Analysis of Multipath Interference of SRAKE Receivers in UWB Systems

This paper analyzes the interference in Direct Sequence Spreading Spectrum (DSSS) systems with Selective RAKE (SRAKE) receivers where channel delay is comparable with spreading sequence length. We build an accurate output model of SRAKE receiver and derive the output Signal to Interference-Noise Ratio (SINR) and Bit Error Rate (BER) of SRAKE receiver, taking multipath effect into consideration. Based on this analysis, we showed that in frequency selective channels with SRAKE receiver, system become interference limited as transmit power increases. Besides, there exists a critical spreading factor. When spreading factor is lower than this critical value, E_b/N₀ have to increase dramatically to compensate the multipath effect. This provide a criterion to adaptively choose the optimal spreading factor under different channel conditions.