scispace - formally typeset
Search or ask a question

Showing papers on "Channel allocation schemes published in 2009"


Journal ArticleDOI
TL;DR: This work proposes a gradient-based scheduling framework for OFDM scheduling that has prohibitively high computational complexity but reveals guiding principles that are used to generate lower complexity sub-optimal algorithms.
Abstract: Orthogonal frequency division multiplexing (OFDM) with dynamic scheduling and resource allocation is a key component of most emerging broadband wireless access networks such as WiMAX and LTE (long term evolution) for 3GPP. However, scheduling and resource allocation in an OFDM system is complicated, especially in the uplink due to two reasons: (i) the discrete nature of subchannel assignments, and (ii) the heterogeneity of the users' subchannel conditions, individual resource constraints and application requirements. We approach this problem using a gradient-based scheduling framework. Physical layer resources (bandwidth and power) are allocated to maximize the projection onto the gradient of a total system utility function which models application-layer Quality of Service (QoS). This is formulated as a convex optimization problem and solved using a dual decomposition approach. This optimal solution has prohibitively high computational complexity but reveals guiding principles that we use to generate lower complexity sub-optimal algorithms. We analyze the complexity and compare the performance of these algorithms via extensive simulations.

311 citations


Journal ArticleDOI
TL;DR: Algorithms for resource allocation in Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, which is the uplink multiple access scheme considered in the 3GPP-LTE standard, are presented and a greedy heuristic algorithm that approaches the optimal performance in cases of practical interest is presented.
Abstract: We present algorithms for resource allocation in Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, which is the uplink multiple access scheme considered in the Third Generation Partnership Project-Long Term Evolution (3GPP-LTE) standard. Unlike the well-studied problem of Orthogonal Frequency Division Multiple Access (OFDMA) resource allocation, the "subchannel adjacency" restriction, whereby users can only be assigned multiple subchannels that are adjacent to each other, makes the problem much harder to solve. We present a novel reformulation of this problem as a pure binary-integer program called the set partitioning problem, which is a well studied problem in operations research. We also present a greedy heuristic algorithm that approaches the optimal performance in cases of practical interest. We present simulation results for 3GPP-LTE uplink scenarios.

203 citations


Journal ArticleDOI
TL;DR: An adaptive regret based learning procedure is applied which tracks the set of correlated equilibria of the game, treated as a distributed stochastic approximation, which is shown to perform very well compared with other similar adaptive algorithms.
Abstract: We consider dynamic spectrum access among cognitive radios from an adaptive, game theoretic learning perspective. Spectrum-agile cognitive radios compete for channels temporarily vacated by licensed primary users in order to satisfy their own demands while minimizing interference. For both slowly varying primary user activity and slowly varying statistics of "fast" primary user activity, we apply an adaptive regret based learning procedure which tracks the set of correlated equilibria of the game, treated as a distributed stochastic approximation. This procedure is shown to perform very well compared with other similar adaptive algorithms. We also estimate channel contention for a simple CSMA channel sharing scheme.

198 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a mapping process between the channel assignment matrix and the chromosome of GA, QGA, and the position of the particle of PSO, respectively, based on the characteristics of the channel availability matrix and interference constraints.
Abstract: Cognitive radio has been regarded as a promising technology to improve spectrum utilization significantly. In this letter, spectrum allocation model is presented firstly, and then spectrum allocation methods based on genetic algorithm (GA), quantum genetic algorithm (QGA), and particle swarm optimization (PSO), are proposed. To decrease the search space we propose a mapping process between the channel assignment matrix and the chromosome of GA, QGA, and the position of the particle of PSO, respectively, based on the characteristics of the channel availability matrix and the interference constraints. Results show that our proposed methods greatly outperform the commonly used color sensitive graph coloring algorithm.

196 citations


Journal ArticleDOI
TL;DR: The important features of CRAHNs are presented, along with the design approaches and research challenges that must be addressed, and each of these functions is described from the viewpoint of multihop infra-structureless networks requiring cooperation among users.
Abstract: The problem of spectrum scarcity and inefficiency in spectrum usage will be addressed by the newly emerging cognitive radio paradigm that allows radios to opportunistically transmit in the vacant portions of the spectrum already assigned to licensed users. For this, the ability for spectrum sensing, spectrum sharing, choosing the best spectrum among the available options, and dynamically adapting transmission parameters based on the activity of the licensed spectrum owners must be integrated within cognitive radio users. Specifically in cognitive radio ad hoc networks, distributed multihop architecture, node mobility, and spatio-temporal variance in spectrum availability are some of the key distinguishing factors. In this article the important features of CRAHNs are presented, along with the design approaches and research challenges that must be addressed. Spectrum management in CRAHNs comprises spectrum sensing, sharing, decision, and mobility. In this article each of these functions are described in detail from the viewpoint of multihop infra-structureless networks requiring cooperation among users.

