SOQPSK-TG STC: A New Decoding Scheme for a Higher Bit Rate and a Better Budget Link

Abstract

To protect telemetry from antenna masking during flight tests, two antennae must be used on-board. To avoid phase opposition of the two transmitted signals at reception, frequency diversity has been used for decades. However with spectrum auctions this technique is no longer compatible with the requirement of higher bit rate. To overcome this issue, well-known modulation format like COFDM may be used at the expense of power efficiency, with few constraints on antennae position. IRIG-106 standard proposed also SOQPSK-TG STC which is efficient both in power and in spectrum at the expense of the antennae position. To demodulate this format a dual-trellis solution has been pro-posed based on XTCQM representation [1] with results very close to SISO as far as distance between antennae does not exceed half bit delay. Therefore this decoding scheme is a hard decision scheme and consequently is less power efficient when a FEC such as LDPC is used. In this paper a new de-coding scheme will be presented with soft decision outputs to increase power efficiency, and with a better tolerance to differential delay.