Zero forcing equalizing filter for MIMO channels with intersymbol interference

Equalization in the time domain is a well-known technique for combating intersymbol interference (ISI) in frequency selective channels. We derive the general structure of the linear zero forcing (ZF) equalizing filters for multiple input multiple output (MIMO) communication systems with more outputs than inputs. These filters are finite impulse response (FIR) filters in general and their structure is determined by the number of inputs and outputs. The relation between the spatial diversity of the system and the necessary filter length is worked out and it is shown, that an optimal time lag in the filter will improve the performance considerably.