179 citations


Proceedings ArticleDOI
28 Sep 2009
TL;DR: An energy efficient MAC protocol (BodyMAC) is proposed that uses flexible bandwidth allocation to improve node energy efficiency by reducing the possibility of packet collisions and by reducing radio transmission times, idle listening and control packets overhead.
Abstract: Wireless Body Area Networks (WBANs) enable placement of tiny biomedical sensors on or inside the human body to monitor vital body signs. The IEEE 802.15.6 task group is developing a standard to optimize WBAN performance by defining the physical layer (PHY) and media access control (MAC) layer specifications. In this paper an energy efficient MAC protocol (BodyMAC) is proposed. It uses flexible bandwidth allocation to improve node energy efficiency by reducing the possibility of packet collisions and by reducing radio transmission times, idle listening and control packets overhead. BodyMAC is based on a Downlink and Uplink scheme in which the Contention Free Part in the Uplink subframe is completely collision free. Three types of bandwidth allocation mechanisms allow for flexible and efficient data and control communications. An efficient Sleep Mode is introduced to reduce the idle listening duration, especially for low duty cycle nodes in the network. Simulation results show superior performance of BodyMAC compared to that of the IEEE 802.15.4 MAC.

177 citations


Journal ArticleDOI
TL;DR: A novel practical low-complexity multicell orthogonal frequency-division multiple access (OFDMA) downlink channel-assignment method that uses a graphic framework that can be used in next-generation cellular systems such as the 3GPP Long-Term Evolution and IEEE 802.16 m.
Abstract: A novel practical low-complexity multicell orthogonal frequency-division multiple access (OFDMA) downlink channel-assignment method that uses a graphic framework is proposed in this paper. Our solution consists of two phases: 1) a coarse-scale intercell interference (ICI) management scheme and 2) a fine-scale channel-aware resource-allocation scheme. In the first phase, state-of-the-art ICI management techniques such as ICI coordination (ICIC) and base-station cooperation (BSC) are incorporated in our framework. In particular, the ICI information is acquired through inference from the diversity set of mobile stations and is presented by an interference graph. Then, ICIC or BSC is mapped to the MAX k-CUT problem in graph theory and is solved in the first phase. In the second phase, channel assignment is accomplished by taking instantaneous channel conditions into account. Heuristic algorithms are proposed to efficiently solve both phases of the problem. Extensive simulation is conducted for various practical scenarios to demonstrate the superior performance of the proposed solution compared with the conventional OFDMA allocation scheme. The proposed scheme can be used in next-generation cellular systems such as the 3GPP Long-Term Evolution and IEEE 802.16 m.

172 citations


Proceedings ArticleDOI
19 Apr 2009
TL;DR: The Staggered TDMA Underwater MAC Protocol (STUMP), a scheduled, collision free TDMA-based MAC protocol that leverages node position diversity and the low propagation speed of the underwater channel, yields several important conclusions.
Abstract: In this paper, we propose the Staggered TDMA Underwater MAC Protocol (STUMP), a scheduled, collision free TDMA-based MAC protocol that leverages node position diversity and the low propagation speed of the underwater channel. STUMP uses propagation delay information to overlap node communication and increase channel utilization. Our work yields several important conclusions. First, leveraging node position diversity through scheduling yields large improvements in channel utilization. Second, STUMP does not require tight node synchronization to achieve high channel utilization, allowing nodes to use simple or more energy efficient synchronization protocols. Finally, we briefly present and evaluate algorithms that derive STUMP schedules.

