Question

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Please read and answer the following questions
Assignment 2
Text Book: B. Sklar “Digital Communication Fundamental and Applications”
Chapter 2: Formatting and Baseband Modulation
Questions
1. What is the similarities and differences between the terms “formatting ” and “source coding”
2. In using PCM for digitizing analog information, explain how the parameters fidelity, bandwidth, and time delay can be traded off.
3. Why is it often preferred to use units of normalized bandwidth, WT (or time –bandwidth product), compared with bandwidth alone?
Chapter 2: Modulation and Coding Trade-offs
4. For MPSK modulation, bandwidth efficiency increases with higher-dimensional signaling, but for MFSK, it decreases. Explain why this is the case.

Answer 1

Ans. of 1. For writing the correct similarities and differences of Formatting and Source Coding. Formatting is the process whereby source data is prepared for the ensuing digital processing. Sometimes this process is included in the functionality of source coding. The purpose of source coding is to reduce the amount of redundant or unnecessary information from the raw data.

Ans. of 2. As per details in analog and digital communication, for reasonable signal quality at the receiver end of a digital communication system, we have to reduce quantization distortion and violations due to channel noise. At the same time, we have to take into consideration the system cost. For this the following trade-offs are possible.

(a) fidelity. A degree of correspondence between the meaning intended by the sender of a message and the meaning understood by its receiver and it helps in increasing the reliability of the data received

(b) Band Width (BW) Higher bit rates consume more BW but they reduce quantization distortion. ADM system gives less quantization distortion up to 32Kbits bit rate. At 32Kbits quantization distortion is -22 dB which gives only satisfactory speech quality at the receiver end. For further improving speech quality at the receiver end by reducing quantization distortion PCM at higher than 32K bits/sec is superior to ADM. Less quantization distortion as compared to PCM can be achieved at the same bit rate by using DPCM or ADPCM.

(c) Time delay: delay is modeled as a random variable from a family of distributions with unknown parameters.

Ans. Of .3. The Figure 1 plots Power Spectral Density in watts/hertz versus normalized bandwidth, WT, where W is bandwidth and T is the duration of the pulse. WT is often referred to as the time-bandwidth rpodcut of the signal.

Since the pulse or symbo lrate Rs id the reciprocal of T, normalized bandwidth can also be expressed as W/Rs.

From the expression W/Rs, the units of normalised bandwidth are hertz/
(pulse/s) or hertz/(symbol/s). This is relative measure of bandwidth, it is valauble as it describes how efficiently the transmission of bandwidth is utilized for each waveform. of interest.

Any waveform type that requires less than 1.0Hz for sending 1 symbol/s is relatively bandwidth efficient. And by comparison any waveform tyoe that requires more than 1.0 Hz for sending 1 symbol/s is relatively bandwidth inefficient.

Measuring Bandwidth Efficiency (R/W) is important parameter having units of bits/s/hz. This measure involves data rate taher than symbol rate. for a given signalling scheme, R/W describes how much data throughput can be transmitted for each Hertz of availabe bandwidth.

Ans. Of .4.