Research On Radio Resource Scheduling Algorithm For Relay-enhanced Cellular Systems

Relaying, as a key component of 4G mobile telecommunication systems, has drawn extensive attention. Introducing relay stations into cellular system, termed relay enhanced cellular (REC) system, is a promising way to improve cell coverage and cell edge user performance at low cost. However, the intro-duction of relay stations also brings in new problems for the resource schedul-ing of traditional cellular system. For instance, users can select alternative routes through direct or relaying communication between the base station. Ra-dio resources should be partitioned to allow relaying transmission to co-exist with traditional direct transmission in the same frequency band. Relaying data packets will go through one or several relay links before arriving at the destina-tion. In summary, deliberately designed radio resource scheduling algorithms are required for REC systems in order to harness the gains from relaying.This dissertation intends to study the design and performance of resource scheduling algorithms for REC networks, with emphasis on solving the radio resource partition, user routing and packet scheduling problems for Orthogonal Frequency-Division Multiplexing (OFDM) based REC systems. Based on the characteristics of REC networks, new resource partition and user routing algo-rithms are proposed which can improve system efficiency while guaranteeing user fairness. In addition, improved packet scheduling algorithms and mecha-nisms are developed for relay stations regarding to different kinds of services. Moreover, the REC system performance is analyzed through system level sim-ulations based on the requirements of LTE-Advanced system.How to partition system resources has a great impact on the overall REC system performance. Regarding the cellular system deployed with multiple relay stations, we first formulate the resource partition problem with the ob-jective of optimizing global proportional fairness. Then, efficient resource par- tition algorithms are provided to tackle with the problem under different re-source reusing assumptions, i.e., fully reuse or no reuse between the access links of base station and relay stations. The proposed schemes can achieve better trade-off between system spectral efficiency and fairness compared to existing fixed partition schemes. In addition, a simplified resource partition mechanism is suggested which can achieve partial reuse between the access links of base station and relay stations. Compared to either the full reuse or the no reuse schemes, this scheme can achieve better trade-off between system average throughput and cell-edge user throughput.User routing is another problem to be solved for the radio resource scheduling of REC systems. For the cellular system enhanced with multiple relay stations, the routing problem is formulated with the aim of providing global fairness based on the previous analysis about radio resource partition. Then, efficient routing algorithms are proposed under the assumptions of full reuse partition and no reuse partition, respectively. Through system level sim-ulations, better system throughput and user fairness performances can be ob-served compared to conventional routing algorithms.With resource partition and user routing determined, packet scheduling for multi-hop links is one more problem to be resolved for REC systems. The de-sign of packet scheduling mechanisms for REC systems has been concerned for different kinds of services. With regard to full buffer (best-effort) data traffic, a new relay link packet scheduling algorithm based on the queue information of relay stations is provided, which can achieve relatively high transmission effi-ciency with limited feedback. For VoIP (Voice over Internet Protocol) traffic, a multi-process semi-persistent scheduling algorithm is designed for the relay backhaul link in order to adapt to the characteristics of aggregated VoIP traffic; moreover, an improved semi-persistent scheduling mechanism for relay access link is also proposed in order to tackle with the potential delay accumulation phenomenon at relay stations. With these improved VoIP packet scheduling schemes, the delay performance of users associated with relay stations can be improved significantly; moreover, the VoIP capacity of REC system can be elevated accordingly.At last, we discuss the application of relaying technique in 3GPP LTE-Advanced systems and analyze the resulting performance. Through developing relay-specific system-level dynamic simulation platform, the performance gain of cellular systems through relaying and its main influential factors have been analyzed.