexing

Multiplexing - Orbital angular momentum multiplexing
Orbital angular momentum multiplexing is a relatively new and experimental technique for multiplexing multiple channels of signals carried using electromagnetic radiation over a single path. It can potentially be used in addition to other physical multiplexing methods to greatly expand the transmission capacity of such systems. As of 2012 it is still in its early research phase, with small-scale laboratory demonstrations of bandwidths of up to 2.5 Tbit/s over a single light path.

Multiplexing - Code-division multiplexing
Advantages over conventional techniques are that variable bandwidth is possible (just as in statistical multiplexing), that the wide bandwidth allows poor signal-to-noise ratio according to Shannon-Hartley theorem, and that multi-path propagation in wireless communication can be combated by rake receivers.

Multiplexing - Code-division multiplexing
Code Division Multiplex techniques are used as an channel access scheme, namely Code Division Multiple Access (CDMA), e.g. for mobile phone service and in wireless networks, with the advantage of spreading intercell interference among many users. Confusingly, the generic term Code Division Multiple access sometimes refers to a specific CDMA based cellular system defined by Qualcomm.

Multiplexing - Relation to multiple access
A multiplexing technique may be further extended into a multiple access method or channel access method, for example TDM into Time-division multiple access (TDMA) and statistical multiplexing into carrier sense multiple access (CSMA). A multiple access method makes it possible for several transmitters connected to the same physical medium to share its capacity.

Multiplexing is provided by the Physical Layer of the OSI model, while multiple access also involves a media access control protocol, which is part of the Data Link Layer.

The Transport layer in the OSI model as well as TCP/IP model provides statistical multiplexing of several application layer data flows to/from the same computer.

Code Division Multiplexing (CDM) is a technique in which each channel transmits its bits as a coded channel-specific sequence of pulses

Multiplexing - Telegraphy
The earliest communication technology using electrical wires, and therefore sharing an interest in the economies afforded by multiplexing, was the electric telegraph. Early experiments allowed two separate messages to travel in opposite directions simultaneously, first using an electric battery at both ends, then at only one end.

Émile Baudot developed a time-multiplexing system of multiple Hughes machines in the 1870s.

In 1874, the quadruplex telegraph developed by Thomas Edison transmitted two messages in each direction simultaneously, for a total of four messages transiting the same wire at the same time.

Several workers were investigating acoustic telegraphy, a frequency-division multiplexing technique, which led to the invention of the telephone.

Multiplexing - Telephony
In telephony, a customer's telephone line now typically ends at the remote concentrator box, where it is multiplexed along with other telephone lines for that neighborhood or other similar area. The multiplexed signal is then carried to the central switching office on significantly fewer wires and for much further distances than a customer's line can practically go. This is likewise also true for digital subscriber lines (DSL).

Fiber in the loop (FITL) is a common method of multiplexing, which uses optical fiber as the backbone. It not only connects POTS phone lines with the rest of the PSTN, but also replaces DSL by connecting directly to Ethernet wired into the home. Asynchronous Transfer Mode is often the communications protocol used.

Because all the phone (and data) lines have been clumped together, none of them can be accessed except through a demultiplexer. Where such demultiplexers are uncommon, this provides for more-secure communications, though the connections are not typically encrypted.

Cable TV has long carried multiplexed television channels, and late in the 20th century began offering the same services as telephone companies. IPTV also depends on multiplexing.

Multiplexing - Video processing
In video editing and processing systems, multiplexing refers to the process of interleaving audio and video into one coherent MPEG transport stream (time-division multiplexing).

Multiplexing - Video processing
In digital video, such a transport stream is normally a feature of a container format which may include metadata and other information, such as subtitles. The audio and video streams may have variable bit rate. Software that produces such a transport stream and/or container is commonly called a statistical multiplexor or muxer. A demuxer is software that extracts or otherwise makes available for separate processing the components of such a stream or container.

Multiplexing - Digital broadcasting
In digital television and digital radio systems, several variable bit-rate data streams are multiplexed together to a fixed bitrate transport stream by means of statistical multiplexing. This makes it possible to transfer several video and audio channels simultaneously over the same frequency channel, together with various services.

In several of these systems, the multiplexing results in an MPEG transport stream

On communications satellites which carry broadcast television networks and radio networks, this is known as multiple channel per carrier or MCPC. Where multiplexing is not practical (such as where there are different sources using a single transponder), single channel per carrier mode is used.

Signal multiplexing of satellite TV and radio channels is typically carried out in a central signal playout and uplink centre, such as SES Platform Services in Germany, which provides playout, digital archiving, encryption, and satellite uplinks, as well as multiplexing, for hundreds of digital TV and radio channels.

In digital radio, both the Eureka 147 system of digital audio broadcasting and the in-band on-channel HD Radio, FMeXtra, and Digital Radio Mondiale systems can multiplex channels. This is essentially required with DAB-type transmissions (where a multiplex is called an ensemble), but is entirely optional with IBOC systems.

Multiplexing - Analog broadcasting
(In fact, the stereo multiplex signal can be generated using time-division multiplexing, by switching between the two (left channel and right channel) input signals at an ultrasonic rate (the subcarrier), and then filtering out the higher harmonics.) Multiplexing in this sense is sometimes known as MPX, which in turn is also an old term for stereophonic FM, seen on stereo systems since the 1960s.

Multiplexing - Other meanings
In spectroscopy the term is used in a related sense to indicate that the experiment is performed with a mixture of frequencies at once and their respective response unravelled afterwards using the Fourier transform principle.

In computer programming, it may refer to using a single in-memory resource (such as a file handle) to handle multiple external resources (such as on-disk files).

Some electrical multiplexing techniques do not require a physical "multiplexer" device, they refer to a "keyboard matrix" or "Charlieplexing" design style:

Multiplexing may refer to the design of a multiplexed display (non-multiplexed displays are immune to the Dorito effect).

Multiplexing may refer to the design of a "switch matrix" (non-multiplexed buttons are immune to "phantom keys" and also immune to "phantom key blocking").

Orbital angular momentum multiplexing - History
OAM multiplexing was demonstrated using light beams as early as 2004.

An experiment in 2011 demonstrated OAM multiplexing of two incoherent radio signals over a distance of 442m. It has been claimed that OAM does not improve on what can achieved with conventional linear-momentum based RF systems which already use MIMO, since theoretical work suggests that, at radio frequencies, conventional MIMO techniques can be shown to duplicate many of the linear-momentum properties of OAM-carrying radio beam, leaving little or no extra performance gain.

OAM multiplexing is used in the optical domain. In 2012, researchers demonstrated OAM-multiplexed optical transmission speeds of up to 2.5 Tbits/s using eight distinct OAM channels in a single beam of light, but only over a very short free-space path of roughly one metre. Work is ongoing on applying OAM techniques to long-range practical free-space optical communication links.

Making OAM multiplexing work over future fibre optic transmission systems, possibly using similar techniques to those used to compensate mode rotation in optical polarization multiplexing, is a subject of ongoing research.

Alternative to direct-detection OAM multiplexing is a computationally complex coherent-detection with (MIMO) digital signal processing (DSP) approach, that can be used to achieve long-haul communication, where strong mode coupling is suggested to be beneficial for coherent-detection based systems.

Orbital angular momentum multiplexing - Criticism
In November 2012, there were reports of disagreement about the basic theoretical concept of OAM multiplexing at radio frequencies between the research groups of Tamburini and Thide, and many different camps of communications engineers and physicists, with some declaring their belief that OAM multiplexing was just an implementation of MIMO, and others holding to their assertion that OAM multiplexing is a distinct, experimentally confirmed phenomenon.

E-carrier - E2: multiplexing level 2: 8 Mbit/s
The 8 Mbit/s frame structure is defined in the ITU-T Rec. G.742. The frame is divided into four groups:

Group I contains the FAS, with sequence " "; the A-bit (remote alarm); the S-bit (spare); and 200 T-bits (tributary) transporting data.

Group IV contains a block of four J-bits, a block of R-bits (justification opportunity), one per tributary, and 204 T-bits. To check whether R-bits have been used, the J-bits are analyzed in each of the groups II, III, and IV (there are three per tributary). Ideally the R-bit does not carry useful information on 42.4% of the occasions. In other words, this percentage is the probability of justification or the insertion of stuffing bits.

The structure of this frame is described in the ITU-T Rec. G.751 (see Figure 20). As in the previous case, the frame is divided into four groups:

Group IV contains a block of four J-bits, a block of R-bits (justification opportunity) one per tributary, and 376 T-bits. To check whether R-bits have been used, the J-bits are analyzed in each of the groups II, III, and IV (there are three per tributary). Ideally the R-bit does not carry useful information on 43.6% of the occasions.

Group I contains the FAS, with sequence " "; the A-bit (remote alarm); the S-bit (spare); and 472 T-bits (tributary) transporting data.

Group VI contains a block of four J-bits, a block of R-bits (justification opportunity), one per tributary, and 376 T-bits. To check whether R-bits have been used, the J-bits are analyzed in each of the groups II, III, IV, V, and VI (there are five per tributary). Ideally the R-bit does not carry useful information on 41.9% of the occasions.

The PDH hierarchy, with four levels from 2 to 140 Mbit/s. Higher rates are not standard.

Level Standard Rate Size Frame/s Code Amplitude Attenuation

Frequency-division multiplexing
In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency sub-bands, each of which is used to carry a separate signal. This allows a single transmission medium such as the radio spectrum, a cable or optical fiber to be shared by many signals.

The most natural example of frequency-division multiplexing is radio and television broadcasting, in which multiple radio signals at different frequencies pass through the air at the same time

An analogous technique called wavelength division multiplexing is used in fiber optic communication, in which multiple channels of data are transmitted over a single optical fiber using different wavelengths (frequencies) of light.

