Distributed spectrum assignment for cognitive networks with heterogeneous spectrum opportunities

This paper presents a distributed and localized interference‐aware channel assignment framework for multi‐radio wireless mesh networks in a cognitive network environment. The availability of multiple interfaces and channels in wireless devices is expected to enhance network throughput in wireless mesh networks. A notable design issue in such networks is how to dynamically assign available channels to multiple radio interfaces for maximizing effective network throughput by minimizing interference. The proposed framework uses a novel interference estimation method by utilizing distributed conflict graphs on a per‐interface basis. Presented results obtained via simulation studies in 802.11 based multi‐radio mesh networks indicate that for both homogeneous and heterogeneous primary networks, the proposed protocol can facilitate a large increase in network throughput in comparison with a Common Channel Assignment mechanism that is used as a benchmark in the literature. Copyright © 2010 John Wiley & Sons, Ltd.     

Network coding for multiple unicast sessions in multi-channel/interface wireless networks

Throughput limitation of wireless networks imposes many practical problems as a result of wireless media broadcast nature. The solutions of the problem are mainly categorized in two groups; the use of multiple orthogonal channels and network coding (NC). The networks with multiple orthogonal channels and possibly multiple interfaces can mitigate co-channel interference among nodes. However, efficient assignment of channels to the available network interfaces is a major problem for network designers. Existing heuristic and theoretical work unanimously focused on joint design of channel assignment with the conventional transport/IP/MAC architecture. Furthermore, NC has been a prominent approach to improve the throughput of unicast traffic in wireless multi-hop networks through opportunistic NC. In this paper we seek a collaboration scheme for NC in multi-channel/interface wireless networks, i.e., the integration of NC, routing and channel assignment problem. First, we extend the NC for multiple unicast sessions to involve both COPE-type and a new proposed scheme named as Star-NC. Then, we propose an analytical framework that jointly optimizes the problem of routing, channel assignment and NC. Our theoretical formulation via a linear programming provides a method for finding source–destination routes and utilizing the best choices of different NC schemes to maximize the aggregate throughput. Through this LP, we propose a novel channel assignment algorithm that is aware of both coding opportunities and co-channel interference. Finally, we evaluate our model for various networks, traffic models, routing and coding strategies over coding-oblivious routing.     

A QoS Routing Protocol with Bandwidth Allocation in Multichannel Ad Hoc Networks

Mobile multimedia applications have recently generated much interest in mobile ad hoc networks (MANETs) supporting quality-of-service (QoS) communications. Multiple non-interfering channels are available in 802.11 and 802.15 based wireless networks. Capacity of such channels can be combined to achieve higher QoS performance than for single channel networks. The capacity of MANETs can be substantially increased by equipping each network node with multiple interfaces that can operate on multiple non-overlapping channels. However, new scheduling, channel assignment, and routing protocols are required to utilize the increased bandwidth in multichannel MANETs. In this paper, we propose an on-demand routing protocol M-QoS-AODV in multichannel MANETs that incorporates a distributed channel assignment scheme and routing discovery process to support multimedia communication and to satisfy QoS bandwidth requirement. The proposed channel assignment scheme can efficiently express the channel usage and interference information within a certain range, which reduces interference and enhances channel reuse rate. This cross-layer design approach can significantly improve the performance of multichannel MANETs over existing routing algorithms. Simulation results show that the proposed M-QoS-AODV protocol can effectively increase throughput and reduce delay, as compared to AODV and M-AODV-R protocols.     

An efficient channel assignment algorithm for multicast wireless mesh networks

Multicast can enhance the performance of wireless mesh networks (WMNs) effectively, which has attracted great attentions in recent years. However, multicast communication in WMNs requires efficient channel assignment strategy to reduce the total network interference and maximize the network throughput. In this paper, the concept of local multicast is proposed to measure interference and solve hidden channel problem in multicast communication. Basing on the concept, we propose a channel assignment algorithm considering the interference of local multicast and forwarding weight of each node (LMFW). The algorithm fully considers partially overlapped channels and orthogonal channels to improve the network performance. Simulations show that the proposed algorithm can reduce interference and improve network capacity of WMNs.     

