Generalized Communication System (GCS)

7/29/2019 Generalized Communication System (GCS)

1/9

1.1

Department of Electrical Engineering

MODULE EEE344: PRINCIPLES OFCOMMUNICATION SYSTEMS

Presented By:

Adnan Mir

Email: [email protected]

Room No. 328


Comsats Institute of Information Technology

Abbottabad 22060

Pakistan
mailto:[email protected]:[email protected]


2/9

1.2


Syllabus: Part 1

1. A Generalised Communication System

2. Linearity and Non-linearity, and their Effects

3. Time and Frequency (Fourier Analysis)

4. Transfer and Unit Impulse Response Functions

5. Continuous and Discrete Systems

6. Digital Baseband and Carrier Modulation


3/9

1.3


1. A Generalised Communication System (GCS)

1.1 Schematic Diagram of GCS

Any practical communication system can be mapped on to this generalised framework.

Objective of the communication system is to reproduce source signal at sink.

Functions of individual elements and their signal processing requirements will now be

considered.

NOISE & DISTORTION

TRANSMITTER SITE

(CODER)

RECEIVER SITE

(DECODER)

SOURCE

ENCODER(SE)

SOURCE

DECODER(SD)

CHANNEL

DECODER(CD)

CHANNEL

ENCODER(CE)

SOURCE SINK

TX

RX


4/9

1.4


1.2 GCS Elements and their Signal Processing (SP) Requirements

1.2.1 Source

INFORMATION REDUNDANCY

(ESSENTIAL) (NON-ESSENTIAL)

Many sources can be processed to remove some of the redundancy and hence allow

the transmission channel to be used more efficiently. This is a function of the sourceencoder.

Also, analogue sources, e.g. speech, may be digitized; this is a further function of the

source encoder and involves sampling and quantization.

As more is known of source characteristics, so a more efficient source encoder can be

designed.

SOURCE


5/9

1.5


1.2.2 Source Encoder

(a) Data

Data compression coding requires statistical analysis of data, e.g.

Data Word Probability Compressed Word

101 0.6 0

010 0.2 10

110 0.05 1101

111 0.05 1110100 0.04 1111

011 0.03 11000

000 0.02 110010

001 0.01 110011

Total 1.00

Average number digits after encoding average number of digits before encoding

for compression to be successful.

Signal processing involves statistical analysis of source data and code design.


6/9

1.6


1.2.2 Source Encoder (cont.)

(b) Speech

Source encoding typically involves ADC and compression.

Only information on high energy regions is digitized and transmitted, together with

voiced/unvoiced decisions. Thus, effective sampling rate is reduced.

Signal processing requires real-time digital spectrum analysis routines, digital filtering

and analogue-to-digital conversion (ADC).

REGIONS OF HIGH ENERGY

FREQUENCY

SPEECH

SPECTRUM

f20 f4f3 4kHzf1


7/91.7


1.2.2 Source Encoder (cont.)

(c) Image

Source encoding involves digitization and compression.

After digitization, typically employs 2-D digital spatial transform to describe areas of

some pixel type efficiently; also frame-to-frame differential encoding, and variable-

length compression coding (MPEG algorithm).

Signal processing requires 2-D transforms, differential encoding, data compression

coding and ADC.

PIXEL

x

y


8/91.8


1.2.3 Channel Encoder

Function of the channel encoder is to protect the source-encoded data against errors

caused by noise/distortion on the transmission channel.

Involves error control coding to detect and/or correct errors:

Involves modulation to match the coded data to the type of channel being used

(baseband or RF carrier).

As more is known about the channel characteristics, so a more efficient channel

encoder can be designed. Signal processing involves time and frequency domain analysis of waveforms and

spectra, together with code design and ADC.

INFORMATION PARITY CHECKS

CODEWORD


9/91.9


1.2.4 Channel

Typical effects:

Gaussian and/or non-Gaussian noise;

Multipath;

Doppler Shifts;

Delay;

Fading.

Signal processing to counter channel effects on the received signal may include noise

suppression, equalisation, frequency offset correction, automatic gain control anddiversity combining.

1.2.5 Channel Decoder

Converse of channel encoder: demodulation and decoding; again time and frequency

domain processing, together with ADC.

1.2.6 Source Decoder

Converse of source encoder: data expansion and possibly DAC.

Generalized Communication System (GCS)

Documents

Transcript of Generalized Communication System (GCS)