165 citations


Journal ArticleDOI
TL;DR: This paper develops optimal resource allocation algorithms for the OFDMA downlink assuming the availability of only partial (imperfect) CSI, and considers both continuous and discrete ergodic weighted sum rate maximization subject to total power constraints, and average bit error rate constraints for the discrete rate case.
Abstract: Previous research efforts on OFDMA resource allocation have typically assumed the availability of perfect channel state information (CSI). Unfortunately, this is unrealistic, primarily due to channel estimation errors, and more importantly, channel feedback delay. In this paper, we develop optimal resource allocation algorithms for the OFDMA downlink assuming the availability of only partial (imperfect) CSI. We consider both continuous and discrete ergodic weighted sum rate maximization subject to total power constraints, and average bit error rate constraints for the discrete rate case. We approach these problems using a dual optimization framework, allowing us to solve these problems with O(MK) complexity per symbol for an OFDMA system with K used subcarriers and M active users, while achieving relative optimality gaps of less than 10-5 for continuous rates and less than 10-3 for discrete rates in simulations based on realistic parameters.

154 citations


Journal ArticleDOI
TL;DR: A multi-thread polling algorithm to effectively and fairly distribute the upstream bandwidth dynamically and to decrease the average packet delay and improve network throughput under varying offered loads is proposed and studied.
Abstract: With the advances in optical technology, the span of a broadband access network using passive optical network (PON) technology can be increased from today's standard of 20 km to 100 km or higher, and thereby serve a lot more users. Such an extended-reach PON is known as SuperPON in the literature, and we call it a long-reach PON (LR-PON). A major challenge in LR-PON is that the propagation delay (for data as well as control signals) between the telecom central office (CO) and the end user is increased by a very significant amount. Now, traditional PON algorithms for scheduling the upstream transmission, such as dynamic bandwidth allocation (DBA) algorithms, may not be sufficient; actually, they may lead to degraded performance because of the long delay of the CO-to- Users "control loop." This challenge motivates us to propose and study a multi-thread polling algorithm to effectively and fairly distribute the upstream bandwidth dynamically. This algorithm exploits the benefits of having multiple polling processes running simultaneously and enabling users to send bandwidth requests before receiving acknowledgement from the CO. We compare the proposed algorithm with traditional DBA, and show its advantage on average packet delay. We then analyze and optimize key parameters of the algorithm, such as initiating and tuning multiple threads, inter-thread scheduling, and fairness among users. Numerical results demonstrate the algorithm's advantage to decrease the average packet delay and improve network throughput under varying offered loads.

153 citations


Proceedings ArticleDOI
22 Jun 2009
TL;DR: A distributed cluster agreement algorithm called Spectrum-Opportunity Clustering (SOC) is proposed to solve the problem of dynamic assignment of coordination (control) channels in cognitive radio networks (CRNs) by exploiting time- and space-varying spectrum opportunities.
Abstract: We address the problem of dynamic assignment of coordination (control) channels in cognitive radio networks (CRNs) by exploiting time- and space-varying spectrum opportunities Motivated by the inherent grouping of Cognitive Radio (CR) users according to channel availability, we propose a cluster-based architecture for control-channel assignment in a CRN CRs are grouped in the same cluster if they roughly sense similar idle channels and are within communication range, either directly or via a clusterhead We formulate the clustering design as a maximum edge biclique problem A distributed cluster agreement algorithm called Spectrum-Opportunity Clustering (SOC) is proposed to solve this problem SOC provides a desirable balance between two competing factors: the set of common idle channels within each cluster and the cluster size A large set of common idle channels within each cluster allows graceful migration from the current control channel should primary radio (PR) activity appear on that channel Hence, SOC provides a stable network partition with respect to local coordination, with no need for frequent reclustering Moreover, when reclustering has to be performed (due to CR mobility or PR activity), CRs agree on new clusters after the broadcast of only three messages, thus incurring low communication overhead

Journal ArticleDOI
TL;DR: Simulation results show that substantial throughput gains are achievable by the proposed two- way relaying and optimal resource allocation schemes over the conventional one-way relays and fixed resource allocation for relay-assisted OFDMA-based wireless networks.
Abstract: This paper studies the resource allocation problem for the relay-assisted orthogonal frequency-division multiple-access (OFDMA)-based multiuser system. A new transmission protocol, named hierarchical OFDMA, is proposed to support two-way communications between the base station (BS) and each mobile user (MU) with or without an assisting relay station (RS) in ldquorelayrdquo or ldquodirectrdquo mode, respectively. In particular, the recently discovered two-way relaying technology, based on the principle of network coding, is applied to MUs in relay mode with two possible relay-operations, namely, decode-and-forward (DF) and amplify-and-forward (AF). By applying convex optimization techniques, efficient algorithms are developed for optimal allocation of transmit resources such as power levels, bit rates, and OFDM subcarriers at the BS, RSs, and MUs. Simulation results show that substantial system throughput gains are achievable by the proposed two-way relaying and optimal resource allocation schemes over the traditional one-way relaying and fixed resource allocation schemes for relay-assisted OFDMA-based wireless networks.