Capacity of wireless networks under SINR interference constraints

A fundamental problem in wireless networks is to estimate their throughput capacity—given a set of wireless nodes and a set of connections, what is the maximum rate at which data can be sent on these connections. Most of the research in this direction has focused either on random distributions of points, or has assumed simple graph-based models for wireless interference. In this paper, we study the capacity estimation problem using a realistic Signal to Interference Plus Noise Ratio (SINR) model for interference, on arbitrary wireless networks without any assumptions on node distributions. The problem becomes much more challenging for this setting, because of the non-locality of the SINR model. Recent work by Moscibroda et al. (IEEE INFOCOM 2006, ACM MobiHoc 2006) has shown that the throughput achieved by using SINR models can differ significantly from that obtained by using graph-based models. In this work, we develop polynomial time algorithms to provably approximate the throughput capacity of wireless network under the SINR model.     

Fixed channel assignment algorithm for multi‐radio multi‐channel MESH networks

Recently, multi‐radio mesh technology in wireless networks has been under extensive research. This is because of its potential of overcoming the inherent wireless multi‐hop throughput, scalability and latency problems caused by the half‐duplex nature of the IEEE 802.11. The concept of deploying multiple radios in wireless network access points (APs) has shown a promising way to enhance the channel selection and the route formation while the MESH topology allows more fine‐grained interference management and topology control. Within this realm, given a set of end‐to‐end objectives, there are multiple issues that need to be identified when we consider the optimization problem for fixed multi‐channel multi‐hop wireless networks with multiple radios. This paper addresses the static channel assignment problem for multichannel multi‐radio static wireless mesh networks. We first discuss its similarities and differences with the channel assignment problem in cellular networks (WMN). Next, we present four metrics based on which mesh channel assignments can be obtained. Three of these metrics attempt to maximize simultaneous transmissions in a mesh network, either directly or indirectly. The fourth metric quantifies the ‘diversity’ of a particular assignment and can be used as a secondary criterion to the other three metrics. Related optimization models have also been developed. Copyright © 2007 John Wiley & Sons, Ltd.     

Tree‐based channel assignment schemes for multi‐channel wireless sensor networks

Many sensor node platforms used for establishing wireless sensor networks (WSNs) can support multiple radio channels for wireless communication. Therefore, rather than using a single radio channel for whole network, multiple channels can be utilized in a sensor network simultaneously to decrease overall network interference, which may help increase the aggregate network throughput and decrease packet collisions and delays. This method, however, requires appropriate schemes to be used for assigning channels to nodes for multi‐channel communication in the network. Because data generated by sensor nodes are usually delivered to the sink node using routing trees, a tree‐based channel assignment scheme is a natural approach for assigning channels in a WSN. We present two fast tree‐based channel assignment schemes (called bottom up channel assignment and neighbor count‐based channel assignment) for multi‐channel WSNs. We also propose a new interference metric that is used by our algorithms in making decisions. We validated and evaluated our proposed schemes via extensive simulation experiments. Our simulation results show that our algorithms can decrease interference in a network, thereby increasing performance, and that our algorithms are good alternatives for static channel assignment in WSNs. Copyright © 2015 John Wiley & Sons, Ltd.     

基于拓扑分割的无线Mesh网络信道分配策略

该文根据无线Mesh网络流量呈现树状拓扑汇聚的特点提出基于拓扑分割的信道分配策略。依据无线干扰对不同链路的影响程度,把无线干扰分类为有确定方向的纵向干扰和横向干扰;提出沿着纵向干扰方向逐跳分割网络拓扑算法;提出最少信道隔离纵向干扰和为吞吐量最小的子拓扑增加信道的子拓扑间信道分配策略;提出横向干扰分块的子拓扑内信道使用方法;理论分析子拓扑内的冲突域及网络性能瓶颈,仿真研究子拓扑的吞吐性能及信道分配顺序。仿真结果表明,隔离纵向干扰和增加信道的分配策略能够有效保证和提升网络吞吐量,横向干扰分块的方法优于802.11s中定义的公共信道框架多信道机制。     

Joint Channel Assignment and Routing for Throughput Optimization in Multiradio Wireless Mesh Networks

