Generalized non-coherent detection.

Abstract

The objective of this thesis is to introduce new power efficient non-coherent receiver structures for linear (Quadrature Amplitude Modulated and Phase Shift Keyed) as well as Continuous Phase Modulated signals. A generalized non-coherent detection theory, addressing single or multi-amplitude/phase signals as well as operation in time dispersive channels has been developed. Structures of optimal non-coherent sequence estimators and symbol-by-symbol receivers are proposed. The analysis carried out provides the relation and link between existing non-coherent receivers and the optimal non-coherent detection concept. Using the framework set by the generalized non-coherent detection theory and applying approximations and reasonable simplifications wherever needed, we were able to propose new families of powerful, yet simple non-coherent receivers. Such receivers are the: (1) Block Decoders for PSK and CPM signals. They process the received signal information in a block form. Evaluation of them in both ideal and time dispersive channels has verified considerable gains (as compared to conventional differential receivers), especially when used with trellis coded schemes. The evaluation results have indicated improvements higher than 3 dB when the operation takes place in a Gaussian channel. In a faded channel, the results have shown improvements higher than 7 dB and a reduction in error floors close to one order of magnitude. (2) Asymptotically optimal decoders for a time dispersive channel and/or multi-amplitude/phase signals. They have been able to considerably improve the system's performance. When evaluated for uncoded and coded schemes they demonstrated excellent performance. Compared to the conventional differential receiver the results demonstrated improvements in excess of 5 dB. With the introduction of these receivers the extension of non-coherent technology to the power and bandwidth efficient family of the multi-amplitude/phase signals has been made possible. (3) Combined Squared Envelope and Multiple Differential Detection (recursive) Algorithms. They process the information provided by the use of a squared envelope and more than one (multiple) differential receivers in a recursive form. When evaluated with various linear and CPM signals they demonstrated considerable improvements. For white Gaussian noise channels, they achieved gains higher than 9 dB (compared to the conventional differential receiver). In a faded channel they were able to reduce the error floors by more than three orders of magnitude. (4) Symbol-by-symbol receivers based on phase correction and signal combining controlled by decision feedback. These receivers achieve their improvements by applying partial (decision directed) intersymbol interference (ISI) cancellation from the phase of the signal and by combining the outputs of more than one differential detector according to the decisions made regarding previous symbols. Evaluations have demonstrated improvements higher than 5 dB. In all of the above proposed receivers, a particular emphasis has been put on the simplicity factor. Possible efficient implementation scenarios of the receivers using today's digital signal processing technology are discussed in various parts of the present work. To evaluate the proposed schemes, an analytical framework has been developed. It covers evaluation in AWGN (ideal or time dispersive) as well as faded channels. Through this analysis, new distance expressions (equivalent to the Euclidean distance we encounter in coherent systems) which characterize the performance of the proposed non-coherent receivers have been identified. These distance metrics can be used for the design of improved coded schemes, developed to "match" the characteristics and operation principles of the proposed non-coherent receivers.