Research On Wireless Resource Scheduling In Broadband Wireless Access Networks

Various wireless applications change the way of our life, bring the ever-increasing of service requirements, which makes the broadband becomes the development objective of the wireless access network. However, it is blocked by the rare spectrum resource and the time-variable wireless channel. Therefore, as an effective method to improve the spectrum efficiency, wireless scheduling is always a hot topic in the field of the wireless access network.In this dissertation, by taking the wireless access network based on OFDM technology into account, some problems on the wireless resource scheduling of the different network architecture are studied deeply: The traditional network architecture, i.e., one antenna and one base station (BS)By considering the scheme of ARQ with selective ACK message in IEEE 802.16, the delivery delay of SDU (Service Date Unit) is analyzed deeply under the multi-user scenario and the static channel model. The results indicate that the delivery delay of a SDU is mainly determined by the first transmission of all PDUs (Protocol Data Unit) in it. Based on this conclusion, a two-level priority scheduling scheme is designed for downlink to decrease the delivery delay of SDU and keep the fairness among users.By considering the uneven distribution of the services among cells/sectors in the broadband wireless access network based on OFDM, a distributed bandwidth borrowing and reusing scheme is proposed for the traditional sectorized structure (the diamond sector or pentagonal sector): the over-loaded sector could not only borrow the idle resource in the adjacent sector of the neighboring cells, but also reuse the used resource by the users near the BS in these cells. The theoretical analysis and the simulation results indicate compared to the traditional scheme without borrowing and reusing, the new scheme could improve the sector throughput by 20% at least and with small overhead.A theoretical model, which uses a cirque to denote an area with the same modulation and coding scheme, is built to analyze the Soft Frequency Reuse (SFR) scheme. The results indicate the boundary between the central area and the edge one in SFR restricts the improvement of the system capacity; therefore, a new Frequency Power Partition (FPP) scheme is proposed to improve SFR. Based on FPP, an Influence based Frequency Allocation scheme (IFA) and a Channel-Sharing-Ratio and Influence based Frequency Allocation scheme (CSRIFA) are proposed, respectively. The former increases the system throughput by 15%; while the latter one improves the system fairness. Finally, considering the unevenly distribution of the services, a power control scheme is designed to further increase the throughput.The new network architectureBy Distributed Antenna System (DAS), a four-antenna based structure for the traditional network, which includes three 120 degree directional antennas located at the cell edge and one omni-directional antenna located at the cell center. Then, a resource allocation scheme in downlink and uplink is given. The theoretical analysis and simulation results indicate the new structure improves the signal to interference plus noise ratio (SINR) of the system, increases the system throughputs in downlink and uplink by 30% and 40% at least, respectively, and enhances the throughput of the edge area even by more than 100%.The theoretical analysis for the two-hop relay network with irregular deployment of the relay stations (RS) is performed, which verifies the importance of improving the throughput of the access link (i.e., BS to mobile station, RS to mobile station). Then, two schemes are proposed to improve the performance of the access link: 1) an isolation band based frequency reuse scheme between BS and mobile station, and the theoretical method for fixing the isolation band; 2) a dynamic frequency power partition scheme among RSs, and a method for allocating the reused resource among them. Finally, based on the frame structure of IEEE 802.16j, an implementation flow of the two schemes is given for the real network. The simulation results indicate a significant improvement of the access link is obtained with little negative influence to the users served by BS.