In this paper, we present a new decoding algorithm for the Wyner-Ziv (WZ) video coding scheme based on turbo codes. In this scheme, a video frame is encoded using a turbo code, and only a subset of the parity bits are sent to the decoder. At the decoder, the temporal correlation of the video sequence is exploited by using the previous frame as noisy side information (SI) for the current frame. However, there is a mismatch between the SI, which is available as pixel values, and the binary code bits. Previous implementations of the decoder use suboptimal approaches that convert pixel values to soft information for code bits. We present a new decoding algorithm for this application based on decoding on a hyper-trellis, in which multiple states of the original code trellis are combined. We show that this approach significantly improves performance without changing the complexity of the decoder. We also introduce a new technique for the WZ decoder to exploit the spatial correlation within a frame without requiring transform-domain encoding at the encoder, thereby reducing its complexity. Simulation results for fixed-rate transmission show a 9-10-dB improvement in the peak signal-to-noise ratio when compared to a WZ video codec that does bitwise decoding and utilizes only the temporal correlation.

We present a cooperative communication scheme in which a group of receivers can collaborate to decode a message that none of the receivers can individually decode. The receivers act as a virtual antenna array in which the combining must be performed over bandwidth-constrained links. The proposed approach is targeted at systems in which the cooperative information must be digitized, such as for wireless or wired links that are constrained to use digital modulation. In such systems, previously proposed schemes such as amplify-and-forward would require that a large amount of information be exchanged when there are many collaborating nodes. The approach presented in this paper, called improved least-reliable bits (I-LRB) collaborative decoding, provides a higher level of adaptation than previously proposed cooperative schemes. The I-LRB scheme utilizes reliability information and information about competing paths in soft-input, soft-output (SISO) decoders to adaptively select the amount of information that is needed to correct a particular part of a message, as well as which bits should be exchanged. Simulation results show that the proposed approach offers a significant performance advantage over a constrained-overhead, incremental form of maximal ratio combining (MRC).

A new approach to design video coding schemes for wireless video applications has emerged recently. Schemes using this approach are based on the principle of distributed source coding, and they exploit the correlation in the frames of the video sequence at the decoder. One such scheme models the correlation between frames as a Laplacian channel, and uses a turbo code to correct errors occurring in this pseudo-channel. Existing implementations use a sub-optimal approximation to compute the channel likelihoods in the BCJR algorithm in the turbo decoder. To resolve this sub-optimality, we propose applying the BCJR algorithm on a trellis-structure with parallel transitions. This trellis structure is called a hyper-trellis. The BCJR maximum a posteriori algorithm is modified to use the hyper-trellis, and computation of the channel-likelihoods are shown to be optimal on the hyper-trellis. Simulation results show that the hyper-trellis approach can yield a 5 dB improvement in peak signal-to-noise ratio.

Cooperative communication techniques are network-based approaches to achieve spatial diversity in systems in which each node only has a single antenna. Many such techniques are based on relaying, which is effective in terms of error performance but requires a large information exchange among the cooperating nodes. Cooperative reception techniques that offer near-optimal performance with a smaller information exchange are an area of ongoing research. One promising approach is to investigate combining techniques that can be used as a model for designing efficient cooperative reception schemes. In this paper, we consider one such technique, called reliability filling, that combines only as much information as needed to meet some reliability threshold. We analyze the performance of this technique for several scenarios of interest. Analytical estimates of the overhead involved in reliability filling are also given. Analysis and simulation results show that reliability filling can offer performance close to maximal-ratio combining while combining fewer symbols.

We investigate reliability exchange schemes that allow a group of radios to act as a distributed antenna array in which radio links are used to exchange information between the various radios. We consider a scenario in which multiple nodes receive independent copies of the same message. Each node independently decodes its message and then participates in a process of "smart" information exchange with the other nodes. Each node transmits its estimates of the a posteriori probabilities of some set of bits, and these estimates are used as a priori information by other receivers. The a priori information is used to perform maximum a posteriori decoding on the received sequence. This process of decoding and information exchange can be repeated several times. Simulation results show that the performance can be significantly improved by careful selection of the bits for which information is exchanged.