Evaluation of CMA+AMA Equalization for SOQPSK Modulation in Aeronautical Telemetry

Abstract

Multipath interference continues to be the dominant cause of telemetry link outages in low-elevation angle reception scenarios. The most reliable and universally applicable solution to this problem is in the form of equalization. Previous work in this area has considered the Constant modulus algorithm (CMA) equalizer operating in a blind adaptive mode. To the extent that knowledge of the multipath channel improves the performance of CMA and related equalizers and permits the use of other equalization techniques, data aided equalizers are of interest. Channel knowledge is obtained by comparing the received samples with the samples corresponding to a known bit pattern (called a pilot block) periodically inserted in the telemetry data stream. The main objective of this research is to evaluate the performance of a modified CMA equalization algorithm, which has the property of automatically resolving the phase of the QPSK modulated symbol, and to determine its suitability for use with SOQPSK-TG by taking into account the capability of exploiting the presence of a periodically inserted pilot block. As an initial effort in that direction, this paper provides simulation results of the error performance of the blind linear combination of CMA and alphabet matched algorithm (AMA) equalizer as compared to that of pilot assisted equalization with SOQPSK modulation over aeronautical channel.