Unified approach to cross-layer scheduling and resource allocation in OFDMA wireless networks

Orthogonal frequency division multiple access (OFDMA) has been selected as the core physical layer access scheme for state-of-the-art and next-generation wireless communications standards. In these systems, scheduling and resource allocation algorithms, jointly assigning transmission data rates, bandwidth and power, become crucial to optimize the resource utilization while providing support to multimedia applications with heterogeneous quality of service (QoS) requirements. In this article, a unified framework for channeland queue-aware QoS-guaranteed cross-layer scheduling and resource allocation algorithms for heterogeneous multiservice OFDMA wireless networks is presented. The framework encompasses different types of traffic, uniform and continuous power allocation, discrete and continuous rate allocation, and protocols with different amounts of channel- and queue-awareness. System parameters and QoS requirements are projected into utility functions and the optimization problem is then formulated as a constrained utility maximization problem. Optimal solutions for this problem are obtained for the uniform power allocation schemes, and novel quasioptimal algorithms are proposed for the adaptive power allocation strategies. Remarkably, these techniques exhibit complexities that are linear in the number of resource units and users. Simulation results demonstrate the validity and merits of the proposed cross-layer unified approach.

Related papers:

title: Multiuser OFDM with adaptive subcarrier, bit, and power allocation
abstract: Multiuser orthogonal frequency division multiplexing (OFDM) with adaptive multiuser subcarrier allocation and adaptive modulation is considered. Assuming knowledge of the instantaneous channel gains for all users, we propose a multiuser OFDM subcarrier, bit, and power allocation algorithm to minimize the total transmit power. This is done by assigning each user a set of subcarriers and by determining the number of bits and the transmit power level for each subcarrier. We obtain the performance of our proposed algorithm in a multiuser frequency selective fading environment for various time delay spread values and various numbers of users. The results show that our proposed algorithm outperforms multiuser OFDM systems with static time-division multiple access (TDMA) or frequency-division multiple access (FDMA) techniques which employ fixed and predetermined time-slot or subcarrier allocation schemes. We have also quantified the improvement in terms of the overall required transmit power, the bit-error rate (BER), or the area of coverage for a given outage probability.

title: Computationally efficient optimal power allocation algorithms for multicarrier communication systems
abstract: We present an optimal, computationally efficient, integer-bit power allocation algorithm for discrete multitone modulation. Using efficient lookup table searches and a Lagrange-multiplier bisection search, our algorithm converges faster to the optimal solution than existing techniques and can replace the use of suboptimal methods because of its low computational complexity. Fast algorithms are developed for the data rate and performance margin maximization problems.

title: Computationally efficient bandwidth allocation and power control for OFDMA
abstract: The paper studies the problem of finding an optimal subcarrier and power allocation strategy for downlink communication to multiple users in an orthogonal-frequency-division multiplexing-based wireless system. The problem of minimizing total power consumption with constraints on bit-error rate and transmission rate for users requiring different classes of service is formulated and simple algorithms with good performance are derived. The problem of joint allocation is divided into two steps. In the first step, the number of subcarriers that each user gets is determined based on the users' average signal-to-noise ratio. The algorithm is shown to find the distribution of subcarriers that minimizes the total power required when every user experiences a flat-fading channel. In the second stage of the algorithm, it finds the best assignment of subcarriers to users. Two different approaches are presented, the rate-craving greedy algorithm and the amplitude-craving greedy algorithm. A single cell with one base station and many mobile stations is considered. Numerical results demonstrate that the proposed low complexity algorithms offer comparable performance with an existing iterative algorithm.