Journal ArticleDOI
TL;DR: A generic spectrum-surveying framework is proposed that introduces both standardization and automation to this process, as well as enables a distributed approach to spectrum surveying.
Abstract: Dynamic spectrum access networks and wireless spectrum policy reforms heavily rely on accurate spectrum utilization statistics, which are obtained via spectrum surveys. In this paper, we propose a generic spectrum-surveying framework that introduces both standardization and automation to this process, as well as enables a distributed approach to spectrum surveying. The proposed framework outlines procedures for the collection, analysis, and modeling of spectrum measurements. Furthermore, we propose two techniques for processing spectrum data without the need for a priori knowledge. In addition, these techniques overcome the challenges associated with spectrum data processing, such as a large dynamic range of signals and the variation of the signal-to-noise ratio across the spectrum. Finally, we present mathematical tools for the analysis and extraction of important spectrum occupancy parameters. The proposed processing techniques have been validated using empirical spectrum measurements collected from the FM, television (TV), cellular, and paging bands. Results show that the primary signals in the FM band can be classified with a miss-detection rate of about 2% at the cost of 50% false-alarm rate, while nearly 100% reliability in classification can be achieved with the other bands. However, the classification accuracy depends on the duration and the range of frequencies over which data are collected, as well as the RF characteristics of the spectrum measurement receiver.

Journal ArticleDOI
TL;DR: A framework for resource allocation in a secondary spectrum access scenario, where a group of cognitive radios access the resources of a primary system, and uses Sequential Quadratic Programming (SQP) to solve the proposed non-linearly constrained CRG optimization problem.
Abstract: In this paper we develop a framework for resource allocation in a secondary spectrum access scenario, where a group of cognitive radios (CR) access the resources of a primary system. We assume the primary system is a cellular OFDM-based network operating in uplink. We develop an optimum resource allocation strategy, using cooperative game theory, which guarantees the primary's required QoS and allocates an achievable rate at a given bit error rate for the secondary, when possible. The proposed cognitive radio game (CRG) is a network-assisted resource management method, where users (both primary and secondary) inform the primary system's BS of their channel state information and power limitation and the base station calculates the optimum sub-channel and power allocation for all users. Using Game theoretic axiom of fairness, i.e., Nash Bargaining Solutions (NBS), we develop an alternative efficient and fair resource allocation and compare its performance with the proposed CRG method. We use Sequential Quadratic Programming (SQP) to solve the proposed non-linearly constrained CRG optimization problem.

Journal ArticleDOI
TL;DR: It is suggested that opportunistic spectrum sharing can significantly improve spectrum efficiency and system capacity, even under unreliable spectrum detection.
Abstract: We analyze the performance of a wireless system consisting of a set of secondary users opportunistically sharing bandwidth with a set of primary users over a coverage area. The secondary users employ spectrum sensing to detect channels that are unused by the primary users and hence make use of the idle channels. If an active secondary user detects the presence of a primary user on a given channel, it releases the channel and switches to another idle channel, if one is available. In the event that no channel is available, the call waits in a buffer until either a channel becomes available or a maximum waiting time is reached. Spectrum sensing errors on the part of a secondary user cause false alarm and mis-detection events, which can potentially degrade the quality-of-service experienced by primary users. We derive system performance metrics of interest such as blocking probabilities. Our results suggest that opportunistic spectrum sharing can significantly improve spectrum efficiency and system capacity, even under unreliable spectrum detection. The proposed model and analysis method can be used to evaluate the performance of future opportunistic spectrum sharing systems.

