Resource Allocation in OFDMA Wireless Networks

Orthogonal frequency division multiple access (OFDMA) is becoming a widely deployed mechanism in broadband wireless networks due to its capability to combat the channel impairments and support high data rate. Besides, dealing with small units of spectrum, named sub-carriers, instead of whole spectrum, results in enhanced flexibility and efficiency of the resource allocation for OFDMA networks. Resource allocation and scheduling in the downlink of OFDMA networks supporting heterogeneous traffic will be considered in this thesis. The purpose of resource allocation is to allocate sub-carriers and power to users to meet their service requirements while maintaining fairness among users and maximizes resource utilization. To achieve these objectives, utility-based resource allocation schemes along with some state-of-the-art resource allocation paradigms such as power control, adaptive modulation and coding, sub-carrier assignment, and scheduling are adopted. On one hand, a utility-based resource allocation scheme improves resource utilization by allocating enough resources based on users' quality of service (QoS) satisfaction. On the other hand, resource allocation based on utilities is not trivial when users demand different traffic types with convex and nonconvex utilities. The first contribution of the thesis is the proposing of a framework, based on joint physical (PHY) and medium access (MAC) layer optimization, for utility-based resource allocation in OFDMA networks with heterogeneous traffic types. The framework considers the network resources limitations while attempting to improve resources utilization and heterogeneous users' satisfaction of service. The resource allocation problem is formulated by continuous optimization techniques, and an algorithm based on interior point and penalty methods is suggested to solve the problem. The numerical results show that the framework is very efficient in treating the nonconvexity problem and the allocation is accurate comparing with the ones obtained by a genetic search algorithm. The second contribution of the thesis is the proposing of an opportunistic fair scheduling scheme for OFDMA networks. The contribution is twofold. First, a vector of fair weights is proposed, which can be used in any scheduling scheme for OFDMA networks to maintain fairness. Second, the fair weights are deployed in an opportunistic scheduling scheme to compensate the unfairness of the scheduling. The proposed scheme efficiently schedules users by exploiting multiuser diversity gain, OFDMA resource allocation flexibility, and utility fair service discipline. It is expected that the research in the thesis contributes to developing practical schemes with low complexity for the MAC layer of OFDMA networks

Energy efficient and quality of service aware resource block allocation in OFDMA systems

This study investigates energy efficient allocation of radio resource blocks in orthogonal frequency division multiple access (OFDMA) systems while considering the status of the users' data buffers to reduce packet dropping rate by the downlink scheduler. The proposed scheme exploits the fluctuations of traffic load to efficiently schedule users' data packets by reducing the overall energy consumption of the system whenever the status of data buffers permits. From information theory point of view, the proposed scheme exploits the fundamental trade-off between energy efficiency and spectral efficiency to perform scheduling. First, the problem is formulated as an optimisation problem and then a novel solution, based on dynamic programming, is applied. By comparing the analytical solution with the ones obtained by exhaustive search, it is demonstrated that the proposed scheme is close to the optimal solution, with low computational complexity. In addition, comprehensive simulations are conducted to evaluate the performance of the suggested algorithm. Both analytical and simulation results demonstrate the superiority of the proposed algorithm compared with the well-known benchmark schemes in terms of energy efficiency and packet dropping rate

Opportunistic fair scheduling for the downlink of IEEE 802.16 wireless metropolitan area networks

In this paper, we propose a novel scheduling scheme for the downlink of IEEE 802.16 networks. A scheduler at the Base Station (BS) decides the order of downlink bursts to be transmitted. The decision is made based on the quality of the channel and the history of transmissions of each Subscriber Station (SS). The scheduler takes advantage of temporal channel fluctuations to increase the BS's throughput and maintain fairness by balancing the long term average throughput of SSs. Simulation results are given to demonstrate the performance of the proposed scheduling scheme

Maintaining utility fairness using weighting factors in wireless networks

Maintaining fairness using weighting factors is a common approach in resource allocation. However, computing weighting factors for multiservice wireless networks is not trivial because users' rate requirements are heterogeneous and their channel gains are variable. In this paper, we propose weighting factor computation and scheduling schemes for orthogonal frequency division multiple access (OFDMA) networks. The weighting factor computation scheme determines each user's share of rate for maintaining a utility notion of fairness. We then present a scheduling scheme which takes the users' weighting factors into consideration to allocate sub-carriers and power in OFDMA networks. The simulation results demonstrate that the proposed scheduling scheme outperforms an opportunistic scheme in terms of fairness performance in different scenarios, where the users are fixed or mobile

Design of fair weights for heterogeneous traffic scheduling in multichannel wireless networks

Fair weights have been implemented to maintain fairness in recent resource allocation schemes. However, designing fair weights for multiservice wireless networks is not trivial because users' rate requirements are heterogeneous and their channel gains are variable. In this paper, we design fair weights for opportunistic scheduling of heterogeneous traffic in orthogonal frequency division multiple access (OFDMA) networks. The fair weights determine each user's share of rate for maintaining a utility notion of fairness. We then present a scheduling scheme which enforces users' long term average transmission rates to be proportional to the fair weights. The proposed scheduler takes the advantage of users' channel state information and the inherent flexibility of OFDMA resource allocation for efficient resource utilization. Furthermore, using the fair weights allows flexibility for realization of different scheduling schemes which accommodate a variety of requirements in terms of heterogeneous traffic types and user mobility. Simulation based performance analysis is presented to demonstrate efficacy of the proposed solution in this paper