Showing papers on "Channel allocation schemes published in 2005"

Architecture and algorithms for an IEEE 802.11-based multi-channel wireless mesh network

Abstract: Even though multiple non-overlapped channels exist in the 2.4 GHz and 5 GHz spectrum, most IEEE 802.11-based multi-hop ad hoc networks today use only a single channel. As a result, these networks rarely can fully exploit the aggregate bandwidth available in the radio spectrum provisioned by the standards. This prevents them from being used as an ISP's wireless last-mile access network or as a wireless enterprise backbone network. In this paper, we propose a multi-channel wireless mesh network (WMN) architecture (called Hyacinth) that equips each mesh network node with multiple 802.11 network interface cards (NICs). The central design issues of this multi-channel WMN architecture are channel assignment and routing. We show that intelligent channel assignment is critical to Hyacinth's performance, present distributed algorithms that utilize only local traffic load information to dynamically assign channels and to route packets, and compare their performance against a centralized algorithm that performs the same functions. Through an extensive simulation study, we show that even with just 2 NICs on each node, it is possible to improve the network throughput by a factor of 6 to 7 when compared with the conventional single-channel ad hoc network architecture. We also describe and evaluate a 9-node Hyacinth prototype that Is built using commodity PCs each equipped with two 802.11a NICs.

Capacity bounds and power allocation for wireless relay channels

Abstract: We consider three-node wireless relay channels in a Rayleigh-fading environment. Assuming transmitter channel state information (CSI), we study upper bounds and lower bounds on the outage capacity and the ergodic capacity. Our studies take into account practical constraints on the transmission/reception duplexing at the relay node and on the synchronization between the source node and the relay node. We also explore power allocation. Compared to the direct transmission and traditional multihop protocols, our results reveal that optimum relay channel signaling can significantly outperform multihop protocols, and that power allocation has a significant impact on the performance.

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.

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.

Idle sense: an optimal access method for high throughput and fairness in rate diverse wireless LANs

Abstract: We consider wireless LANs such as IEEE 802.11 operating in the unlicensed radio spectrum. While their nominal bit rates have increased considerably, the MAC layer remains practically unchanged despite much research effort spent on improving its performance. We observe that most proposals for tuning the access method focus on a single aspect and disregard others. Our objective is to define an access method optimized for throughput and fairness, able to dynamically adapt to physical channel conditions, to operate near optimum for a wide range of error rates, and to provide equal time shares when hosts use different bit rates.We propose a novel access method derived from 802.11 DCF [2] (Distributed Coordination Function) in which all hosts use similar values of the contention window CW to benefit from good short-term access fairness. We call our method Idle Sense, because each host observes the mean number of idle slots between transmission attempts to dynamically control its contention window. Unlike other proposals, Idle Sense enables each host to estimate its frame error rate, which can be used for switching to the right bit rate. We present simulations showing how the method leads to high throughput, low collision overhead, and low delay. The method also features fast reactivity and time-fair channel allocation.

Distributed coordination in dynamic spectrum allocation networks

Abstract: Device coordination in open spectrum systems is a challenging problem, particularly since users experience varying spectrum availability over time and location. We propose a distributed coordination approach that handles spectrum heterogeneity without relying on the existence of a preassigned common control channel. Our approach carries potential to provide robust operation under network dynamics. While this approach can be implemented by upgrading the legacy protocol stack without modifying the MAC protocol, we also describe modifications to the MAC protocol that address spectrum heterogeneity and significantly improve system performance. Experimental results show that the proposed distributed coordination scheme outperforms the existing coordination schemes by 25-35% in throughput and provides 50% of delay reduction

A topology control approach for utilizing multiple channels in multi-radio wireless mesh networks

Abstract: We consider the channel assignment problem in a multi-radio wireless mesh network that involves assigning channels to radio interfaces for achieving efficient channel utilization. We propose the notion of a traffic-independent base channel assignment to ease coordination and enable dynamic, efficient and flexible channel assignment. We present a novel formulation of the base channel assignment as a topology control problem, and show that the resulting optimization problem is NP-complete. We then develop a new greedy heuristic channel assignment algorithm (termed CLICA) for finding connected, low interference topologies by utilizing multiple channels. Our extensive simulation studies show that the proposed CLICA algorithm can provide large reduction in interference (even with a small number of radios per node), which in turn leads to significant gains in both link layer and multihop performance in 802.11-based multi-radio mesh networks.