Frequency-division multiplexing - How it works
At the source end, for each frequency channel, an electronic oscillator generates a carrier signal, a steady oscillating waveform at a single frequency such as a sine wave, that serves to "carry" information

Each modulated carrier consists of a narrow band of frequencies, centered on the carrier frequency

At the destination end of the cable or fiber, for each channel, an electronic filter extracts the channel's signal from all the other channels. A local oscillator generates a signal at the channel's carrier frequency. The incoming signal and the local oscillator signal are applied to a demodulator circuit. This translates the data signal in the sidebands back to its original baseband frequency. An electronic filter removes the carrier frequency, and the data signal is output for use.

Modern FDM systems often use sophisticated modulation methods that allow several data signals to be transmitted through each frequency channel.

Frequency-division multiplexing - Telephone
For long distance telephone connections, 20th century telephone companies used L-carrier and similar co-axial cable systems carrying thousands of voice circuits multiplexed in multiple stages by channel banks.

Modern telephone systems employ digital transmission, in which time-division multiplexing (TDM) is used instead of FDM.

Since the late 20th century Digital Subscriber Lines have used a Discrete multitone (DMT) system to divide their spectrum into frequency channels.

The concept corresponding to frequency-division multiplexing in the optical domain is known as wavelength-division multiplexing.

Frequency-division multiplexing - Group and supergroup
A once commonplace FDM system, used for example in L-carrier, uses crystal filters which operate at the 8 MHz range to form a Channel Group of 12 channels, 48 kHz bandwidth in the range 8140 to 8188 kHz by selecting carriers in the range 8140 to 8184 kHz selecting upper sideband this group can then be translated to the standard range 60 to 108 kHz by a carrier of 8248 kHz. Such systems are used in DTL (Direct To Line) and DFSG (Directly formed super group).

132 voice channels (2SG + 1G) can be formed using DTL plane the modulation and frequency plan are given in FIG1 and FIG2 use of DTL technique allows the formation of a maximum of 132 voice channels that can be placed direct to line. DTL eliminates group and super group equipment.

DFSG can take similar steps where a direct formation of a number of super groups can be obtained in the 8 kHz the DFSG also eliminates group equipment and can offer:

Less equipment to install and maintain

Increased reliability due to less equipment

Both DTL and DFSG can fit the requirement of low density system (using DTL) and higher density system (using DFSG). The DFSG terminal is similar to DTL terminal except instead of two super groups many super groups are combined. A Mastergroup of 600 channels (10 super-groups) is an example based on DFSG.

Frequency-division multiplexing - Other usage example: non related to telephone
FDM can also be used to combine signals before final modulation onto a carrier wave

Where frequency-division multiplexing is used as to allow multiple users to share a physical communications channel, it is called frequency-division multiple access (FDMA).

In the 1860s and 70s, several inventors attempted FDM under the names of Acoustic telegraphy and Harmonic telegraphy. Practical FDM was only achieved in the electronic age. Meanwhile their efforts led to an elementary understanding of electroacoustic technology, resulting in the invention of the telephone.

Polarization-division multiplexing

Polarization-division multiplexing
Polarization-division multiplexing (PDM) is a physical layer method for multiplexing signals carried on electromagnetic waves using the polarization of the electromagnetic waves to distinguish between the different orthogonal signals.

Polarization-division multiplexing - Radio
Polarization techniques have long been used in radio transmission to reduce interference between channels, particularly at VHF frequencies and beyond.

Polarization-division multiplexing - Photonics
Polarization-division multiplexing is typically used together with phase modulation or optical QAM, allowing transmission speeds of 100 Gbit/s or more over a single wavelength. Sets of PDM wavelength signals can then be carried over wavelength-division multiplexing infrastructure, potentially substantially expanding its capacity.

The major problem with the practical use of PDM over fiber-optic transmission systems are the drifts in polarization state that occur continuously over time due to physical changes in the fibre environment

For this reason, PDM is generally used in conjunction with advanced channel coding techniques, allowing the use of digital signal processing to decode the signal in a way that is resilient to polarization-related signal artifacts. Modulations used include PM-QPSK and PM-DQPSK.

Companies working on commercial PDM technology include Ciena, Cisco Systems, Huawei and Infinera.

Flow-based programming - Multiplexing processes
Flow-Based Programming supports process multiplexing in a very natural way. Since components are read-only, any number of instances of a given component ("processes") can run asynchronously with each other.

Flow-based programming - Multiplexing processes
When computers usually had a single processor, this was useful when a lot of I/O was going on; now that machines usually have multiple processors, this is starting to become useful when processes are CPU-intensive as well. The diagram in this section shows a single "Load Balancer" process distributing data between 3 processes, labeled S1, S2 and S3, respectively, which are instances of a single component, which in turn feed into a single process on a "first-come, first served" basis.

Statistical time division multiplexing

When performed correctly, statistical multiplexing can provide a link utilization improvement, called the statistical multiplexing gain.

Statistical multiplexing is facilitated through packet mode or packet-oriented communication, which among others is utilized in packet switched computer networks. Each stream is divided into packets that normally are delivered asynchronously in a first-come first-served fashion. In alternative fashion, the packets may be delivered according to some scheduling discipline for fair queuing or differentiated and/or guaranteed quality of service.

Statistical multiplexing of an analog channel, for example a wireless channel, is also facilitated through the following schemes:

Random frequency-hopping orthogonal frequency division multiple access (RFH-OFDMA)

Code-division multiple access (CDMA), where different amount of spreading codes or spreading factors can be assigned to different users.

Statistical multiplexing normally implies "on-demand" service rather than one that preallocates resources for each data stream. Statistical multiplexing schemes do not control user data transmissions.

Statistical time division multiplexing - Comparison with static TDM
Time domain statistical multiplexing (packet mode communication) is similar to time-division multiplexing (TDM), except that, rather than assigning a data stream to the same recurrent time slot in every TDM frame, each data stream is assigned time slots (of fixed length) or data frames (of variable lengths) that often appear to be scheduled in a randomized order, and experience varying delay (while the delay is fixed in TDM).

Statistical multiplexing allows the bandwidth to be divided arbitrarily among a variable number of channels (while the number of channels and the channel data rate are fixed in TDM).

Statistical multiplexing ensures that slots will not be wasted (whereas TDM can waste slots). The transmission capacity of the link will be shared by only those users who have packets.

Static TDM and other circuit switching is carried out at the physical layer in the OSI model and TCP/IP model, while statistical multiplexing is carried out at the data link layer and above.

Statistical time division multiplexing - Channel identification
In statistical multiplexing, each packet or frame contains a channel/data stream identification number, or (in the case of datagram communication) complete destination address information.

Statistical time division multiplexing - Usage
Examples of statistical multiplexing are:

The MPEG transport stream for digital TV transmission. Statistical multiplexing is used to allow several video, audio and data streams of different data rates to be transmitted over a bandwidth-limited channel (see #Statistical multiplexer). The packets have constant lengths. The channel number is denoted Program ID (PID).

The UDP and TCP protocols, where data streams from several application processes are multiplexed together. The packets may have varying lengths. The port numbers constitute channel identification numbers (and also address information).

The X.25 and Frame relay packet-switching protocols, where the packets have varying lengths, and the channel number is denoted Virtual Connection Identifier (VCI). The international collection of X.25 providers, using the X.25 protocol suite was colloquially known as "the Packet switched network" in the 1980s and into the beginning of the 1990s.

The Asynchronous Transfer Mode packet-switched protocol, where the packets have fixed length. The channel identification number consists of a Virtual Connection Identifier (VCI) and a Virtual Path Identifier (VPI).

Statistical time division multiplexing - Statistical multiplexer
In digital audio and video broadcasting, for example, a statistical multiplexer is a content aggregating device that allows broadcasters to provide the greatest number of audio or video services for a given bandwidth by sharing a pool of fixed bandwidth among multiple services or streams of varying bitrates

Time-division multiplexing
This form of signal multiplexing was developed in telecommunications for telegraphy systems in the late 1800s, but found its most common application in Digital data|digital telephony in the second half of the 20th century.

Time-division multiplexing - Technology
Time-division multiplexing is used primarily for Digital data|digital signals, but may be applied in Pulse-amplitude modulation|analog multiplexing in which two or more signals or bit streams are transferred appearing simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel

Time-division multiplexing - Application examples
* The plesiochronous digital hierarchy (PDH) system, also known as the Pulse-code modulation|PCM system, for digital transmission of several telephone calls over the same four-wire copper cable (T-carrier or E-carrier) or fiber cable in the circuit switched digital telephone network

* The synchronous optical networking|synchronous digital hierarchy (SDH)/synchronous optical networking (SONET) network transmission standards that have replaced PDH.

* The RIFF (File format)|RIFF (WAV) audio standard interleaves left and right stereo signals on a per-sample basis

* The left-right channel splitting in use for stereoscopic liquid crystal shutter glasses

TDM can be further extended into the time division multiple access (TDMA) scheme, where several stations connected to the same physical medium, for example sharing the same Frequency-division multiplexing|frequency channel, can communicate. Application examples include:

* The Global system for mobile communications|GSM telephone system

Time-division multiplexing - TDM versus packet-mode communication
In its primary form, TDM is used for circuit mode communication with a fixed number of channels and constant bandwidth per channel.

Bandwidth reservation distinguishes time-division multiplexing from statistical multiplexing such as packet mode communication (also known as 'statistical time-domain multiplexing', see below) i.e. the time slots are recurrent in a fixed order and pre-allocated to the channels, rather than scheduled on a packet-by-packet basis. Statistical time-domain multiplexing resembles, but should not be considered the same as time-division multiplexing.

In dynamic TDMA, a scheduling algorithm dynamically reserves a variable number of time slots in each frame to variable bit-rate data streams, based on the traffic demand of each data stream. Dynamic TDMA is used in:

* Dynamic synchronous transfer mode

Time-division multiplexing - History
Time-division multiplexing was first developed for applications in Multiplexing#Telegraphy|telegraphy to route multiple transmissions simultaneously over a single transmission line. In the 1870s, Émile Baudot developed a time-multiplexing system of multiple David E. Hughes|Hughes machines.