Journal ArticleDOI
TL;DR: This paper proposes an efficient solution to minimize the total transmit power subject to each user's data rate requirement, using a Lagrangian dual decomposition to keep the complexity low.
Abstract: With the proliferation of wireless services, personal connectivity is quickly becoming ubiquitous. As the user population demands greater multimedia interactivity, data rate requirements are set to soar. Future wireless systems, e.g., multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM), need to cater to not only a burgeoning subscriber pool but also to a higher throughput per user. Furthermore, resource allocation for multiuser MIMO-OFDM systems is vital for the optimization of the subcarrier and power allocations to improve overall system performance. Using convex optimization techniques, this paper proposes an efficient solution to minimize the total transmit power subject to each user's data rate requirement. Using a Lagrangian dual decomposition, the complexity is reduced from one that is exponential in the number of subcarriers M to one that is only linear in M. To keep the complexity low, linear beamforming is incorporated at both the transmitter and the receiver. Although frequency-flat fading has been known to plague OFDM resource allocation systems, a modification, i.e., dual proportional fairness, seamlessly handles flat or partially frequency-selective fading. Due to the nonconvexity of the optimization problem, the proposed solution is not guaranteed to be optimal. However, for a realistic number of subcarriers, the duality gap is practically zero, and optimal resource allocation can be evaluated efficiently. Simulation results show large performance gains over a fixed subcarrier allocation.

Proceedings ArticleDOI
23 Jun 2009
TL;DR: This work addresses the joint link scheduling and channel assignment problem for convergecast in networks operating according to the recent WirelessHART standard and presents jointly time- and channel-optimal scheduling policies with complexity O(N2).
Abstract: Convergecast, in which data from a set of sources is routed toward one data sink, is a critical functionality for wireless networks deployed for industrial monitoring and control. We address the joint link scheduling and channel assignment problem for convergecast in networks operating according to the recent WirelessHART standard. For a linear network with N single-buffer devices, we demonstrate that the minimum time to complete convergecast is 2N-1 time-slots, and that the minimum number of channels required for this operation is ⌈N/2⌉. When the devices are allowed to buffer multiple packets, we prove that the optimal convergecast time remains the same while the number of required channels can be reduced to . For both cases, we present jointly time- and channel-optimal scheduling policies with complexity O(N2). Numerical results demonstrate that our schemes are also efficient in terms of memory utilization.

Journal ArticleDOI
TL;DR: A forwarding paradigm is developed to achieve the resulting set of flow rates while using a standard MAC using a bi-dimensional Markov chain model of the proposed forwarding paradigm to analyze its behavior.
Abstract: The availability of cost-effective wireless network interface cards makes it practical to design network devices with multiple radios which can be exploited to simultane-ously transmit/receive over different frequency channels. It has been shown that using multiple radios per node increases the throughput of multi-hop wireless mesh networks. However, multi-radios create several research challenges. A fundamental problem is the joint channel assignment and routing problem, i.e., how the channels can be assigned to radios and how a set of flow rates can be determined for every network link in order to achieve an anticipated objective. This joint problem is NP-com-plete. Thus, an approximate solution is developed by solving the channel assignment and the routing problems separately. The channel assignment problem turns out to be the problem to assign channels such that a given set of flow rates are schedulable and itself is shown to be also NP-complete. This paper shows that not only the channels but also the transmission rates of the links have to be properly selected to make a given set of flow rates schedulable. Thus, a greedy heuristic for the channel and rate assignment problem is developed. Algorithms to schedule the resulting set of flow rates have been proposed in the literature, which require synchronization among nodes and hence modified coordination functions. Unlike previous work, in this paper a forwarding paradigm is developed to achieve the resulting set of flow rates while using a standard MAC. A bi-dimensional Markov chain model of the proposed forwarding paradigm is presented to analyze its behavior. Thorough performance studies are con-ducted to: a) compare the proposed greedy heuristic to other channel assignment algorithms; b) analyze the behavior of the forwarding paradigm through numerical simulations based on the Markov chain model; c) simulate the operations of the forwarding paradigm and evaluate the achieved network throughput.

