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Improving transmission reliability in wireless sensor networks using network coding

Wireless sensor networks employed in industrial and other special applications have strict requirements concerning the transmission reliability, delays and energy efficiency. This paper proposes a scalable approach for increasing transmission reliability in wireless sensor networks, based on a cooperative scheme that uses Reed–Solomon codes as network code. The block error rate of the proposed coded transmission technique is analyzed in several scenarios and it is shown that our solution improves the error performance even for high coding rates. The paper proposes also a genetic algorithm based optimization of the network code functionality by selecting the most cooperation capable devices. The proposed network coding based solution is compared with automatic repeat request transmissions from the point of view of the resource usage, which influences the energy efficiency and the transmission delays. The evaluations performed show that network coded transmissions can ensure better error performance with significantly less resources.

Analysis of a transport protocol based on rateless erasure correcting codes

This paper presents a protocol designed as an alternative to classical TCP for channels which experience high loss-rates. The protocol is simplified with respect to TCP by eliminating the need of retransmissions and the associated buffers. This is achieved by applying a rateless erasure correcting code to the data that is going to be transferred. A modified version of the TCP congestion control algorithms is used in order to better differentiate between losses caused by errors on the channel and losses caused by congestion in the network. A statistical model for the steady-state throughput of the protocol is included in the paper as well. Using simulations performed in ns-2 the throughput model is validated. Other aspects of the behavior of the protocol are also investigated. The results are promising, mainly showing that the protocol does not experience any significant performance degradation in terms of steady-state throughput, even if the loss rate on the channel is high.

Link performance prediction methods for cooperative relaying in wireless networks

Next generation wireless networks are likely to include cooperative relaying in their design. The performance of certain cooperation schemes in realistic scenarios should be evaluated by system level simulations (SLS). Moreover, the link adaptation (LA) and radio resource management become more complex, since cooperation schemes involve transmissions on more than one link and joint processing at the receiver. Both LA and SLS require quality metrics of the composite cooperative links, which capture the performance of the transmission scheme. This paper proposes performance prediction methods which rely on mutual information based metrics for two cooperation schemes which use one relay. Simulations show that, yet simple, these methods are accurate in predicting the coded block error rate (BLER).

Network coding solution for improving transmission reliability in wireless sensor networks employed in industrial monitoring

One of the most appropriate techniques to increase the reliability of wireless sensor networks used in industrial environments are the network coding techniques. This paper proposes an effective, yet simple and scalable approach based on a relay-assisted cooperative scheme that uses Reed Solomon codes as network codes for such wireless sensor networks with cluster-tree topologies. The global Block Error Rate performances of this approach are analyzed in three different scenarios, characterized by different Block Error Rate distributions of the component paths. The results obtained show that this solution significantly improves the performances even for great coding rates. The paper also proposes an optimization of the network code functionality, based on a genetic algorithm, and concludes that it is effective in improving the performances for high coding rates.

Combined distributed turbo coding and space frequency block coding techniques

The distributed space-time (frequency) coding and distributed channel turbo coding used independently represent two cooperative techniques that can provide increased throughput and spectral efficiency at an imposed maximum Bit Error Rate (BER) and delay required from the new generation of cellular networks. This paper proposes two cooperative algorithms that employ jointly the two types of techniques, analyzes their BER and spectral efficiency performances versus the qualities of the channels involved, and presents some conclusions regarding the adaptive employment of these algorithms.