In 1953 a 24-channel TDM was placed in commercial operation by RCA Communications to send audio information between RCA's facility at Broad Street, New York and their transmitting station at Rocky Point and the receiving station at Riverhead, Long Island, New York

In 1962, engineers from Bell Labs developed the first D1 Channel Banks, which combined 24 digitised voice calls over a 4-wire copper trunk between Bell telephone exchange|central office analogue switches

Time-division multiplexing - Multiplexed digital transmission
In circuit-switched networks, such as the public switched telephone network (PSTN), it is desirable to transmit multiple subscriber calls over the same transmission medium to effectively utilize the bandwidth of the medium.

TDM allows transmitting and receiving telephone switches to create channels (tributaries) within a transmission stream

Each voice time slot in the TDM frame is called a channel. In European systems, standard TDM frames contain 30 digital voice channels (E1), and in American systems (T1), they contain 24 channels. Both standards also contain extra bits (or bit time slots) for signaling and synchronization bits.

Multiplexing more than 24 or 30 digital voice channels is called higher order multiplexing. Higher order multiplexing is accomplished by multiplexing the standard TDM frames. For example, a European 120 channel TDM frame is formed by multiplexing four standard 30 channel TDM frames. At each higher order multiplex, four TDM frames from the immediate lower order are combined, creating multiplexes with a bandwidth of n*64 kbit/s, where n = 120, 480, 1920, etc.

Time-division multiplexing - Synchronous time-division multiplexing
There are three types of synchronous TDM: T1, SONET/SDH, and ISDN.

Time-division multiplexing - Synchronous Digital Hierarchy (SDH)
Plesiochronous digital hierarchy (PDH) was developed as a standard for multiplexing higher order frames. PDH created larger numbers of channels by multiplexing the standard Europeans 30 channel TDM frames. This solution worked for a while; however PDH suffered from several inherent drawbacks which ultimately resulted in the development of the Synchronous Digital Hierarchy (SDH). The requirements which drove the development of SDH were these:

*Be synchronous ndash; All clocks in the system must align with a reference clock.

*Be service-oriented ndash; SDH must route traffic from End Exchange to End Exchange without worrying about exchanges in between, where the bandwidth can be reserved at a fixed level for a fixed period of time.

*Provide high levels of recovery from faults.

*Provide high data rates by multiplexing any size frame, limited only by technology.

*Give reduced bit rate errors.

SDH has become the primary transmission protocol in most PSTN networks. It was developed to allow streams Mbit/s and above to be multiplexed, in order to create larger SDH frames known as Synchronous Transport Modules (STM). The STM-1 frame consists of smaller streams that are multiplexed to create a Mbit/s frame. SDH can also multiplex packet based frames e.g. Ethernet, PPP and ATM.

While SDH is considered to be a transmission protocol (Layer 1 in the OSI reference model|OSI Reference Model), it also performs some switching functions, as stated in the third bullet point requirement listed above. The most common SDH Networking functions are these:

*SDH Crossconnect ndash; The SDH Crossconnect is the SDH version of a Time-Space-Time crosspoint switch. It connects any channel on any of its inputs to any channel on any of its outputs. The SDH Crossconnect is used in Transit Exchanges, where all inputs and outputs are connected to other exchanges.

*SDH Add-Drop Multiplexer ndash; The SDH Add-Drop Multiplexer (ADM) can add or remove any multiplexed frame down to 1.544Mb. Below this level, standard TDM can be performed. SDH ADMs can also perform the task of an SDH Crossconnect and are used in End Exchanges where the channels from subscribers are connected to the core PSTN network.

SDH network functions are connected using high-speed optic fibre. Optic fibre uses light pulses to transmit data and is therefore extremely fast. Modern optic fibre transmission makes use of wavelength-division multiplexing (WDM) where signals transmitted across the fibre are transmitted at different wavelengths, creating additional channels for transmission. This increases the speed and capacity of the link, which in turn reduces both unit and total costs.

Time-division multiplexing - Statistical time-division multiplexing
Statistical time division multiplexing (STDM) is an advanced version of TDM in which both the address of the terminal and the data itself are transmitted together for better routing. Using STDM allows bandwidth to be split over one line. Many college and corporate campuses use this type of TDM to distribute bandwidth.

On a 10-Mbit line entering a network, STDM can be used to provide 178 terminals with a dedicated 56k connection (178 * 56k = 9.96Mb). A more common use however is to only grant the bandwidth when that much is needed. STDM does not reserve a time slot for each terminal, rather it assigns a slot when the terminal is requiring data to be sent or received.

Asynchronous time-division multiplexing (ATDM), is an alternative nomenclature in which STDM designates synchronous time-division multiplexing, the older method that uses fixed time slots.

CDMA - Code division multiplexing (Synchronous CDMA)
Synchronous CDMA exploits mathematical properties of orthogonality between coordinate vector|vectors representing the data strings

CDMA - Code division multiplexing (Synchronous CDMA)
Each user in synchronous CDMA uses a code orthogonal to the others' codes to modulate their signal

Multiplexer - List of ICs which provide multiplexing
The 7400 series has several ICs that contain multiplexer(s):

Fiber-optic communication - Wavelength-division multiplexing
Arrayed waveguide gratings are commonly used for multiplexing and demultiplexing in WDM

* Allows simultaneous low-data-rate transmission from several users.
OFDMA - Claimed advantages over OFDM with time-domain statistical multiplexing * Allows simultaneous low-data-rate transmission from several users.

* Pulsed carrier can be avoided.
OFDMA - Claimed advantages over OFDM with time-domain statistical multiplexing * Pulsed carrier can be avoided.

* Lower maximum transmission power for low data rate users.
OFDMA - Claimed advantages over OFDM with time-domain statistical multiplexing * Lower maximum transmission power for low data rate users.

OFDMA - Claimed advantages over OFDM with time-domain statistical multiplexing
* Contention-based multiple access (collision avoidance) is simplified.

* Further improves OFDM robustness to fading and interference.
OFDMA - Claimed advantages over OFDM with time-domain statistical multiplexing * Further improves OFDM robustness to fading and interference.

G.992.1 - Coded orthogonal frequency-division multiplexing (COFDM)
The use of bins produces a transmission system known as coded orthogonal frequency-division multiplexing (COFDM). In the context of G.992.1, the term Discrete Multi-Tone (DMT) is used instead, hence the alternative name of the standard, G.dmt.

G.992.1 - Coded orthogonal frequency-division multiplexing (COFDM)
Using DMT is useful since it allows the communications equipment (user modem/router and exchange/DSLAM) to select only bins which are usable on the line thus effectively obtaining the best overall bit rate from the line at any given moment in time. With COFDM, a combined signal containing many frequencies (for each bin) is transmitted down the line. Fast Fourier Transform (and the inverse iFFT) is used to convert the signal on the line into the individual bins.

Spatial multiplexing 'Spatial multiplexing' (seen abbreviated 'SM' or 'SMX') is a transmission technique in Multiple-input multiple-output communications|MIMO wireless communication to transmit independent and separately encoded data signals, so-called streams, from each of the multiple transmit antennas. Therefore, the space dimension is reused, or Multiplexing|multiplexed, more than one time.

Spatial multiplexing If the transmitter is equipped with N_t antennas and the receiver has N_r antennas, the maximum spatial multiplexing order (the number of streams) is,

Spatial multiplexing if a linear receiver is used. This means that N_s streams can be transmitted in parallel, ideally leading to an N_s increase of the spectral efficiency (the number of bits per second and per Hz that can be transmitted over the wireless channel). The practical multiplexing gain can be limited by Spatial Correlation|spatial correlation, which means that some of the parallel streams may have very weak channel gains.

Spatial multiplexing - Open-loop approach
In an open loop (wireless)|open-loop MIMO system with N_t transmitter antennas and N_r receiver antennas, the input-output relationship can be described as

Spatial multiplexing - Open-loop approach
[ Enhanced Spatial Multiplexing for Rate-2 MIMO of DVB-NGH System], Invited paper in the 19th International Conference on Telecommunications, April 2012.

Spatial multiplexing - Closed-loop approach
A closed-loop MIMO system utilizes Channel State Information (CSI) at the transmitter. In most cases, only partial CSI is available at the transmitter because of the limitations of the feedback channel. In a closed-loop MIMO system the input-output relationship with a closed-loop approach can be described as

Spatial multiplexing - Closed-loop approach
A precoding matrix \mathbf is used to precode the symbols in the vector to enhance the performance. The column dimension N_s of \mathbf can be selected smaller than N_t which is useful if the system requires N_s (\neq N_t) streams because of several reasons. Examples of the reasons are as follows: either the rank of the MIMO channel or the number of receiver antennas is smaller than the number of transmit antennas.

Spatial multiplexing - History
** Per Antenna Rate Control (PARC), Varanasi, Guess (1998), Chung, Huang, Lozano (2001)

*Advanced MIMO communication#Multi-user MIMO|Multi-user MIMO: Samsung, Qualcomm, Quantenna, Ericsson, TI, Huawei, Philipse, Alcatel-Lucent, Freescale, et al.

** PU2RC allows the network to allocate each antenna to the different user which is not considered in single-user MIMO scheduling

* 'Enhanced multiuser MIMO'

** Employ advanced decoding techniques

** Employ advanced precoding techniques

WiMAX MIMO - Spatial Multiplexing
The specification also supports the MIMO technique of Spatial multiplexing|Spatial Multiplexing (SMX), also known as Transmit Diversity rate = 2 (aka Matrix B in the standard)

WiMAX MIMO - WiMAX Network use of Spatial Multiplexing
One specific use of Spatial Multiplexing is to apply it to users who have the best signal quality, so that less time is spent transmitting to them. Users whose signal quality is too low to allow the spatially multiplexed signals to be resolved stay with conventional transmission. This allows an operator to offer higher data rates to some users and/or to serve more users. The WiMAX specification's dynamic negotiation mechanism helps enable this use.

