A CHANNEL ASSIGNMENT ALGORITHM VIA CONFLICT SHIFTING FOR DISTRIBUTED COGNITIVE NETWORKS

Channel assignment is a challenge for distributed cognitive networks due to spectrum mobility and lack of centralized entity.We present a dynamic and efficient algorithm via conflict shifting,referred as Shifting-based Channel Assignment(SCA).In this algorithm,the system was modeled with a conflict graph,and users cannot assign the channels that primary users(legacy users) and neighbors already occupied.In order to eliminate the conflicts between neighbors efficiently,secondary users(unlicensed users) try to transfer them through a straight path to the boundary,where conflicts are easier to solve as there are less neighbors for boundary users.Actions in one shift are executed in slots,and users act in a synchronous and separated manner.As a result,some of the conflicting channels are avoid from directly abandoned,and for this,utility of the entire network can be improved.Simulation results show that the proposed algorithm can provide similar utility performance while obviously reducing the communication cost than bargaining-base algorithms.In small scale networks with low user mobility(under 20%),it reduces 50% of the communication overhead than the later.

Joint channel assignment and cross-layer routing protocol for multi-radio multi-channel Ad Hoc networks

To study multi-radio multi-channel （MR-MC） Ad Hoc networks based on 802.11, an efficient cross-layer routing protocol with the function of joint channel assignment, called joint channel assignment and cross-layer routing （JCACR）, is presented. Firstly, this paper introduces a new concept called channel utilization percentage （CUP）, which is for measuring the contention level of different channels in a node’s neighborhood, and deduces its optimal value for determining whether a channel is overloaded or not. Then, a metric parameter named channel selection metric （CSM） is designed, which actually reffects not only the channel status but also corresponding node’s capacity to seize it. JCACR evaluates channel assignment by CSM, performs a local optimization by assigning each node a channel with the smaller CSM value, and changes the working channel dynamically when the channel is overloaded. Therefore, the network load balancing can be achieved. In addition, simulation shows that, when compared with the protocol of weighted cumulative expected transfer time （WCETT）, the new protocol can improve the network throughput and reduce the end-to-end average delay with fewer overheads.

3D placement of unmanned aerial vehicles and partially overlapped channel assignment for throughput maximization

This paper investigates a wireless system with multi-Unmanned Aerial Vehicles(UAVs)for improving the overall throughput.In contrast to previous studies that optimize the locations of UAVs and channel assignment separately,this paper considers the two issues jointly by exploiting Partially Overlapped Channels(POCs).The optimization problem of maximizing network throughput is formulated as a non-convex and non-linear problem.In order to find a practical solution,the problem is decomposed into two subproblems,which are iteratively optimized.First,the optimal locations of UAVs are determined under a fixed channel assignment scheme by solving the mixed-integer second-order cone problem.Second,an efficient POC allocation scheme is determined via the proposed channel assignment algorithm.Simulation results show that the proposed approach not only significantly improves system throughput and service reliability compared with the cases in which only orthogonal channels and stationary UAVs are considered,but also achieves similar performance using the exhaustive search algorithm with lower time complexity.

A TRUST MECHANISM-BASED CHANNEL ASSIGNMENT AND ROUTING SCHEME IN COGNITIVE WIRELESS MESH NETWORKS WITH INTRUSION DETECTION

Cognitive Wireless Mesh Networks(CWMN) is a novel wireless network which combines the advantage of Cognitive Radio(CR) and wireless mesh networks.CWMN can realize seamless in-tegration of heterogeneous wireless networks and achieve better radio resource utilization.However,it is particularly vulnerable due to its features of open medium,dynamic spectrum,dynamic topology,and multi-top routing,etc..Being a dynamic positive security strategy,intrusion detection can provide powerful safeguard to CWMN.In this paper,we introduce trust mechanism into CWMN with intrusion detection and present a trust establishment model based on intrusion detection.Node trust degree and the trust degree of data transmission channels between nodes are defined and an algorithm of calcu-lating trust degree is given based on distributed detection of attack to networks.A channel assignment and routing scheme is proposed,in which selects the trusted nodes and allocates data channel with high trust degree for the transmission between neighbor nodes to establish a trusted route.Simulation re-sults indicate that the scheme can vary channel allocation and routing dynamically according to network security state so as to avoid suspect nodes and unsafe channels,and improve the packet safe delivery fraction effectively.