Multihop infrastructure wireless mesh networks offer increased reliability, coverage, and reduced equipment costs over their single-hop counterpart, wireless local area networks. Equipping wireless routers with multiple radios further improves the capacity by transmitting over multiple radios simultaneously using orthogonal channels. Efficient channel assignment and routing is essential for throughput optimization of mesh clients. Efficient channel assignment schemes can greatly relieve the interference effect of close-by transmissions; effective routing schemes can alleviate potential congestion on any gateways to the Internet, thereby improving per-client throughput. Unlike previous heuristic approaches, we mathematically formulate the joint channel assignment and routing problem, taking into account the interference constraints, the number of channels in the network, and the number of radios available at each mesh router. We then use this formulation to develop a solution for our problem that optimizes the overall network throughput subject to fairness constraints on allocation of scarce wireless capacity among mobile clients. We show that the performance of our algorithms is within a constant factor of that of any optimal algorithm for the joint channel assignment and routing problem. Our evaluation demonstrates that our algorithm can effectively exploit the increased number of channels and radios, and it performs much better than the theoretical worst case bounds     

An optimization framework for multicasting in MCMR wireless mesh network with partially overlapping channels

This paper focuses on the problem of maximizing throughput in multicast routing in Multi-Channel, Multi-Radio (MCMR) wireless mesh network. We propose an optimization framework based on binary integer programming that minimizes interference in multicast communication. Our Multicasting with multiple Gateways and Partially Overlapped Channels (MG-POC) framework utilizes a rational node selection to construct multicast tree that increases network performance. MG-POC is efficient as it (1) constructs the paths between source and receivers with minimal number of data forwarding nodes; (2) employs multiple gateways to substantially reduce interference and usage of resources; (3) benefits from wireless broadcast advantage and partially overlapped channels in channel assignment; (4) solves channel assignment and tree construction problems simultaneously. A weakly decoupled approach is also presented which finds a nearly optimal solution for large network problems in a reasonably short amount of time. Our schemes are proved to offer a connected and loop-free tree; and their performance are well compared to that of several existing methods on different simulation scenarios. The results of our simulations also demonstrate that incorporating multi-gateway and partially overlapping channels has a significant impact on minimizing network interference which, in turn, dramatically enhances network throughput.     

Efficient MAC protocol design and performance analysis for dense WLANs

In this paper, we analytically study the dense basic service set network transmission problems in very high throughput (VHT, namely IEEE 802.11ac) wireless local area networks (WLANs) due to nervous bandwidth resources. Our contributions are threefold as follows. Firstly, we derive the closed-form expressions of throughput gains for primary channel establishment from multi-band selection using the optimal skipping rule, which balances the throughput gain from finding a good quality band with the overhead of measuring multiple bands. Secondly, in order to satisfy the quality of service of overlapping BSS users, we design a space interference avoidance mechanism, which can improve the system throughput for the whole dense WLANs. Thirdly, in order to further improve the transmission performance of dense BSS networks, we propose an unequal bandwidth transmission mechanism based on the VHT WLANs, which can not only clear the redundant network allocation vector duration timely but also use the limited bandwidth efficiently. The proposed protocols and mechanisms exploit both time and frequency diversity sufficiently, and are shown to result in typical throughput gains compared with the traditional IEEE 802.11 MAC protocol.     

Graph coloring based channel assignment framework for rural wireless mesh networks

IEEE 802.11 based wireless mesh networks with directional antennas are expected to be a new promising technology and an economic approach for providing wireless broadband services in rural areas. In this paper, we discuss interference models and address how they can affect the design of channel assignment in rural mesh networks. We present a new channel assignment framework based on graph coloring for rural wireless mesh networks. The goal of the framework is to allow synchronously transmitting or receiving data from multiple neighbor links at the same time, and continuously doing full-duplex data transfer on every link, creating an efficient rural mesh network without interference. Channel assignment is shown to be NP-hard. We frame this channel allocation problem in terms of Adjacent Vertex Distinguishing Edge Coloring （AVDEC）. Detailed assignment results on grid topology are presented and discussed. Furthermore, we design an algorithm. Finally, we evaluate the perform- ance of the proposed algorithm through extensive simulations and show the algorithm is effective to the regular grid topologies, and the number of colors used by the algorithm is upper bounded by A ~ 1. Hence the algorithm guarantees that the number of channels available in standards such as IEEE 802.11a is sufficient to have a valid AVDEC for many grid topologies. We also evaluate the proposed algorithm for arbitrary graphs. The algorithm provides a lower upper bound on the minimum number of channels to the AVDEC index channel assignment problem.     