Spatial Division Multiplexing
In radio, 'multi-user MIMO' ('MU-MIMO') is a set of advanced 'MIMO' (pronounced mee-moh or my-moh), multiple-input and multiple-output, technologies where the available antennas are spread over a multitude of independent access points and independent radio terminals - each having one or multiple antennas

Like the relationship between OFDM and OFDMA, MU-MIMO (and, similarly, SDMA) can be thought of as an extension of MIMO applied in various ways as a multiple access strategy

Multiple access MIMO, MIMO-SDMA,N

Spatial Division Multiplexing - MIMO
* Beamforming alters the phase of each element in an antenna array to create spatial beam patterns through constructive and destructive interference.

* Space–time code|Space-time coding/processing performs antenna diversity with multiple antennas at either transmitter or receiver side or both sides, where every antenna element is separated from its nearest element by around 4 to 10 times the wavelength to keep the signal through each multi-path independent. The distance between two adjacent antenna elements is relying on the angular spread of the beam signal.

* Multi-user MIMO#Space-division multiple access .28SDMA.29|SDMA is a common and typical multiple input multiple output scheme in cellular wireless systems. SDMA is often referred to as simply a MIMO system since the half port of a SDMA system also consists of multiple users. Although SDMA is indeed a MIMO technique, MIMO is not necessarily SDMA.

* Spatial multiplexing is performed by multiple antennas equipped at both a transmitter and a receiver front end.

* Cooperative wireless communications|Cooperation are known as network MIMO systems, distributed MIMO systems or virtual antenna array systems. Mobile devices use the partnered mobile devices' antennas, antenna arrays, or antenna elements as virtual antennas.

* Combinations of above techniques, etc.

Spatial Division Multiplexing - MIMO enhancement
Enhancement techniques can be categorized into evolutionary and revolutionary approaches:

* Evolutionary approaches:

*# Use an existing technique with enhanced PHY capabilities, perhaps a 16×16 array configuration, or

*# Use new MIMO algorithms such as precoding or multi-user scheduling at the transmitter.

* Revolutionary approaches: developing fundamentally new MIMO concepts. Examples of revolution approaches are cooperative and virtual antenna MIMO and intelligent spatial processing such as RADAR beamforming.

Here, based on the literature, we summarize a number of advanced MIMO techniques that leverage multiple users:

* Cross-layer MIMO: Scheduling, etc.

* Advanced decoding MIMO: Multi-user detection such as MLD.

* Beamforming and Space-division multiple access|SDMA: widely known multi-user MIMO scheme.

* Cognitive MIMO based on intelligent techniques.

* Competitive: Game theory, autonomous packets, implicit MAC fairness, etc.

Spatial Division Multiplexing - MU-MIMO
Multi-user MIMO can leverage multiple users as spatially distributed transmission resources, at the cost of somewhat more expensive signal processing

Spatial Division Multiplexing - MU-MIMO
To remove ambiguity of the words receiver and transmitter, we can adopt the terms access point (AP; or, base station), and user. An AP is the transmitter and a user is the receiver for downlink environments, whereas an AP is the receiver and a user is the transmitter for uplink environments. Homogeneous networks are somewhat freed from this distinction.

Spatial Division Multiplexing - Space-division multiple access
Space-Division Multiple Access (SDMA) enables creating [ parallel spatial pipes] next to higher capacity pipes through spatial multiplexing and/or diversity, by which it is able to offer superior performance in radio multiple access communication systems

Spatial Division Multiplexing - Space-division multiple access
In GSM cellular networks, the base station is aware of the mobile phone's position by use of a technique called Timing Advance (TA)

Spatial Division Multiplexing - Many antennas
Many Antennas is a smart antenna technique, which overcomes the performance limitation of single user MIMO techniques

Space-division multiple access|SDMA: Enabling MU-MIMO, network MIMO (CoMP), and remote radio equipments

Precoding: linear precoding such as MRT, ZF and MMSE perform almost as well as non-linear precoding

Remote and wireless antenna array: distributed antenna array and cooperative beamforming

Spatial Division Multiplexing - MIMO broadcast (MIMO BC)
'MIMO broadcast' represents a MIMO downlink case in a single sender to multiple receiver wireless network

Spatial Division Multiplexing - MIMO MAC
Conversely, 'MIMO MAC' represents a MIMO uplink case in the multiple sender to single receiver wireless network

Spatial Division Multiplexing - Cross-layer MIMO
'Cross-layer MIMO' enhances the performance of MIMO links by solving certain cross-layer problems that may occur when MIMO configurations are employed in a system. Cross-layer techniques can be used to enhance the performance of SISO links as well. Examples of cross-layer techniques are Joint Source-Channel Coding, Adaptive Modulation and Coding (AMC, or Link Adaptation), Hybrid ARQ (HARQ), and user scheduling.

Spatial Division Multiplexing - Multi-user to multi-user
The highly interconnected wireless ad hoc network increases the flexibility of wireless networking at the cost of increased multi-user interference

* Cooperative multiple antenna research — Apply multiple antenna research|multiple antenna technologies in situations with antennas distributed among neighboring wireless terminals.

** Cooperative diversity — Achieve antenna diversity gain by the cooperation of distributed antennas belonging to each independent node.

** Cooperative MIMO — Achieve Multiple-input multiple-output communications|MIMO advantages, including the spatial multiplexing gain, using the transmit or receiver cooperation of distributed antennas belonging to many different nodes.

* Cooperative relay — Apply cooperative concepts onto relay techniques, which is similar to cooperative diversity in terms of cooperative signalling. However, the main criterion of cooperative relay is to improve the tradeoff region between delay and performance, while that of cooperative diversity and MIMO is to improve the link and system performance at the expense of minimal cooperation loss.

* Relaying techniques for cooperation

Spatial Division Multiplexing - Cooperative MIMO (CO-MIMO)
CO-MIMO improves the performance of a wireless network by introducing multiple antenna advantages, such as diversity, multiplexing and beamforming

CO-MIMO is a technique useful for future cellular networks which consider wireless mesh networking or wireless Ad Hoc networking

Of analogical interest here may be the comparison between the evolution of computing cores and mobile antennas

Wavelength-division multiplexing
In fiber-optic communications, 'wavelength-division multiplexing' ('WDM') is a technology which Multiplexing|multiplexes a number of Optical Carrier|optical carrier signals onto a single optical fiber by using different wavelengths (i.e. colors) of laser light. This technique enables Duplex (telecommunications)|bidirectional communications over one strand of fiber, as well as multiplication of capacity.

Wavelength-division multiplexing
The term wavelength-division multiplexing is commonly applied to an optical carrier (which is typically described by its wavelength), whereas frequency-division multiplexing typically applies to a radio carrier (which is more often described by frequency). Since wavelength and frequency are tied together through a simple directly inverse relationship, in which the product of frequency and wavelength equals (the propagation speed of light), the two terms actually describe the same concept.

Wavelength-division multiplexing - Dense WDM
Dense wavelength division multiplexing (DWDM) refers originally to optical signals multiplexed within the 1550nm band so as to leverage the capabilities (and cost) of Optical amplifier#Erbium-doped fibre amplifiers|erbium doped fiber amplifiers (EDFAs), which are effective for wavelengths between approximately 1525–1565nm (C band), or 1570–1610nm (L band)

Wavelength-division multiplexing - DWDM systems
# A DWDM 'terminal multiplexer'

# An 'intermediate line repeater' is placed approximately every 80 – 100km to compensate for the loss of optical power as the signal travels along the fiber. The 'multi-wavelength optical signal' is amplified by an EDFA, which usually consists of several amplifier stages.

# An 'intermediate optical terminal', or 'optical add-drop multiplexer'

Originally, this de-multiplexing was performed entirely passively, except for some telemetry, as most SONET systems can receive 1550nm signals

# 'Optical Supervisory Channel (OSC)'

The introduction of the ITU-T G.694.1ITU-T G.694.1, Spectral grids for WDM applications: DWDM frequency grid [ ITU-T website] frequency grid in 2002 has made it easier to integrate WDM with older but more standard Synchronous optical networking|SONET/SDH systems

DWDM systems have to maintain more stable wavelength or frequency than those needed for CWDM because of the closer spacing of the wavelengths

Recent innovations in DWDM transport systems include pluggable and software-tunable transceiver modules capable of operating on 40 or 80 channels. This dramatically reduces the need for discrete spare pluggable modules, when a handful of pluggable devices can handle the full range of wavelengths.

Wavelength-division multiplexing - Enhanced WDM
Cisco's Enhanced WDM system combines 1 GB Coarse Wave Division Multiplexing (CWDM) connections using SFPs and GBICs with 10 GB Dense Wave Division Multiplexing (DWDM) connections using XENPAK, X2, or XFP DWDM modules. These DWDM connections can either be passive or boosted to allow a longer range for the connection

Wavelength-division multiplexing - Implementations
There are several simulation tools that can be used to design WDM systems. Popular commercial tools have been developed by [ Optiwave Systems Inc.] and VPI Systems.

Orbital angular momentum multiplexing
'Orbital angular momentum' ('OAM') 'multiplexing' is a physical layer method for multiplexing signals carried on electromagnetic waves using the light orbital angular momentum|orbital angular momentum of the electromagnetic waves to distinguish between the different orthogonal signals.

OAM multiplexing can (at least in theory) access a potentially unbounded set of OAM quantum states, and thus offer a much larger number of channels, subject only to the constraints of real-world optics.

, although OAM multiplexing promises very significant improvements in bandwidth when used in concert with other existing modulation and multiplexing schemes, it is still an experimental technique, and has so far only been demonstrated in the laboratory.

OAM multiplexing was demonstrated using light beams in free space as early as Since then, research into OAM has proceeded in two areas: radio frequency and optical transmission.