Partially Overlapping Channel Assignment Using Bonded and Non-Bonded Channels in IEEE 802.11n WLAN

Nowadays,wireless local area network(WLAN)has become prevalent Internet access due to its low-cost gadgets,flexible coverage and hasslefree simple wireless installation.WLAN facilitates wireless Internet services to users with mobile devices like smart phones,tablets,and laptops through deployment of multiple access points(APs)in a network field.Every AP operates on a frequency band called channel.Popular wireless standard such as IEEE 802.11n has a limited number of channels where frequency spectrum of adjacent channels overlaps partially with each other.In a crowded environment,users may experience poor Internet services due to channel collision i.e.,interference from surrounding APs that affects the performance of the WLAN system.Therefore,it becomes a challenge to maintain expected performance in a crowded environment.A mathematical model of throughput considering interferences from surrounding APs can play an important role to set up a WLAN system properly.While set up,assignment of channels considering interference can maximize network performance.In this paper,we investigate the signal propagation of APs under interference of partially overlapping channels for both bonded and non-bonded channels.Then,a throughput estimation model is proposed using difference of operating channels and received signal strength indicator(RSSI).Then,a channel assignment algorithm is introduced using proposed throughput estimation model.Finally,the efficiency of the proposal is verified by numerical experiments using simulator.The results show that the proposal selects the best channel combination of bonded and non-bonded channels that maximize the performance.

Cooperative Channel Assignment for VANETs Based on Dual Reinforcement Learning

Dynamic channel assignment(DCA)is significant for extending vehicular ad hoc network(VANET)capacity and mitigating congestion.However,the un-known global state information and the lack of centralized control make channel assignment performances a challenging task in a distributed vehicular direct communication scenario.In our preliminary field test for communication under V2X scenario,we find that the existing DCA technology cannot fully meet the communication performance requirements of VANET.In order to improve the communication performance,we firstly demonstrate the feasibility and potential of reinforcement learning(RL)method in joint channel selection decision and access fallback adaptation design in this paper.Besides,a dual reinforcement learning(DRL)-based cooperative DCA(DRL-CDCA)mechanism is proposed.Specifically,DRL-CDCA jointly optimizes the decision-making behaviors of both the channel selection and back-off adaptation based on a multi-agent dual reinforcement learning framework.Besides,nodes locally share and incorporate their individual rewards after each communication to achieve regional consistency optimization.Simulation results show that the proposed DRL-CDCA can better reduce the one-hop packet delay,improve the packet delivery ratio on average when compared with two other existing mechanisms.

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 performance 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+1.Hence the algorithm guarantees that the number of channels available in standards such as IEEE802.11a 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.

Distributed channel assignment combined with routing over multi-radio multi-channel wireless mesh networks

In order to realize the reduction of equipment cost and the demand of higher capacity, wireless mesh network （WMN） router devices usually have several interfaces and work on multi-channels. Jointing channel allocation, interface assignment and routing can efficiently improve the network capacity. This paper presents an efficient channel assignment scheme combined with the multi-radio link quality source routing （MR-LQSR） protocol, which is called channel assignment with MR-LQSR （CA-LQSR）. In this scheme, a physical interference model is established： calculated transmission time （CTT） is proposed as the metric of channel assignment, which can reflect the real network environment and channel interference best, and enhanced weighted cumulative expected transmission time （EWCETT） is proposed as the routing metric, which preserves load balancing and bandwidth of links. Meantime, the expression of EWCETT contains the value of CTT, thus the total cost time of channel assignment and routing can be reduced. Simulation results show that our method has advantage of higher throughput, lower end-to-end time delay, and less network cost over some other existing methods.

Fairness-oriented routing algorithm joint with power control and channel assignment for multi-radio multi-channel wireless mesh networks

The multi-radio multi-channel wireless mesh network （MRMC-WMN） draws general attention because of its excellent throughput performance, robustness and relative low cost. The closed interactions among power control （PC）, channel assignment （CA） and routing is contributed to the performance of multi-radio multi-channel wireless mesh networks （MRMC-WMNs）. However, the joint PC, CA and routing （JPCR） design, desired to achieve a global optimization, was poor addressed. The authors present a routing algorithm joint with PC and CA （JPCRA） to seek the routing, power and channel scheme for each flow, which can improve the fairness performance. Firstly, considering available channels and power levels, the routing metric, called minimum flow rate, is designed based on the physical interference and Shannon channel models. The JPCRA is presented based on the genetic algorithm （GA） with simulated annealing to maximize the minimum flow rate, an non-deterministic polynomial-time hard （NP-Hard） problem. Simulations show the JPCRA obtains better fairness among different flows and higher network throughput.

