The Application Of A New Approach For Small Delay Multipath Diversity In The Spread Spectrum System

In the spread spectrum communication system, the received signal is the superposition of the transmitted signal which has different delay and attenuation because of the complexity of the communication channel. The multipath component can not be distinguished by the RAKE receiver when the delay is smaller than a chip period. So in this paper a new approach for reception of small delay multipath diversity is proposed to remove the intersymbol interference (1ST) in spread spectrum system.The channel is assumed to be expanded as a f-power series and modeled as a three-term Taylor's series expansion: it is then quadratically frequency-selective channel. The received signals after the designed filters are equivalent to those through the flat fading channels, so the ISI from the other two branches is cancelled. These three branches are then combined with the maximal ratio coherent combining and the final output signal is acquired. The bit error ratio (BER) of the coherent detector is also derived in the paper, and the results of the simulation are comparison to those of the receiver which is based on the linearly frequency-selective channel model.Both the numerical and simulation results demonstrate that the proposed receiver achieves smaller modeling error and significant diversity gains for a given factor comparison to the model of linearly frequency-selective channel.