Ordonnancement du trafic dans un réseau maillé sans fil

International audienceDe nombreux travaux ont montré que la capacité des réseaux maillés de type 802.11 était contrainte par la congestion autour des passerelles permettant l'interconnexion à Internet ; elles forment alors les goulots d'étranglement limitant la capacité du réseau, capacité exprimée en terme de trafic écoulé. En particulier, la limitation de ce goulot d'étranglement peut se faire à travers l'utilisation d'un ordonnancement de type TDMA. Dans ce papier, nous étudions l'impact sur la capacité d'un accès au médium TDMA dans le k-voisinage de la passerelle et CSMA/CA au-delà. Deux stratégies sont considérées : la première augmentant le nombre de slots dans la zone TDMA après avoir déterminé son ordonnancement optimal tandis que la seconde vise à augmenter la taille de la région TDMA. En se basant sur un large éventail de simulations, nous montrons que ces deux approches permettent d'accroitre les performances du réseau en terme de capacité et de taux de pertes

Wireless transmission protocols using relays for broadcast and information exchange channels

Relays have been used to overcome existing network performance bottlenecks in meeting the growing demand for large bandwidth and high quality of service (QoS) in wireless networks. This thesis proposes several wireless transmission protocols using relays in practical multi-user broadcast and information exchange channels. The main theme is to demonstrate that efficient use of relays provides an additional dimension to improve reliability, throughput, power efficiency and secrecy. First, a spectrally efficient cooperative transmission protocol is proposed for the multiple-input and singleoutput (MISO) broadcast channel to improve the reliability of wireless transmission. The proposed protocol mitigates co-channel interference and provides another dimension to improve the diversity gain. Analytical and simulation results show that outage probability and the diversity and multiplexing tradeoff of the proposed cooperative protocol outperforms the non-cooperative scheme. Second, a two-way relaying protocol is proposed for the multi-pair, two-way relaying channel to improve the throughput and reliability. The proposed protocol enables both the users and the relay to participate in interference cancellation. Several beamforming schemes are proposed for the multi-antenna relay. Analytical and simulation results reveal that the proposed protocol delivers significant improvements in ergodic capacity, outage probability and the diversity and multiplexing tradeoff if compared to existing schemes. Third, a joint beamforming and power management scheme is proposed for multiple-input and multiple-output (MIMO) two-way relaying channel to improve the sum-rate. Network power allocation and power control optimisation problems are formulated and solved using convex optimisation techniques. Simulation results verify that the proposed scheme delivers better sum-rate or consumes lower power when compared to existing schemes. Fourth, two-way secrecy schemes which combine one-time pad and wiretap coding are proposed for the scalar broadcast channel to improve secrecy rate. The proposed schemes utilise the channel reciprocity and employ relays to forward secret messages. Analytical and simulation results reveal that the proposed schemes are able to achieve positive secrecy rates even when the number of users is large. All of these new wireless transmission protocols help to realise better throughput, reliability, power efficiency and secrecy for wireless broadcast and information exchange channels through the efficient use of relays