Image frequency rejection ratio The image frequency rejection ratio (IFRR) is the measure of the ability of pre selector to reject the image frequency. Ratio of gain at the signal frequency to the gain at the image frequency Mathematically ,IFRR is IFRR =(1+Q2ρ2)1/2 Where ρ = (fsi/fs)-(fs/fsi)

Continued

Multiplexing Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. A Multiplexer (MUX) is a device that combines several signals into a single signal. A Demultiplexer (DEMUX) is a device that performs the inverse operation.

Categories of Multiplexing

Frequency-division Multiplexing (FDM) Individual FDM users are assigned to distinct frequency slots but jumbled together in the time domain FDM is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted.

Frequency-division Multiplexing (FDM) In FDM signals generated by each device modulate different carrier frequencies. These modulated signals are combined into a single composite signal that can be transported by the link. Carrier frequencies are separated by enough bandwidth to accommodate the modulated signal. Channels must separated by strips of unused bandwidth (guard bands) to prevent signal overlapping.

Frequency-division Multiplexing (FDM) In FDM, signals are modulated onto separate carrier frequencies using either AM or FM modulation.

Frequency-division Multiplexing (FDM) FDM is an analog multiplexing technique that combines signals.

Example 1 Assume that a voice channel occupies a bandwidth of 4 KHz. We need to combine three voice channels into a link with a bandwidth of 12 KHz, from 20 to 32 KHz. Show the configuration using the frequency domain without the use of guard bands. Solution Shift (modulate) each of the three voice channels to a different bandwidth, as shown in Figure 6.6.

Example 1

Example 2 Five channels, each with a 100-KHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 KHz between the channels to prevent interference? Solution For five channels, we need at least four guard bands. This means that the required bandwidth is at least 5 x 100 + 4 x 10 = 540 KHz, as shown in Figure 6.7.

Example 2

Time-division Multiplexing (TDM) Individual TDM users are assigned to distinct time slots but jumbled together in the frequency domain Time-division multiplexing (TDM) is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices.

Continued TDM

Continued

TDM is a digital multiplexing technique to combine data.

Continued Interleaving: TDM can be visualized as two fast-rotating switches, one on the multiplexing side and the other on the de multiplexing side. The switches are synchronized and rotate at the same speed, but in opposite directions. On the multiplexing side, as the switch closed in front of a connection, that connection has the opportunity to send a unit onto the path. This process is called interleaving.

Continued On the demultiplexing side, as the switch closed in front of a connection, that connection has the opportunity to receive a unit from the path.

Time-division Multiplexing (TDM) TDM can be implemented in two ways: synchronous TDM and asynchronous TDM.

Synchronous TDM In synchronous time-division multiplexing, the term synchronous means that the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit. Frames Time slots are grouped into frames. A frame consists of a one complete cycle of time slots, including one or more slots dedicated to each sending device.

TDM frames

Interleaving

Continued Framing Bits Because the time slot order in a synchronous TDM system doest no vary from frame to frame, very little overhead information needs to be included in each frame. However, one or more synchronization bits are usually added to the beginning of each frame. These bits, called framing bits, allows the demultiplexer to synchronize with the incoming stream so that it can separate the time slot accurately.

Framing bits

Asynchronous TDM Synchronous TDM does not guarantee that the full capacity of a link is used. Because the time slots are pre assigned and fixed, whenever a connected device is not transmitting, the corresponding slot is empty. Asynchronous time-division multiplexing, or statistical time-division multiplexing, is designed to avoid this type of waste. Like synchronous TDM, asynchronous TDM allows a number of lower-speed input lines to be multiplexed to a single higher-speed line. However, in asynchronous TDM the total speed of the input lines can be greater than the capacity of the link.

In an asynchronous system, if we have n input lines, the frame contains no more than m slots, with m less than n. The number of time slots in an asynchronous TDM frame (m) is based on statistical analysis of the number of input lines that are likely to be transmitting at any given time. In this case any slot is available to any of the attached input lines that has data to send.

Asynchronous TDM Addressing and Overhead In asynchronous TDM each time slot must carry an address telling the demultiplexer how to direct the data. This address, for local use only, is attached by the multiplexer and discarded by the demultiplexer once it has been read. Asynchronous TDM is efficient only when the size of the time slots kept relatively large.

Inverse Multiplexing Inverse multiplexing takes the data stream from one high-speed line and breaks it into portions that can be sent across several lower-speed lines simultaneously, with no loss in the collective data rate.

FM Stereo Multiplexing

Continue The left speaker and right speaker signals are first matrixed and pre emphasis to produce xL(t)+xR(t) and xL(t)-xR(t). The sum is heard with a monophonic receiver. xL(t)-xR(t) DSB modulated at 38KHz subcarrier 19KHz pilot tone is added for receiver synchronization. SCA-Subsidiary communication Athority

FM stereo multiplex receiver

Quadrature carrier Multiplexing Quadrature carrier Multiplexing also known as QAM Utilizes carrier phase shifting and synchronous detection to permit two DSB signal to occupy the same frequency band. The transmitted signal has the form

Quadrature carrier Multiplexing