Cellular Relay Network And Its Software Radio Experiments

Relay technology is one of the hot topics in wireless communication in recent years. Most of the existing works focus on the physical layer or MAC layer. But the performance and feasibility of relay technology should be investigated when we want to use relay in real celluar environment. This dissertation studies the performance of relay from the system level, in three possible scenarios: outdoor fixed relay, vehicle relay and indoor relay, and discussed the interference problems in these three scenarios.Based on the system model analysis and simulation, the system spectrum efficiencies are evaluated, and the corresponding novel interference avoidance algorithms are proposed then verified. In addition, some channel measurement experiments based on SDR (software defined radio) platform are performed to verify the system model parameters.In the first part, the outdoor fixed relay is studied. Here the fixed relay means the position of relay node is fixed. This type of relay is the simplest one, and widely discussed in acdamic works. Firstly, the capacity gains of different types of outdoor fixed relay are analyzed and simulated. Furthermore, the total cost of ownership when relay is deployed is estimated and compared with its capacity gain. The conclusion of this part is:one layer 1 relay per sector can bring 10-30% capacity gain; layer 2 relay can bring 30-100% capacity gain; the cost of layer 1 relay is around 34% cost of layer 2 relay. Layer 1 relay is suitable to solve coverage problem and layer 2 relay can be used to improve the hot spot capacity.The second part is about the vehicle relay. Vehicle relay is a kind of relay node equipped on the bus or train to provide service only for the passengers. Vehicle relay can not only increase the signal level at cellphone receiver, but also reduce the overhead of group handover and save cellphone battery power. In this part, firstly the performance of vehicle relay is analyzed and simulated. When the SNR gain of base station-relay link is 3dB, and the proportion of vehicle users is 50%, the average vehicle user throughput increases 17% and the total cell throughput increases 14%. Secondly one interference coordination method is proposed to solve the interference problem in this vehicle relay scenario. Third, one SDR experiment is performed to measure the signal level gain from vehicle relay. The experiment results show that such gain is very small then we have to optimize the backhaul performance through other way.The third part focuses on the indoor relay. Its application scenario and deployment methods are firstly discussed. The capacity of indoor relay is also analyzed. The simulation results show that there is 57.6～206.9% gain in the indoor user average throughput. After that, one problem is discussed to see when indoor relay is useful. The conclusion is indoor relay is useful in most of the area because indoor relay has rich reused radio resource but few users in its cell. Interference problem is also discussed in this part. One improved resource allocation method and power control scheme are proposed to solve the interference problem. In addition, the signal strength distribution in one apartment is measured by SDR experiment. In this apartment, we found indoor relay can be used to improve coverage. Furthermore, inner wall penetration loss and floor penetration loss are also measured in several dormitories. The measurement results show that the interference level in simulation model is high enough compared with the real situation.In the last part, the applications of SDR technology in relay network are discussed. The architecture of SDR-based relay is introduced and the corresponding challenges are clarified. One example of relay implementation on SDR is given, where one GSM relay with wifi backhaul is implemented. In the previous research work, SDR is used as a network dimensioning and optimization tool, so the novel measurement methods and functions are summarized in this part.