Efficient Resource Reuse And Interference Coordination For Next Generation Cellular Networks

OFDMA-based multi-hop relay cellular networks (MRCNs) have drawn tremendous attention due to its high throughput and extensive converage. However, there are still three issues not well addressed:1) with the introduction of relay stations (RSs), how to efficiently allocate frequency resource to relay links becomes a challenging design issue;2) for mobile stations (MSs) near the cell edge, co-channel interference (CCI) becomes severe, which significantly affects the network performance;3) in real network environment, users are not evenly distributed in cells/sectors, so too many users accessing one station (BS or RS) probably yields load imbalance, which makes the station congested and violates the quality of service (QoS) requirements of the users. Based on the downlink of radio resource management, with technologies such as time division duplex (TDD), spatial reuse and frequency reuse, this paper studies the design and optimization of path selection, local forwarding, resource scheduling, interference coordination (IC), load balancing (LB), and power control according to IEEE802.16j/m specification, which can be elaborated as follows:Firstly, an efficient frequency reuse scheme for OFDMA-based MRCNs is proposed. The effect of different algorithms on system performance is analyzed in terms of both path selection and frequency planning. The author also puts forward an efficient resource reuse scheme focuses on FFR in both theoretical analysis and performance simulation. Furthermore, a proper resource reuse scheme and multi-hop relay downlink sub-frame are designed to deal with the inter-cell interference for the implementation of overall frequency reuse scheme. It not only guarantees the efficient utilization of resource in networks but also protect the users in the edge of adjacent cell from interference, which is conducive to the implement of full frequency reuse scheme. Compared with the traditional MRCN, the MRCN adopting the proposed scheme is able to make full use of spectrum resource. Its throughput gain and cell coverage probability gain is13.8%and5.4%, respectively.Secondly, a local forwarding transmission scheme for OFDMA-based MRCN is imtroduced. For the optimization of the data transmission link of the users associated with RSs. the scheme allows the data transmission between MSs via RSs instead of the re-delivery of data to Base Station (BS). It not only mitigates the air-interface at BS. promotes the system resource utilization level, but also reduces the number of hops in the data transmission between MSs. A path selection algorithm for local forwarding mode is also proposed with jointly considering the characteristics of local forwarding mode and the resource allocation scheme, and the optimum path selected whereby can enhance the optimization of the system performance. Additionally, according to the networks structure and signaling mechanism of IEEE802.16j/m, the author analyzes the mechanism of control signaling interaction supporting administrable local forwarding. Compared with the traditional MRCN, the MRCN jointly considering local forwarding transmission and FFR can increase the system throughput by36.2%.Thirdly, a spatial reuse with interference coordination scheme for OFDMA-based MRCN is put forward. The scheme is designed and optimized with spatial reuse, time division multiplexing and frequency reuse considered jointly according to the characteristics of MRCNs. Based on FFR. two schemes are proposed, namely BS Adopts FFR and RS Adopts FFR (BFRF) scheme and BS Adopts FFR and RS Adopts Orthogonal Allocation (BFRO) scheme. The two proposed schemes can both mitigate the CCI and maintain high resource utilization. Moreover, the key issues on frequency planning, power control, path selection and zone selection, and slot allocation that are involved in the two proposed schemes are specifically analyzed. The two proposed schemes can give an effective resolution to the serious interference caused by intra-sector spatial reuse. Compared with the orthogonal allocation scheme and NT-RS with centralized allocation mode, the schemes, although causing a bit decrease in the coverage probability, can not only satisfy the requirement of95%, but also highly improve the sector throughput by16%.Fourthly, a resource allocation based on load balancing for OFDMA-based MRCNs is raised. Since it is difficult to solve a joint optimization problem, the author provides a step-by-step sub-optimal allocation scheme on the premise of reducing the computational complexity. With advance sub-channel allocation by proportional fair algorithm, the paper introduces the math modeling for power allocation algorithm. According to convex optimization and water-filling algorithm, the paper determines the certain conditions to satisfy the optimal power allocation solution, and also calculates the results of transmission power among BS and RSs for approaching the optimal solution. The proposed resource allocation scheme based on load balancing (RALB) takes efficiency and fairness into consideration. Under conditions of transmission power and number of subcarrier, the scheme is adaptable to different user distributions and can solve load unbalancing. In four different typical use distribution scenes, compared to traditional static resource allocation (SRA), the schemes can improve throughput by7.8%,22.6%,31.1%and46.7%, respectively.At last, a scheme jointly considering interference coordination and load balancing for OFDMA-based MRCNs is given. Firstly, present a novel frequency reuse scheme to mitigate interference and maintain high spectral efficiency; secondly, apply the efficient PF algorithm to MRCN, combined with IC; thirdly, design practical LB-based handover mechanisms which can evenly distribute the traffic load and guarantee QoS of users. The proposed scheme can do adaptive resource management according to channel quality and service load, make the best of frequency reuse and power control, and realize joint optimization of parameters of system performance, in order to promote spectrum efficiency to the most extent, improve the fairness of use transmission rate, reduce transmission outage probability, and overcome low throughput and coverage probability caused by changing interference power constraint.