ABSTRACT
This chapter begins 'by examining the technology of adaptive equalizers – the devices that make distributed transmission possible with standard modulation techniques. It looks at the interrelationships between the various possibilities in system design. The chapter also looks at an alternate modulation approach (COFDM) that is claimed not to require adaptive equalizers and that may not require directional receiving antennas. The adaptive equalizer treats the transmission channel as though it is some form of filter. Filters can cause variations in frequency and phase response; they can cause various time delays; and they can create signal reflections or echoes. The capabilities of an adaptive equalizer are determined primarily by the length of the delay line and the number of taps/multipliers in the filter. For signals with quadrature modulation, filters are required for both the in-phase and quadrature senses of the signals. Another characteristic of adaptive equalizers is that they require some difference in amplitude between the primary signal and the echoes.