title: Transmit power adaptation for multiuser OFDM systems
abstract: In this paper, we develop a transmit power adaptation method that maximizes the total data rate of multiuser orthogonal frequency division multiplexing (OFDM) systems in a downlink transmission. We generally formulate the data rate maximization problem by allowing that a subcarrier could be shared by multiple users. The transmit power adaptation scheme is derived by solving the maximization problem via two steps: subcarrier assignment for users and power allocation for subcarriers. We have found that the data rate of a multiuser OFDM system is maximized when each subcarrier is assigned to only one user with the best channel gain for that subcarrier and the transmit power is distributed over the subcarriers by the water-filling policy. In order to reduce the computational complexity in calculating water-filling level in the proposed transmit power adaptation method, we also propose a simple method where users with the best channel gain for each subcarrier are selected and then the transmit power is equally distributed among the subcarriers. Results show that the total data rate for the proposed transmit power adaptation methods significantly increases with the number of users owing to the multiuser diversity effects and is greater than that for the conventional frequency-division multiple access (FDMA)-like transmit power adaptation schemes. Furthermore, we have found that the total data rate of the multiuser OFDM system with the proposed transmit power adaptation methods becomes even higher than the capacity of the AWGN channel when the number of users is large enough.

title: Multiuser transmit optimization for multicarrier broadcast channels: asymptotic FDMA capacity region and algorithms
abstract: We derive optimal and suboptimal multiuser transmit-optimization methods for a multicarrier broadcast channel with intersymbol interference under the frequency-division multiple-access (FDMA) restriction. The general FDMA-based multicarrier broadcast problem is formulated as a maximum weighted rate-sum problem. Given each user's subchannel assignment, the optimal transmit strategy is achieved by multilevel waterfilling. Unfortunately, the problem of finding the optimal subchannel assignments is combinatorial. However, by relaxing the FDMA restriction, we obtain a convex reformulation that allows for efficient computation of the optimal solution, and therefore, a characterization of the FDMA capacity region for a broadcast channel. If all users share the same transmission medium, we prove that the optimal frequency partitioning among the users has an ordered structure that can be exploited to significantly reduce the computational complexity. To make multiuser transmit-optimization schemes practical for applications with relatively fast time-varying user data-rate requirements or priorities, further reduction in computational complexity is necessary. This is achieved by restricting the energy distribution to be constant across the used subchannels. Simulations indicate the low-complexity constant-energy methods presented are very robust, and suffer from negligible performance loss.

title: Resource Allocation in Multiuser Multicarrier Wireless Systems
abstract: Many algorithms have already been proposed in the past to solve the problem of allocating resources in a multi-user multicarrier wireless system. Due to the difficulty of the problem, most of the previous work in this area has focused on developing suboptimal heuristics without performance guarantees.  Allocation in Multiuser Multicarrier Wireless Systems proposes a unified algorithmic framework based on dual optimization techniques that have complexities that are linear in the number of subcarriers and users, and that achieve negligible optimality gaps in standards-based numerical simulations. Adaptive algorithms based on stochastic approximation techniques are also proposed, which are shown to achieve similar performance with even much lower complexity.  With theoretical derivations, practical algorithms, and complexity analysis this book makes an accessible reference for researchers and industry practioners alike All the algorithms proposed are clearly presented in concise block diagrams allowing the reader to implement these algorithms quite easily in the software of their choice The results of each section of the book are based on the 3GPP-LTE standard a fourth generation cellular standard of timely importance Presents chapter on the least complex algorithms that still achieve stochastically optimal results without the need for channel distribution information The section on future work presents several relevant avenues for further investigation of interest to researchers in the field

title: QoS aware adaptive resource allocation techniques for fair scheduling in OFDMA based broadband wireless access systems
abstract: A system based on orthogonal frequency division multiple access (OFDMA) has been developed to deliver mobile broadband data service at data rates comparable to those of wired services, such as DSL and cable modems. We consider the resource allocation problem of assigning a set of subcarriers and determining the number of bits to be transmitted for each subcarrier in OFDMA systems. We compare simplicity, fairness and efficiency of our algorithm with the optimal and proposed suboptimal algorithms for varying values of delay spread, number of users and total power constraint. The results show that the performance of our approach is appealing and can be close to optimal. We also consider another resource allocation scheme in which there is no fixed QoS requirements per symbol but capacity is maximized.

title: A proportional fair scheduling for multicarrier transmission systems
abstract: In this paper, we proposed a proportional fair (PF) scheduling algorithm for systems with multiple carriers such as orthogonal frequency division multiple access systems. The scheduler assigns users to carriers to maximize the sum of logarithmic transmission rate, which is compatible with the definition by RE Kelly ( 1998). It is shown that the PF scheduling in the high data rate (HDR) system proposed by Qualcomm is a special case of our proposed scheme. A simple system is presented, which proves its superiority over other schemes for multicarrier transmission, e.g. extended round robin and the PF scheduling scheme for the HDR system.

