Reduced Complexity Implementation of Passband Adaptive Equalizers

High-speed modems typically employ quadrature amplitude modulation (QAM) so that two signal paths, in-phase and quadrature, are simultaneously being used. The standard receiver structure has, in effect, four adaptive equalizers, one for each of the two signal paths and two to correct for cross coupling between signal paths. As a result, equalization normally requires
8N
multiplications per baud interval, where
N
is the number of taps, to perform the needed signal processing including adaptive updating of the weights., In this correspondence, we present a new signal processing algorithm which requires only
6N
multiplications per baud interval. For fractionally spaced equalization and adaptive cancellation,
N
is quite large so that this saving can be of practical value in improwng throughput capability of custom chips, or depending on the architecture, with programmable signal processor chips. Specifically, the algorithm is advantageous for implementations where multiplications require a longer execution time than additions.