| In this work, we consider receiver design for lattice coded transmission over linear Gaussian channels. The lattice code framework allows for a natural approach for joint detection and decoding that considers the combined effect of channel distortion and the code, thus removing the need for distinct detection and decoding operations. In our receiver design, we adopt the tree search approach and separate the joint detection and decoding process into two stages: preprocessing and tree search. The role of the preprocessing stage is to expose the tree structure in a form matched to the search stage. We argue that the forward and feedback (matrix) filters of the minimum mean square error decision feedback equalizer (MMSE-DFE) are instrumental for solving the joint detection and decoding problem in a single search stage, and allow formulating the detection/decoding problem as a Closest Lattice Point Search (CLPS) at the expense of a marginal performance loss. We further show that MMSE-DFE filtering facilitates use of lattice reduction methods to reduce complexity and also allows efficient search for solutions in under-determined linear systems.;For the search stage, we present a generic tree search algorithm for CLPS based on branch and bound (BB) techniques, and show that it encompasses all existing sphere decoders as special cases. The proposed generic algorithm further allows for an interesting classification of tree search decoders, sheds more light on the structural properties of all known sphere decoders, and inspires the design of more efficient decoders. In particular, an efficient decoding algorithm that resembles the well known Fano sequential decoder is identified. The excellent performance-complexity tradeoff achieved by the proposed MMSE-DFE Fano decoder is established via simulation results and analytical arguments in several scenarios.;Finally, we use the lattice coding/decoding framework for outage-limited cooperative channels for practical implementations of the optimal cooperation protocols proposed by Azarian et al. In particular, for the relay channel we implement a variant of the dynamic decode and forward (DDF) protocol, which uses orthogonal constellations to reduce the channel seen by the destination to a single-input single-output (SISO) time-selective one, while inheriting the same diversity-multiplexing tradeoff (DMT). (Abstract shortened by UMI.)... |