title: Adaptive resource allocation in multiuser OFDM systems with proportional rate constraints
abstract: Multiuser orthogonal frequency division multiplexing (MU-OFDM) is a promising technique for achieving high downlink capacities in future cellular and wireless local area network (LAN) systems. The sum capacity of MU-OFDM is maximized when each subchannel is assigned to the user with the best channel-to-noise ratio for that subchannel, with power subsequently distributed by water-filling. However, fairness among the users cannot generally be achieved with such a scheme. In this paper, a set of proportional fairness constraints is imposed to assure that each user can achieve a required data rate, as in a system with quality of service guarantees. Since the optimal solution to the constrained fairness problem is extremely computationally complex to obtain, a low-complexity suboptimal algorithm that separates subchannel allocation and power allocation is proposed. In the proposed algorithm, subchannel allocation is first performed by assuming an equal power distribution. An optimal power allocation algorithm then maximizes the sum capacity while maintaining proportional fairness. The proposed algorithm is shown to achieve about 95% of the optimal capacity in a two-user system, while reducing the complexity from exponential to linear in the number of subchannels. It is also shown that with the proposed resource allocation algorithm, the sum capacity is distributed more fairly and flexibly among users than the sum capacity maximization method.

title: Fair multiuser channel allocation for OFDMA networks using Nash bargaining solutions and coalitions
abstract: In this paper, a fair scheme to allocate subcarrier, rate, and power for multiuser orthogonal frequency-division multiple-access systems is proposed. The problem is to maximize the overall system rate, under each user's maximal power and minimal rate constraints, while considering the fairness among users. The approach considers a new fairness criterion, which is a generalized proportional fairness based on Nash bargaining solutions and coalitions. First, a two-user algorithm is developed to bargain subcarrier usage between two users. Then a multiuser bargaining algorithm is developed based on optimal coalition pairs among users. The simulation results show that the proposed algorithms not only provide fair resource allocation among users, but also have a comparable overall system rate with the scheme maximizing the total rate without considering fairness. They also have much higher rates than that of the scheme with max-min fairness. Moreover, the proposed iterative fast implementation has the complexity for each iteration of only O(K/sup 2/Nlog/sub 2/N+K/sup 4/), where N is the number of subcarriers and K is the number of users.

title: Cross-layer optimization for OFDM wireless networks-part I: theoretical framework
abstract: In this paper, we provide a theoretical framework for cross-layer optimization for orthogonal frequency division multiplexing (OFDM) wireless networks. The utility is used in our study to build a bridge between the physical layer and the media access control (MAC) layer and to balance the efficiency and fairness of wireless resource allocation. We formulate the cross-layer optimization problem as one that maximizes the average utility of all active users subject to certain conditions, which are determined by adaptive resource allocation schemes. We present necessary and sufficient conditions for utility-based optimal subcarrier assignment and power allocation and discuss the convergence properties of optimization. Numerical results demonstrate a significant performance gain for the cross-layer optimization and the gain increases with the number of active users in the networks.

title: Cross-layer optimization for OFDM wireless networks-part I: theoretical framework
abstract: In this paper, we provide a theoretical framework for cross-layer optimization for orthogonal frequency division multiplexing (OFDM) wireless networks. The utility is used in our study to build a bridge between the physical layer and the media access control (MAC) layer and to balance the efficiency and fairness of wireless resource allocation. We formulate the cross-layer optimization problem as one that maximizes the average utility of all active users subject to certain conditions, which are determined by adaptive resource allocation schemes. We present necessary and sufficient conditions for utility-based optimal subcarrier assignment and power allocation and discuss the convergence properties of optimization. Numerical results demonstrate a significant performance gain for the cross-layer optimization and the gain increases with the number of active users in the networks.

