Cross-layer Congestion Control, Routing and Scheduling Design in Ad Hoc Wireless Networks

This paper considers jointly optimal design of crosslayer congestion control, routing and scheduling for ad hoc wireless networks. We first formulate the rate constraint and scheduling constraint using multicommodity flow variables, and formulate resource allocation in networks with fixed wireless channels (or single-rate wireless devices that can mask channel variations) as a utility maximization problem with these constraints. By dual decomposition, the resource allocation problem naturally decomposes into three subproblems: congestion control, routing and scheduling that interact through congestion price. The global convergence property of this algorithm is proved. We next extend the dual algorithm to handle networks with timevarying channels and adaptive multi-rate devices. The stability of the resulting system is established, and its performance is characterized with respect to an ideal reference system which has the best feasible rate region at link layer. We then generalize the aforementioned results to a general model of queueing network served by a set of interdependent parallel servers with time-varying service capabilities, which models many design problems in communication networks. We show that for a general convex optimization problem where a subset of variables lie in a polytope and the rest in a convex set, the dual-based algorithm remains stable and optimal when the constraint set is modulated by an irreducible finite-state Markov chain. This paper thus presents a step toward a systematic way to carry out cross-layer design in the framework of “layering as optimization decomposition” for time-varying channel models

Analysis and optimization of resource control in high-speed railway wireless networks

This paper considers a joint optimal design of admission control and resource allocation for multimedia services delivery in highspeed railway (HSR) wireless networks. A stochastic network optimization problem is formulated which aims at maximizing the system utility while stabilizing all transmission queues under the average power constraint. By introducing virtual queues, the original problem is equivalently transformed into a queue stability problem, which can be naturally decomposed into three separate subproblems: utility maximization, admission control, and resource allocation. A threshold-based admission control strategy is proposed for the admission control subproblem. And a distributed resource allocation scheme is developed for the mixed-integer resource allocation subproblem with guaranteed global optimality. Then a dynamic admission control and resource allocation algorithm is proposed, which is suitable for distributed implementation. Finally, the performance of the proposed algorithm is evaluated by theoretical analysis and numerical simulations under realistic conditions of HSR wireless networks

Optimal 4G OFDMA Dynamic Subcarrier and Power Auction-based Allocation towards H.264 Scalable Video Transmission

In this paper, authors presented a price maximization scheme for optimal orthogonal frequency division for multiple access (OFDMA) subcarrier allocation for wireless video unicast/multicast scenarios. They formulate a pricing based video utility function for H.264 based wireless scalable video streaming, thereby achieving a trade-off between price and QoS fairness. These parametric models for scalable video rate and quality characterization arederived from the standard JSVM reference codec for the SVC extension of the H.264/AVC, and hence are directly applicable in practical wireless scenarios. With the aid of these models, they proposed auction based framework for revenue maximization of the transmitted video streams in the unicast and multicast 4G scenario. A closedform expression is derived for the optimal scalable video quantization step-size subject to the constraints of theunicast/multicast users in 4G wireless systems. This yields the optimal OFDMA subcarrier allocation for multi-userscalable video multiplexing. The proposed scheme is cognizant of the user modulation and code rate, and is henceamenable to adaptive modulation and coding (AMC) feature of 4G wireless networks. Further, they also consider aframework for optimal power allocation based on a novel revenue maximization scheme in OFDMA based wireless broadband 4G systems employing auction bidding models. This is formulated as a constrained convex optimization problem towards sum video utility maximization. We observe that as the demand for a video stream increases inbroadcast/multicast scenarios, higher power is allocated to the corresponding video stream leading to a gain in the overall revenue/utility. We simulate a standard WiMAX based 4G video transmission scenario to validate the performance of the proposed optimal 4G scalable video resource allocation schemes. Simulations illustrate that the proposed optimal band width and power allocation schemes result in a significant performance improvement over the suboptimal equal resource allocation schemes for scalable video transmission.Defence Science Journal, 2013, 63(1), pp.15-24, DOI:http://dx.doi.org/10.14429/dsj.63.375

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

Resource allocation for multi-cell OFDMA based cooperative relay network

University of Technology, Sydney. Faculty of Engineering and Information Technology.Cooperative communications is emerging as an important area within the field of wireless communication systems. The fundamental idea is that intermediary nodes, called relay stations (RSs), who are neither the data source nor destination, are used to assist in communication between sender and receiver. In order to maximise their performance, networks which employ RSs require a new resource allocation and optimisation technique, which takes the RSs into account as a new resource. Several proposals have been presented for the purpose of optimising the distribution of available resources between users. These proposals were developed based on various network scenarios and assumptions. In most cases, impractical assumptions such as; inter-cell interference (ICI) free and full availability of channel state information (CSI) were considered. However, the need for more robust, fair and practical resource allocation algorithms motivated us to study the resource allocation algorithm for OFDMA based cooperative relay networks with more realistic assumptions. This thesis focuses on the resource allocation for the uplink OFDMA based cooperative relay networks. Multiple cells were considered, each composed of a single base station (destination), multiple amplify and forward (AF) relay stations and multiple subscriber stations (sources). The effects of inter-cell interference (ICI) have been considered to optimise the subcarrier allocation with low complexity. The optimisation problem aims to maximise the sum rate of all sources while maintaining a satisfactory degree of fairness amongst them. Furthermore, a utility based resource allocation algorithm has been developed assuming full and partial channel state information for the interference limited OFDMA-based cooperative relay network. In the proposed algorithm, relay selection is initially performed based on the level of ICI. Then, subcarrier allocation is performed on the basis of maximum achieved utility under the assumption of equal power allocation. Finally, based on the amount of ICI, a modified waterfilling power distribution algorithm is proposed and used to optimise the subcarrier power allocation across the allocated set of subcarriers. This thesis also investigates the impact of the relay-to-destination channel gain on subcarrier allocation for uplink OFDMA based cooperative relay networks using multiple amplify-and- forward (AF) relaying protocols. The closed form outage probability is derived for the system under partial channel state information (PCSI) and considering the presence of inter-cell interference (ICI). The proposed resource allocation algorithms as well as the mathematical analysis were validated through computer simulations and the results were presented for each chapter. The results show that, compared to conventional algorithms, the proposed algorithms significantly improve system performance in terms of total sum data rate, outage probability, complexity and fairness

Downlink radio resource allocation for coordinated cellular OFDMA networks

Base station coordination is considered as a promising technique to mitigate inter-cell interference and improve the cell-edge performance in cellular orthogonal frequency division multiple-access (OFDMA) networks. The problem to design an efficient radio resource allocation scheme for coordinated cellular OFDMA networks incorporating base station coordination has been only partially investigated. In this contribution, a novel radio resource allocation algorithm with universal frequency reuse is proposed to support base station coordinated transmission. Firstly, with the assumption of global coordination between all base station sectors in the network, a coordinated subchannel assignment algorithm is proposed. Then, by dividing the entire network into a number of disjoint coordinated clusters of base station sectors, a reduced-feedback algorithm for subchannel assignment is proposed for practical use. The utility function based on the user average throughput is used to balance the efficiency and fairness of wireless resource allocation. System level simulation results demonstrate that the reduced-feedback subchannel assignment algorithm significantly improves the cell-edge average throughput and the fairness index of users in the network, with acceptable degradation of cell-average performance