Code Tracking Loop for M-ary/SS Systems Using Outputs Addition of Correlators

摘要

A correlator output addition method is proposed for the code tracking of a communications system based on M-ary/SS scheme in which one of several sequences prepared on the transmitter side is transmitted depending on several bits of data. In the correlator output addition method, M advance correlators and M delay correlators are used in addition to M correlators for signal demodulation. A DLL is configured by using the sum of the M correlator outputs. In the code tracking system using the conventional locking PN sequence, there occurs a fixed deterioration of the SN ratio due to splitting of the signal power for the locking PN sequence. In the proposed method, this deterioration does not occur. However, this method is more likely to be affected by the output noise of each correlator if the number of sequences M is increased. Also, by comparison with another conventional method DFL scheme, it is found that the present method has better code tracking characteristics under a large noise. Hence, the method is suitable for cases where locking must be maintained even if the number of sequences M is small and the noise is large.