1. 3F4 Data Transmission Introduction
Dr. I. J. Wassell

2. Pre-requisites Familiarity with IB courses
Signal and Data Analysis (Paper 7)
Linear Systems and Control (Paper 6)
Communications (Paper 6)

3. Booklist
Couch, L. W, “Digital and Analog Communication Systems,” Prentice Hall (5th Edition). Covers all except DFE.
Shanmugam, K. S. Digital and Analog Communication Systems,” Wiley. All except DFE.
Proakis, J. G, “Digital Communications,” McGraw Hill.
Wicker, S. B., “Error Control Systems for Digital Communication and Storage,” Prentice Hall, 1995.

4. Applications
Data transmission over copper cables and optical fibres, e.g.,
computer local area networks (LANs)
integrated services digital network (ISDN) connections, e.g., Basic rate (2B+D) and primary rate (30B+2D) channels. B=64kBit/s, D=16kBit/s.
30 channel pulse code modulation (PCM), i.e., 30 telephony channels, 2.048MBit/s.
Asynchronous transfer mode (ATM) in wide area networks (WANs), e.g., 25MBit/s, 155MBit/s

5. Applications Data storage, magnetic disk drives magnetic tape drives
optical disk drives

6. Topics Covered Communications System Model
Pulse Amplitude Modulation (PAM) for baseband data transmission
Intersymbol Interference (ISI), noise and bit error rates (BER)
Pulse Shaping for bandwidth control and elimination of ISI

7. Topics Covered Line coding schemes
Optimum Transmit and Receive Filtering
Equalisation to compensate for undesirable channel characteristics
Error control coding (ECC)

8. Baseband Transmission
The transmitted signal is limited to a range from -B Hz to +B Hz.
|X(f)|
|X(f)| -B B f
-fc fc f
Baseband
Bandpass
Example baseband channels include
copper cable, magnetic disk, CD-(ROM)

9. Comms System Model
Transmission of digital data in communications channels
True digital data, eg, comms in a computer network
Analogue information which has been converted to a digital format, eg anti-alias LPF followed by A/D conversion

10. Transmission Model X(w) Hc(w) Transmitter N(w) + Y(w) Receiver Digital
Source
Encoder
Error
Control
Coding
Line
Modulator
(Transmit
Filter, etc)
Channel
Noise
Sink
Decoder
Decoding
Demod
(Receive +
Transmitter
Receiver
X(w)
Hc(w)
N(w)
Y(w)

11. Components of the Model
Assume input source is in the form of symbols, eg bytes from a PC, or 16-bit audio samples
Source encoding- Transforms digital symbols into a stream of binary digits (BITS), eg PCM
Error Control Coding- Adding extra bits (redundancy) to allow error checking and correction.

12. Components of the Model
Line Coding- Coding of the bit stream to make its spectrum suitable for the channel response. Also to ensure the presence of frequency components to permit bit timing extraction at the receiver.
Transmit Filtering- Generation of analogue pulses for transmission by the channel.

13. Components of the Model
Channel- Will affect the shape of the received pulses. Noise is also present at the receiver input, eg thermal noise, electrical interference etc.
We will concentrate on the components to the right of the vertical dashed line.

14. Channel Response Assumptions
Linear time-invariant (LTI) frequency response, ie, the channel frequency response Hc(w) is fixed, known and linear.
Additive Gaussian noise- The channel noise has a Gaussian amplitude distribution (pdf) is often assumed to be uncorrelated (ie white, flat power spectral density) and additive.

15. Channel Response Thus the received signal may be expressed as,
Y(w)= Hc(w) X(w)+N(w)
Where,
Hc (w) is the channel frequency response
X(w) is the transmitted signal spectrum
N(w) is the noise spectrum
In practice,
Channel response may be non-linear, time-varying or unknown
Noise may be non-Gaussian, particularly interference.