title: Cross-Layer Design for OFDMA Wireless Systems With Heterogeneous Delay Requirements
abstract: This paper proposes a cross-layer scheduling scheme for OFDMA wireless systems with heterogeneous delay requirements. We shall focus on the cross-layer design which takes into account both queueing theory and information theory in modeling the system dynamics. We propose a delay-sensitive cross-layer design, which determines the optimal subcarrier allocation and power allocation policies to maximize the total system throughput, subject to the individual user's delay constraint and total base station transmit power constraint. The delay-sensitive power allocation was found to be multilevel water-filling in which urgent users have higher water-filling levels. The delay-sensitive subcarrier allocation strategy has linear complexity with respect to number of users and number of subcarriers. Simulation results show that substantial throughput gain is obtained while satisfying the delay constraints when the delay-sensitive jointly optimal power and subcarrier allocation policy is adopted.

title: Joint Subcarrier and Power Allocation in Channel-Aware Queue-Aware Scheduling for Multiuser OFDM
abstract: In an orthogonal frequency division multiplexing (OFDM) downlink scenario, we propose joint subcarrier and power allocation for channel-aware queue-aware scheduling while allowing multiple users to share a single OFDM symbol. Our approach is to combine subcarrier and power allocation by optimizing a user's power allocation immediately after the user has been allocated a subcarrier. Simulation results show that joint subcarrier and power allocation yields a significant performance improvement compared to other existing schemes which perform subcarrier allocation with a fixed (uniform) power allocation assumption. Joint subcarrier and power allocation is also extended to band-wise allocation of subcarriers in order to help reduce signaling overhead in time varying channels. We examine the trade-off between increasing the sub-band size and the corresponding degradation in system performance for different values of the channel multipath delay spread.

title: A Low-Complexity QoS-Aware Proportional Fair Multicarrier Scheduling Algorithm for OFDM Systems
abstract: Orthogonal frequency-division multiplexing (OFDM) systems are the major cellular platforms for supporting ubiquitous high-speed mobile applications. However, a number of research challenges remain to be tackled. One of the most important challenges is the design of a judicious packet scheduler that will make efficient use of the spectrum bandwidth. Due to the multicarrier nature of the OFDM systems, the applicability and performance of traditional wireless packet-scheduling algorithms, which are usually designed for single-carrier systems, are largely unknown. In th.is paper, we propose a new quality-of-service (QoS)-aware proportional fairness (QPF) packet-scheduling policy with low complexity for the downlink of multiuser OFDM systems to allocate radio resources among users. Our proposed algorithm is based on a cross-layer design in that the scheduler is aware of both the channel (i.e., physical layer) and the queue state (i.e., data link layer) information to achieve proportional fairness while maximizing each user's packet-level QoS performance. The simulation results show that the proposed QPF algorithm is efficient in terms of average system throughput, packet-dropping probability, and packet delay, while maintaining adequate fairness among users with relatively low scheduling overhead.

title: Joint channel- and queue-aware scheduling for multiuser diversity in wireless OFDMA networks
abstract: In this paper, packet scheduling in an orthogonal frequency division multiplex access downlink is investigated based on cross-layer design and optimization. We first develop max-delay-utility scheduling with the help of channel and queue state information to exploit multiuser diversity and guarantee quality of service. The stability property of a scheduling policy is characterized by the stability region, which is the largest region on arrival rates for which the queueing system can be stabilized by the scheduling policy. It is shown in this paper that under very loose conditions, the max-delay-utility scheduling has the maximum stability region. In environments with insufficient scattering or strong line-of-sight components, delay transmit diversity can increase the fluctuation in the frequency domain to improve the performance. The simulation results show that the max-delay-utility scheduling with a frugality constraint is highly advantageous to data transmission with a low latency requirement over shared multiple channels, and that joint scheduling and power allocation can substantially boost the performance.