Adaptive channel allocation spectrum etiquette for cognitive radio networks

Abstract: In this work, we propose a game theoretic framework to analyze the behavior of cognitive radios for distributed adaptive channel allocation. We define two different objective functions for the spectrum sharing games, which capture the utility of selfish users and cooperative users, respectively. Based on the utility definition for cooperative users, we show that the channel allocation problem can be formulated as a potential game, and thus converges to a deterministic channel allocation Nash equilibrium point. Alternatively, a no-regret learning implementation is proposed for both scenarios and it is shown to have similar performance with the potential game when cooperation is enforced, but with a higher variability across users. The no-regret learning formulation is particularly useful to accommodate selfish users. Non-cooperative learning games have the advantage of a very low overhead for information exchange in the network. We show that cooperation based spectrum sharing etiquette improves the overall network performance at the expense of an increased overhead required for information exchange

Dynamic open spectrum sharing MAC protocol for wireless ad hoc networks

Abstract: In legacy wireless communication systems, spectrum allocation is static, resulting in extremely low spectrum utilization. On the other hand, there is little spectrum left for allocation to an increasing number of emerging wireless applications. A promising approach to solving this paradox is opening up most of the spectrum for unlicensed spectrum users in ways that co-exist with legacy users. Following this direction, this paper proposes the dynamic open spectrum sharing (DOSS) MAC protocol. This protocol allows nodes to adaptively select an arbitrary spectrum for the incipient communication subject to spectrum availability. It offers real-time dynamic spectrum allocation and high spectrum utilization without relying on any infrastructure. It also coexists with legacy wireless applications, while avoiding the hidden and exposed terminal problems. We conduct theoretical analysis of the protocol, and study its performance via simulations. In addition, we covers the radio receiver design

Decentralized cognitive mac for dynamic spectrum access

Abstract: We consider the problem of opportunistic dynamic spectrum access (DSA) in an ad hoc network in which unlicensed secondary users communicate through channels not used by the primary users. Decentralized cognitive medium access control protocols are presented that allow secondary users to recognize spectrum opportunity and transmit based on a partial observation of the instantaneous spectrum availability. Under a framework of partially observable Markov decision process (POMDP), we derive optimal and suboptimal decentralized strategies for the secondary users to decide which channel(s) to sense and access for the maximization of the overall network throughput

Demand responsive pricing and competitive spectrum allocation via a spectrum server

Abstract: In this paper we develop a framework for competition of future operators likely to operate in a mixed commons/property-rights regime under the regulation of a spectrum policy server (SPS). The operators dynamically compete for customers as well as portions of available spectrum. The operators are charged by the SPS for the amount of bandwidth they use in their services. Through demand responsive pricing, the operators try to come up with convincing service offers for the customers, while trying to maximize their profits. We first consider a single-user system as an illustrative example. We formulate the competition between the operators as a non-cooperative game and propose an SPS-based iterative bidding scheme that results in a Nash equilibrium of the game. Numerical results suggest that, competition increases the user's (customer's) acceptance probability of the offered service, while reducing the profits achieved by the operators. It is also observed that as the cost of unit bandwidth increases relative to the cost of unit infrastructure (fixed cost), the operator with superior technology (higher fixed cost) becomes more competitive. We then extend the framework to a multiuser setting where the operators are competing for a number of users at once. We propose an SPS-based bandwidth allocation scheme in which the SPS optimally allocates bandwidth portions for each user-operator session to maximize its overall expected revenue resulting from the operator payments. Comparison of the performance of this scheme to one in which the bandwidth is equally shared between the user-operator pairs reveals that such an SPS-based scheme improves the user acceptance probabilities and the bandwidth utilization in multiuser systems

