Analysis of SAW correlator based communication systems employing binary encoded orthogonal frequency coding

Surface acoustic wave (SAW) correlators using orthogonal frequency coding (OFC) in communication systems provide high code diversity and enhanced processing gain. The SAW correlator is a single compact device that computes correlation operation in real time without external power and simplifies the transceiver circuits. An OFC SAW correlator with N_c number of chips can have maximum N_c number of completely orthogonal sequences. This paper presents two algorithms which describe the procedure of selection of N_c sequences for an N_c-chip OFC SAW correlator. In a SAW correlator based communication system, N_c is limited as increase in N_c leads to increase in the device length making the device operation impractical. The paper describes a binary encoding technique using Walsh code for OFC correlators to increase the number of usable sequences in SAW correlator based communication systems. Mathematical expressions are formulated to calculate possible number of sequences generated using the proposed encoding technique. Multiuser and MIMO communication systems using Walsh coded OFC SAW correlator are presented. Simulations are carried out to investigate the performance of multiuser communication for additive white Gaussian noise (AWGN) and Rayleigh fading channels. Performance of MIMO system is investigated in Rayleigh fading channel.