Mobile data services are now available in cellular networks and their use will increase in the next few years. Providing high data rate is then a major issue for operators. As the propagation conditions are very variable in wireless mobile systems, a lot of attention has been paid to optimize the transmission protocols between mobile phones and the network (fast link adaptation, hybrid protocols that combine automatic repeat request and forward error correction). In a lot of cases, a given mobile phone may have poor transmission conditions though another phone close to that one has good conditions. Developping cooperation between terminals is then a natural idea to improve the overall performance. Cooperative transmissions has already received a lot of attention but mainly from a signal and digital communication point of view. Our research focuses on the definition and the optimisation of link layer cooperative protocols.
In a fist step, we studied automatic repeat request (ARQ) protocols on a block fading channel without cooperation. We developped a comprehensive analytical study based on a simple packet error mode (report TRITA – ICT – COS – 1001). We showed that the performance of ARQ and Hybrid ARQ are similar on a slow varying channel and a fast one.
The second step is to study the performance of a simple cooperative protocol with 2 senders and one recipient.
Guest researcher at KTH