Digital Signaling on ISI Channels

Land mobile radio channels are modeled as fading dispersive channels, because of the multipath propagation and the randomly changing medium characteristics. Many types of impairments are observed on these channels such as multipath spread (or delay spread), fading, Doppler spread, nonlinear distortion, frequency offset, phase jitter, impulse noise, thermal noise, and co-channel and adjacent channel interference arising from spectrum sharing. This chapter concentrates on the effects of delay spread, fading, Doppler spread, thermal noise, and co-channel interference. Delay spread causes interference between adjacent symbols, known as intersymbol interference (ISI), a large Doppler spread indicates rapid channel variations and necessitates a fast convergent algorithm when an adaptive receiver is employed, and fading results in a very low received signal-to-noise ratio or signal-to-interference ratio when the channel exhibits a deep fade.