Performance Characteristics Evaluation for Cooperative Communication

Wireless channels suffer severely from the effect of multi-path and fading. To mitigate these effects of fading and, cooperative diversity protocols are used. In cooperative diversity, two or more users share their antennas to create a virtual MIMO system. Hence in cooperative communication several single antenna relays assist the transmission between a source and a destination. In this work, cooperative communication protocols such as amplify and forward and decode and forward are simulated for relaying. The received signals at the destination are combined using various diversity combination protocols such as Maximal Ratio Combining (MRC) and Fixed Ratio Combining (FRC). For the performance study of cooperative communication protocol in wireless network, the symbol error rate (SER), outage probability and channel capacity are simulated for single relay and multiple relay in a flat fading Rayleigh channel.. In addition to this, for a 3 node cooperative communication containing a source , a relay and a destination the impact of relay location is studied for 3 different location of relay i.e. relay placed closer to the source, closer to the destination and at the midway between the source and the destination. When the relay is located in the middle of source and destination, it gives the best system performance. When the relay is located closer to the source, the quality of source-relay link is good, and the relay can decode the received information. On the other hand, when the relay node is located close to the destination, the system performance degrades. Through simulation results, it is shown the positive role that the relay plays, as it improves significantly the performance of the system and leads to lower SER and lower outage probability

Energy efficient relay selection schemes for cooperative uniformly distributed wireless sensor networks

Wireless sensor networks (WSNs) are commonly used in many applications. The energy efficiency of the system has become the subject of extensive research lately. In this thesis we will introduce relay selection schemes that attempt to optimize the transmission of data. We use a two phase WSN model where a message is broadcasted from the source then relayed by the overhearing sensors (nodes) to a fusion center (FC). These schemes will reduce the number of bits transmitted from the sensors to the destination as well as minimize the activity of these sensors and lead to a more energy efficient system. The main idea is to have the smallest subset of sensors that contain the entire information relay the message; in an ideal situation the subset will only contain a pair of sensors. We then investigate the addition of error correcting codes (ECCs) to the node-FC channels. We observe the outage probability of the relay selection schemes using turbo codes on the node-FC channels. We also examine the expected number of bits (including extra parity bits) in the transmissions. We show that under certain channel conditions introducing turbo codes to the node-FC channels leads to longer sensor lifetimes

Relais coopératifs dans un réseau de capteurs : performances limites et stratégies

Les réseaux de capteurs ont connu un grand essor ces dix dernières années. Ils interviennent dans tous les domaines de notre vie quotidienne et la rendent plus aisée. Malgré ce grand succès des réseaux de capteurs, plusieurs problèmes restent encore ouverts. La capacité énergétique et la fragilité du canal radio des réseaux de capteurs affectent gravement leurs performances. La communication coopérative représente une solution efficace pour lutter contre l'instabilité du canal radio et afin d'économiser plus d'énergie. Nous proposons dans ce manuscrit, d'utiliser la communication coopérative, en premier lieu, au niveau de la couche MAC afin de mettre en place un accès au canal coopératif et non égoïste. En second lieu, nous utilisons la communication coopérative au niveau de la couche réseau dans le but d'établir des chemins de routage plus stables et plus robustes. ABSTRACT : Wireless sensor networks (WSN) have known a great development during the last decade. They intervene in all the domain of our everyday life to make it easier. Despite the success of WSN several problems have to be solved. The restricted energy capacity and the randomness of the wireless channel seriously affect the performances of the WSN. Cooperative communication represents an efficient solution to reduce the instability of the wireless channel and to optimize energy. In this thesis we propose to use cooperative communications at the MAC and network layer in order to set up a cooperative access to the channel and to establish more robust routing paths