Spread spectrum code pulse position modulated receiver having delay

Abstract

A spread spectrum code pulse position modulated communication system is disclosed. The communication system includes a spread spectrum code pulse position modulated receiver that compensates for the delay spread of a transmission medium, such as a wireless radio channel of a local area network. Delay spread may cause signal components of one transmitted spread spectrum codeword to spill over into chip positions of adjacent symbols, causing intersymbol interference, or into chip positions on quadrature channels of a given symbol interval, such as in a QPSK implementation, causing interchip interference. The disclosed receiver decodes a transmitted spread spectrum code pulse position modulated signal in the presence of such delay spread, utilizing a tentative symbol estimator to sample the matched filter data. The tentative symbol estimator will assign a weight to each potential symbol value, taking into account the cross-rail or bias influence caused by the residual coupling between the signals on quadrature channels for a given symbol duration. In addition, the disclosed receiver includes a mode sifter which evaluates the weighted values for each symbol estimate and assigns final estimates to each symbol value, taking into account the influence of codewords transmitted during one or more successive symbol intervals on one another.