Coexistence of IEEE802.15.4 with other Systems in the 2.4 GHz-ISM-Band

Abstract: Wireless systems continue to rapidly gain popularity. This is extremely true for data networks in the local and personal area, which are called WLAN and WPAN, respectively. However, most of those systems are working in the license-free industrial scientific medical (ISM) frequency bands, where neither resource planning nor bandwidth allocation can be guaranteed. To date, the most widespread systems in the 2.4 GHz ISM band are IEEE802.11 as stated in IEEE Std. 802-11 (1997) and Bluetooth, with ZigBee based in IEEE Std. 802.15.4 (2003) and IEEE802.15.4 as upcoming standards for short range wireless networks. In this paper we examine the mutual effects of these different communication standards. Measurements are performed with real-life equipment, in order to quantify coexistence issues

Gaussian orthogonal relay channels: optimal resource allocation and capacity

Abstract: A Gaussian orthogonal relay model is investigated, where the source transmits to the relay and destination in channel 1, and the relay transmits to the destination in channel 2, with channels 1 and 2 being orthogonalized in the time-frequency plane in order to satisfy practical constraints. The total available channel resource (time and bandwidth) is split into the two orthogonal channels, and the resource allocation to the two channels is considered to be a design parameter that needs to be optimized. The main focus of the analysis is on the case where the source-to-relay link is better than the source-to-destination link, which is the usual scenario encountered in practice. A lower bound on the capacity (achievable rate) is derived, and optimized over the parameter /spl theta/, which represents the fraction of the resource assigned to channel 1. It is shown that the lower bound achieves the max-flow min-cut upper bound at the optimizing /spl theta/, the common value thus being the capacity of the channel at the optimizing /spl theta/. Furthermore, it is shown that when the relay-to-destination signal-to-noise ratio (SNR) is less than a certain threshold, the capacity at the optimizing /spl theta/ is also the maximum capacity of the channel over all possible resource allocation parameters /spl theta/. Finally, the achievable rates for optimal and equal resource allocations are compared, and it is shown that optimizing the resource allocation yields significant performance gains.

Fairness and throughput analysis for generalized proportional fair frequency scheduling in OFDMA

Abstract: In this paper, a generalized proportional fair (GPF) scheduling algorithm is presented, which allows tweaking the trade-off between fairness and throughput performance for best effort traffic in a cellular downlink scenario. The GPF is extended to frequency scheduling in an OFDMA system by performing dynamic channel allocation on a subband basis including link adaptation by adaptive modulation and coding. In this way, multiuser diversity can be utilized in time domain - as for CDMA - and in frequency domain. Compared to a system without frequency scheduling, this increases the system throughput and yields an improved fairness with respect to the allocated resources and with respect to the achieved data-rate per user. OFDMA system level simulations are carried out in order to analyze short/long-term fairness, multiuser diversity gain and system throughput of various GPF configurations with and without applying frequency scheduling.