title: Low complexity cross-layer design with packet dependent scheduling for heterogeneous traffic in multiuser OFDM systems
abstract: We propose an adaptive cross-layer design for the downlink multiuser orthogonal frequency division multiplexing (OFDM) systems, to maximize the weighted sum capacity of all users, where each user has multiple heterogeneous traffic queues simultaneously. A packet dependent (PD) scheduling scheme is employed at the medium access control (MAC) layer, which determines the packet transmission order by assigning different weights to different packets, and is shown by simulations more efficient than the previous methods where all packets in a queue have the same weight. The weight design in PD scheduling considers the delay, size and quality of service (QoS) priority level of packets. Each user weight employed in resource allocation at the physical (PHY) layer is obtained by summing up the weights of selected packets for the user. By properly choosing the number of packets used for weight calculation, the proposed cross-layer design requires a much lower overall complexity than the conventional queue based designs. It is also proven to achieve the maximum system stability region. Furthermore, simulation results show that the proposed suboptimal resource allocation algorithm provides a near-optimal performance while requiring a relatively low complexity.

title: A Unified Approach to QoS-Guaranteed Scheduling for Channel-Adaptive Wireless Networks
abstract: Scheduling amounts to allocating optimally channel, rate and power resources to multiple connections with diverse quality-of-service (QoS) requirements. It constitutes a throughput-critical task at the medium access control layer of today's wireless networks that has been tackled by seemingly unrelated information-theoretic and protocol design approaches. Capitalizing on convex optimization and stochastic approximation tools, the present paper develops a unified framework for channel-aware QoS-guaranteed scheduling protocols for use in adaptive wireless networks whereby multiple terminals are linked through orthogonal fading channels to an access point, and transmissions are (opportunistically) adjusted to the intended channel. The unification encompasses downlink and uplink with time-division or frequency-division duplex operation; full and quantized channel state information comprising a few bits communicated over a limited-rate feedback channel; different types of traffic (best effort, non-real-time, real-time); uniform and optimal power loading; off-line optimal scheduling schemes benchmarking fundamentally achievable rate limits; as well as on-line scheduling algorithms capable of dynamically learning the intended channel statistics and converging to the optimal benchmarks from any initial value. The take-home message offers an important cross-layer design guideline: judiciously developed, yet surprisingly simple, channel-adaptive, on-line schedulers can approach information-theoretic rate limits with QoS guarantees.

title: Resource Allocation in MIMO-OFDMA Wireless Systems Based on Linearly Precoded Orthogonal Space-Time Block Codes
abstract: This paper proposes and analyzes efficient rate and power allocation algorithms for MIMO-OFDMA broadcast channels based on linearly precoded orthogonal space-time block codes. The weighted sum-rate maximization problem is considered for both continuous and discrete rate allocation schemes. Since this problem is non-convex and combinatorial in nature, the Lagrange dual decomposition method is used to find an accurate near-optimal solution. The effects of using different MIMO configurations and realistic channel models with space and frequency correlation over the weighted sum-rate of the system is considered.

title: Dual methods for channel- and QoS-aware resource allocation in MIMO-OFDMA networks
abstract: This work addresses the application of the cross-layer paradigm to the design of efficient resource allocation algorithms for the downlink of a MIMO-OFDMA system with a physical layer employing optimal single-stream/single-user linear precoding. Mathematical programming tools are used to solve the problem of weighted throughput maximization using both channel state information from the physical layer and queue state information supplied by the data link control layer. Due to the complex combinatorial nature of the problem, low-complexity Lagrange decomposition methods combined with subgradient projection algorithms are used to find a solution in the dual domain. The analytical framework proposed in this paper is used to assess the multiuser capacity, packet delay performance and fairness for different channel- and/or QoS-aware resource allocation algorithms proposed in the literature and different MIMO channel configurations.

title: Dual methods for nonconvex spectrum optimization of multicarrier systems
abstract: The design and optimization of multicarrier communications systems often involve a maximization of the total throughput subject to system resource constraints. The optimization problem is numerically difficult to solve when the problem does not have a convexity structure. This paper makes progress toward solving optimization problems of this type by showing that under a certain condition called the time-sharing condition, the duality gap of the optimization problem is always zero, regardless of the convexity of the objective function. Further, we show that the time-sharing condition is satisfied for practical multiuser spectrum optimization problems in multicarrier systems in the limit as the number of carriers goes to infinity. This result leads to efficient numerical algorithms that solve the nonconvex problem in the dual domain. We show that the recently proposed optimal spectrum balancing algorithm for digital subscriber lines can be interpreted as a dual algorithm. This new interpretation gives rise to more efficient dual update methods. It also suggests ways in which the dual objective may be evaluated approximately, further improving the numerical efficiency of the algorithm. We propose a low-complexity iterative spectrum balancing algorithm based on these ideas, and show that the new algorithm achieves near-optimal performance in many practical situations

