Improved carrier recovery for signals affected by multipath fading

In this communication we consider the squaring loop carrier recovery scheme, with BPSK signals transmitted through a multipath channel. First starting from a multiray model for the multipath channel, the performance of the squaring loop is derived by suitably simplifying the channel model. We observe that the pattern disturbance is a cyclostationary process with correlated quadrature and in-phase components. Based on this fact we propose a new loop to follow the squarer that explores this correlation. The performance analysis is then extended to take into account the additive noise either in the standard squaring loop or in the new scheme. The improvement offered by the new scheme depends on the noise level and on the fading parameters, because the pattern jitter, even for a constant signal to noise ratios, is highly dependent on the specific channel parameters. Numerical results show that the improvement may be significant, even for some situations of moderate signal to noise ratios