OFDM-Based Broadband Wireless Networks – Design and Optimization

Abstract: Preface. 1. Introduction. 1.1 OFDM-based wireless network overview. 1.1.1 Digital broadcasting and DVB-T. 1.1.2 Wireless LAN and IEEE 802.11. 1.1.3 WiMAX and IEEE 802.16. 1.2 The need for "cross-layer" design. 1.3 Organization of this text. 2. OFDM Fundamentals. 2.1 Broadband radio channel characteristics. 2.1.1 Envelope fading. 2.1.2 Time dispersive channel. 2.1.3 Frequency dispersive channel. 2.1.4 Statistical characteristics of broadband channels. 2.2 Canonical form of broadband transmission. 2.3 OFDM realization. 2.4 Summary. 3. PHY Layer Issues - System Imperfections. 3.1 Frequency synchronization. 3.1.1 OFDM carrier offset data mode. 3.1.2 Pilot-based estimation. 3.1.3 Non-pilot based estimation. 3.2 Channel estimation. 3.2.1 Pilots for 2D OFDM channel estimation . 3.2.2 2DMMSE channel estimation. 3.2.3 Reduced complexity channel estimation. 3.3 I/Q imbalance compensation. 3.3.1 I/Q Imbalance Model. 3.3.2 Digital compensation receiver. 3.3.3 Frequency offset estimation with I/Q imbalance. 3.4 Phase noise compensation. 3.4.1 Mathematical models for phase noise. 3.4.2 CPE estimation with channel state information. 3.4.3 Time domain channel estimation in the presence of CPE. 3.4.4 CPE estimation without explicit CSI. 3.5 Summary. 4. PHY Layer Issues - Spatial Processing. 4.1 Antenna array fundamentals. 4.2 Beam forming. 4.2.1 Coherent combining. 4.2.2 Zero-forcing. 4.2.3 MMSE reception (optimum linear receiver). 4.2.4 SDMA. 4.2.5 Broadband beam forming. 4.3 MIMO channels and capacity. 4.4 Space-time coding. 4.4.1 Spatial multiplexing. 4.4.2 Orthogonal space-time block coding. 4.4.3 Concatenated ST transmitter. 4.4.4 Beam forming with ST coding. 4.4.5 ST beam forming in OFDM. 4.5 Wide-area MIMO beam forming. 4.5.1 Data model. 4.5.2 Uncoded OFDM design criterion. 4.5.3 Coded OFDM design criterion. 4.6 Summary. 4.7 Appendix I: Derivation of Pe. 4.8 Appendix II: Proof of Proposition 5. 4.9 Appendix III: Proof of Proposition 6. 5. Multiple Access Control Protocols. 5.1 Introduction. 5.2 Basic MAC protocols. 5.2.1 Contention based protocols. 5.2.2 Non-contention based MAC protocols. 5.3 OFDMA advantages. 5.4 Multiuser diversity. 5.5 OFDMA optimality. 5.5.1 Multiuser multicarrier SISO systems. 5.5.2 Multiuser multicarrierMIMO systems. 5.6 Summary. 5.7 Appendix I: Cn(p) is a convex function in OFDMA/SISO case. 5.8 Appendix II: C(p) is a convex function in OFDMA/MIMO case. 6. OFDMA Design Considerations. 6.1 Cross layer design introduction. 6.2 Mobility-dependent OFDMA traffic channels. 6.2.1 OFDMA traffic channel. 6.2.2 System model. 6.2.3 Channel configuration for fixed/portable applications. 6.2.4 Channel configuration for mobile application. 6.3 IEEE 802.16e traffic channels. 6.4 Summary. 7. Frequency Planning in Multi-cell Networks. 7.1 Introduction. 7.1.1 Fixed channel allocation. 7.1.2 Dynamic channel allocation. 7.2 OFDMA DCA. 7.2.1 Protocol design. 7.2.2 Problem formulation for the RNC. 7.2.3 Problem formulation for BSs. 7.2.4 Fast algorithm for the RNC. 7.2.5 Fast algorithm for BSs. 7.3 Spectrum efficiency under different cell/sector configurations. 7.3.1 System configuration and signaling overhead. 7.3.2 Channel loading gains. 7.4 Summary. 8. Appendix. 8.1 IEEE 802.11 and WiFi. 8.1.1 802.11 overview. 8.1.2 802.11 network architecture. 8.1.3 The MAC layer technologies. 8.1.4 The physical layer technologies. 8.2 IEEE 802.16e and Mobile WiMAX. 8.2.1 Overview. 8.2.2 The physical layer technologies. 8.2.3 The MAC layer technologies. 8.3 Performance analysis of WiMAX systems. 8.3.1 WiMAX OFDMA-TDD. 8.3.2 Comparison Method. Notations and Acronym. About the Authors. Index.

Power allocation for cooperative relaying in wireless networks

Abstract: Power allocation strategies are developed for amplify-and-forward cooperative relaying networks in fading channels. The average signal-to-noise ratio (SNR) and outage performances are optimized in some sense by maximizing the sum and product, respectively, of the average SNR of the direct link and an upper bound on the SNR of the relay link. The power allocation strategies require knowledge of only the mean strengths of the channels.

