Smart Phone and Next Generation Mobile Computing

Supporting Wireless Technologies 109

changes. To cope with noises in received signals, a wireless system

has to ensure that the transmitted signals are sufficiently stronger

than the noises. Another approach is to employ spread spectrum

schemes (explained below) that convert a signal over a wide range of

frequencies of low power density as random noise. Wireless signals

are subject to various impairments or distortion along the way from

the transmitter to the receiver. To quantify these effects, the signal-

to-noise ratio (SNR) is used to represent the ratio of the power in a

signal to the power of the noise. SNR is usually computed in decibels

as the product of 10 and the logarithm of the raw power ratio.

3.2.1.3 Multi-Path Propagation

The receiver