Non-coherent detection and FM-VCO modulation techniques for quasi-constant amplitude QPSK signals

Abstract

In this thesis, we propose new modulation and demodulation techniques for Feher patented quadrature phase shift keying (FQPSK) signals based on the continuous phase modulation (CPM) interpretation of FQPSK signals. It results from the quasi-constant amplitude and continuous phase characteristics of FQPSK-B signals. First, a new class of non-coherent detection techniques for FQPSK systems is proposed and studied. Non-coherent demodulation enables much faster synchronization and re-synchronization as well as it offers advantages for relatively low bit rate and large Doppler shift or phase noise controlled system environments than coherent demodulation. The theoretical concepts of the described non-coherent detection techniques are based on the instantaneous frequency or phase transition characteristics of FQPSK-B signals. These are accomplished by Limiter-Discriminator (LD), Limiter-Discriminator followed by Integrate-and-Dump (LD I&D) or differential detection methods. We derive the bit error rate (BER) expression for the LD I&D followed by symbol-by-symbol decision, which shows excellent agreement with simulation result. It is shown that significant BER performance improvements can be obtained by increasing the received signal’s observation time over multi-symbols as well as by adopting trellis-demodulation. While the FQPSK transmitted signal is not trellis coded, its trellis coded interpretation based on CPM interpretation of FQPSK signals leads to trellis demodulation. Simulation result shows that a $BER=$10^{-4}$ can be obtained for an $E_b/N_0=12.7dB$. Furthermore, it is shown that the maximum likelihood sequence detection (MLSD) with multiple differential detection can achieve the BER=$10^{-4}$ at $E_b/N_0=11.5dB$, which is only 2.4dB worse than 9.1dB ever reported for coherent MLSD of FQPSK signals. Second, we propose the FM-VCO (CPM) modulation architecture of FQPSK-B signals. Based on the fact that FQPSK-B signal has quasi-constant amplitude and conti...