List-coloring based channel allocation for open-spectrum wireless networks

Abstract: The current fixed spectrum allocation scheme leads to low spectrum utilization across the whole spectrum. It requires a more effective spectrum allocation and utilization policy, which allows unused parts of spectrum to become available temporarily for other usage so that the scarcity of the spectrum can be largely mitigated. This paper is an attempt to study such wireless networks with opportunistic spectrum availability and access. We study the dynamics in the available channels caused by the location and traffic load of the primary users and proposed several distributed algorithms to exploit the available channels for secondary users. The performance of different algorithms is evaluated in networks with static and time-varying channel availability. I. INTRODUCTION The current fixed spectrum allocation scheme leads to sig- nificant spectrum underutilization. For instance, experiments conducted by Shared Spectrum Company indicate as much as 62% of white space below 3GHz band even in the most crowed area near downtown Washington DC, where both government and commercial spectrum usage are intensive (1). Such low utilization and increasing demand for the radio spectrum suggest that a more effective spectrum allocation and utilization policy is necessary, where unused parts of spectra can be temporarily utilized by other users so that the scarcity of the spectrum can be largely mitigated. In this paper, we focus on the opportunistic exploration of the white space by users other than the primary licensed ones on a non-interfering or leasing basis. Such usage is being enabled by regulatory policy initiatives and radio technology advances. First, both the Federal Communications Commis- sion (FCC) and the federal government have made important initiatives towards more flexible and dynamic spectrum usage, e.g., (2), (3). Further, opportunistic spectrum sharing is enabled by software-defined radio or cognitive radio technologies. Such technology advances provide the capability for a radio device to sense and operate on a wide range of frequencies us- ing appropriate communication mechanisms, and thus enable dynamic and more intense spectrum reuse in space, time, and frequency dimensions. We focus on the study of the secondary users who ob- serve the channel availability dynamically and explore it opportunistically. Here, secondary users refer to spectrum users who are not owner of the spectrum and operate based on agreements/etiquettes imposed by the primary users or regulatory entities. We study the impact of the opportunistic spectrum availability on the secondary users who explore the spectrum when allowed by the primary users of the spectrum. (Note that the secondary users may have their own licensed/allocated bandwidth where they are primary users, which is not the concern of this paper.) Because of the traffic load and the distribution of the primary users, the available channels observed by the secondary users are time- varying and location-dependent. We study the impact of the characteristics of primary users on the spectrum opportunistic availability. We present a general framework to model the correlation between primary and secondary users. We also propose several distributed spectrum access schemes and study their performance under the above-mentioned time-varying and location-dependent channel availabilities.

A novel layered graph model for topology formation and routing in dynamic spectrum access networks

Abstract: This paper studies a fundamental problem in dynamic spectrum access (DSA) networks: given a set of detected spectrum bands that can be temporarily used by each node in a DSA network, how to form a topology by selecting spectrum bands for each radio interface of each node, called topology formation in this paper. We propose a novel layered graph to model the temporarily available spectrum bands, called spectrum opportunities (SOPs) in this paper, and use this layered graph model to develop effective and efficient routing and interface assignment algorithms to form near-optimal topologies for DSA networks. We have evaluated the performance of our layered graph approach and compared it to a sequential interface assignment algorithm. The numerical results show that the layered graph approach significantly outperforms the sequential interface assignment

Discontiguous OFDM considerations for dynamic spectrum access in idle TV channels

Abstract: Sharing spectrum with systems that employ frequency reuse over large geographical areas (e.g., TV stations) provides an opportunity to improve spectrum utilization. The Federal Communications Commission (FCC) is considering such sharing in the TV hands (2004). This technical and regulatory opportunity prompted the IEEE to create a new committee, 802.22, that will develop a wireless regional area network (WRAN) standard for operating on vacant TV channels. This paper quantifies the idle bandwidth in the current TV band assignments; although the TV station information incorporated here is specific to the United States, the methodology and findings should be relevant to a global audience. The methodology for this analysis is distinct from prior literature on spectrum use measurements and offers a complementary perspective. Furthermore, the statistics from the analysis point to the value of systems that can operate on discontiguous portions of the radio spectrum. One approach, a modified form of OFDM here termed Discontiguous OFDM (DOFDM), could be well-suited to this dynamic spectrum access application. This paper provides a preliminary description of a DOFDM prototype and describes special considerations for its implementation

Spectrum management in coordinated dynamic spectrum access based cellular networks