Proceedings ArticleDOI
22 Jun 2009
TL;DR: A variable power/bandwidth efficient modulation strategy where the modulation level is adjusted by cognitively determining the assignment and use of the available spectrum, taking into account the channel occupancy probability is described.
Abstract: This paper discusses different ways of delivering ‘green’ cognitive radio based systems. Fundamental is the need to exploit the free spectrum available and power efficient modulation where possible. The paper describes a variable power/bandwidth efficient modulation strategy where the modulation level is adjusted by cognitively determining the assignment and use of the available spectrum, taking into account the channel occupancy probability. Battery life for different techniques is also considered. Secondly, the paper discusses ways to reduce the complexity overall of cognitive radio systems, particularly in the need for spectrum sensing by exploiting distributed artificial intelligence. Techniques presented show how it is possible to largely eliminate the need for spectrum sensing, along with the associated energy consumption, by using reinforcement learning to develop a preferred channel set in each device. Finally, the paper discusses the potential benefits of the use of antenna directionality to improve energy efficiency, and the associated problems that still must be solved before this technique can deliver ‘green’ radio.

Journal ArticleDOI
TL;DR: This paper models and evaluates the throughput that can be achieved in a system where nodes compete for bandwidth using a generalized version of slotted-Aloha protocols and reveals that under heavy loads, a greedy strategy reduces the utilization, and that attackers cannot do much better than attacking during randomly selected slots.
Abstract: Aloha and its slotted variation are commonly deployed medium access control (MAC) protocols in environments where multiple transmitting devices compete for a medium, yet may have difficulty sensing each other's presence (the "hidden terminal problem''). Competing 802.11 gateways, as well as most modern digital cellular systems, like GSM, are examples. This paper models and evaluates the throughput that can be achieved in a system where nodes compete for bandwidth using a generalized version of slotted-Aloha protocols. The protocol is implemented as a two-state system, where the probability that a node transmits in a given slot depends on whether the node's prior transmission attempt was successful. Using Markov models, we evaluate the channel utilization and fairness of this class of protocols for a variety of node objectives, including maximizing aggregate throughput of the channel, each node selfishly maximizing its own throughput, and attacker nodes attempting to jam the channel. If all nodes are selfish and strategically attempt to maximize their own throughput, a situation similar to the traditional Prisoner's Dilemma arises. Our results reveal that under heavy loads, a greedy strategy reduces the utilization, and that attackers cannot do much better than attacking during randomly selected slots.

Proceedings ArticleDOI
01 Sep 2009
TL;DR: The performance of the model is evaluated and it is shown that limited access contributes to seriously reduce cross-layer interference while guaranteeing a minimum performance to the femtocell subscribers.
Abstract: Femtocells are a promising solution for the provision of high indoor coverage and capacity. Furthermore, OFDMA-based femtocells have proven to be highly versatile when dealing with cross-layer co-channel interference thanks to the allocation of frequency subchannels. However, concerns still exist related to the impact of the different access methods to femtocells in an overlayed network. Femtocells based on a Closed Subscribers Group, where only device owners are allowed connectivity introduce severe interference to macrocell users. On the other hand, Open Access femtocells where any user can connect, does not bring many advantages to the femtocell owner. In this paper, an intermediate access method based on a limited access is proposed. The performance of the model is evaluated throughout systemlevel simulations and it is shown that limited access contributes to seriously reduce cross-layer interference while guaranteeing a minimum performance to the femtocell subscribers.

Journal IssueDOI
01 Apr 2009
TL;DR: A CA algorithm named Minimum interference Multi-channel Multi-radio Multicast (M4) is proposed that minimizes interference among nodes in a multicast routing tree and uses both orthogonal and overlapping channels such as those in IEEE 802.11b-g systems.
Abstract: One of the most effective approaches to enhance the throughput capacity of wireless mesh networks (WMN) is to use systems with multiple channels and multiple radios per node. Multi-channel multi-radio (MCMR) networks require efficient channel assignment (CA) algorithms to determine which channel a link should use for data transmission in order to maximize network throughput. The problem of CA has been studied extensively for unicast communications, but addressed only recently for multicast. We propose a CA algorithm named Minimum interference Multi-channel Multi-radio Multicast (M4) that minimizes interference among nodes in a multicast routing tree and uses both orthogonal and overlapping channels such as those in IEEE 802.11b-g systems. Simulation results show that M4 outperforms the Multi Channel Multicast algorithm proposed. in various scenarios with respect to average packet delivery ratio, throughput and end-to-end delay. Copyright © 2008 John Wiley & Sons, Ltd.

