Turbo Packet Combining for Broadband Space-Time BICM Hybrid-ARQ Systems with Co-Channel Interference

In this paper, efficient turbo packet combining for single carrier (SC) broadband multiple-input--multiple-output (MIMO) hybrid--automatic repeat request (ARQ) transmission with unknown co-channel interference (CCI) is studied. We propose a new frequency domain soft minimum mean square error (MMSE)-based signal level combining technique where received signals and channel frequency responses (CFR)s corresponding to all retransmissions are used to decode the data packet. We provide a recursive implementation algorithm for the introduced scheme, and show that both its computational complexity and memory requirements are quite insensitive to the ARQ delay, i.e., maximum number of ARQ rounds. Furthermore, we analyze the asymptotic performance, and show that under a sum-rank condition on the CCI MIMO ARQ channel, the proposed packet combining scheme is not interference-limited. Simulation results are provided to demonstrate the gains offered by the proposed technique.Comment: 12 pages, 7 figures, and 2 table

Wireless Data Acquisition for Edge Learning: Data-Importance Aware Retransmission

By deploying machine-learning algorithms at the network edge, edge learning can leverage the enormous real-time data generated by billions of mobile devices to train AI models, which enable intelligent mobile applications. In this emerging research area, one key direction is to efficiently utilize radio resources for wireless data acquisition to minimize the latency of executing a learning task at an edge server. Along this direction, we consider the specific problem of retransmission decision in each communication round to ensure both reliability and quantity of those training data for accelerating model convergence. To solve the problem, a new retransmission protocol called data-importance aware automatic-repeat-request (importance ARQ) is proposed. Unlike the classic ARQ focusing merely on reliability, importance ARQ selectively retransmits a data sample based on its uncertainty which helps learning and can be measured using the model under training. Underpinning the proposed protocol is a derived elegant communication-learning relation between two corresponding metrics, i.e., signal-to-noise ratio (SNR) and data uncertainty. This relation facilitates the design of a simple threshold based policy for importance ARQ. The policy is first derived based on the classic classifier model of support vector machine (SVM), where the uncertainty of a data sample is measured by its distance to the decision boundary. The policy is then extended to the more complex model of convolutional neural networks (CNN) where data uncertainty is measured by entropy. Extensive experiments have been conducted for both the SVM and CNN using real datasets with balanced and imbalanced distributions. Experimental results demonstrate that importance ARQ effectively copes with channel fading and noise in wireless data acquisition to achieve faster model convergence than the conventional channel-aware ARQ.Comment: This is an updated version: 1) extension to general classifiers; 2) consideration of imbalanced classification in the experiments. Submitted to IEEE Journal for possible publicatio

Turbo Packet Combining Strategies for the MIMO-ISI ARQ Channel

This paper addresses the issue of efficient turbo packet combining techniques for coded transmission with a Chase-type automatic repeat request (ARQ) protocol operating over a multiple-input--multiple-output (MIMO) channel with intersymbol interference (ISI). First of all, we investigate the outage probability and the outage-based power loss of the MIMO-ISI ARQ channel when optimal maximum a posteriori (MAP) turbo packet combining is used at the receiver. We show that the ARQ delay (i.e., the maximum number of ARQ rounds) does not completely translate into a diversity gain. We then introduce two efficient turbo packet combining algorithms that are inspired by minimum mean square error (MMSE)-based turbo equalization techniques. Both schemes can be viewed as low-complexity versions of the optimal MAP turbo combiner. The first scheme is called signal-level turbo combining and performs packet combining and multiple transmission ISI cancellation jointly at the signal-level. The second scheme, called symbol-level turbo combining, allows ARQ rounds to be separately turbo equalized, while combining is performed at the filter output. We conduct a complexity analysis where we demonstrate that both algorithms have almost the same computational cost as the conventional log-likelihood ratio (LLR)-level combiner. Simulation results show that both proposed techniques outperform LLR-level combining, while for some representative MIMO configurations, signal-level combining has better ISI cancellation capability and achievable diversity order than that of symbol-level combining.Comment: 13 pages, 7 figures, and 2 table

New hybrid automatic repeat request (HARQ) scheme for 4x4 MIMO system, based on the extended alamouti quasi-orthogonal space-time bloc coding (Q-STBC), in invariant and variant fading channel