Abstract: This paper focuses on spectrum management in next generation cellular networks that employ coordinated dynamic spectrum access (DSA). In our model, a spectrum broker controls and provides time-bounded access to a band of spectrum to wireless service providers and/or end users and implements the spectrum pricing and allocation schemes and policies. We introduce several concepts that are central to the design of spectrum management algorithms. These include: (1) demand processing model (batched vs. online), (2) spectrum pricing models (merchant mode, simple bidding, and iterative bidding), (3) different network infrastructure options such as shared base stations with collocated antennas, non-shared base stations with collocated antennas, and non-shared base stations and non-collocated antennas, and (4) important spectrum management concepts of scope, access fairness, "stickiness" and spectrum utilization. Based on these concepts, we investigate practically realizable candidate algorithms for spectrum allocation for homogeneous CDMA networks

Device-centric spectrum management

Abstract: Efficient spectrum allocation in open spectrum systems is a challenging problem, particularly for devices with constrained communication resources such as sensor and mobile ad hoc networks. We propose a device-centric spectrum management scheme with low communication costs, where users observe local interference patterns and act independently according to preset spectrum rules. We propose five rules that tradeoff performance with implementation complexity and communication costs, and derive a lower bound on each user's allocation based on these rules. Experimental results show that our proposed rule-based approach reduces communication costs from efficient collaborative approaches by a factor of 3-4 while providing good performance

Multiple Frequency Band Operation in Wireless Networks

Abstract: Embodiments for bandwidth allocation methods, detecting interference with other systems, and/or redeploying in alternate bandwidth are described Higher bandwidth channels may be deployed at channel boundaries (410), which are a subset of those for lower bandwidth channels (310), and may be restricted from overlapping Interference may be detected (930) on primary, secondary, or a combination of channels, and may be detected in response to energy measurements (910) of the various channels When interference is detected, a higher bandwidth Basic Service Set (BSS)(100) may be relocated to an alternate channel, or may have its bandwidth reduced to avoid interference Interference may be detected based on energy measured on the primary or secondary channel, and/or a difference between the two An FFT (1010) may be used in energy measurement in either or both of the primary and secondary channels Stations may also monitor messages from alternate systems to make channel allocation decisions Various other aspects are also presented

Spectrum sharing with distributed interference compensation

Abstract: We consider a spectrum sharing problem in which each wireless transmitter can select a single channel from a set of available channels, along with the transmission power. An asynchronous distributed pricing (ADP) scheme is proposed, in which users exchange "price" signals that indicate the negative effect of interference at the receivers. Given this set of prices, each transmitter chooses a channel and power level to maximize its net benefit (utility minus cost). We show that a sequential version of this single-channel (SC)-ADP algorithm converges with two users and an arbitrary number of channels, and observe via simulation that it exhibits rapid convergence with more users in the network. The pricing algorithm always outperforms the heuristic algorithm in which each user picks the best channel without exchanging interference prices. In a dense network with heavy interference, the SC-ADP algorithm can also perform better than the iterative water-filling algorithm where each user transmits over multiple channels but the users do not exchange any information. The performance of the SC-ADP algorithm is also compared with a multi-channel (MC)-ADP algorithm in which users can transmit over multiple channels and exchange interference prices over each channel

A sub-optimal joint subcarrier and power allocation algorithm for multiuser OFDM

Abstract: This paper investigates subcarrier and power allocation in multiuser OFDM. The aim is to maximize the overall rate while achieving proportional fairness amongst users under a total power constraint. Achieving the optimal solution is computationally demanding thereby necessitating the use of sub-optimal techniques. Existing sub-optimal techniques either use fixed power allocation and perform only subcarrier allocation or handle subcarrier and power allocation separately. In this paper, we propose an algorithm that performs joint subcarrier and power allocation. Simulation results are shown to compare the performance of the proposed algorithm with that of existing algorithms.

