| University of Dar es Salaam | Department of Electronics and Telecommunications Engineering | _______________________________________________________________________________

| TE 412 Introduction to Wireless Communications | Christine Mwase | 10/03/2014 |

Tutorial Set 9 – from past exam paper

Question One

(a) Discuss how the following aspects are interrelated in mobile communication

systems:

reuse factor / cluster size co-channel interference base-station antenna height

network capacity network coverage

(b) A cellular system covering a total area of 2100 km2 has a total of 1001 radio

channels available for handling traffic. Assume that the area of a cell is 6 km2.

(i) Work out the number of channels if a cluster size of 7 is used.

(ii) How many times would a cluster of size 4 have to be replicated in order to

approximately cover the entire cellular area?

(iii)Work out the number of channels if a cluster size of 4 is used.

(iv) Based on your answers above, explain how the cluster size impacts the

system capacity.

(c) As spectrum is a scarce resource, various spectrum efficient methods and

techniques are always being researched and tested to find a means of better utilising

the available spectrum. Provide a brief outline of cognitive radio from the viewpoint

of efficient utilisation of spectrum.

Question Two

(a) Explain briefly the following concepts in connection with mobile cellular networks:

(i) Handover

(ii) VLR,HLR

(iii)Paging

(b) GSM

(i) The GMSK modulation scheme is used in GSM. What advantage does this

modulation scheme have?

(ii) Explain how a user is authenticated in a GSM network (not the use of a PIN

code).

(iii)Why and where are IMSI, TMSI and MSISDN numbers used in GSM?

(c) Provide your judgement on the evolution and challenges of future wireless

communications. What do you predict will be next and what are the challenges that

we would have to cope with.