title: Maximum ratio transmission
abstract: This paper presents the concept, principles, and analysis of maximum ratio transmission for wireless communications where multiple antennas are used for both transmission and reception. The principles and analysis are applicable to general cases, including maximum ratio combining. Simulation results agree with the analysis. The analysis shows that the average overall SNR is proportional to the cross-correlation between channel vectors and that error probability decreases inversely with the (L/spl times/K)th power of the average SNR.

title: On the Asymptotic Optimality of the Gradient Scheduling Algorithm for Multiuser Throughput Allocation
abstract: We consider the model whereN queues (users) are served in discrete time by a generalized switch. The switch state is random, and it determines the set of possible service rate choices (scheduling decisions) in each time slot. This model is primarily motivated by the problem of scheduling transmissions ofN data users in a shared time-varying wireless environment, but also includes other applications such as input-queued cross-bar switches and parallel flexible server systems.The objective is to find a scheduling strategy maximizing a concave utility functionH( u1,..., uN ), whereu n s are long-term average service rates (data throughputs) of the users, assuming users always have data to be served.We prove asymptotic optimality of the gradient scheduling algorithm (which generalizes the well-known proportional fair algorithm) for our model, which, in particular, allows for simultaneous service of multiple users and for discrete sets of scheduling decisions. Analysis of the transient dynamics of user throughputs is the key part of this work.

title: Information capacity and power control in single-cell multiuser communications
abstract: We consider a power control scheme for maximizing the information capacity of the uplink in single-cell multiuser communications with frequency-flat fading, under the assumption that the users attenuations are measured perfectly. Its main characteristics are that only one user transmits over the entire bandwidth at any particular time instant and that the users are allocated more power when their channels are good, and less when they are bad. Moreover, these features are independent of the statistics of the fading. Numerical results are presented for the case of single-path Rayleigh fading. We show that an increase in capacity over a perfectly-power controlled (Gaussian) channel can be achieved, especially if the number of users is large. By examining the bit error-rate with antipodal signalling, we show the inherent diversity in multiuser communications over fading channels.

title: Dynamic bandwidth allocation algorithms for high-speed data wireless networks
abstract: Next-generation wireless networks are expected to support a wide range of high-speed data services, with Web browsing as one of the major applications. Although high data rates have been shown feasible in a single-user setting, the resource allocation issues that arise in a multiple-user context remain extremely challenging. Compared with voice, data traffic is typically more bursty, while the users are less sensitive to delay. These characteristics require resource allocation strategies to operate in a fundamentally different manner if the spectrum is to be used efficiently. In this paper we propose several algorithms for scheduling the efficient transmission of data to multiple users. As a new feature, the various schemes exploit knowledge of the buffer contents to achieve high throughput, while maintaining fairness by providing quality of service (QoS) to individual users. The proposed algorithms are backward compatible with existing cellular and personal communications services (PCS) standards such as IS-136. They provide a powerful approach to improving spectrum efficiency in forthcoming high-speed data cellular services. The extensive simulation experiments we present in this paper demonstrate that the algorithms significantly outperform conventional schemes.

title: Providing quality of service over a shared wireless link
abstract: We propose an efficient way to support quality of service of multiple real-time data users sharing a wireless channel. We show how scheduling algorithms exploiting asynchronous variations of channel quality can be used to maximize the channel capacity (i.e., maximize the number of users that can be supported with the desired QoS).

title: Scheduling for multiple flows sharing a time-varying channel: the exponential rule
abstract: We consider the following queueing system which arises as a model of a wireless link shared by multiple users. Multiple ows must be served by a \channel" (server). The channel capacity (service rate) changes in time randomly and asynchronously with respect to di erent ows. In each time slot, a scheduling discipline (rule) picks a ow for service based on the current state of the channel and the queues. We study a scheduling rule, which we call the exponential rule, and prove that this rule is throughput-optimal, i.e., it makes the queues stable if there exists any rule which can do so. In the proof we use the uid limit technique, along with a separation of time scales argument. Namely, the proof of the desired property of a \conventional" uid limit involves a study of a di erent uid limit arising on a \ ner" time scale. In our companion paper  it is demonstrated that the exponential rule can be used to provide Quality of Service guarantees over a shared wireless link.