Cognitive radio emergency networks - requirements and design

Abstract: Currently deployed wireless emergency networks possess low spectrum efficiency, similar to their civilian wireless counterparts. It's due to the traditional radio frequency partitioning where each service has uniquely assigned bandwidth. To alleviate the problem one can propose dynamic channel assignment as a promising foundation for physical and link layer design of future wireless emergency communication networks. Here we identify functional requirements and system specifications for mobile ad hoc emergency networks built on top of cognitive radio. We also propose a simple Cognitive Radio medium access control protocol applicable to our network model, adopted from distributed channel assignment algorithm of IEEE 802.11

Subcarrier allocation and bit loading algorithms for OFDMA-based wireless networks

Abstract: Orthogonal Frequency Division Multiple Access (OFDMA) is an emerging multiple access technology. In this paper, we consider OFDMA in the context of fixed wireless networks. This paper addresses the problem of assigning subcarriers and bits to point-to-point wireless links in the presence of cochannel interference and Rayleigh fading. The objective is to minimize the total transmitted power over the entire network while satisfying the data rate requirement of each link. We formulate this problem as a constrained optimization problem and present centralized algorithms. The simulation results show that our approach results in an efficient assignment of subcarriers and transmitter power levels in terms of the energy required for transmitting each bit of information. However, centralized algorithms require knowledge of the entire network topology and channel characteristics of every link. In a practical scenario, that would not be the situation and there is a need for distributed rate allocation algorithms. To address this need, we also present a distributed algorithm for allocating subcarriers and bits in order to satisfy the rate requirements of the links.

Method and system for switching antenna and channel assignments in broadband wireless networks

Abstract: A method and apparatus for antenna switching, grouping, and channel assignments in wireless communication systems. The invention allows multiuser diversity to be exploited with simple antenna operations, therefore increasing the capacity and performance of wireless communications systems. Channel characteristics indicative of signal reception quality for downlink or bi-directional traffic for each channel/antenna resource combination are measured or estimated at a subscriber. Corresponding channel characteristic information is returned to the base station. Channel characteristics information may also be measured or estimated for uplink or bi-directional signals received at each of multiple receive antenna resources. The base station employs channel allocation logic to assign uplink, downlink and/or bi-directional channels for multiple subscribers based on channel characteristics measured and/or estimated for the uplink, downlink and/or bi-directional channels.

Adaptive radio channel allocation for supporting coexistence of 802.15.4 and 802.11b

Abstract: As the explosive growth of the ISM band usage continues, there are many scenarios where different systems operate in the same place at the same time. One of growing concerns is the coexistence of wireless systems [18]. For the successful deployment of mission-critical systems such as wireless sensor networks, it is required to provide a solution for the coexistence. In this paper, we propose a new scheme using multiple radio channels for the coexistence of 802.15.4 LRWPAN and 802.11b WLAN. To evaluate the effectiveness of the proposed scheme, measurement and simulation study are conducted. The simulation results show that the proposed scheme is effective in performance improvement for multi-hop largescale network of 802.15.4. Keywords-component; coexistence; interference; ISM band; 802.15.4; 802.11b

Ultrascience net: network testbed for large-scale science applications

Abstract: UltraScienceNet is an experimental wide area network testbed to enable the development of networking technologies required for next-generation large-scale scientific applications. It provides on-demand dedicated high-bandwidth channels for large data transfers, and also high-resolution high-precision channels for fine control operations. In the initial deployment its data plane consists of several thousand miles of dual 10 Gb/s lambdas. The channels are provisioned on demand using layer 1 and 2 switches in the backbone and multiple service provisioning platforms at the edges in a flexible configuration using a secure control plane. A centralized scheduler is employed to compute future channel allocations, and a signaling daemon is used to generate the configuration signals to switches at appropriate times. The control plane is implemented using an out-of-band virtual private network, which encrypts the switching signals, and also provides authenticated user and application access. Transport experiments are conducted on a smaller test connection that provides us useful information about the basic properties and issues of utilizing dedicated channels in applications.

Frequency allocation for WLANs using graph colouring techniques

Abstract: At present, no standard frequency allocation mechanism exists for wireless LAN access points. In this article, we introduce a number of techniques based on graph colouring algorithms, and demonstrate their effectiveness using simulations. We also suggest a preliminary message format the access points could employ to exchange information regarding the wireless channel and elaborate on the possible protocol architectures that could be used in the actual channel allocation process.