Mobile Handset Design

3

Design Solutions Analysis for Mobile Handsets

3.1 Introduction

In the previous chapter, we discussed about various problems (multi-path, scattering, Doppler spread, etc.) associated with wireless fading channels. These effects have a strong negative impact on the bit error rate of any modulation technique. The main reason why detection in a fading channel shows poor performance compared with an AWGN channel is because of the randomness of the channel gain due to the deep fade event. Thus, in order to combat these effects, we have to establish the corresponding radio receiver design solutions. In this chapter, we will mainly focus on baseband design solutions and in the next chapter we will consider the RF design solutions.

To improve the received signal quality and to reduce the bit error rate it is mainly diversity, equalization, and channel coding techniques that will be used. These are discussed below.

3.2 Diversity

We learnt about these following points in Chapter 2. (1) The channel conditions (channel transfer function or channel gain) vary with respect to time, this variation may be very fast or slow (depending on the coherent time of the channel). (2) The channel reacts (showing different attenuation, delay, etc.) differently to signals with various frequencies passing through the channel, and signals coming via a variety of paths may experience different types of attenuation due to temperature, moisture content, reflector, and obstacle variation. (3) The signal strength ...