Presentation on theme: "Introduction to Telecommunications by Gokhale WIRELESS COMMUNICATIONS"— Presentation transcript:
1 Introduction to Telecommunications by Gokhale WIRELESS COMMUNICATIONS CHAPTER 5WIRELESS COMMUNICATIONSIntroduction to Telecommunications by Gokhale
2 Introduction Wireless Communications system in which electromagnetic waves carry a signal through atmospheric space rather than along a wireMost systems use radio frequency (RF, which ranges from 3 kHz to 300 GHz) or infrared (IR, which ranges from 3 THz to 430 THz) wavesIR products do not require any form of licensing by the FCC
3 Timeline of Major Developments Mobile Telephone System (MTS)Introduced in 1946Simplex (one-way transmission) and manual operationImproved Mobile Telephone System (IMTS)Introduced in 1969 using a 450 MHz bandAdvanced Mobile Phone Service (AMPS)Introduced in 1983First system to employ a “cellular” concept
4 Cellular Topology Cellular network: Cellular network components Series of overlapping hexagonal cells in a honeycomb patternCellular network componentsBase Station:Transmitter, Receiver, Controller, AntennaCell: Base station’s span of coverageMobile Switching Center: Contains all of the control and switching elements to connect the caller to the receiver, even as the receiver moves from one cell to another
5 Personal Communications Systems (PCS) PCS is also called Personal Communications Networks (PCN)Goal of PCS is to provide integrated voice, data and video communicationsThree categories of PCS:Broadband: cellular and cordless handsetsNarrowband: enhanced paging functionsUnlicensed: allows short distance operation
6 Hierarchical Cell Structure Key features of PCSVariable cell sizeHierarchical cell structure (picocell, microcell, macrocell, supermacrocell)
8 Analog Access Analog Cellular Systems First generation system Based on FDMA (Frequency Division Multiple Access), where frequency band is divided into a number of channels. Each channel carries only one voice conversation at a time.AMPS operates on 800 MHz or 1800 MHzAdvantages:Widest coverageLimitations:Inadequate to satisfy the increasing demandPoor securityNot optimized for data
10 Digital wireless technologies provide greater system capacity. Digital AccessD-AMPS (Digital-AMPS)TDMA (Time Division Multiple Access)CDMA (Code Division Multiple Access)Digital wireless technologies provide greater system capacity.
11 TDMA TDMA Second generation system Enables users to access the whole channel bandwidth for a fraction of the time, called slot, on a periodic basisHas applications in satellite communicationsAdvantagesImproved capacity
13 CDMA CDMA Third generation system Separates users by assigning them digital codes within a broad range of the radio frequencyFirst technology to use soft-handoffEmploys spread spectrum techniqueAdvantagesImproved capacity, coverage, voice quality, and immunity from interference
15 Spread Spectrum Technique: FHSS Frequency Hopping Spread Spectrum (FHSS)Resists interference by jumping rapidly from frequency to frequency in a pseudo-random wayAdvantageIncreases the total amount of available bandwidth through the assignment of multiple hopping sequences within the same physical areaMore flexible than DSSSApplicationIn large facilities especially with multiple floors
16 Spread Spectrum Technique: DSSS Direct Sequence Spread Spectrum (DSSS)Resists interference by mixing in a series of pseudo-random bits with the actual dataAdvantageIf bits are damaged in transmission, the original data can be recovered as opposed to having to be retransmittedApplicationIs substituted for point-to-point or multi-point connectivity to bridge LAN segmentsLimitationRoaming capabilities are less robust
17 Spread Spectrum Technique: CDPD Cellular Digital Packet DataAllows for a packet of information to be transmitted in between voice telephone callsEnables data specific technology to be tacked onto existing cellular telephone infrastructure
18 Wireless Applications Cellular PhoneHigh mobility and narrow bandwidth (20 to 30 kHz)Cordless PhoneLow mobility and narrow bandwidth (20 to 30 kHz)Wireless LANLow mobility and high bandwidth (typically 10 Mbps)Wireless Application Protocol (WAP) is a standard for wireless data delivery, loading web pages, and navigation
20 Narrowband, Broadband, and Spread Spectrum Signals Narrowband - a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies.Broadband - a type of signaling that uses a relatively wide band of the wireless spectrum.Spread spectrum - the use of multiple frequencies to transmit a signal.
21 Cellular Communications Mobile telephone service - a system for providing telephone services to multiple, mobile receivers using two-way radio communication over a limited number of frequencies.Mobile wireless evolution:First generationSecond generationThird generation
22 Cellular Call Completion Components of a signal:Mobile Identification Number (MIN) - an enclosed representation of the mobile telephone’s 10-digit telephone number.Electronic Serial Number (ESN) - a fixed number assigned to the telephone by the manufacturer.System Identification Number (SID) - a number assigned to the particular wireless carrier to which the telephone’s user has subscribed.
27 Code Division Multiple Access (CDMA) Each voice signal is digitized and assigned a unique code, and then small components of the signal are issued over multiple frequencies using the spread spectrum technique.
28 Global System for Mobile Communications (GSM) A version of time division multiple access (TDMA) technology, because it divides frequency bands into channels and assigns signals time slots within each channel.Makes more efficient use of limited bandwidth than the IS-136 TDMA standard common in the United States.Makes use of silences in a phone call to increase its signal compression, leaving more open time slots in the channel.
29 Emerging Third Generation (3G) Technologies The promise of these technologies is that a user can access all her telecommunication services from one mobile phone.CDMA a packet switched version of CDMA.Wideband CDMA (W-CDMA) - based on technology developed by Ericson, is also packet-based and its maximum throughput is also 2.4 Mbps.
30 Wireless Local Loop (WLL) A generic term that describes a wireless link used in the PSTN to connect LEC central offices with subscribers.Acts the same as a copper local loop.Used to transmit both voice and data signals.
31 Local Multipoint Distribution Service (LMDS) A point-to-multipoint, fixed wireless technology that was conceived to supply wireless local loop service in densely populated urban areas and later on a trial basis to issue television signals.A disadvantage is that its use of very high frequencies limits its signal’s transmission distance to no more than 4km between antennas.
32 Multipoint Multichannel Distribution System (MMDS) Uses microwaves with frequencies in the 2.1 to 2.7 GHz range of the wireless spectrum.One advantage is that because of its lower frequency range, MMDS is less susceptible to interference.MMDS does not require a line-of-sight path between the transmitter and receiver.