Proceedings ArticleDOI
01 Sep 2009
TL;DR: Simulation results confirm the derived analytical results for the growth of the system goodput and illustrate that the proposed distributed cross-layer scheduler only requires a small number of iterations to achieve practically the same performance as the optimal centralized scheduler.
Abstract: In this paper, we consider cross-layer scheduling for the downlink of amplify-and-forward (AF) relay-assisted orthogonal frequency-division multiple-access (OFDMA) networks. The proposed cross-layer design takes into account the effects of imperfect channel-state information (CSI) at the transmitter (CSIT) in slow fading. The rate, power, and subcarrier allocation policies are optimized to maximize the system goodput (in bits per second per hertz successfully received by the users). The optimization problem is solved by using dual decomposition, resulting in a highly scalable distributed iterative resource-allocation algorithm. We also investigate the asymptotic performance of the proposed scheduler with respect to (w.r.t.) the numbers of users and relays. We find that the number of relays should grow faster than the number of users to fully exploit the multiuser diversity (MUD) gain. On the other hand, diversity from multiple relays can be exploited to enhance system performance when the MUD gain is saturated due to noise amplification at the AF relays. Furthermore, we introduce a feedback-reduction scheme to reduce the computational burden and the required amount of CSI feedback from the users to the relays. Simulation results confirm the derived analytical results for the growth of the system goodput and illustrate that the proposed distributed cross-layer scheduler only requires a small number of iterations to achieve practically the same performance as the optimal centralized scheduler, even if the information exchanged between the base station (BS) and the relays in each iteration is quantized, and the proposed CSI feedback reduction scheme is employed.

Proceedings ArticleDOI
20 Jun 2009
TL;DR: This work presents a framework for application-aware routing that assures deadlock-freedom under one or more channels by forcing routes to conform to an acyclic channel dependence graph and presents a mixed integer-linear programming (MILP) approach and a heuristic approach for producing deadlocked routes that minimize maximum channel load.
Abstract: Conventional oblivious routing algorithms are either not application-aware or assume that each flow has its own private channel to ensure deadlock avoidance. We present a framework for application-aware routing that assures deadlock-freedom under one or more channels by forcing routes to conform to an acyclic channel dependence graph. Arbitrary minimal routes can be made deadlock-free through appropriate static channel allocation when two or more channels are available. Given bandwidth estimates for flows, we present a mixed integer-linear programming (MILP) approach and a heuristic approach for producing deadlock-free routes that minimize maximum channel load. The heuristic algorithm is calibrated using the MILP algorithm and evaluated on a number of benchmarks through detailed network simulation. Our framework can be used to produce application-aware routes that target the minimization of latency, number of flows through a link, bandwidth, or any combination thereof.

01 Jan 2009
TL;DR: In this paper, the authors present a framework for application-aware routing that assures deadlock-freedom under one or more channels by forcing routes to conform to an acyclic channel dependence graph.
Abstract: Conventional oblivious routing algorithms are either not application-aware or assume that each flow has its own private channel to ensure deadlock avoidance. We present a framework for application-aware routing that assures deadlock-freedom under one or more channels by forcing routes to conform to an acyclic channel dependence graph. Arbitrary minimal routes can be made deadlock-free through appropriate static channel allocation when two or more channels are available. Given bandwidth estimates for flows, we present a mixed integer-linear programming (MILP) approach and a heuristic approach for producing deadlock-free routes that minimize maximum channel load. The heuristic algorithm is calibrated using the MILP algorithm and evaluated on a number of benchmarks through detailed network simulation. Our framework can be used to produce application-aware routes that target the minimization of latency, number of flows through a link, bandwidth, or any combination thereof.

Journal ArticleDOI
TL;DR: An iterative algorithm is developed to efficiently obtain the optimal solution of the weighted sum rate problem for the C-MAC, and it is shown that the proposed algorithm, although developed for single channel transmission, can be extended to the case of multiple channel transmission.
Abstract: Cognitive radio is an emerging technology that shows great promise to dramatically improve the efficiency of spectrum utilization. This paper considers a cognitive radio model, in which the secondary network is allowed to use the radio spectrum concurrently with primary users (PUs) provided that interference from the secondary users (SUs) to the PUs is constrained by certain thresholds. The weighted sum rate maximization problem is studied under interference power constraints and individual transmit power constraints, for a cognitive multiple access channel (C-MAC), in which each SU having a single transmit antenna communicates with the base station having multiple receive antennas. An iterative algorithm is developed to efficiently obtain the optimal solution of the weighted sum rate problem for the C-MAC. It is further shown that the proposed algorithm, although developed for single channel transmission, can be extended to the case of multiple channel transmission. Corroborating numerical examples illustrate the convergence behavior of the algorithm and present comparisons with other existing alternative algorithms.

