Time tracking error in direct-sequence spread-spectrum networks due to coherence among signals

Data are presented which reveal a time synchronization error in CDMA (code division multiple access) spread-spectrum networks where mutual signal phase coherence is high among communicators. The error is not white noise but is, in fact, periodic with an amplitude, phase, and mean offset which appears to be related to a mixture of the carrier frequency, chip rate, and code frame rate. This periodicity is more evident as carrier and code phase coherence increases among participants in a network and high tracking accuracy is the goal. This has implications for future high-rate data communications and navigation networks in which errors may be attributed to local oscillator instabilities more than a transmission link. The data using a commercial modem suggest that improvements in local oscillator stabilities will improve coherence among network participants but will not necessarily reduce time synchronization errors.<
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