Real-Time CMA Equalization for SOQPSK for Aeronautical Telemetry

Abstract

This paper presents the results of using the constant modulus algorithm (CMA) to recover a shaped offset quadrature-phase shift keying (SOQPSK)-TG modulated signal, which has been transmitted over an aeronautical telemetry channel using the iNET data packet structure. The iNET-packet structure contains known data bits (the preamble and asynchronous marker (ASM) bits) within each data packet, which can be used to determine the minimum mean square error (MMSE) equalizer and is then used as an initializer for the CMA algorithm. A baseline analysis of the performance of the MMSE-initialized CMA equalizer has been previously done using average bit error rates (BER). In order to achieve realtime processing, in this implementation the CMA equalizer weights are updated using a new data packet for each adaptation of the equalizer during which the bit error analysis is being done. Two implementations of the block processing CMA are compared. The first achieves convergence of the equalizer in the startup phase by processing a single fixed packet and the second achieves convergence by processing the multiple packets of received data. Performance evaluation results based on bit error rates, are presented for these two methods and they are compared to a previously determined baseline performance. We note that with the proper choice of parameters these real-time methods can achieve the baseline performance.