Journal ArticleDOI
TL;DR: The unique characteristics of multihop cognitive radio networks are highlighted, key MAC design challenges specific to such networks are discussed, and some of the work that has been done on MAC design for CRNs is presented.
Abstract: Heavy traffic over the unlicensed portion of the spectrum along with inefficient usage of the licensed spectrum gave impetus for a new spectrum allocation policy, the main purpose of which is to improve spectrum efficiency through opportunistic spectrum access. Cognitive radios have been proposed as a key enabling technology for such an opportunistic policy. One of the key challenges to enabling multihop CR communications is how to perform opportunistic medium access control while limiting the interference imposed on licensed users. In this article we highlight the unique characteristics of multihop cognitive radio networks, discuss key MAC design challenges specific to such networks, and present some of the work that has been done on MAC design for CRNs.

Journal ArticleDOI
TL;DR: Simple mechanisms are proposed that enable selfish cognitive radio devices not only to coordinate efficiently on the available channels but also to optimally use every single allocated channel.
Abstract: In this paper, we study the problem of efficient medium access control (MAC) among cognitive radio devices that are equipped with multiple radios and thus are capable of transmitting simultaneously at different frequencies (channels). We assume that radios contend on each channel using the carrier sense multiple access with collision avoidance (CSMA/CA) protocol. We study two MAC problems: (i) the allocation of the available channels among radios, and (ii) the optimal usage of each allocated channel by the radios occupying it. Both problems are studied in a game-theoretic setting, where devices aim to selfishly maximize their share of the available bandwidth. As for the first problem, we show that the ldquoprice of anarchyrdquo is close to 1, that is, Nash equilibria imply nearly system optimal allocations of the available channels. For the second problem, we design a game such that it admits a unique Nash equilibrium that is is both fair and Pareto-optimal. Furthermore, we propose simple mechanisms that enable selfish cognitive radio devices not only to coordinate efficiently on the available channels but also to optimally use every single allocated channel.

Proceedings ArticleDOI
19 Apr 2009
TL;DR: An efficient protocol for reliably exchanging information in a single-hop, multi-channel radio network subject to unpredictable interference is presented, and it is proved that exponential-time is unavoidable in the latter case.
Abstract: This paper presents an efficient protocol for reliably exchanging information in a single-hop, multi-channel radio network subject to unpredictable interference. We model the interference by an adversary that can simultaneously disrupt up to t of the C available channels. We assume no shared secret keys or third-party infrastructure. The running time of our protocol depends on the gap between C and t: when the number of channels C =Omega(t^2), the running time is linear; when only C = t+1 channels are available, the running time is exponential. We prove that exponential-time is unavoidable in the latter case. At the core of our protocol lies a combinatorial function, possibly of independent interest, described for the first time in this paper: the multi-selector. A multi-selector generates a sequence of channel assignments for each device such that every sufficiently large subset of devices is partitioned onto distinct channels by at least one of these assignments.

Journal ArticleDOI
TL;DR: Two different adaptive subcarrier allocation algorithms are proposed and analyzed and their aim is to share the network bandwidth among users on the basis of specific channel conditions without loosing bandwidth efficiency and fairness.
Abstract: WiMax is one of the most important technologies for providing a broadband wireless access (BWA) in a metropolitan area. The use of OFDM transmissions has been proposed to reduce the effect of multipath fading in wireless communications. Moreover, multiple access is achieved by resorting to the OFDMA scheme. Adaptive subcarrier allocation techniques have been selected to exploit the multiuser diversity, leading to an improvement of performance by assigning subchannels to the users accordingly with their channel conditions. A method to allocate subcarriers is to assign almost an equal bandwidth to all users (fair allocation). However, it is well known that this method limits the bandwidth efficiency of the system. In order to lower this drawback, in this paper, two different adaptive subcarrier allocation algorithms are proposed and analyzed. Their aim is to share the network bandwidth among users on the basis of specific channel conditions without loosing bandwidth efficiency and fairness. Performance comparisons with the static and the fair allocation approaches are presented in terms of bit error rate and throughput to highlight the better behavior of the proposed schemes in particular when users have different distances from the BS.