Performance of Filter Bank-Based Spreading Codes for Multipath/Multiuser Interference

Spread Spectrum Communications is a technique in which the transmission bandwidth is much larger than that normally required to transmit at the given data rate. The use of this excess bandwidth provides the system with advantages in the areas of anti-jam communications, high resolution ranging, resistance to multipath fading, and low probability of intercept/detection of the transmissions. The traditional spreading sequences used in spread spectrum communications are the maximal length sequences, due their good randomness properties as well as their ease of generation. Recently, a new class of spreading codes has been developed based upon the time-frequency duality of multirate lter bank structures. Unlike the maximal length sequences, these new codes are not limited to being binary valued. Instead, the elements of the sequences are determined by an optimization process which emphasizes certain desirable code properties. In this paper, spreading codes based upon multirate lter banks are developed for use in a channel characterized by both multiuser and multipath interference. Several sets of codes are designed for various channel conditions and analytical bit error rate results are generated. These results are then compared to those for conventional maximal length sequences.