title: Cross-Layer Resource Allocation and Scheduling in Wireless Multicarrier Networks
abstract: iii ACKNOWLEDGEMENTS My thesis advisor, Professor Ye (Geoffrey) Li, has my sincerest gratitude for having taught me so much about doing research. It was his insight that helped me to initiate this topic. This thesis has significantly benefited from his valuable guidance and constant encouragement. I also greatly appreciate his care and concern for my intellectual and personal growth. perspective and suggestions have helped me in refining this thesis. I appreciate Professor Raghupathy Sivakumar attending my defense and presenting valuable comments. for being a great office neighbor for four years, Jianxuan Du for sharing views on almost anything, and Ghurumuruhan Ganesan for intensive technical discussions. I am so proud of being a part of the brilliant and fruitful group. I also want to thank Yingqun Yu at the University of Minnesota for many inspiring discussions. His intellectual curiosity is always a source of inspiration for me. Last but not least, I would like to thank my parents for their love, encouragement, and support. This thesis is dedicated to them.  Besides avoiding inter-symbol interference and leading to high capacity, wireless orthogonal frequency division multiplexing (OFDM) or other multicarrier systems provide fine granularity for resource allocation since they are capable of dynamically assigning sub-carriers to multiple users and adaptively allocating transmit power. The current dominate layered networking architecture, in which each layer is designed and operated independently, results in inefficient and inflexible resource use in wireless networks due to the nature of the wireless medium, such as time-varying channel fading, mutual interference, and topology variations. Thus, we need an integrated adaptive design across different layers. In this thesis, we focus on resource allocation and scheduling in wireless OFDM networks based on joint physical and medium access control (MAC) layer optimization. To achieve orders of magnitude gains in system performance, we use two major mechanisms in resource management: exploiting the time variance and frequency selectivity of wireless channels through adaptive modulation, coding, as well as packet scheduling and regulating resource allocation through network economics. With the help of utility functions that capture the satisfaction level of users for a given resource assignment, we establish a utility optimization framework for resource allocation in OFDM networks, in which the network utility at the level of applications is maximized subject to the current channel conditions and the modulation and coding techniques employed in the network. Although the nonlinear and combinatorial nature of the cross-layer optimization …

title: Fair Class-Based Downlink Scheduling with Revenue Considerations in Next Generation Broadband Wireless Access Systems
abstract: The success of emerging Broadband Wireless Access Systems (BWASs) will depend, among other factors, on their ability to manage their shared wireless resources in the most efficient way. This is a complex task due to the heterogeneous nature, and hence, diverse Quality of Service (QoS) requirements of different applications that these systems support. Therefore, QoS provisioning is crucial for the success of such wireless access systems. In this paper, we propose a novel downlink packet scheduling scheme for QoS provisioning in BWASs. The proposed scheme employs practical economic models through the use of novel utility and opportunity cost functions to simultaneously satisfy the diverse QoS requirements of mobile users and maximize the revenues of network operators. Unlike existing schemes, the proposed scheme is general and can support multiple QoS classes with users having different QoS and traffic demands. To demonstrate its generality, we show how the utility function can be used to support three different types of traffic, namely best-effort traffic, traffic with minimum data rate requirements, and traffic with maximum packet delay requirements. Extensive performance analysis is carried out to show the effectiveness and strengths of the proposed packet scheduling scheme.

title: Design of Fair Weights for Heterogeneous Traffic Scheduling in Multichannel Wireless Networks
abstract: 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.

title: Convex Optimization
abstract: Convex optimization problems arise frequently in many different fields. A comprehensive introduction to the subject, this book shows in detail how such problems can be solved numerically with great efficiency. The focus is on recognizing convex optimization problems and then finding the most appropriate technique for solving them. The text contains many worked examples and homework exercises and will appeal to students, researchers and practitioners in fields such as engineering, computer science, mathematics, statistics, finance, and economics.