Sinda Smirani

Achievable Rate Regions for Two-Way Relay Channel using Nested Lattice Coding

This paper studies a Gaussian two-way relay channel where two communication nodes exchange messages with each other via a relay. It is assumed that all nodes operate in half-duplex mode without any direct link between the communication nodes. A compress-and-forward relaying strategy using nested lattice codes is first proposed. Then, the proposed scheme is improved by performing layered coding: A common layer is decoded by both receivers, and a refinement layer is recovered only by the receiver that has the best channel conditions. The achievable rates of the new scheme are characterized and are shown to be higher than those provided by the decode-and-forward strategy in some regions.

Wyner-Ziv lattice coding for two-way relay channel

A Two-Way Relay Channel (TWRC) in which duplex transmission between two users via a relay station is considered. A physical layer network coding strategy based on compress-and-forward relaying scheme for the TWRC is proposed. In the underlying coding strategy, we use nested lattices for Wyner-Ziv coding and decoding. The relay uses the weaker side information available at the receivers from the first transmission phase to broadcast a common quantized version of its received signal. We characterize the achievable rate region of the presented scheme. Then we show that lattice codes can achieve random coding rates.

Lattice-based Wyner-Ziv coding for parallel Gaussian two-way relay channels

Parallel two-way relay channel models a cooperative communication scenario where a relay helps two terminals to exchange their messages over independent Gaussian channels. For the single channel case, we have shown previously that lattice-based physical layer network coding achieves the same rate as compress-and-forward scheme with a random coding strategy. A direct extension of this lattice-based scheme to parallel Gaussian channel is to repeat the same strategy for each subchannel. However this approach is not scalable with the number of sub-channels since the complexity of the scheme becomes prohibitive when a large number of sub-channels is employed. In this contribution, we investigate a lattice-based physical layer network coding scheme where the relay jointly processes all the sub-channels together. We characterize the rate region allowed by our coding scheme and assess the performance penalty compared to the separate channel processing approach.

Physical network coding for TWR channel: Capacity region and error exponents

Two way relay channel (TWRC) is being proposed as a competitive strategy for data transmission in cooperative networks. The capacity region of this model has been recently extensively investigated and achievable bounds are derived based on the cut-set theorem and decode and forward relaying strategy. However, capacity limits that have been derived assume infinite block length which is impractical for real approaches. We present in this contribution a new information-theoretic framework to reconstruct the maximum achievable rate region in the TWRC by taking into account fixed block length and physical network coding. In particular, individual error probabilities are treated using random error exponents. We characterize the rate region for discrete memoryless channel by using optimal time division between links and constrained error probabilities. We evaluate the system performance for different SNR regimes with/without power control. All results are generalized to additive white Gaussian network with power constraints.

Multilayered Wyner-Ziv lattice coding for single-cell point-to-multipoint communications

This paper addresses the problem of single-cell point-to-multipoint communications. We consider a base station that needs to transmit a common information to a group of users. We propose a layered Wyner-Ziv coding (WZC) scheme based on nested lattice quantization. In our scheme, we use the base layer generated by a standard coder as the decoders side information. Then, WZC is performed for quality enhancement of the transmitted message. With the proposed layered coding, multiple refinement messages will be generated. The layered messages can be decoded each by a subgroup of users based on their channel conditions. We optimize the scheme parameters in order to maximize the end-to-end multicast rate and minimize the reconstruction distortions experienced at each subgroup of users. Numerical results show that our scheme performs well when compared with the basic multicasting scheme.

On the distributed approaches with imperfect channel estimation for MIMO interference channel

This paper considers distributed approaches for the downlink of multi-user MIMO interference network where all nodes iteratively and distributedly update their precoders or receive filters. Those include the distributed interference alignment and minimum sum mean-squared error schemes. We analyse these algorithms in presence of effective imperfect channel estimation at each iteration and we present the pre-coders and receive filters updates in this case. The numerical results show that the algorithms converge in average. However, the sum-rate performance is degraded with respect to the estimation errors. Based on these results, we show that for a useful design in practice it is preferable to ameliorate the quality of the estimators and reduce the number of iterations.

Finite dimension Wyner-Ziv lattice coding for two-way relay channel

Two-way relay channel (TWRC) models a cooperative communication situation performing duplex transmission via a relay station. For this channel, we have shown previously that a lattice-based physical layer network coding strategy achieves, at the limit of arbitrarily large dimension, the same rate as that offered by the random coding-based regular compress-and-forward. In this paper, we investigate a practical coding scheme using finite dimension lattices and offering a reasonable performance-complexity trade-off. The algorithm relies on lattice based quantization for Wyner-Ziv coding. We characterize the rate region allowed by our coding scheme, discuss the design criteria, and illustrate our results with some numerical examples.