Security and Prioritization in Multiple Access Relay Networks

In this work, we considered a multiple access relay network and investigated the following three problems: 1- Tradeoff between reliability and security under falsified data injection attacks; 2-Prioritized analog relaying; 3- mitigation of Forwarding Misbehaviors in Multiple access relay network. In the first problem, we consider a multiple access relay network where multiple sources send independent data to a single destination through multiple relays which may inject a falsified data into the network. To detect the malicious relays and discard (erase) data from them, tracing bits are embedded in the information data at each source node. Parity bits may be also added to correct the errors caused by fading and noise. When the total amount of redundancy, tracing bits plus parity bits, is fixed, an increase in parity bits to increase the reliability requires a decrease in tracing bits which leads to a less accurate detection of malicious behavior of relays, and vice versa. We investigate the tradeoff between the tracing bits and the parity bits in minimizing the probability of decoding error and maximizing the throughput in multi-source, multi-relay networks under falsified data injection attacks. The energy and throughput gains provided by the optimal allocation of redundancy and the tradeoff between reliability and security are analyzed. In the second problem, we consider a multiple access relay network where multiple sources send independent data simultaneously to a common destination through multiple relay nodes. We present three prioritized analog cooperative relaying schemes that provide different class of service (CoS) to different sources while being relayed at the same time in the same frequency band. The three schemes take the channel variations into account in determining the relay encoding (combining) rule, but differ in terms of whether or how relays cooperate. Simulation results on the symbol error probability and outage probability are provided to show the effectiveness of the proposed schemes. In the third problem, we propose a physical layer approach to detect the relay node that injects false data or adds channel errors into the network encoder in multiple access relay networks. The misbehaving relay is detected by using the maximum a posteriori (MAP) detection rule which is optimal in the sense of minimizing the probability of incorrect decision (false alarm and miss detection). The proposed scheme does not require sending extra bits at the source, such as hash function or message authentication check bits, and hence there is no transmission overhead. The side information regarding the presence of forwarding misbehavior is exploited at the decoder to enhance the reliability of decoding. We derive the probability of false alarm and miss detection and the probability of bit error, taking into account the lossy nature of wireless links

Analyse des performances de réseaux coopératifs à relais multiples

Résumé Dans une communication coopérative, des nœuds relais coopèrent conjointement avec un nœud source afin de transmettre ses informations vers sa destination. Ceci permet d'augmenter la fiabilité de la communication lorsque le canal entre la source et la destination est de mauvaise qualité.Les communications coopératives à plusieurs relais présentent un intérêt grandissant dans le domaine des communications. En effet, la présence de plusieurs relais favorise l'exploitation des propriétés des systèmes MIMO telles le Multiplexage Spatial (SM) et la diversité. Cependant, plusieurs techniques de communication à relais multiples se limitent au modèle avec des relais à une seule antenne. De plus, les modèles de communication supposent une connaissance parfaite du canal de transmission au récepteur, ce qui ne reflète pas le cas réel d'une transmission sur un canal radio à évanouissements. Finalement, la communication coopérative à sauts multiples (à plusieurs niveaux de relais) a été étudiée partiellement. Les travaux antérieurs se sont limités à des modèles simples de réseau (généralement à deux sauts) et à des transmissions avec codage spatio-temporel unitaire. Afin de remédier à toutes ces limitations du modèle de communication coopérative à relais multiples, nous développons et analysons des modèles qui intègrent chacune de ces contraintes.Le premier modèle développé considère des relais à plusieurs antennes exploitant les techniques de transmission Amplify-and-Forward (AF) ou bien Decode-and-Forward (DF) avec une connaissance parfaite ou imparfaite des canaux de transmissions aux récepteurs. Les relais utilisent un codage spatio-temporel distribué (pour augmenter la diversité) ou le multiplexage spatial distribué (pour accroitre le taux de transmission). Dans le but d'améliorer la fiabilité de la communication à un taux de transmission fixe, nous proposons une technique de communication adaptative décentralisée basée sur la sélection entre le codage spatio-temporel et le multiplexage spatial à une valeur de SNR (rapport signal- à -bruit) donnée.Enfin, nous développons et analysons le modèle de la communication coopérative à plusieurs sauts (à plusieurs niveaux de relais) de transmission. Nous développons l'analyse du modèle de communication coopérative avec un nombre de sauts supérieur à trois, où le codage spatio-temporel est utilisé à un ou plusieurs niveaux de relais. Les résultats des simulations montrent les gains de performances et les comportements (en termes d'erreur) des nouveaux modèles de transmission développés. Ceci nous a permis de comprendre le comportement du réseau coopératif avec les techniques de transmissions proposées et d'en extraire les structures de réseau et techniques de transmission offrant les meilleures performances en taux d'erreur binaire.----------Abstract In a cooperative communication system, a set of relay nodes works jointly with a source node in order to forward its information to the destination. This technique permits to increase the reliability of the communication when the direct link is corrupted.Cooperative communications with multiple relays have an important interest in telecommunications. By the presence of multiple relay nodes, point-to-point MIMO properties such as spatial multiplexing and diversity could be exploited in this new type of communications. Meanwhile, many cooperation techniques with multiple relays are limited to the model where the relays are single antenna. Moreover, the system models assume a perfect Channel State Information (CSI) at the receiver, which is not the real case for a fading channel. Finally, multi-hop cooperative communication has been treated partially. The authors were limited in their works to double hops networks (generally small number of hops) and to transmissions with space-time coding with unitary code matrices. In order to rectify these limitations in the system model of cooperative communications with multiple relays, we develop and analyze system models that include each of these constraints.The first developed system model assumes MIMO relay nodes using AF or DF transmission techniques with a perfect CSI or imperfect CSI at the receivers. The relay nodes exploit distributed space-time coding (to strengthen the communication) or distributed spatial multiplexing (to increase the transmission rate). To increase the communication reliability at a fixed transmission rate, we propose a decentralized selection technique between space-time coding and spatial multiplexing based on the estimated SNR.Finally, we develop and analyze the model of a multi-hop cooperative communication. We develop the analysis of the multi-hop (multi-levels) cooperative communication model where the space-time coding is used at one or many relays' levels. The simulation results show the performance gains and the behaviors (in error rates) of the new developed system models. This help us to understand better the behavior of the cooperative system using the proposed transmission techniques and then extract the network structure and transmission technique providing the best error rate performances

Cooperative spatial multiplexing in multi-hop wireless networks.

It is well known that a multiple-input-multiple-output (MIMO) system can provide spatial diversity gain as well as spatial multiplexing capability. The MIMO con-cept has been extended to cooperative wireless networks to form distributed MIMO systems using virtual an-tennas located at cooperating terminals. The primary interest of cooperative MIMO networks, however, has been focused on the cooperative diversity (C-DIV) ap-proaches to achieve spatial diversity gain. Recent work proposed cooperative spatial multiplexing (C-SM) to sim-plify the transmit and receive processing requirement on the relay nodes while providing significant energy sav-ings. So far C-SM has been only considered for single-hop relaying. In this paper, we propose the use of multi-hop relaying C-SM systems for transmit energy reduc-tion and performance improvement. 1