Network and Channel Coded Cooperation Algorithms for Cellular Networks

The paper analyzes the performances provided by two algorithms that combine the network and distributed channel coding in cooperative schemes with a relay-node serving two mobile stations, placed symmetrically and asymmetrically vs. the base-station. The analysis is performed in scenarios that consider error-affected mobile - relay node channels. It also proposes a low complexity hybrid coded cooperation algorithm that employs adaptively the cooperative or the non-cooperative transmissions. The selection of the cooperation mode is based on the bit error probability estimation on the mobile - relay node channels. I. INTRODUCTION Relaying and cooperation between terminals are considered as some of the most promising approaches for the improvement of the wireless networks performance. The channel-coded (CC) cooperation included in schemes where a relay-node (RN) serves only one mobile station (MS) in its transmission to the base station (BS) is one of the techniques proposed in literature to accomplish those improvements (1) (2). Though this approach is shown to bring performance improvements for the served MS in terms of bit error rate (BER), packet error rate (PER) and/or coverage, the additional time-frequency resources (TFR) required by the RN are used to serve only one MS leading to a loss of performances in terms of spectral efficiency. In order to decrease the effect of the additional TFR upon the spectral efficiency of the MS-BS transmission, Network Coding (NC) techniques were included in coded cooperation algorithms. Since the NC techniques allow cooperation structures within which the RN serves more MSs, such an approach leads to a more efficient employment of the additional TFR of the RN. But, making these techniques effective raises new questions that have to be addressed. The combined use of NC and channel coding was considered in several papers, e.g. (3) (4). NC-based or joint NC-CC coding cooperation algorithms were proposed and their performances were studied in different scenarios, but some practical aspects are still not completely addressed. This paper considers the cooperative scheme within which one RN serves the uplink connections of two MSs, using combined NC and distributed CC (DCC) techniques. It studies some practical aspects related to the selection of the best NC-DCC cooperation algorithm, the simplification of the cooperation techniques for a better and easier integration into cellular systems. The NC-DCC based cooperation algorithms are compared to cooperative algorithms based on DCC and on non-cooperative coded transmissions, in several scenarios. The paper is organized as follows: section II presents briefly the cooperative coding algorithms employed, as well as the scenarios within which their performances are evaluated. Section III presents a comparative study of these cooperative coding algorithms performances in ideal and more realistic transmission scenarios and discusses briefly the possibility of their adaptive employment. Section IV presents a solution proposed by the authors for a simplified and adaptive NC-CC based cooperation algorithm. Finally, section V concludes the paper.

Link adaptation algorithm for distributed coded transmissions in relay-aided OFDMA systems

We propose a link adaptation algorithm for cooperative transmissions in an OFDMA-based wireless system. The algorithm aims at maximizing the spectral efficiency of a relay-aided communication link, while satisfying the block error rate constraints at both the relay and the destination nodes. The optimal solution would be to perform an exhaustive search over a high-dimensional space determined by all possible combinations of modulations, code rates and information block lengths on the individual links; clearly, such an approach has an intractable complexity. Our solution is to use a link performance prediction method and a trellis diagram representation such that the resulting algorithm outputs a link configuration that conveys as many as possible information bits and also fulfills the block error rate constraints. The proposed link adaptation algorithm has linear complexity with the number of available resource blocks, but still provides a very good performance, as shown by simulation results.

Cooperation protocol for the uplink of relay assisted cellular networks

The paper proposes a network coded cooperation protocol for the uplink transmission of relay assisted cellular networks characterized by non-ideal source - relay links. The proposed protocol employs Reed Solomon codes as network codes in order to improve the Block Error Rate (BLER) and Bit Error Rate (BER) performance over the slow varying fading channels. The paper presents also an algorithm for the computation of the BLER ensured by the cooperation protocol when the cooperative links are modeled as Block Erasure Channels (BLEC), as well as an analysis of the performance obtained, showing the significant improvement brought by the employment of RS network codes.

Link adaptation algorithm for distributed coded transmissions in cooperative OFDMA systems

This paper proposes a link adaptation algorithm for cooperative transmissions in the down-link connection of an OFDMA-based wireless system. The algorithm aims at maximizing the spectral efficiency of a relay-aided communication link, while satisfying the block error rate constraints at both the relay and the destination nodes. The optimal solution would be to perform an exhaustive search over a high-dimensional space determined by all possible combinations of modulations, code rates and information block lengths on the individual channels of the cooperative link; clearly, such an approach has an intractable complexity. Our solution is to use a link performance prediction method and a trellis diagram representation such that the resulting algorithm outputs the link configuration that conveys as many information bits as possible and also fulfilling the block error rate constraints. The proposed link adaptation algorithm has linear complexity with the number of available resource blocks, while still provides a very good performance, as shown by simulation results.

Comparison between measured and computed values of the mean mutual information per coded bits in OFDM based wireless transmissions

To provide a high system performance, the link adaptation algorithms need an accurate method to predict the Block Error Rate (BLER) performance of a transmission on a given realization of the wireless multipath propagation channel. A promising BLER prediction technique is based on mean mutual information of the received bits (MI). The main objective of this paper is to compare the MI values obtained at the reception of a real physical transmission, with the ones provided by the available analytical models. For this we implemented a transmission chain on an Universal Software Radio Peripheral (USRP) device. The obtained results shows relatively good coincidence, but as might be expected, in some cases the measured values slightly differ from the computed ones.