Sinusoidal SBPSK Modulation Waveform for UHF SATCOM Channels with Improved Adjacent Channel Emissions

It has long been established that all transmissions over US-owned UHF SATCOM channels be adjacent channel emissions (ACE) compliant according to the MIL-STD-188-181 series of standards. 50% Shaped Binary Phase Shift Keying (SBPSK) and 50% SOQPSK are specifically called out for use as the modulation formats of choice for the 5 kHz (narrowband) and 25 kHz (wideband) channels. The ACE requirements are levied in terms of relative RF power spilling over into the adjacent channels above and below the main transmitting frequency. The SOQPSK modulation waveform offers outstanding side lobe suppression such that the ACE requirements are readily met with the standard SOQPSK waveform. The 50% SBPSK waveform, however, has very little ACE margin in the first two 5 kHz offset channels, nor for 9600 bps in the first two 25 kHz offset channels. Methods like the piece-wise-linear approach have been introduced to improve the ACE performance for the 5 kHz channels. This paper introduces a sinusoidal (non-linear) phase shaping method that offers good ACE performance, good bit error rate performance and a relatively easy hardware implementation. This nonlinear phase transition shaping method offers superior ACE suppression with little or no additional modem implementation loss as compared to a coherent BPSK demodulator. The phase transitions from zero to π are achieved by using a sinusoidal function with no phase discontinuity in the transition region. The transition time can vary from zero to the full baud time, achieving a 0 % to 100 % shaping as defined in the SBPSK case.