Orbital angular momentum multiplexing - Practical demonstration in optical fiber system
A paper by Bozinovic. et. al. published in Science in 2013 claims the successful demonstration of an OAM multiplexed fiber optic transmission system over a 1.1km test path. The test system was capable of using up to four different OAM channels simultaneously, using a fiber with a vortex refractive index profile. They also demonstrated combined OAM and WDM using the same apparatus, but using only two OAM modes.

100BaseVG - Multiplexing Instead of following the Fast Ethernet standard for twisted pair cabling by using only 2 pairs of wires, 100VG-AnyLAN used all four pairs in either Category 3 or Category 5 twisted pair cable

Orthogonal frequency-division multiplexing
'Orthogonal frequency-division multiplexing' ('OFDM') is a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, Digital subscriber line|DSL Internet access, wireless networks, powerline networks, and 4G mobile communications.

OFDM is essentially identical to 'coded OFDM' ('COFDM') and 'discrete multi-tone modulation' ('DMT'), and is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method

The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel (communications)|channel conditions (for example, attenuation distortion|attenuation of high frequencies in a long copper wire, narrowband Interference (communication)|interference and frequency-selective fading due to Multipath propagation|multipath) without complex equalization filters

Orthogonal frequency-division multiplexing - Example of applications
The following list is a summary of existing OFDM based standards and products. For further details, see the #Usage|Usage section at the end of the article.

Orthogonal frequency-division multiplexing - Cable
* Power line communication (PLC),

* ITU-T G.hn, a standard which provides high-speed local area networking of existing home wiring (power lines, phone lines and coaxial cables),

* Multimedia over Coax Alliance (MoCA) home networking.

Orthogonal frequency-division multiplexing - Wireless
* The digital radio systems Eureka 147|DAB/EUREKA 147, DAB+, Digital Radio Mondiale, HD Radio, T-DMB and ISDB-TSB.

* The wireless personal area network (PAN) ultra-wideband (UWB) IEEE a implementation suggested by WiMedia Alliance.

The OFDM based multiple access technology Orthogonal frequency-division multiple access|OFDMA is also used in several 4G and pre-4G cellular networks and mobile broadband standards:

* the downlink of the 3GPP Long Term Evolution (LTE) fourth generation mobile broadband standard. The radio interface was formerly named High Speed OFDM Packet Access (HSOPA), now named Evolved UMTS Terrestrial Radio Access (E-UTRA).

Orthogonal frequency-division multiplexing - Key features
The advantages and disadvantages listed below are further discussed in the #Characteristics and principles of operation|Characteristics and principles of operation section below.

Orthogonal frequency-division multiplexing - Summary of advantages
* High spectral efficiency as compared to other double sideband modulation schemes, spread spectrum, etc.

* Can easily adapt to severe channel conditions without complex time-domain equalization.

* Robust against narrow-band co-channel interference.

* Robust against intersymbol interference (ISI) and fading caused by multipath propagation.

* Efficient implementation using Fast Fourier Transform (FFT).

* Tuned sub-channel receiver filters are not required (unlike conventional frequency-division multiplexing|FDM).

* Facilitates single frequency networks (SFNs); i.e., transmitter macrodiversity.

Orthogonal frequency-division multiplexing - Summary of disadvantages
* Sensitive to frequency synchronization problems.

* High Crest factor|peak-to-average-power ratio (PAPR), requiring linear transmitter circuitry, which suffers from poor power efficiency.

* Loss of efficiency caused by cyclic prefix/guard interval.

Orthogonal frequency-division multiplexing - Orthogonality
Conceptually, OFDM is a specialized FDM, the additional constraint being: all the carrier signals are orthogonal to each other.

In OFDM, the sub-carrier frequencies are chosen so that the sub-carriers are orthogonality#Communications|orthogonal to each other, meaning that crosstalk (electronics)|cross-talk between the sub-channels is eliminated and inter-carrier guard bands are not required. This greatly simplifies the design of both the transmitter and the receiver (radio)|receiver; unlike conventional frequency-division multiplexing|FDM, a separate filter for each sub-channel is not required.

The orthogonality requires that the sub-carrier spacing is \scriptstyle\Delta f \,=\, \frac Hertz, where TU seconds is the useful symbol duration (the receiver side window size), and k is a positive integer, typically equal to 1. Therefore, with N sub-carriers, the total passband bandwidth will be B = N·Δf (Hz).

The orthogonality also allows high spectral efficiency, with a total symbol rate near the Nyquist rate for the equivalent baseband signal (i.e. near half the Nyquist rate for the double-side band physical passband signal). Almost the whole available frequency band can be utilized. OFDM generally has a nearly 'white' spectrum, giving it benign electromagnetic interference properties with respect to other co-channel users.

:A simple example: A useful symbol duration TU = 1ms would require a sub-carrier spacing of \scriptstyle\Delta f \,=\, \frac are the data symbols, \scriptstyle N is the number of sub-carriers, and \scriptstyle T is the OFDM symbol time. The sub-carrier spacing of \scriptstyle \frac makes them orthogonal over each symbol period; this property is expressed as:

where \scriptstyle (\cdot)^* denotes the complex conjugate operator and \scriptstyle\delta\, is the Kronecker delta.

To avoid intersymbol interference in multipath fading channels, a guard interval of length \scriptstyle T_\mathrm is inserted prior to the OFDM block. During this interval, a cyclic prefix is transmitted such that the signal in the interval \scriptstyle -T_\mathrm \,\le\, t \,

Orthogonal frequency-division multiplexing - OFDM system comparison table
Key features of some common OFDM based systems are presented in the following table.

Orthogonal frequency-division multiplexing - ADSL
OFDM is used in asymmetric digital subscriber line|ADSL connections that follow the G.DMT (ITU G.992.1) standard, in which existing copper wires are used to achieve high-speed data connections.

Long copper wires suffer from attenuation at high frequencies. The fact that OFDM can cope with this frequency selective attenuation and with narrow-band interference are the main reasons it is frequently used in applications such as ADSL modems. However, DSL cannot be used on every copper pair; interference may become significant if more than 25% of phone lines coming into a Telephone exchange|central office are used for DSL.

For experimental amateur radio applications, users have even hooked up commercial off-the-shelf ADSL equipment to radio transceivers which simply shift the bands used to the radio frequencies the user has licensed.

Orthogonal frequency-division multiplexing - Powerline Technology
OFDM is used by many power line communication|powerline devices to extend digital connections through power wiring. Adaptive modulation is particularly important with such a noisy channel as electrical wiring.

Some medium speed smart metering modems, Prime and G3 use OFDM at modest frequencies (30–100kHz)with modest numbers of channels (several hundred) in order to overcome the intersymbol interference in the power line environment.[ Hoch, Martin; Comparison of PLC G3 and Prime, 2011 IEEE Symposium on Powerline Communication and its Applications

The IEEE 1901 standards include two incompatible physical layers that both use OFDM. An overview of P1901 PHY/MAC proposal.

The ITU-T G.hn standard, which provides high-speed local area networking over existing home wiring (power lines, phone lines and coaxial cables) is based on a PHY layer that specifies OFDM with adaptive modulation and a Low-Density Parity-Check (LDPC) FEC code.

Orthogonal frequency-division multiplexing - Wireless local area networks (LAN) and metropolitan area networks (MAN) OFDM is extensively used in wireless LAN and MAN applications, including IEEE |IEEE a/g/n and WiMAX.

Orthogonal frequency-division multiplexing - Wireless local area networks (LAN) and metropolitan area networks (MAN) IEEE a/g/n operating in the 2.4 and 5GHz bands, specifies a per-stream airside data rates ranging from 6 to 54Mbit/s

Orthogonal frequency-division multiplexing - Wireless personal area networks (PAN)
OFDM is also now being used in the [ WiMedia/Ecma-368 standard] for high-speed wireless personal area networks in the 3.1–10.6GHz ultrawideband spectrum (see MultiBand-OFDM).

Orthogonal frequency-division multiplexing - Terrestrial digital radio and television broadcasting
Much of Europe and Asia has adopted OFDM for terrestrial broadcasting of digital television (DVB-T, DVB-H and T-DMB) and radio (EUREKA 147 Digital Audio Broadcasting|DAB, Digital Radio Mondiale, HD Radio and T-DMB).

Orthogonal frequency-division multiplexing - DVB-T
By Directive of the European Commission, all television services transmitted to viewers in the European Community must use a transmission system that has been standardized by a recognized European standardization body,[ DIRECTIVE 95/47/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on the use of standards for the transmission of television signals] and such a standard has been developed and codified by the DVB Project, Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television.ETSI Standard: EN V1.5.1 ( )

Orthogonal frequency-division multiplexing - SDARS
The ground segments of the Digital Audio Radio Service (SDARS) systems used by XM Satellite Radio and Sirius Satellite Radio are transmitted using COFDM. Agere gets Sirius about satellite radio design

Orthogonal frequency-division multiplexing - COFDM vs VSB
The question of the relative technical merits of COFDM versus 8VSB for terrestrial digital television has been a subject of some controversy, especially between European and North American technologists and regulators. The United States has rejected several proposals to adopt the COFDM based DVB-T system for its digital television services, and has instead opted for 8VSB (vestigial sideband modulation) operation.

One of the major benefits provided by COFDM is in rendering radio broadcasts relatively immune to multipath interference|multipath distortion and signal fading due to atmospheric conditions or passing aircraft. Proponents of COFDM argue it resists multipath far better than 8VSB. Early 8VSB Digital television|DTV (digital television) receivers often had difficulty receiving a signal. Also, COFDM allows single-frequency networks, which is not possible with 8VSB.

