Telemetry applications of SOQPSK and GMSK based modulation for airborne platforms

Bandwidth restrictions for flight test operations have led the designers world over to graduate from analog telemetry schemes to more compact digital telemetry schemes. Proper precoding and pulse shaping of non-return to zero (NRZ) waveforms are necessary prior to digital modulation for limiting the bandwidth of power spectrum of the NRZ pulses. The most common pulse shapes used are Gaussian filter for Gaussian minimum shift keying (GMSK), raised cosine filters, etc. Recently shaped offset quadrature phase shift keying (SOQPSK) is introduced as a bandwidth efficient modulation technique. In this paper, we report the bandwidth efficiency of SOQPSK for S-band airborne data links working at 4 Mbps rate [1]. Our results show that the SOQPSK-TG is the more bandwidth efficient modulation scheme than GMSK for telemetry applications.