Spectrally efficient high data rate waveforms for the UFO SATCOM channel

This paper describes the application of spectrally efficient phase shaped 8PSK trellis coded modulation (8PSK-TCM) to the 5 and 25 kHz UHF follow-on (UFO) SATCOM channels. The satellite channel is characterized by a multi-pole linear filter followed by a hardlimiter, zonal filter and traveling wave tube (TWT) amplifier. For the additive white Gaussian noise (AWGN) channel the trellis coding provides about 2.9 dB of coding gain at P_be=10^-5 without bandwidth expansion, however, a high-rate Reed Solomon outer code is used to obtain an additional 1.1 dB resulting in a bandwidth expansion of less than 7%. The performance is examined for symbol rates as high as the channel bandwidth (B_cT⩾1). For operation at lower symbol rates, B _cT>1, the outer code rate is adjusted downwards to fully utilize the channel bandwidth while achieving additional coding gain for disadvantaged terminals, i.e., those with lower C/N₀ capability. Demodulator equalization is required to minimize intersymbol interference (ISI). Spectral control is achieved by shaping the symbol phase transitions, and the resulting constant envelope waveform exhibits very little spectral re-growth following the satellite bandlimiting and non-linearity. The use of periodically inserted pilot bits to maintain coherent detection with dedicated channel applications also serve as stuff bits for matching the symbol rate to the user data rate and the internal clock. The pilot bits result in a bandwidth expansion of typically 3-5%. The paper describes the performance results based on detailed Monte-Carlo simulations of both the spectral characteristics and the bit-error performance and compares the results with laboratory measurement data