Dynamic Channel Assignment Algorithms Research Articles

Pinball attacks against Dynamic Channel assignment in wireless networks

In this paper, we expose a class of stealthy attacks, which we coin pinball attacks, that exploit the adaptive nature of Dynamic Channel Assignment algorithms in wireless networks. In a pinball attack, the attacker strategically induces interference in the neighborhood of certain nodes to cause a cascading channel switching behavior, thereby exploiting the topology of the network to his own advantage. The attacker’s problem is formulated as a Markov Decision Process in which the attacker seeks to maximize his long-term net rewards. To overcome the exponential size of the state space, we derive suboptimal attack policies through approximation methods. We expose the pinball attacks on two general setups that arise practically in wireless communication systems. In the first setup, each wireless node is an access point aiming to select a channel that has minimum interference with its neighbors. In the second setup, we consider wireless nodes with multiple antennas whereby every node should communicate with each of its neighbors on a separate channel. We formally establish the equivalence of both setups by showing that the identified pinball attack policies on one can be directly mapped to attack policies on the other. We present numerical results to assess the impact of the obtained pinball attack policies under various topologies, and show that they outperform other known attack policies over all topologies considered. We also propose a novel approach to scale up the attack to larger size networks with special structures.

English

Dynamic channel assignment (DCA) has been a topic of intense research for many years, and a variety of DCA algorithms have been proposed. Nonetheless, some important issues have been neglected because of the complexity involved in their study. In particular, the impact of user motion on the performance of DCA systems has not received enough attention. In this paper, we quantify the impact of motion on the capacity and cost—in terms of average number of reassignments per call—of a variety of representative distributed fixed-power DCA algorithms. A novel adaptive algorithm especially suited for mobility environments is proposed, which achieves high capacity while controlling the reassignment rate. We also prove that most of this capacity can be effectively realized with a reduced number of radio transceivers per base station. Finally, we evaluate the degradation associated with the use of estimates of local-mean signal and interference levels—obtained by averaging instantaneous measurements—in-stead of the actual local-mean values.

Channel switching control policy for wireless mesh networks

Dynamic channel assignment algorithms allow wireless nodes to switch channels when their traffic loads exceed certain thresholds. These thresholds represent estimations of their throughput capacities. Unfortunately, the threshold estimation may not be accurate due to co-channel interference (CCI) and adjacent-channel interference (ACI), especially with high traffic loads in dense networks. When the link capacity is over-estimated, these channel assignment algorithms are not effective. This is because the channel switch is not triggered even with overloaded data traffic and the link quality decreases significantly as the channel is overloaded. When the link capacity is under-estimated, the link is under-utilized. Moreover, when link traffic load increases from time to time, channel switch occurs frequently. Such frequent channel switches increase latency and degrade throughput, and can even cause network wide channel oscillations. In this paper, we propose a novel threshold-based control system, called balanced control system (BCS). The proposed threshold-based control policy consists of deciding, according to the real time traffic load and interference, whether to switch to another channel, which channel should be switched to and how to perform the switch. Our control model is based on a fuzzy logic control. The threshold which assists to make the channel switch decisions, could be deduced dynamically according to the real-time traffic of each node. We also design a novel dynamic channel assignment scheme, which is used for the selection of the new channel. The channel switch scheduler is provided to perform channel-switch processing for sender and receiver over enhanced routing protocols. We implement our system in NS2, and the simulation results show that with our proposed system, the performance improves by 12.3%–72.8% in throughput and reduces 23.2%–52.3% in latency.

A dynamic channel assignment strategy based on cross‐layer design for wireless mesh networks

SUMMARYIn wireless mesh networks (WMNs), if nonoverlapped channels or partially overlapped channels are used properly, the throughput can be improved drastically. However, the number of nonoverlapped channels is limited in wireless communication standards. An effective channel assignment algorithm for a WMN is necessary to increase the utilization rate of space and nonoverlapped channels. Static channel assignment algorithms can improve network throughput, but their accuracies are not satisfactory in common scenarios. Dynamic channel assignment algorithms can allocate channels according to the status of adjacent links in WMNs. A dynamic channel assignment algorithm needs cross‐layer design to get the information of routing. A routing‐information‐aware channel assignment algorithm based on a cross‐layer design is proposed, which is named R‐CA. The proposed method can dynamically allocate channels for wireless nodes when they need communication and release channels after data transmission. In R‐CA, limited channel resources can be used efficiently by more wireless nodes, and hence the communication throughput can be improved. Simulation results show that our channel allocation strategy can effectively ensure and enhance the network throughput and packet delivery rate in WMNs. Copyright © 2012 John Wiley & Sons, Ltd.