However, newer 8VSB receivers are far better at dealing with multipath, hence the difference in performance may diminish with advances in Equalization filter|equalizer design

Orthogonal frequency-division multiplexing - Digital radio
COFDM is also used for other radio standards, for Digital Audio Broadcasting (DAB), the standard for digital audio broadcasting at VHF frequencies, for Digital Radio Mondiale (DRM), the standard for digital broadcasting at shortwave and medium wave frequencies (below 30MHz) and for Digital Radio Mondiale#DRM Plus|DRM+ a more recently introduced standard for digital audio broadcasting at VHF frequencies. (30 to 174MHz)

The USA again uses an alternate standard, a proprietary system developed by iBiquity dubbed HD Radio. However, it uses COFDM as the underlying broadcast technology to add digital audio to AM (medium wave) and FM broadcasts.

Both Digital Radio Mondiale and HD Radio are classified as in-band on-channel systems, unlike Eureka 147 (DAB: Digital Audio Broadcasting) which uses separate VHF or Ultra high frequency|UHF frequency bands instead.

Orthogonal frequency-division multiplexing - BST-OFDM used in ISDB
The band-segmented transmission orthogonal frequency division multiplexing (BST-OFDM) system proposed for Japan (in the ISDB-T, ISDB-TSB, and ISDB-C broadcasting systems) improves upon COFDM by exploiting the fact that some OFDM carriers may be modulated differently from others within the same multiplex

Orthogonal frequency-division multiplexing - BST-OFDM used in ISDB
It is possible, for example, to send an audio service on a segment that includes a segment composed of a number of carriers, a data service on another segment and a television service on yet another segment—all within the same 6MHz television channel

Orthogonal frequency-division multiplexing - Ultra-wideband
Ultra-wideband (UWB) wireless personal area network technology may also utilise OFDM, such as in Multiband OFDM (MB-OFDM). This UWB specification is advocated by the WiMedia Alliance (formerly by both the Multiband OFDM Alliance [MBOA] and the WiMedia Alliance, but the two have now merged), and is one of the competing UWB radio interfaces.

Orthogonal frequency-division multiplexing - FLASH-OFDM
Fast low-latency access with seamless handoff orthogonal frequency division multiplexing (Flash-OFDM), also referred to as F-OFDM, was based on OFDM and also specified higher open systems architecture|protocol layers

In Finland, the license holder Digita began deployment of a wireless network in parts of the country since April It was purchased by Datame in In February 2012 Datame announced they would upgrade the 450MHz network to competing CDMA2000 technology.

Slovak Telekom in Slovakia offers Flash-OFDM connections with a maximum downstream speed of 5.3Mbit/s, and a maximum upstream speed of 1.8Mbit/s, with a coverage of over 70 percent of Slovak population.

T-Mobile Germany uses Flash-OFDM to backhaul Wi-Fi HotSpots on the Deutsche Bahn's ICE high speed trains.

American wireless carrier Nextel Communications field tested wireless broadband network technologies including Flash-OFDM in Sprint Nextel|Sprint purchased the carrier in 2006 and decided to deploy the mobile version of WiMAX, which is based on Orthogonal frequency-division multiple access|Scalable Orthogonal Frequency Division Multiple Access (SOFDMA) technology.

Citizens Telephone Cooperative launched a mobile broadband service based on Flash-OFDM technology to subscribers in parts of Virginia in March The maximum speed available was 1.5Mbit/s. The service was discontinued on April 30, 2009.

Digiweb|Digiweb Ltd. launched a mobile broadband network using Flash-OFDM technology at 872MHz in July 2007 in Ireland and Digiweb also owns a national 872MHz license in Norway. Voice handsets are not yet available as of November The deployment is live in a small area north of Dublin only.

Butler Networks operates a Flash-OFDM network in Denmark at 872MHz.

In The Netherlands, KPN-telecom will start a pilot around July 2007.

Orthogonal frequency-division multiplexing - History
*1957: Kineplex, multi-carrier HF modem (R.R. Mosier R.G. Clabaugh)

*1966: Chang, Bell Labs: OFDM paperChang, R. W. (1966). Synthesis of band-limited orthogonal signals for multi-channel data transmission, Bell System Technical Journal volume 45 issue 10, and patent

*1971: Weinstein Ebert proposed use of Fast Fourier transform|FFT and guard intervalS.Weinstein and P. Ebert, Data transmission by frequency-division multiplexing using the discrete Fourier transform, IEEE Transactions on Communication

*1985: Cimini described use of OFDM for mobile communications

*1985: Telebit Trailblazer Modem introduced a Packet Ensemble Protocol ()

*1989: OFDM international patent application PCT/FR 89/00546, filed in the name of THOMSON-CSF, Fouche, de Couasnon, Travert, Monnier and allhttp://

*October 1990: TH-CSF LER, first OFDM equipment field test, 34 Mbit/s in an 8MHz channel, experiments in Paris area

*December 1990: TH-CSF LER, first OFDM test bed comparison with VSB in Princeton USA

*September 1992: TH-CSF LER, second generation equipment field test, 70 Mbit/s in an 8MHz channel, twin polarisations. Wuppertal, Germany

*October 1992: TH-CSF LER, second generation field test and test bed with BBC, near London, UK

*1993: TH-CSF show in Montreux SW, 4 TV channel and one HDTV channel in a single 8MHz channel

*1994: , Method and apparatus for multiple access between transceivers in wireless communications using OFDM spread spectrum by Michel Fattouche and Hatim Zaghloul

*1995: ETSI Digital Audio Broadcasting standard EUreka: first OFDM based standard

*2005: OFDMA is candidate for the 3GPP Long Term Evolution (LTE) air interface E-UTRA downlink.

*2007: The first complete LTE air interface implementation was demonstrated, including OFDM-MIMO, SC-FDMA and multi-user MIMO uplink[ Nortel 3G World Congress Press Release]

I²C - Buffering and multiplexing
When there are many I²C devices in a system, there can be a need to include bus Data buffer|buffers or multiplexers to split large bus segments into smaller ones

Buffers can be used to isolate capacitance on one segment from another and/or allow I²C to be sent over longer cables or traces

Alternatively, other types of buffers exist that implement current amplifiers, or keep track of the state (i.e. which side drove the bus low) to prevent latch-up. The state method typically means that an unintended pulse is created during a hand-off when one side is driving the bus low, then the other drives it low, then the first side releases (this is common during an I²C acknowledgement).

Parallax barrier - Time multiplexing to increase resolution
Time multiplexing provides a means of increasing the resolution of a parallax barrier system. In the design shown each eye is able to see the full resolution of the panel.

Parallax barrier - Time multiplexing to increase resolution
The design requires a display that can switch fast enough to avoid image flicker as the images swap each frame.

Application delivery network - TCP multiplexing
TCP Multiplexing is loosely based on established connection pooling techniques utilized by application server platforms to optimize the execution of database queries from within applications

Application delivery network - TCP multiplexing
Some ADN implementations take this technique one step further and also multiplex HTTP and application requests. This has the benefit of executing requests in parallel, which enhances the performance of the application.

Digital holography - Multiplexing of holograms
arXiv preprint arXiv: , 2012 multiplexing schemes

ATM Adaptation Layer 5 - Packet type and multiplexing
The AAL5 trailer does not include a type field

RFC 2684, Multiprotocol Encapsulation over ATM, describes two encapsulation mechanisms for network traffic, one of which implements the former scheme and one of which implements the latter scheme.

The former scheme, in which the hosts agree on the high-level protocol for a given circuit, is referred to in RFC 2684 as Virtual Circuit Multiplexing|VC Multiplexing

The latter scheme, in which the hosts use a single virtual circuit for multiple protocols, is referred to in RFC 2684 as LLC Encapsulation

RFC 2684 specifies that hosts can choose between the two methods of using AAL5. Both the sender and receiver must agree on how the circuit will be used. The agreement may involve manual configuration.

Analog filter - Early multiplexing
combine) the wider bandwidth of telephone channels (as opposed to telegraph) without either an unacceptable restriction of speech bandwidth or a channel spacing so wide as to make the benefits of multiplexing uneconomic.Blanchard, pp

The basic technical reason for this difficulty is that the frequency response of a simple filter approaches a fall of 6 Octave (electronics)|dB/octave far from the point of resonance

At the turn of the century as telephone lines became available, it became popular to add telegraph onto telephone lines with an earth return phantom circuit.Telegraph lines are typically unbalanced line|unbalanced with only a single conductor provided, the return path is achieved through an ground (electricity)|earth connection which is common to all the telegraph lines on a route

Subcarrier multiplexing
'Subcarrier Multiplexing (SCM)' is a method for combining (multiplexing) many different communications signals so that they can be transmitted along a single optical fiber. SCM (also known as SCMA, SubCarrier Multiple Access) is used in passive optical network (PON) access infrastructures as a variant of wavelength division multiplexing (WDM).

SCM follows a different approach compared to WDM

The operation of multiplexing and demultiplexing the single subcarriers is carried out electronically. The conversion into the optical carrier is done at the multiplexer side. This gives an advantage over a pure WDM access, due to the lower cost of the electrical components if compared with an optical multiplexer.

SCM has the disadvantage of being limited in maximum subcarrier frequencies and data rates by the available bandwidth of the electrical and optical components. Therefore, SCM must be used in conjunction with WDM in order to take advantage of most of the available fiber bandwidth, but it can be used effectively for lower-speed, lower-cost multiuser systems.

Statistical multiplexing
When performed correctly, statistical multiplexing can provide a link utilization improvement, called the statistical multiplexing gain.

Statistical multiplexing is facilitated through 'packet mode' or 'packet-oriented' communication, which among others is utilized in packet switched computer networks. Each stream is divided into packets that normally are delivered asynchronously in a first-come first-served fashion. In alternative fashion, the packets may be delivered according to some scheduling discipline for fair queuing or differentiated and/or guaranteed quality of service.

* Random frequency-hopping orthogonal frequency division multiple access (RFH-OFDMA)

* Code-division multiple access (CDMA), where different amount of spreading codes or spreading factors can be assigned to different users.

Statistical multiplexing normally implies on-demand service rather than one that preallocates resources for each data stream. Statistical multiplexing schemes do not control user data transmissions.