A topology preserving cluster‐based channel assignment for wireless mesh networks

Wireless Mesh Networks (WMN) with multiple radios and multiple channels are expected to resolve the capacity limitation problem of simpler wireless networks. However, optimal WMN channel assignment (CA) is NP complete, and it requires an optimal mapping of available channels to interfaces mounted over mesh routers. Acceptable solutions to CA must minimize network interference and maximize available network throughput. In this paper, we propose a CA solution called as cluster‐based channel assignment (CBCA). CBCA aims at minimizing co‐channel interference yet retaining topology through non‐default CA. Topology preservation is important because it avoids network partitions and is compatible with single‐interface routers in the network. A ‘non‐default’ CA solution is desired because it uses interfaces over different channels and reduces medium contention among neighbors. To the best of our knowledge, CBCA is a unique cluster‐based CA algorithm that addresses topology preservation using a non‐default channel approach. The main advantage of CBCA is it runs in a distributed manner by allowing cluster heads to perform CA independently. CBCA runs in three stages, where first the WMN nodes are partitioned into clusters. The second stage performs binding of interfaces to neighbors and third stage performs CA. The proposed algorithm improves over previous work because it retains network topology and minimizes network interference, which in turn improves available network throughput. Further, when compared with two other CBCA algorithms, CBCA provides better performance in terms of improved network interference, throughput, delay, and packet delivery ratios when tested upon network topologies with various network densities and traffic loads. Copyright © 2014 John Wiley & Sons, Ltd.     

Channel Assignment Strategies for Multiradio Wireless Mesh Networks: Issues and Solutions

Next-generation wireless mobile communications will be driven by converged networks that integrate disparate technologies and services. The wireless mesh network is envisaged to be one of the key components in the converged networks of the future, providing flexible high- bandwidth wireless backhaul over large geographical areas. While single radio mesh nodes operating on a single channel suffer from capacity constraints, equipping mesh routers with multiple radios using multiple nonoverlap- ping channels can significantly alleviate the capacity problem and increase the aggregate bandwidth available to the network. However, the assignment of channels to the radio interfaces poses significant challenges. The goal of channel assignment algorithms in multiradio mesh networks is to minimize interference while improving the aggregate network capacity and maintaining the connectivity of the network. In this article we examine the unique constraints of channel assignment in wireless mesh networks and identify the key factors governing assignment schemes, with particular reference to interference, traffic patterns, and multipath connectivity. After presenting a taxonomy of existing channel assignment algorithms for WMNs, we describe a new channel assignment scheme called MesTiC, which incorporates the mesh traffic pattern together with connectivity issues in order to minimize interference in multi- radio mesh networks.     

Multichannel mesh networks: challenges and protocols

Supporting high throughput is an important challenge in multihop mesh networks. Popular wireless LAN standards, such as IEEE 802.11, provision for multiple channels. In this article, we consider the use of multiple wireless channels to improve network throughput. Commercially available wireless network interfaces can typically operate over only one channel at a time. Due to cost and complexity constraints, the total number of interfaces at each host is expected to be smaller than the total channels available in the network. Under this scenario, several challenges need to be addressed before all the available channels can be fully utilized. In this article, we highlight the main challenges, and present two link-layer protocols for utilizing multiple channels. We also present a new abstraction layer that simplifies the implementation of new multichannel protocols in existing operating systems. This article demonstrates the feasibility of utilizing multiple channels, even if each host has fewer interfaces than the number of available channels.     

Design of logical topology with K‐connected constraints and channel assignment for multi‐radio wireless mesh networks

In multi‐radio multi‐channel wireless mesh networks, the design of logical topology is different from that in single channel wireless mesh networks. The same channel assignment algorithm used for various logical topologies will lead to diverse network performance. In this paper, we study the relationship between k ‐connected logical topology and the maximum number of assigned channels. Meanwhile, we analyze the issues affecting channel assignment performance, and present the lower and upper bounds of the maximum allowable number of assigned channels for k ‐connected logical topology. We then develop a k ‐connected logical topology design algorithm based on shortest disjoint paths and minimum interference disjoint paths for each node‐pair. In addition, we propose a static channel assignment algorithm according to minimum spanning tree search. Extensive simulations show that our proposed algorithm achieves higher throughput and lower end‐to‐end delay than fault tolerant topology control algorithms, which validates the involved trade‐off between path length and nodal interference. Moreover, numerical results demonstrate that our proposed channel assignment further improves network performance under the context of limited radio interfaces. Copyright © 2014 John Wiley & Sons, Ltd.     

