A Chip Timing Recovery Scheme for Walsh-Hadamard Code Division Multiplexing

Walsh-Hadamard (WH) code division multiplexing (CDM) is CDM employing WH code as spreading codes. This paper addresses chip timing recovery in band-limited WHCDM using Nyquist pulse shaping. In direct-sequence spread spectrum communications employing pseudo-noise (PN) spreading code, chip timing recovery is achieved with delay-locked loop (DLL). DLL recovers the chip timing on the basis of the impulse-like autocorrelation of PN codes. However, WH code has many side lobes in its autocorrelation function. This makes it impossible to apply DLL to WHCDM. In this paper, we propose a novel chip timing recovery scheme for band-limited WHCDM. The proposed scheme detects the chip timing by using the cross-correlation between the received signal and the WH code whose autocorrelation has the period of twice the chip duration. The results of computer simulation show that the proposed scheme achieves excellent chip synchronization performance.