CELLULAR LEARNING AUTOMATA BASED DYNAMIC CHANNEL ASSIGNMENT ALGORITHMS

A solution to channel assignment problem in cellular networks is self-organizing channel assignment algorithm with distributed control. In this paper, we propose three cellular learning automata based dynamic channel assignment algorithms. In the first two algorithms, no information about the status of channels in the whole network will be used by cells for channel assignment whereas in the third algorithm, the additional information regarding status of channels may be gathered and then used by cells in order to allocate channels. The simulation results show that by using the proposed channel assignment algorithms the micro-cellular network can self-organize itself. The simulation results also show that the additional information used by the third algorithm help the cellular learning automata to find an assignment which results in lower blocking probability of calls for the network.

Utilizing the synchrony among base stations for better performance of channel assignment algorithms

A radio spectrum is a shared, limited, and expensive resource in cellular networks. A network allocates a channel from the spectrum to provide connectivity to a user. With the ever increasing number of users, it is a challenge and a business opportunity to support as many simultaneous users as possible. Hence, designing better channel assignment algorithms remains a topic of continued research interest. In this paper, we propose a new technique to reduce the failure rates of a class of dynamic channel assignment algorithms, namely, channel assignment without measurement (CAWM). The technique assumes that all the base stations in a network are synchronized. By synchronized base stations, we mean the time slots on all the carriers in all the cells have the same start times. This assumption allows a base station to acquire one channel when there is a need, rather than acquire all the channels on a carrier when there is a need for just one channel. This is expected to lead to better availability of channels in the entire network when there is a need, because channels are not held up without any use. By using this assumption, we have redesigned four dynamic channel assignment algorithms, namely, the Nanda–Goodman strategy, the Geometric strategy, the Bidirectional Channel Locking (BDCL) strategy, and the Two-Step Dynamic Priority (TSDP) strategy. Simulation results confirm our initial expectation. There is significant improvement in the failure rates of the Nanda–Goodman and the TSDP strategies, whereas the Geometric and the BDCL strategies show significant improvements up to certain call arrival rates.

Call-on-Hold for Improving the Performance of Dynamic Channel-Assignment Strategies in Cellular Networks

Efficient use of the limited radio spectrum is of paramount importance to supporting the ever-increasing number of mobile terminals. There is a need for devising complementing techniques to improve the performance of dynamic channel-assignment (DCA) algorithms to increase the capacity of cellular systems. In this paper, we study the concept of call-on-hold to improve the performance of a class of DCA algorithms called coordinated assignment without measurement (CAWM). DCA algorithms such as the Geometric strategy, the Nanda-Goodman strategy, the borrowing with directional channel locking (BDCL) strategy, and the two-step dynamic priority (TSDP) strategy fall into the CAWM class. To gain insight into the CAWM DCA algorithms, we simulated those algorithms and monitored carrier availability and failure to assign a channel characteristics in a cell. After observing these characteristics, we formulated a hypothesis as follows: If a new or handoff call is put on hold for a short while in a cell in the absence of an available channel, it is highly likely that the local base station will soon find a channel for the call. In the proposed approach, a DCA algorithm is said to have failed to assign a channel to a call only if a waiting call is delayed for longer than a threshold period called maximum delay. Our simulation-based study shows that it is possible to significantly reduce failure rates of the CAWM class of DCA algorithms by putting those calls on hold which would otherwise be blocked or dropped. The impact of small values of maximum delay on the average delay suffered by all calls in a network is negligible, but the reduction in failure rate is significant. We have explained how the call-on-hold idea can be easily integrated with the GSM system.

Distributed dynamic channel assignment in TDMA mobile communication systems

Dynamic channel assignment (DCA) has been a topic of intense research for many years, and a variety of DCA algorithms have been proposed. Nonetheless, some important issues have been neglected because of the complexity involved in their study. In particular, the impact of user motion on the performance of DCA systems has not received enough attention. In this paper, we quantify the impact of motion on the capacity and cost-in terms of average number of reassignments per call-of a variety of representative distributed fixed-power DCA algorithms. A novel adaptive algorithm especially suited for mobility environments is proposed, which achieves high capacity while controlling the reassignment rate. We also prove that most of this capacity can be effectively realized with a reduced number of radio transceivers per base station. Finally, we evaluate the degradation associated with the use of estimates of local-mean signal and interference levels-obtained by averaging instantaneous measurements-instead of the actual local-mean values.

