Cork Institute of Technology
Bachelor of Engineering (Honours) in Electronic Engineering- Award
(NFQ Level 8)
Summer 2007
Mobile Communication Systems Engineering
(Time: 2 Hours)
Answer any three questions for full marks Examiners: Dr. K. Murray
Maximum available marks is 100 Prof. G. Hurley
Dr. S. Foley
Q1. (a) Explain the term Channel Coding in relation to data transmission over a wireless channel.
Briefly describe two FEC coding schemes commonly used in GSM.
[7 marks]
(b) Consider the ½ convolutional encoder with constraint length K = 3 shown in Figure 1.
Draw the trellis diagram for this encoder and show the path through the trellis created by
encoding the message M = 11001011. Write down the channel encoded binary sequence
generated for the source message M. Assume that all shift registers have an initial value
of zero. [10 marks]
Figure 1
(c) A DS-CDMA system has an available bandwidth of B = 1.25MHz. Individual users
transmit at a data rate of R = 16kb/s. The system can sustain a signal to interference ratio
of S/I = -12dB, and the system stability factor η = 0.12. Calculate the Erlang capacity of
the DS-CDMA system.
You may find some of the information given in the Appendix below useful for the
required calculations. [8 marks]
(Total: 25 marks)
U2
U1
In
p
ut
1
2
3
Out
p
ut