A new Hybrid Automatic Repeat reQuest (HARQ) combining scheme for a 4x4 Multiple Input Multiple Output (MIMO) system in invariant and variant fading channel conditions is proposed and analized. Based on the Extended Alamouti Quasi-orthogonal Space-Time Block Coding (Q-STBC), the use of the so-called Alternative Matrices for transmission, depending on the Channel State Information (CSI) received as feedback, is compared to other existing solutions. Sign changes and permutations in the retransmission sequences allow reducing the interference while exploiting the spatial diversity to introduce some gain in the signal power. The best transmission order is selected by the Determinant Criterion, which optimizes the SNR in each receiver antenna to minimize the Bit Error Rate (BER) and maximize the throughput. Studying the performance of a priori different alternatives, both analytically and empirically, several equivalents are found. Finally, the simulation results show that the proposed scheme achieves an improvement for the case of an invariant channel, but not for the time varying model, where the Auto-Regressive of order 1 (AR-i) is chosen for simplicity

Cross-layer hybrid automatic repeat request error control with turbo processing for wireless system

The increasing demand for wireless communication system requires an efficient design in wireless communication system. One of the main challenges is to design error control mechanism in noisy wireless channel. Forward Error Correction (FEC) and Automatic Repeat reQuest (ARQ) are two main error control mechanisms. Hybrid ARQ allows the use of either FEC or ARQ when required. The issues with existing Hybrid ARQ are reliability, complexity and inefficient design. Therefore, the design of Hybrid ARQ needs to be further improved in order to achieve performance close to the Shannon capacity. The objective of this research is to develop a Cross-Layer Design Hybrid ARQ defined as CLD_ARQ to further minimize error in wireless communication system. CLD_ARQ comprises of three main stages. First, a low complexity FEC defined as IRC_FEC for error detection and correction has been developed by using Irregular Repetition Code (IRC) with Turbo processing. The second stage is the enhancement of IRC_FEC defined as EM_IRC_FEC to improve the reliability of error detection by adopting extended mapping. The last stage is the development of efficient CLD_ARQ to include retransmission for error correction that exploits EM_IRC_FEC and ARQ. In the proposed design, serial iterative decoding and parallel iterative decoding are deployed in the error detection and correction. The performance of the CLD_ARQ is evaluated in the Additive White Gaussian Noise (AWGN) channel using EXtrinsic Information Transfer (EXIT) chart, bit error rate (BER) and throughput analysis. The results show significant Signal-to-Noise Ratio (SNR) gain from the theoretical limit at BER of 10-5. IRC_FEC outperforms Recursive Systematic Convolutional Code (RSCC) by SNR gain up to 7% due to the use of IRC as a simple channel coding code. The usage of CLD_ARQ enhances the SNR gain by 53% compared to without ARQ due to feedback for retransmission. The adoption of extended mapping in the CLD_ARQ improves the SNR gain up to 50% due to error detection enhancement. In general, the proposed CLD_ARQ can achieve low BER and close to the Shannon‘s capacity even in worse channel condition

A new automatic repeat request protocol based on Alamouti space-time block code over Rayleigh fading channels.

Masters Degree. University of KwaZulu-Natal, Durban.Spatial and multiplexing diversity of multiple-input multiple-output (MIMO) schemes improves link reliability and data rates of wireless networks. MIMO-based space-time block codes (STBCs) improve wireless network reliability by using different copies of the receiver’s original data. Recently automatic repeat request (ARQ) technique was introduced for MIMO schemes to enhance the system's link reliability. ARQ improves the link reliability by using acknowledgments and timeouts to ensure efficient transmission of data over an insecure system. In this dissertation, we propose a new ARQ protocol based on Alamouti space-time block code (STBC) over Rayleigh fading channels. The proposed system transmits data by employing two transmit antennas ( ) and four receive antennas , and it is developed by applying the recent technique called uncoded space-time labeling diversity (USTLD). The main idea behind the proposed technique is to use two distinct mappers to improve the error performance of the system. The theoretical expression of the proposed technique is derived employing the union bound approach, and the theoretical analysis is validated with the simulation results. Furthermore, the results revealed that there is a symbol error probability (SEP) performance improvement of 4 dB for 16-QAM and 4.90 dB for 64-QAM when one mapper is employed as compared to the Alamouti system at a SEP of . The results also revealed that when the proposed system uses two mappers, there is a SEP performance improvement of 7.98 dB for 16-QAM and 9.8 dB for 64-QAM compared to the Alamouti system at a SEP of