Distributed dynamic channel assignment with violation to the reuse pattern for microcellular networks

In this paper, the frequency reuse and the distributed dynamic channel assignment for microcellular networks are studied. We show that it is possible to use carriers with violation to the frequency reuse pattern with an insignificant degradation of the quality of service. As a result, a new family of distributed dynamic channel assignment algorithms is presented: the DDCA with violation to the reuse pattern (DDCA with VRP) strategies. The DDCA with VRP schemes allow the use of carriers with at most one violation to the reuse pattern, under the restriction that both cells using simultaneously the same carrier must be the farthest cells of their interference neighborhoods. The results show that the use of carriers with VRP is an effective strategy to increase the system capacity at the expense of an insignificant degradation of the quality of service. This is due to the fact that the carriers are employed with VRP by short time intervals in the least harmful situations. We propose and evaluate five DDCA with VRP schemes and everyone overcomes the performance of the maximum packing (MP) algorithm, with limited carrier usage information and without the need of centralized coordination neither global carrier rearrangements.

Performance analysis of dynamic channel assignment algorithms in cellular mobile systems with hand‐off

AbstractIn this paper, the traffic performance of dynamic channel assignment (DCA) in cellular mobile system with hand‐off is investigated. A traffic model for cellular system incorporating hand‐off is established first. Under the framework of the model, a hand‐off priority scheme is developed to reduce the forced termination of calls in progress. This paper analyses and derives the traffic performance bound for DCA strategies with hand‐off by extending the maximum packing (MP) scheme to include the hand‐off procedure. For practical implementation, a distributed DCA algorithm (DDCA) is also proposed. A non‐priority scheme and the proposed priority scheme can be combined with either MP or DDCA. It is shown that the simulation results of DDCA scheme are comparable with the analytical bounds given by MP for both the non‐prioritized case and prioritized case. A reasonable trade‐off between the new call blocking probability and forced termination probability can be achieved by using the proposed prioritized scheme in DCA. Copyright © 2002 John Wiley & Sons, Ltd.

Network-assisted resource management for wireless data networks

We propose a framework for network-assisted radio resource management in wireless data networks. This type of radio resource management techniques offer implementation and capacity benefits compared to conventional, interference-measurement based, dynamic channel assignment (DCA) algorithms. The basic idea is to use interbase signaling to shift most of the burden of the resource allocation from the air interface to the backbone infrastructure. By exchanging channel assignment as well as other relevant information in real time through the backbone network, each base can calculate the impact of a resource assignment on the system. As a result, rapid interference measurements, which are typically needed to implement DCA schemes, are replaced by a limited amount of path loss measurements and the computation of interference conditions by the base stations. This significantly reduces the measurement and over-the-air signaling requirements, and can also provide an opportunity for a better optimization of the system performance. We focus on two specific algorithms: network-assisted least-interference-based dynamic packet assignment (NA-LI-DPA) and network-assisted dynamic packet assignment with throughput optimization (NA-DPA). NA-LI-DPA closely resembles a least-interference-based dynamic channel assignment algorithm, and NA-DPA attempts to further improve the overall system throughput. The algorithms, as defined, are appropriate for a best-effort data service, where the primary goal is to provide a higher throughput. However, it will be clear from the discussion that it is also feasible to alter the algorithms to optimize performance metrics other than throughput, e.g., to ensure a certain quality of service. We show through simulation that, for a system like enhanced general packet radio service (EGPRS) system, NA-DPA can provide a throughput that is 50% higher than random packet assignment, and 25% higher than that obtained by conventional DCA algorithms.

Mixed Power Control with Directed Assignment (MPCDA), a Method for Interference Reduction in Channelized Wireless Systems

Power control, often coupled with dynamic channel assignment, has been viewed as a promising answer to the challenge of reducing interference and increasing capacity. Indiscriminate use of power control, however, may exacerbate the near-far-end problem on the down link, and give rise to other complications when users are mobile. We propose a power control policy that can alleviate the near-far-end interference caused by the use of either the same channel or neighbor channels inside the same cell, while at the same time aiding in the reduction of interference from different cells through user matching. We present a heuristic algorithm for user matching, which is distributed and simple to implement. The method can be combined with an array of either fixed or dynamic channel assignment algorithms and applies to both circuit-based and packet-based traffic. It is ideal for fixed or slow circuit-based traffic and for packet-based traffic. A duality relationship is derived for the proposed power control policy between the signal-to-interference ratio of two interfering users experienced in the two communication directions. This relationship enables one to validate channel assignment decisions on both communication directions by analyzing only the decisions for one.

Reducing call dropping in distributed dynamic channel assignment algorithms by incorporating power control in wireless ad hoc networks

Methods of substantially reducing call dropping in networks which use distributed dynamic channel assignment (DDCA) schemes are discussed. Interference and received power thresholds coupled with power control are used to maintain performance, without the need for intra-cell handoffs. It is shown that the schemes reduce call dropping and increase capacity compared to those using fixed transmitter power. The schemes are developed with the aid of mathematical analysis and a pictorial model. Results are presented which show that call dropping may be virtually eliminated in shadowing environments with the median transmitter power being reduced by 15 dB. The various call dropping mechanisms are discussed, and it is suggested that the residual level of call dropping is principally a result of multiple additional call arrivals close to an active link. Methods to make further reductions in the call dropping probability are also proposed.

