Analysis, simulation and design of a pseudo noise synchronization system



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An accurate and reliable synchronization reference was required for use in a laser communication link. To provide such a reference, a Pseudo Noise (PN) synchronization system is selected because of its accuracy and reliability under low signal-to-noise ratios. Also, such a system can be realized with a relatively simple hardware system. When this scheme is used in a coherent communication system low bit error rates may be obtained. Basically, a PN synchronization system is a nonlinear feedback system employing correlation functions in the feedback loop. A crosscorrelation between received and locally generated signals will force the loop to acquire synchronization and track the received signal. The particular crosscorrelation function is generated by PN sequences. The PN synchronization system and its operation are analyzed. Special problems of sync acquisition and system performance with additive Gaussian noise are discussed. A set of equations is developed which provides system parameters for given system requirements. To verify and examine the performance of a PN synchronization system designed with the system equations, a digital computer program simulating system operation was written. After the successful functioning of the model system program, which met design constraints, a hardware PN system was designed and constructed. The parameters used in the hardware system were those used in the computer simulation. Testing of the hardware system revealed that all requirements were met and exceeded, and that it performed as predicted by the computer simulation. It is concluded that a PN synchronization system possessed excellent synchronization and tracking properties, even under low input signal-to-noise ratio. Its use as part of a laser beam communication system would seem appropriate and is recommended.