Cooperative Communications in Ad Hoc Networks

Les techniques de communication coopératives ont été proposées pour améliorer la qualité des signaux reçus par les terminaux sans fil grâce au principe de diversité spatiale. Cette propriété est obtenue par une duplication du signal, envoyé par l’émetteur au niveau d’un terminal relais situé entre l’émetteur et le récepteur. Les travaux de recherche menés en communications coopératives concernent deux domaines principaux: certains traitent la transmission physique alors que d’autres sont étudient l’interaction de la couche physique avec les couches protocolaires supérieures, en particulier les niveaux MAC (Medium Access Control) et réseau. Si ces domaines de recherche sont généralement séparés, des études conjointes s’avèrent nécessaires pour obtenir des systèmes coopératifs implantables. C’est dans ce contexte que se situent les travaux de la thèse avec, comme cadre applicatif, les réseaux ad hoc. En premier lieu, dans la mesure où il n’existe pas de modèle complet de système coopératif, un cadre de modélisation original est proposé pour représenter le fonctionnement d’un système coopératif, sa mise en place et son fonctionnement. Une caractéristique du modèle est de faire abstraction des couches protocolaires. Cette façon de procéder permet d’analyser de façon similaire différentes solutions proposées dans la littérature. De plus, ce modèle facilite la conception de solutions coopératives, en particulier la conception du processus de mise en place du système de coopération qui initialise les rôles de relais, destinataire et source en fonctionnement coopératif. Le modèle de système coopératif est utilisé pour la conception d’une solution de transmission coopérative adaptative où le relais agit en tant que proxy entre la source et le destinataire. L’intérêt de notre proposition, ProxyCoop, par rapport à d’autres propositions, est d’être compatible avec le protocole IEEE 802.11 que ce soit dans son mode de base ou dans son mode optionnel. Pour chaque trame, le mode de transmission à la source est dynamiquement défini soit en mode proxy coopératif soit en mode non coopératif, et ce en fonction de la réception ou la non réception d’un acquittement du destinataire. Les résultats de simulation montrent, sous certaines conditions, une amélioration des performances en termes de nombre de trames effectivement reçues. Le nombre de retransmissions dues à des trames reçues erronées est diminué, et les transmissions en mode multi saut, coûteuses en temps et en bande passante sont également diminuées. Les conditions favorables à la coopération sont dépendantes de la qualité et de l’accessibilité du canal. Une méthode pour la mise en place du système coopératif est également proposée. Elle repose sur l’utilisation d’un protocole standard de routage pour réseaux ad hoc, AODV. Les évaluations de performances indiquent que la mise en place du système de coopération coûte peu en termes de bande passante, les performances du système (mise en place et fonctionnement) sont supérieures à celles d’un système non-coopératif, pour des conditions données. Finalement, l’application de la solution proposée à un réseau ad hoc spécifique, un réseau maillé (mesh) conforme au standard IEEE 802.11s illustre où et comment déployer la solution proposée. ABSTRACT : Cooperative communication techniques have been proposed in order to improve the quality of the received signals at the receivers by using the diversity added by duplication of signals sent by relay terminals situated between each transmission pair. Researches related to cooperative communication can be categorized into two fields; Cooperative transmissions and Cooperative setup. The first research field concerns with cooperative transmission techniques in the physical layer while the second research field concerns with issues on inter-layer interaction between cooperative transmissions in the physical layer to protocols in the upper layers (especially the MAC layer and the network layer). These research topics have been separately concerned but, for implementations, they have to work together. Since there is not any existing common frame work to describe entire functions in cooperative communication, we proposed an original framework of cooperative network at the system level called “Cooperative Network Model”. The model does not reflect the protocol layering; thus, we can generalize the cooperation process and obtain an analysis that is available for many solutions. For validity, the proposed model can clearly illustrate and systematically describe existing cooperative setup protocols. In addition, the proposed cooperative network model facilitates us to find and to solve problems in cooperative designs; especially in cooperative setup, which is in charge on the initiation of the terminal’s role (i.e., a source, a relay, and a destination terminal). Thus, we believe that this model can facilitate the design and updating of existing and future propositions in this domain. The cooperative network protocol is used to design an adaptive cooperative transmission called Proxy Cooperative Transmission. In contrast to other adaptive cooperative transmission techniques, our proposition is compatible to both of the basic access mode and the optional access mode of IEEE 802.11 Medium Access Control (MAC) protocol. The transmission mode for each data frame is adaptively switched between a proxy cooperative mode and a non-cooperative mode based on the absence of acknowledge (ACK) frame. Simulation results show that transmission performance is improved by decreasing the number of re-transmissions due to frame errors; thus, chances of multi-hop mode transitions that are costly in time and bandwidth are alleviated. Then, in order to fulfill ProxyCoop communications in part of cooperative setup, we propose a cooperative setup method called “Proxy Cooperative Setup”. The proposition is based on a routing standard protocol for ad hoc networks, AODV, so that it could be easily deployed. The impacts of ProxyCoopSetup when it works with ProxyCoop transmissions have been studied. From simulation results, it shows that ProxyCoop transmissions with ProxyCoopSetup has similar performance to the ProxyCoop transmissions without ProxyCoopSetup. Finally, when the implementation of the proxy cooperative communication and how it can be integrated on existing networks have been considered, it is shown that the design of proxy cooperative communication is also valuable for the 802.11s WLAN Mesh Network environments