Implementation of DSP carrier recovery using all-digital phase-locked loop with vector rotation techniques for high-speed 8-PSK modems.

摘要

Rapidly growing demands for higher multimedia quality require faster and more robust modem sub-systems to compensate system impairments such as frequency offsets in a satellite communication environment. As a result, the development of more robust carrier recovery methods for satellite modems is becoming more and more important.; As an attempt to facilitate such development, this thesis introduces a simple, yet effective, coherent carrier recovery method for high speed, coherent 8-PSK modems using an all-digital phase-locked loop structure and a novel vector rotation computational realization that is easily implementable in any DSP chip architecture. The effectiveness of this method is demonstrated by its ability to successfully combat phase and fine frequency offsets of at least 1% of the symbol rate that are typical of a satellite communication environment. As it is intended for real-time DSP chip deployment, the method is computationally simple because it does not require table look-up, trigonometric evaluations and arithmetic divisions, and is therefore suitable for implementation in both fixed-point and floating-point DSP chips.; The performance of this carrier recovery method is first evaluated using Matlab{dollar}sp{lcub}rm TM{rcub}{dollar} and C simulations. Then it is implemented on the Texas Instruments TMS320c6201, one of the world's fastest commercial fixed-point digital signal processors, to see the possibility of DSP chip deployment of the carrier recovery subsystem. Evaluations in both simulation and DSP implementation are done with Bit-Error Rate (BER) measurements against a Doppler-shifted, additive white Gaussian noise channel with signal-to-noise ratios of as low as 6dB. Evaluation results show that the modem realizing this carrier recovery method has excellent BER performance with less than 0.3dB loss compared to the theoretical performance. The highest achievable bit-rate of the modem application realizing this carrier recovery method is about 100-170kbps, when it is implemented in the high-performance TMS320c6201 DSP chip.