Statistical multiplexing - Comparison with static TDM
Time domain statistical multiplexing (packet mode communication) is similar to time-division multiplexing (TDM), except that, rather than assigning a data stream to the same recurrent time slot in every TDM data frame|frame, each data stream is assigned time slots (of fixed length) or data frames (of variable lengths) that often appear to be scheduled in a randomized order, and experience varying delay (while the delay is fixed in TDM).

Statistical multiplexing - Usage
* The MPEG transport stream for digital TV transmission. Statistical multiplexing is used to allow several video, audio and data streams of different data rates to be transmitted over a bandwidth-limited channel (see Statistical multiplexer). The packets have constant lengths. The channel number is denoted Program ID (PID).

* The User Datagram Protocol|UDP and Transmission Control Protocol|TCP protocols, where data streams from several application processes are multiplexed together. The packets may have varying lengths. The port numbers constitute channel identification numbers (and also address information).

* The X.25 and Frame relay packet-switching protocols, where the packets have varying lengths, and the channel number is denoted Virtual Connection Identifier (VCI). The international collection of X.25 providers, using the X.25 protocol suite was colloquially known as the Packet switched network in the 1980s and into the beginning of the 1990s.

* The Asynchronous Transfer Mode packet-switched protocol, where the packets have fixed length. The channel identification number consists of a Virtual_Circuit_Identifier|Virtual Connection Identifier (VCI) and a Asynchronous Transfer Mode#Why_virtual_circuits.3F|Virtual Path Identifier (VPI).

Space-division multiplexing - MIMO
* Cooperative wireless communications|Cooperation are known as network MIMO systems, distributed MIMO systems, macrodiversity MIMO, or virtual antenna array systems. Mobile devices use the partnered mobile devices' antennas, antenna arrays, or antenna elements as virtual antennas.

Space-division multiplexing - MIMO broadcast (MIMO BC)
MIMO broadcast represents a MIMO downlink case in a single sender to multiple receiver wireless network

Space-division multiplexing - MIMO MAC
Conversely, MIMO MAC represents a MIMO uplink case in the multiple sender to single receiver wireless network

Space-division multiplexing - Cross-layer MIMO
Cross-layer MIMO enhances the performance of MIMO links by solving certain cross-layer problems that may occur when MIMO configurations are employed in a system. Cross-layer techniques can be used to enhance the performance of SISO links as well. Examples of cross-layer techniques are Joint Source-Channel Coding, Adaptive Modulation and Coding (AMC, or Link Adaptation), Hybrid ARQ (HARQ), and user scheduling.

Space-division multiplexing - Cooperative MIMO (CO-MIMO)
CO-MIMO improves the performance of a wireless network by introducing multiple antenna advantages, such as diversity, multiplexing and beamforming

Code division multiplexing
'Code division multiple access' ('CDMA') is a channel access method used by various radio communication technologies.

CDMA is an example of multiple access, which is where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth (signal processing)|bandwidth). To permit this to be achieved without undue interference between the users, CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code).

CDMA is used as the access method in many List of mobile phone standards|mobile phone standards such as IS-95|cdmaOne, CDMA2000 (the 3G evolution of cdmaOne), and WCDMA (the 3G standard used by GSM carriers), which are often referred to as simply CDMA.

Code division multiplexing - History
The technology of code division multiple access channels has long been known

Code division multiplexing - Uses
* One of the early applications for code division multiplexing is in the Global Positioning System (GPS). This predates and is distinct from its use in mobile phones.

* The Qualcomm standard IS-95, marketed as cdmaOne.

* The Qualcomm standard IS-2000, known as CDMA2000, is used by several mobile phone companies, including the Globalstar satellite phone network.

* The UMTS 3G mobile phone standard, which uses W-CDMA.

* CDMA has been used in the 'OmniTRACS' satellite system for transportation logistics.

Code division multiplexing - Steps in CDMA modulation
CDMA is a spread-spectrum multiple access technique

Each user in a CDMA system uses a different code to modulate their signal

An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously

In general, CDMA belongs to two basic categories: synchronous (orthogonal codes) and asynchronous (pseudorandom codes).

Code division multiplexing - Code division multiplexing (synchronous CDMA)
The digital modulation method is analogous to those used in simple radio transceivers

Charlieplexing - Traditional multiplexing
Display multiplexing is very different from multiplexing used in data transmission, although it has the same basic principles. In display multiplexing, the data lines of the displays are connected in parallel to a common bus on the microcontroller. Then, the displays are turned on and addressed individually. This allows use of fewer I/O pins than it would normally take to drive the same number of displays directly.

Bursting - Multiplexing and routing
Intrinsically bursting neurons can use this band-pass filtering effect in order to encode for specific destination neurons and multiplexing|multiplex signals along a single axon

Frequency division multiplexing
In telecommunications, 'frequency-division multiplexing' ('FDM') is a technique by which the total bandwidth (signal processing)|bandwidth available in a communication channel|communication medium is divided into a series of non-overlapping frequency sub-bands, each of which is used to carry a separate signal

Frequency division multiplexing
The most natural example of frequency-division multiplexing is radio and television broadcasting, in which multiple radio signals at different frequencies pass through the air at the same time

Frequency division multiplexing - How it works
The multiple separate information signals that are sent over a FDM system, such as the video signals of the television channels that are sent over a cable TV system, are called baseband signals

The carrier center frequency produces sub-frequencies from the mixing of the modulated baseband. The information from the modulated signal is carried in sidebands on each side of the carrier frequency. Therefore all the information carried by the channel is in a narrow band of frequencies clustered around the carrier frequency, this is called the passband of the channel.

Similarly, additional baseband signals are used to modulate carriers at other frequencies, creating other channels of information

For example, the coaxial cable used by cable television systems has a bandwidth of about 1000 MHz, but the passband of each television channel is only 6 MHz wide, so there is room for many channels on the cable.

At the destination end of the cable or fiber, or the radio receiver, for each channel a local oscillator produces a signal at the carrier frequency of that channel, that is mixed with the incoming modulated signal. The frequencies subtract, producing the baseband signal for that channel again. This is called demodulation. The resulting baseband signal is filtered out of the other frequencies and output to the user.

Frequency division multiplexing - Telephone
Modern telephone systems employ digital transmission, in which time-division multiplexing (TDM) is used instead of FDM

Frequency division multiplexing - Telephone
Since the late 20th century Digital Subscriber Lines have used a Orthogonal frequency-division multiplexing|Discrete multitone (DMT) system to divide their spectrum into frequency channels.

Frequency division multiplexing - Group and supergroup
A once commonplace FDM system, used for example in L-carrier, uses crystal filters which operate at the 8MHz range to form a Channel Group of 12 channels, 48kHz bandwidth in the range 8140 to 8188kHz by selecting carriers in the range 8140 to 8184kHz selecting upper sideband this group can then be translated to the standard range 60 to 108kHz by a carrier of 8248kHz. Such systems are used in DTL (Direct To Line) and DFSG (Directly formed super group).

132 voice channels (2SG + 1G) can be formed using 'DTL' plane the modulation and frequency plan are given in FIG1 and FIG2 use of DTL technique allows the formation of a maximum of 132 voice channels that can be placed direct to line. DTL eliminates group and super group equipment.

'DFSG' can take similar steps where a direct formation of a number of super groups can be obtained in the 8kHz the DFSG also eliminates group equipment and can offer:

* Less equipment to install and maintain

* Increased reliability due to less equipment

Both DTL and DFSG can fit the requirement of low density system (using DTL) and higher density system (using DFSG). The DFSG terminal is similar to DTL terminal except instead of two super groups many super groups are combined. A Mastergroup of 600 channels (10 super-groups) is an example based on DFSG.

Frequency division multiplexing - Other usage example: non related to telephone
FDM can also be used to combine signals before final modulation onto a carrier wave. In this case the carrier wave|carrier signals are referred to as subcarriers: an example is stereo FM transmission, where a 38kHz subcarrier is used to separate the left-right difference signal from the central left-right sum channel, prior to the frequency modulation of the composite signal.

A NTSC|television channel is divided into Subcarrier#Television|subcarrier frequencies for video, color, and audio.

Digital Subscriber Line|DSL uses different frequencies for voice and for upstream (networking)|upstream and downstream (computer science)|downstream data transmission on the same conductors, which is also an example of frequency duplex.

E-carrier level 1 - E2: multiplexing level 2: 8Mbit/s
The 8Mbit/s frame structure is defined in the ITU-T Rec. G.742. The frame is divided into four groups:

* Group I contains the FAS, with sequence ; the A-bit (remote alarm); the S-bit (spare); and 200 T-bits (tributary) transporting data.

* Group IV contains a block of four J-bits, a block of R-bits (justification opportunity), one per tributary, and 204 T-bits. To check whether R-bits have been used, the J-bits are analyzed in each of the groups II, III, and IV (there are three per tributary). Ideally the R-bit does not carry useful information on 42.4% of the occasions. In other words, this percentage is the probability of justification or the insertion of stuffing bits.

* Group IV contains a block of four J-bits, a block of R-bits (justification opportunity) one per tributary, and 376 T-bits. To check whether R-bits have been used, the J-bits are analyzed in each of the groups II, III, and IV (there are three per tributary). Ideally the R-bit does not carry useful information on 43.6% of the occasions.

* Group I contains the FAS, with sequence ; the A-bit (remote alarm); the S-bit (spare); and 472 T-bits (tributary) transporting data.

* Group VI contains a block of four J-bits, a block of R-bits (justification opportunity), one per tributary, and 376 T-bits. To check whether R-bits have been used, the J-bits are analyzed in each of the groups II, III, IV, V, and VI (there are five per tributary). Ideally the R-bit does not carry useful information on 41.9% of the occasions.