Integrated dynamic channel assignment and power control in TDMA mobile wireless communication systems

With the evolution of analog mobile wireless communications systems into digital second- and third-generation systems, there is growing interest in finding more efficient ways of managing the available resources, in particular radio spectrum and power. In the context of time division multiple access (TDMA) systems, this interest has led to the development of a variety of dynamic channel assignment (DCA) and power control (PC) algorithms. Despite the intense activity in both the DCA and the PC arenas and some proposals for combined DCA with PC, not enough work has been devoted to effectively integrating them. In this paper, the integration of DCA and PC is investigated and a family of integrated algorithms is presented. These algorithms, fully distributed and cost adaptive, achieve capacity levels significantly higher than those of a system with only DCA or PC. With respect to a system without any DCA or PC, several-fold capacity increases are obtained. Furthermore, these capacity levels are attained with user mobility included in the analysis.

Performance issues and algorithms for dynamic channel assignment

Using dynamic channel assignment (DCA) algorithms to select communications channels as needed, time-division multiple access (TDMA) or frequency-division multiple access (FDMA) systems can serve dynamic and nonuniform traffic demands without frequency planning as long as quality is sufficient and equipment is available. Here, performance issues and algorithms for DCA in a TDMA portable radio system are considered. A fixed number of traffic servers (time slots) per radio port is assumed: therefore, the system capacity is hard-limited by the equipment availability, and the DCA efficiency is compared mainly through the signal-to-interference ratio in both the uplink and downlink directions. >

Asymptotic bounds on the performance of a class of dynamic channel assignment algorithms

Dynamic channel assignment, adapting both to traffic variations as well as to changing mobile locations, is investigated. Several ad hoc schemes of this type have been described in the literature and found to yield interesting performance improvements. However, very little is known about the performance of the optimum assignment schemes. Both upper and lower bounds for the performance of optimum algorithms within the class of reuse-type dynamic channel assignment (DCA) for a simple propagation model are established. The authors focus on the asymptotic performance, i.e., the performance in systems with large traffic loads. As a performance measure, the probability of assignment failure (intracell handoff failure) is used. Results show that the capacity one may expect to achieve with these algorithms in the asymptotic case is just above twice the capacity of a fixed channel allocation scheme.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance of optimum transmitter power control in cellular radio systems

Most cellular radio systems provide for the use of transmitter power control to reduce cochannel interference for a given channel allocation. Efficient interference management aims at achieving acceptable carrier-to-interference ratios in all active communication links in the system. Such schemes for the control of cochannel interference are investigated. The effect of adjacent channel interference is neglected. As a performance measure, the interference (outage) probability is used, i.e., the probability that a randomly chosen link is subject to excessive interference. In order to derive upper performance bounds for transmitter power control schemes, algorithms that are optimum in the sense that the interference probability is minimized are suggested. Numerical results indicate that these upper bounds exceed the performance of conventional systems by an order of magnitude regarding interference suppression and by a factor of 3 to 4 regarding the system capacity. The structure of the optimum algorithm shows that efficient power control and dynamic channel assignment algorithms are closely related.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Distributed assignment algorithms for multihop packet radio networks

New distributed dynamic channel assignment algorithms for a multihop packet radio network are introduced. The algorithms ensure conflict-free transmissions by the nodes of the network. The basic idea of the algorithms is to split the shared channel into a control segment and a transmission segment. The control segment is used to avoid conflicts among nodes and to increase the utilization of the transmission segment. It is shown how these algorithms can be used in order to determine time-division multiple access (TDMA) cycles with spatial reuse of the channel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Simulation Study of Some Dynamic Channel Assignment Algorithms in a High Capacity Mobile Telecommunications System

This paper reports the results of an investigation of the increase in traffic capacity in a cellular high capacity mobile telecommunications system attainable with dynamic instead of fixed channel assignment. Three dynamic channel assignment algorithms were studied by simulation using a 21-cell hexagonal array as a representative system layout. Detailed results for each algorithm are presented. For the particular system studied, traffic capacity can be increased by approximately 25 percent with dynamic channel assignment. A general upper bound on this increase has been found.

A simulation study of some dynamic channel assignment algorithms in a high capacity mobile telecommunications system

This paper reports the results of an investigation of the increase in traffic capacity in a cellular high capacity mobile telecommunications system attainable with dynamic instead of fixed channel assignment. Three dynamic channel assignment algorithms were studied by simulation using a 21-cell hexagonal array as a representative system layout. Detailed results for each algorithm are presented. For the particular system studied, traffic capacity can be increased by approximately 25 percent with dynamic channel assignment. A general upper bound on this increase has been found.