ABSTRACT
In digital communications, a precise knowledge of the parameters characterizing the quality of a communication channel is extremely important for efficient data transmission. The classical Shannon result states that the data rate of a communication channel is a function of the signal-to-noise ratio (SNR). This chapter describes the problem of determining the quality of a communication channel and, more particularly, how to reliably estimate the SNR of a channel in a complex multipath propagation environment. It presents methods for estimating the level of interferers in a spectral window of a given bandwidth of a communication channel. The chapter provides another method of determining the level of interferers with a wave form termed frequency-spanning Nyquist set. The basic idea is not to generate sine waves on a Nyquist frequency while spanning the entire phase range evenly but rather to span the frequency range in a small vicinity of the Nyquist frequency.
