Turbo Receiver for Multicarrier Spread Spectrum Systems Employing Parity Bit Selected Spreading Sequences

Abstract

In this paper a turbo receiver for multicarrier spread spectrum systems employing parity bit selected spreading code (MC-SS-PB) is proposed where detection and decoding are performed iteratively for each detected bit in the receiver. In MC-SS-PB systems, the parity bits generated by a linear block encoder are used to select a spreading code from a set of orthogonal spreading sequences. The selected spreading code is then used to spread the signals in all subcarriers. In the proposed receiver, soft information passes between the detector and the decoder on multiple iterations. Detection is performed by using the received signal in combination with the extrinsic likelihood provided by a soft input soft output decoder. The turbo receiver is further extended to a multiple user system where the multiple access interference is estimated in each iteration and subtracted out from the received signal. Simulations show a significant reduction in bit error rates when a turbo receiver is used in these systems.