SPREAD SPECTRUM SYNCHRONIZATION USING MATCHED FILTER AND CYCLIC ACCUMULATION

Abstract

Direct sequence spread spectrum communications have become an increasingly popular technique over the decades. Code phase acquisition is a critical and difficult operation in any spread spectrum system. Acquisition must be accomplished within a short period of time and at low signal to noise ratio (SNR) in most communication environments. Conventional acquisition scheme scan not achieve a short acquisition time at low SNR and the estimate can be corrupted by transitions in a source data. To overcome these disadvantages,two new acquisition schemes have been proposed in this study. One is a direct estimate of the code sequence phase while the other is a transition based estimate. Both schemes use a matched filter and cyclic accumulation to provide noise averaging. The direct estimate scheme can operate at a very low SNR while the transition based scheme is more noise sensitive. The transition based sequence estimate scheme makes the acquisition process insensitive to data transitions in the input signal and to small frequency offsets in demodulation. A statistical test system was developed on a DEC station-50001125 using Signal Processing WorkSystem (SPW) software. Simulations were performed with three codephase estimation schemes and transition probabilities were evaluated. Mean acquisition times over a range of SNR were then determined using a system model. Results indicate that both proposed schemes will achieve much better acquisition time performance than previously reported methods.