Transmitter-receiver rake diversity combining for ultra-wideband communications

Since channel information is available at the transmitter for time-division duplex ultra-wideband (UWB) systems, it is possible to perform pre-rake combining before transmission. Such a scheme increases the number of received paths, and enables better detection performance as more of the paths are combined effectively. In this work, it is shown that when the total number of rake fingers is limited, and the pre- and the post-rake finger weights are determined jointly, there exists an optimum distribution of fingers between the transmitter and the receiver to maximize the received signal-to-noise ratio (SNR). There is a performance degradation associated with leaving some of the received paths uncombined, but with the same number of fingers available as a pre-rake or a post-rake only system, a larger SNR is obtained.