Electrical & Computer Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2765
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Item Dynamic Resource Allocation in Wireless Heterogeneous Networks(2015) Singh, Vaibhav; Shayman, Prof. Mark; La, Prof. Richard; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Deployment of low power basestations within cellular networks can potentially increase both capacity and coverage. However, such deployments require efficient resource allocation schemes for managing interference from the low power and macro basestations that are located within each other’s transmission range. In this dissertation, we propose novel and efficient dynamic resource allocation algorithms in the frequency, time and space domains. We show that the proposed algorithms perform better than the current state-of-art resource management algorithms. In the first part of the dissertation, we propose an interference management solution in the frequency domain. We introduce a distributed frequency allocation scheme that shares frequencies between macro and low power pico basestations, and guarantees a minimum average throughput to users. The scheme seeks to minimize the total number of frequencies needed to honor the minimum throughput requirements. We evaluate our scheme using detailed simulations and show that it performs on par with the centralized optimum allocation. Moreover, our proposed scheme outperforms a static frequency reuse scheme and the centralized optimal partitioning between the macro and picos. In the second part of the dissertation, we propose a time domain solution to the interference problem. We consider the problem of maximizing the alpha-fairness utility over heterogeneous wireless networks (HetNets) by jointly optimizing user association, wherein each user is associated to any one transmission point (TP) in the network, and activation fractions of all TPs. Activation fraction of a TP is the fraction of the frame duration for which it is active, and together these fractions influence the interference seen in the network. To address this joint optimization problem which we show is NP-hard, we propose an alternating optimization based approach wherein the activation fractions and the user association are optimized in an alternating manner. The subproblem of determining the optimal activation fractions is solved using a provably convergent auxiliary function method. On the other hand, the subproblem of determining the user association is solved via a simple combinatorial algorithm. Meaningful performance guarantees are derived in either case. Simulation results over a practical HetNet topology reveal the superior performance of the proposed algorithms and underscore the significant benefits of the joint optimization. In the final part of the dissertation, we propose a space domain solution to the interference problem. We consider the problem of maximizing system utility by optimizing over the set of user and TP pairs in each subframe, where each user can be served by multiple TPs. To address this optimization problem which is NP-hard, we propose a solution scheme based on difference of submodular function optimization approach. We evaluate our scheme using detailed simulations and show that it performs on par with a much more computationally demanding difference of convex function optimization scheme. Moreover, the proposed scheme performs within a reasonable percentage of the optimal solution. We further demonstrate the advantage of the proposed scheme by studying its performance with variation in different network topology parameters.Item Resource Allocation in Relay-based Satellite and Wireless Communication Networks(2008-11-24) Zeng, Hui; Baras, John S; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A two-level bandwidth allocation scheme is proposed for a slotted Time-Division Multiple Access high data rate relay satellite communication link to provide efficient and fair channel utilization. The long-term allocation is implemented to provide per-flow/per-user Quality-of-Service guarantees and shape the average behavior. The time-varying short-term allocation is determined by solving an optimal timeslot scheduling problem based on the requests and other parameters. Through extensive simulations, the performance of a suitable MAC protocol with two-level bandwidth allocation is analyzed and compared with that of the existing static fixed-assignment scheme in terms of end-to-end delay and successful throughput. It is also shown that pseudo-proportional fairness is achieved for our hybrid protocol. We study rate control systems with heterogeneous time-varying propagation delays, based on analytic fluid flow models composed of first-order delay-differential equations. Both single-flow and multi-flow system models are analyzed, with special attention paid to the Mitra-Seery algorithm. The stationary solutions are investigated. For the fluctuating solutions, their dynamic behavior is analyzed in detail, analytically and numerically, in terms of amplitude, transient behavior, fairness and adaptability, etc.. Especially the effects of heterogeneous time-varying delays are investigated. It is shown that with proper parameter design the system can achieve stable behavior with close to pointwise proportional fairness among flows. Finally we investigate the resource allocation in 802.16j multi-hop relay systems with rate fairness constraints for two mutually exclusive options: transparent and non-transparent relay systems (T-RS and NT-RS). Single-Input Single-Output and Multi-Input Multi-Output antenna systems are considered in the links between the Base Station (BS) and Relay Stations (RS). 1 and 3 RSs per sector are considered. The Mobile Station (MS) association rule, which determines the access station (BS or RS) for each MS, is also studied. Two rules: Highest MCS scheme with the highest modulation and coding rate, and Highest (Mod) ESE scheme with the highest (modified) effective spectrum efficiency, are studied along with the optimal rule that maximizes system capacity with rate fairness constraints. Our simulation results show that the highest capacity is always achieved by NT-RS with 3 RSs per sector in distributed scheduling mode, and that the Highest (Mod) ESE scheme performs closely to the optimal rule in terms of system capacity.Item Cross-Layer Resource Allocation Protocols for Multimedia CDMA Networks(2004-11-11) Kwasinski, Andres; Farvardin, Nariman; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The design of mechanisms to efficiently allow many users to maintain simultaneous communications while sharing the same transmission medium is a crucial step during a wireless network design. The resource allocation process needs to meet numerous requirements that are sometimes conflicting, such as high efficiency, network utilization and flexibility and good communication quality. Due to limited resources, wireless cellular networks are normally seen as having some limit on the network capacity, in terms of the maximum number of calls that may be supported. Being able to dynamically extend network operation beyond the set limit at the cost of a smooth and small increase in distortion is a valuable and useful idea because it provides the means to flexibly adjust the network to situations where it is more important to service a call rather than to guarantee the best quality. In this thesis we study designs for resource allocation in CDMA networks carrying conversational-type calls. The designs are based on a cross-layer approach where the source encoder, the channel encoder and, in some cases, the processing gains are adapted. The primary focus of the study is on optimally multiplexing multimedia sources. Therefore, we study optimal resource allocation to resolve interference-generated congestion for an arbitrary set of real-time variable-rate source encoders in a multimedia CDMA network. Importantly, we show that the problem could be viewed as the one of statistical multiplexing in source-adapted multimedia CDMA. We present analysis and optimal solutions for different system setups. The result is a flexible system that sets an efficient tradeoff between end-to-end distortion and number of users. Because in the presented cross-layer designs channel-induced errors are kept at a subjectively acceptable level, the proposed designs are able to outperform equivalent CDMA systems where capacity is increased in the traditional way, by allowing a reduction in SINR. An important application and part of this study, is the use of the proposed designs to extend operation of the CDMA network beyond a defined congestion operating point. Also, the general framework for statistical multiplexing in CDMA is used to study some issues in integrated real-time/data networks.