Inverse multiplexing An 'inverse multiplexer' (often abbreviated to 'inverse mux.' or 'imux.') allows a data stream to be broken into multiple lower data rate communication links. An inverse multiplexer differs from a demultiplexer because the multiple output streams from the former stay inter-related, whereas those from the latter are unrelated. An inverse multiplexer is the opposite of a multiplexer which divides one high-speed link into multiple low-speed links.

Inverse multiplexing This provides an end to end connection of several times the data rate available on each of the low rate data links. Note that, as with multiplexers, links are often used in bi-directional pairs and, at either end of the link, an inverse mux will be combined with its reverse (an inverse demux) and still be called an inverse mux.

Inverse multiplexing Inverse multiplexers are used, for example, to combine a number of Integrated Services Digital Network|ISDN channels together into one high rate circuit, where a higher rate connection than is available from a single Integrated Services Digital Network|ISDN connection is needed. This is typically useful in areas where higher rate circuits are not available.

Inverse multiplexing An alternative to an inverse mux. is to use three separate links and load sharing of data between them. In the case of IP, network packets could be sent in round-robin scheduling#Data packet scheduling|round-robin mode between each separate link. Advantages of using inverse multiplexing over separate links include:

* Fairer load balancing (computing)|load balancing
Inverse multiplexing * Fairer load balancing (computing)|load balancing

Inverse multiplexing * Network simplicity (no Router (computing)|router needed between boxes with high-speed network interface|interfaces)

This is analogous to inverse multiplexing.

MPEG-1 - Multiplexing To generate the PS, the multiplexer will interleave the (two or more) packetized elementary streams. This is done so the packets of the simultaneous streams can be transferred over the same Channel (communications)|channel and are guaranteed to both arrive at the decoder at precisely the same time. This is a case of time-division multiplexing.

MPEG-1 - Multiplexing Determining how much data from each stream should be in each interleaved segment (the size of the interleave) is complicated, yet an important requirement

Satellite modem - Multiplexing
A multiplexer transforms several digital streams into one stream. This is often referred to as 'Muxing.'

Generally, a demultiplexer is a device which transforms one multiplexing|multiplexed data stream to several streams which it consists of. Satellite modem doesn't have so many outputs, so a demultiplexer here performs a drop and insert|drop operation, allowing to choose channels that will be transferred to output.

A demultiplexer achieves this goal by maintaining frame synchronization.

Ion Television - Multiplexing
Ion Television's stations have made notable use of multiplexing, or splitting a digital broadcast television signal into separate digital subchannel|subchannels. The network's stations usually carry up to six of these digital subchannels, broadcasting as separate networks.

Central Office Multiplexing
This type of multiplexing is needed when the customer wants to terminate the Digital Signal 1|DS1 or DS3 in the central office and wants to ‘pick up’ lower level services

Time–frequency analysis - Modulation and multiplexing
Conventionally, the operation of modulation and multiplexing concentrates in time or in frequency, separately. By taking advantage of the time–frequency distribution, we can make it more efficient to modulate and multiplex. All we have to do is to fill up the time–frequency plane. We present an example as below.

Time–frequency analysis - Modulation and multiplexing
As illustrated in the upper example, using the WDF is not smart since the serious cross-term problem make it difficult to multiplex and modulation.

Time-multiplexing - TDM versus packet-mode communication
Bandwidth reservation distinguishes time-division multiplexing from statistical multiplexing such as statistical time division multiplexing i.e. the time slots are recurrent in a fixed order and pre-allocated to the channels, rather than scheduled on a packet-by-packet basis.

History of smart antennas - Orthogonal frequency division multiplexing (OFDM)
OFDM emerged in the 1950s when engineers at Collins Radio Company found that a series of non-contiguous sub-channels are less vulnerable to inter-symbol interference (ISI)

History of smart antennas - Orthogonal frequency division multiplexing (OFDM)
Dial-up modems developed by Gandalf Technologies and Telebit in the 1970s and 1980s used OFDM to achieve higher speeds

Orthogonal frequency division multiplexing
OFDM is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method

Orthogonal frequency division multiplexing - ADSL
OFDM is used in asymmetric digital subscriber line|ADSL connections that follow the ANSI T1.413 Issue 2|ANSI T1.413 and G.dmt (ITU G.992.1) standards, where it is called discrete multitone modulation (DMT). DSL achieves high-speed data connections on existing copper wires. OFDM is also used in the successor standards ADSL2, ADSL2+, VDSL, VDSL2, and G.fast.

Orthogonal frequency division multiplexing - SDARS
The ground segments of the Digital Audio Radio Service (SDARS) systems used by XM Satellite Radio and Sirius Satellite Radio are transmitted using Coded OFDM (COFDM). Agere gets Sirius about satellite radio design The word coded comes from the use of forward error correction (FEC).

Digital terrestrial television in the United Kingdom - Use of multiplexing technology
Each multiplex is an error-protected bitstream of 24, 27 or 40 megabits per second, which can be used for almost any combination of digitally-encoded Video compression|video, Sound|audio and data. The DVB-T standard provides a multiplex service that can make trade-offs between the number of services and the picture and audio quality.

* a number of services use the same Bandwidth (signal processing)|bandwidth at different times. For example CBeebies and BBC Four currently use the same space in their multiplex, with CBeebies broadcasting from 6am until 7pm and BBC Four from 7pm; similarly for CBBC and BBC Three.

* some multiplexes allocate more bandwidth to services, providing a smaller number of higher-quality services.

* The modulation of the multiplexes can be varied to squeeze higher Digital data|digital bitrates out of the same portion of the electromagnetic spectrum, but require a stronger signal for good reception. The modulation schemes used in the UK are, in order of bandwidth efficiency, each with a progressively higher bitrate, at the cost of progressively higher likelihood of signal degradation:

**Quadrature phase-shift keying|QPSK (only used for tests in the Oxford and London areas)

**Quadrature amplitude modulation|16-QAM (no longer used as of digital switchover)

**Quadrature amplitude modulation|64-QAM (only used on the DVB-T multiplex)

**Quadrature amplitude modulation|256-QAM (only used on the DVB-T2 multiplex)

:By late 2009 multiplexes 2 and A used '64-QAM' and were consequently more prone to poor reception, while the other multiplexes used '16-QAM'. At switchover the transmission mode was changed from '16-QAM' to '64-QAM' on Multiplex 1 (PSB1), increasing the effective bandwidth of the multiplex. The switch to '64-QAM' mode also provided extra bandwidth on Multiplexes C (COM5) and D (COM6).

:By late 2012 the digital switchover was complete, with all DVB-T multiplexes using '64-QAM'. The switchover allowed the transmitters to broadcast at a higher power level, reducing the likelihood of reception errors when receiving '64-QAM' encoded broadcasts.

*Multiplexes can make use of statistical multiplexing at the MPEG video coder whereby the bitrate allocated to a channel within the multiplex can vary dynamically depending on how difficult it's to code the picture content at that precise time, and how much demand there is for bandwidth from other channels

Muxer - Types of multiplexing
Multiple variable bit rate digital bit streams may be transferred efficiently over a single fixed Bandwidth (signal processing)|bandwidth channel by means of statistical multiplexing. This is an asynchronous mode time-domain multiplexing which is a form of time-division multiplexing.

Digital bit streams can be transferred over an analog channel by means of code-division multiplexing techniques such as frequency-hopping spread spectrum (FHSS) and direct-sequence spread spectrum (DSSS).

In wireless communications, multiplexing can also be accomplished through alternating polarization (waves)|polarization (Horizontal plane|horizontal/vertical direction|vertical or clockwise/counterclockwise) on each adjacent channel and satellite, or through phased array|phased multi-antenna array combined with a multiple-input multiple-output communications (MIMO) scheme.

Muxer - Space-division multiplexing
These techniques may also be utilized for space diversity (improved robustness to fading) or beamforming (improved selectivity) rather than multiplexing.

Muxer - Frequency-division multiplexing
One of FDM's most common applications is the old traditional radio and television broadcasting from terrestrial, mobile or satellite stations, using the natural atmosphere of Earth, or the cable television. Only one cable reaches a customer's residential area, but the service provider can send multiple television channels or signals simultaneously over that cable to all subscribers without interference. Receivers must tune to the appropriate frequency (channel) to access the desired signal.

Muxer - Time-division multiplexing
Time-division multiplexing (TDM) is a digital (or in rare cases, analog) technology which uses time, instead of space or frequency, to separate the different data streams

Consider an application requiring four terminals at an airport to reach a central computer. Each terminal communicated at 2400 baud, so rather than acquire four individual circuits to carry such a low-speed transmission, the airline has installed a pair of multiplexers. A pair of 9600 baud modems and one dedicated analog communications circuit from the airport ticket desk back to the airline data center are also installed.

Carrier sense multiple access and multidrop communication methods are similar to time-division multiplexing in that multiple data streams are separated by time on the same medium, but because the signals have separate origins instead of being combined into a single signal, are best viewed as channel access methods, rather than a form of multiplexing.

Muxer - Polarization-division multiplexing
Polarization-division multiplexing uses the polarization (waves)|polarization of electromagnetic radiation to separate orthogonal channels. It is in practical use in both radio and optical communications, particularly in 100 Gbit/s per channel fiber optic transmission systems.

Muxer - Orbital angular momentum multiplexing
Orbital angular momentum multiplexing is a relatively new and experimental technique for multiplexing multiple channels of signals carried using electromagnetic radiation over a single path. It can potentially be used in addition to other physical multiplexing methods to greatly expand the transmission capacity of such systems

For More Information, Visit:
The Art of Service

Multiplexing https://store.theartofservice.com/the-multiplexing-toolkit.html.

Similar presentations

Presentation on theme: "Multiplexing https://store.theartofservice.com/the-multiplexing-toolkit.html."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Multiplexing https://store.theartofservice.com/the-multiplexing-toolkit.html.

Similar presentations

Presentation on theme: "Multiplexing https://store.theartofservice.com/the-multiplexing-toolkit.html."— Presentation transcript:

Similar presentations

About project

Feedback