Minimum Interference Channel Assignment in Multiradio Wireless Mesh Networks

In this paper, we consider multi-hop wireless mesh networks, where each router node is equipped with multiple radio interfaces and multiple channels are available for communication. We address the problem of assigning channels to communication links in the network with the objective of minimizing overall network interference. Since the number of radios on any node can be less than the number of available channels, the channel assignment must obey the constraint that the number of different channels assigned to the links incident on any node is atmost the number of radio interfaces on that node. The above optimization problem is known to be NP-hard. We design centralized and distributed algorithms for the above channel assignment problem. To evaluate the quality of the solutions obtained by our algorithms, we develop a semidefinite program and a linear program formulation of our optimization problem to obtain lower bounds on overall network interference. Empirical evaluations on randomly generated network graphs show that our algorithms perform close to the above established lower bounds, with the difference diminishing rapidly with increase in number of radios. Also, ns-2 simulations as well as experimental studies on testbed demonstrate the performance potential of our channel assignment algorithms in 802.11-based multi-radio mesh networks.     

Power-Efficient Spatial Reusable Channel Assignment Scheme in WLAN Mesh Networks

Interference has strong effect on the available bandwidth of wireless local area network (WLAN) based mesh networks. The channel assignment problem for multi-radio multi-channel multihop WLAN mesh networks is complex NP-hard, and channel assignment, routing and power control are tightly coupled. To mitigate the co-channel interference and improve capacity in multi-channel and multi-interface WLAN mesh networks, a power-efficient spatial reusable channel assignment scheme is proposed, which considers both channel diversity and spatial reusability to reduce co-channel interference by joint adjusting channel, transmission power and routing. In order to assign channel appropriately, an efficient power control scheme and a simple heuristic algorithm is introduced to achieve this objective, which adjust the channel and power level of each radio according to the current channel conditions so as to increase the opportunity of channel spatial reusability. The proposed channel assignment scheme also takes load, capacity and interference of links into consideration. Simulation results show the effectiveness of our approach and demonstrate that the proposed scheme can get better performance than other approaches in terms of throughput, blocking ratio, energy consumption and end-to-end delay.     

A Cross-layer Approach to Channel Assignment in Wireless Ad Hoc Networks

To improve the capacity of wireless ad hoc networks by exploiting multiple available channels, we propose a distributed channel assignment protocol that is based on a cross-layer approach. By combining channel assignment with routing protocols, the proposed channel assignment protocol is shown to require fewer channels and exhibit lower communication, computation, and storage complexity than existing channel assignment schemes. A multi-channel MAC (MC-MAC) protocol that works with the proposed channel assignment protocol is also presented. We prove the correctness of the proposed channel assignment protocol. In addition, through a performance study, we show that the proposed protocol can substantially increase throughput and reduce delay in wireless ad hoc networks, compared to the IEEE 802.11 MAC protocol and an existing multi-channel scheme.

Joint Throughput Optimization for Wireless Mesh Networks

In this paper, we address the problem of joint channel assignment, link scheduling, and routing for throughput optimization in wireless networks with multiradios and multichannels. We mathematically formulate this problem by taking into account the interference, the number of available radios the set of usable channels, and other resource constraints at nodes. We also consider the possible combining of several consecutive channels into one so that a network interface card (NIC) can use the channel with larger range of frequencies and thus improve the channel capacity. Furthermore, we consider several interference models and assume a general yet practical network model in which two nodes may still not communicate directly even if one is within the transmission range of the other. We designed efficient algorithm for throughput (or fairness) optimization by finding flow routing, scheduling of transmissions, and dynamic channel assignment and combining. We show that the performance, fairness and throughput, achieved by our method is within a constant factor of the optimum. Our model also can deal with the situation when each node will charge a certain amount for relaying data to a neighboring node and each flow has a budget constraint. Our extensive evaluation shows that our algorithm can effectively exploit the number of channels and radios. In addition, it shows that combining multiple channels and assigning them to a single user at some time slots indeed increases the maximum throughput of the system compared to assigning a single channel.