Cooperative channel assignment for VANETs based on multiagent reinforcement learning

Dynamic channel assignment(DCA)plays a key role in extending vehicular ad-hoc network capacity and mitigating congestion.However,channel assignment under vehicular direct communication scenarios faces mutual influence of large-scale nodes,the lack of centralized coordination,unknown global state information,and other challenges.To solve this problem,a multiagent reinforcement learning(RL)based cooperative DCA(RLCDCA)mechanism is proposed.Specifically,each vehicular node can successfully learn the proper strategies of channel selection and backoff adaptation from the real-time channel state information(CSI)using two cooperative RL models.In addition,neural networks are constructed as nonlinear Q-function approximators,which facilitates the mapping of the continuously sensed input to the mixed policy output.Nodes are driven to locally share and incorporate their individual rewards such that they can optimize their policies in a distributed collaborative manner.Simulation results show that the proposed multiagent RL-CDCA can better reduce the one-hop packet delay by no less than 73.73%,improve the packet delivery ratio by no less than 12.66%on average in a highly dense situation,and improve the fairness of the global network resource allocation.

Q-learning for dynamic channel assignment in cognitive wireless local area network with fibre-connected distributed antennas

Cognitive wireless local area network with fibre-connected distributed antennas （CWLAN-FDA） is a promising and efficient architecture that combines radio over fiber, cognitive radio and distributed antenna technologies to provide high speed/high capacity wireless access at a reasonable cost. In this paper, a Q-learning approach is applied to implement dynamic channel assignment （DCA） in CWLAN-FDA. The cognitive access points （CAPs） select and assign the best channels among the industrial, scientific, and medical （ISM） band for data packet transmission, given that the objective is to minimize external interference and acquire better network-wide performance. The Q-learning method avoids solving complex optimization problem while being able to explore the states of a CWLAN-FDA system during normal operations. Simulation results reveal that the proposed strategy is effective in reducing outage probability and improving network throughput.

Frequency Assignment through Combinatorial Optimization Approach

An L（2, 1）-labeling of a graph G is a function f from the vertex set V（G） to the set of all nonnegative integers such that ｜f（x） - f（y）｜ 〉 2 if d（x, y） = 1 and ｜f（x）-f（y）｜ ≥ 1 ifd（x, y） = 2. The L（2, 1）-labeling number λ（G） of G is the smallest number k such that G has an L（2, 1）-labeling with max{f（v） ： v ∈ V（G）} = k. We study the L（3, 2, 1）-labeling which is a generalization of the L（2, 1）-labeling on the graph formed by the （Cartesian） product and composition of 3 graphs and derive the upper bounds of λ3（G） of the graph.

A ROUTING PROTOCOL BASED ON INTERFERENCE-AWARE AND CHANNEL-LOAD IN MULTI-RADIO MULTI-CHANNEL AD HOC NETWORKS

Improving capacity and reducing delay are the most challenging topics in wireless ad hoc networks. Nodes that equip multiple radios working on different channels simultaneously permit ef-fective utility of frequency spectrum and can also reduce interference. In this paper, after analyzing several current protocols in Multi-Radio Multi-Channel (MR-MC) ad hoc networks, a new multi-channel routing metric called Integrative Route Metric (IRM) is designed. It takes channel load, inter-flow, and intra-flow interference into consideration. In addition, an MR-MC routing protocol based on Interference-Aware and Channel-Load (MR-IACL) is also presented. The MR-IACL can assign channels and routings for nodes according to channel load and interference degree of links, and optimize channel distribution dynamically to satisfy the features of topology changing and traffic frequent fluctuation during network running. The simulation results show that the new protocol outperforms others in terms of network throughput, end-to-end delay, routing overhead, and network lifetime.

L(h, k)-Labeling of Circulant Graphs

An L(h,k)-labeling of a graph G is an assignment of non-negative integers to the vertices such that if two vertices u and v are adjacent then they receive labels that differ by at least h, and when u and v are not adjacent but there is a two-hop path between them, then they receive labels that differ by at least k. The span λ of such a labeling is the difference between the largest and the smallest vertex labels assigned. Let λhk ( G )denote the least λ such that G admits an L(h,k) -labeling using labels from {0,1,...λ}. A Cayley graph of group is called circulant graph of order n, if the group is isomorphic to Zn. In this paper, initially we investigate the L(h,k) -labeling for circulant graphs with “large” connection sets, and then we extend our observation and find the span of L(h,k) -labeling for any circulants of order n. .

基于图论的无线传感器网络并行禁忌搜索信道分配办法(英文)

Wireless sensor networks are suffering from serious frequency interference.In this paper,we propose a channel assignment algorithm based on graph theory in wireless sensor networks.We first model the conflict infection graph for channel assignment with the goal of global optimization minimizing the total interferences in wireless sensor networks.The channel assignment problem is equivalent to the generalized graph-coloring problem which is a NP-complete problem.We further present a meta-heuristic Wireless Sensor Network Parallel Tabu Search(WSN-PTS) algorithm,which can optimize global networks with small numbers of iterations.The results from a simulation experiment reveal that the novel algorithm can effectively solve the channel assignment problem.

The L(3,2,1)-labeling on Bipartite Graphs

An L（3, 2, 1）-labeling of a graph G is a function from the vertex set V（G） to the set of all nonnegative integers such that ｜f（u）-f（v）｜≥3 if dG（u,v） = 1, ｜f（u）-f（v）｜≥2 if dG（u,v） = 2, and ｜f（u）-f（v）｜≥1 if dG（u,v） = 3. The L（3, 2,1）-labeling problem is to find the smallest number λ3（G） such that there exists an L（3, 2,1）-labeling function with no label greater than it. This paper studies the problem for bipartite graphs. We obtain some bounds of λ3 for bipartite graphs and its subclasses. Moreover, we provide a best possible condition for a tree T such that λ3（T） attains the minimum value.

N-Set Distance-Labelings for Cycle Graphs

Let G = (V, E) be a graph and Cm be the cycle graph with m vertices. In this paper, we continued Yeh’s work [1] on the distance labeling of the cycle graph Cm. An n-set distance labeling of a graph G is the labeling of the vertices (with n labels per vertex) of G under certain constraints depending on the distance between each pair of the vertices in G. Following Yeh’s notation [1], the smallest value for the largest label in an n-set distance labeling of G is denoted by λ1(n)(G). Basic results were presented in [1] for λ1(2)(Cm) for all m and λ1(n)(Cm) for some m where n ≥ 3. However, there were still gaps left unstudied due to case-by-case complexities. For these uncovered cases, we proved a lower bound for λ1(n)(Cm). Then we proposed an algorithm for finding an n-set distance labeling for n ≥ 3 based on our proof of the lower bound. We verified every single case for n = 3 up to n = 500 by this same algorithm, which indicated that the upper bound is the same as the lower bound for n ≤ 500.

Chanel Assignment Optimization Algorithm Based on Link Throughput and Node Priority

How to reduce interference among neighbor nodes in wireless mesh networks is still an important and key issue nowa- days. In this paper, an optimized channel assignment algorithm （OCA） is proposed to solve this problem based on link throughput and node priority. The effects of the numbers of network interface cards and channels on the network throughput are analyzed and evaluated, When there are seven of the numbers of both network interface cards and channels, the efficiency of utilizing network interface card and channel reaches highest. Compared with cen- tralized channel assignment algorithm （CCA）, the proposed algo- rithm has less packet loss rate and more network throughput sig- nificantly.

A General Approach to L(h,k)-Label Interconnection Networks

Given two non-negative integers h and k, an L（h, k）-labeling of a graph G = （V, E） is a function from the set V to a set of colors, such that adjacent nodes take colors at distance at least h, and nodes at distance 2 take colors at distance at least k. The aim of the L（h, k）-labeling problem is to minimize the greatest used color. Since the decisional version of this problem is NP-complete, it is important to investigate particular classes of graphs for which the problem can be efficiently solved. It is well known that the most common interconnection topologies, such as Butterfly-like, Beneg, CCC, Trivalent Cayley networks, are all characterized by a similar structure： they have nodes organized as a matrix and connections are divided into layers. So we naturally introduce a new class of graphs, called （l × n）-multistage graphs, containing the most common interconnection topologies, on which we study the L（h, k）-labeling. A general algorithm for L（h, k）-labeling these graphs is presented, and from this method an efficient L（2, 1）-labeling for Butterfly and CCC networks is derived. Finally we describe a possible generalization of our approach.