A Network-Based Dynamic Channel Assignment Scheme for TDMA Cellular Systems

Network-based dynamic channel assignment (DCA) schemes can be used to increase the capacity of TDMA cellular systems. In this paper, a new distributed network-based DCA scheme, known as DCA with interference information, DCA-WI, is proposed and its performance is studied. In this scheme, a base station (BS) assigns a channel in such a way as to minimize the effect on the availability of channels for use in its interfering cells. To accomplish this, each BS maintains an interference information table which contains information about the local cell and its interfering cells. DCA-WI does not require system-wide information. Channel reassignment for new and completed calls are used to further reduce the call blocking probability. Simulation results show that DCA-WI provides a lower call blocking probability compared to other existing schemes in both uniform and nonuniform traffic distributions.     

Dynamic Channel Assignment with Flexible Reuse Partitioning in Cellular Systems

In cellular communications, one of the main research issues is how to achieve optimum system capacity with limited frequency spectrum. For many years, researchers have proposed and studied many dynamic channel assignment (DCA) schemes to increase the capacity of cellular systems. Another proposed technique, Reuse Partitioning (RP), is used to achieve higher capacity by reducing the overall reuse distance. In convention, when RP is exploited in network-based DCA, a portion of channels will be assigned permanently to each partitioned region. However, the number of channels assigned to each region may not be~optimum due to factors like the uneven and time-varying traffics. In this paper, a new network-based DCA scheme is proposed with the flexible use of RP technique, named as flexible dynamic reuse partitioning with interference information (FDRP-WI). In this scheme, channels are open to all incoming calls and no channel pre-allocation for each region is required. As long as the channel assignment satisfies the co-channel interference constraints, any user from any region can use any channel. The scheme aims to minimize the effect of assigned channels on the availability of channels for use in the interfering cells and to reduce overall reuse distance. Both FDRP-WI with stationary users and mobile users are investigated. Simulation results have confirmed the effectiveness of FDRP-WI scheme. In the case with stationary users, FDRP-WI exhibits outstanding performance in improving the system capacity under both uniform and non-uniform traffic distributions. Under the uniform traffic case, the scheme can provide over 100% capacity improvement as compared to conventional fixed channel assignment scheme with 70 system channels at 1% blocking probability. In the case with mobile users, the impact of mobility on the new call probability, P _b, and the call dropping probability, P _d, is evaluated. The effect on system capacity of reserving some channels for handoff calls is first studied. Then, we propose a new handoff scheme, called “Reverse Overflow” (RO), to improve the utilization of channels with smaller reuse distances under mobile environment. Simulation results show that, with RO handoff, the system capacity of FDRP-WI is effectively improved at the expense of higher handoff rates in the cellular system.     

Handover prioritizing scheme for reducing call failure probability in cellular wireless network

This paper proposes a scheme suitable for managing handover in wireless cellular network. The main objective of the proposed scheme is to reduce the probability of forced termination of ongoing call due to handover failure. The scheme employs a queuing discipline, and the priority of queued is based on the residual time of the mobile user in the overlap region between two adjacent cells, assuming that the user's location and speed can be determined, then we applied the ascending priority; it means that the users having a shorter residual time join the head of the queue (i.e., high priority) while those having longer residual time at the end of the queue (i.e., low priority). Fixed channel allocation strategy (FCA) is employed and simulation results obtained concern: call blocking probability (CBP), handover failure probability, and average waiting time in the queue. Also simulation results are compared to those obtained by: non‐prioritized scheme (FCA), and FCA queuing with FIFO discipline. Results show that our proposed method decreases significantly handover failure probability compared with other two schemes. Copyright © 2009 John Wiley & Sons, Ltd.     

A New Distributed Dynamic Channel Assignment Strategy in a Cellular Mobile Communication Network

A distributed dynamic channel assignment (DDCA)plays an important role in a microcellular mobilecommunication network. This paper proposes a new DDCAscheme based on channel priority (PDCA). This new strategy uses the cochannel interference andchannel reuse frequency to define the channel priority.The strategy improves performance of the forced calltermination rate and interference rate applied to multimedia traffic. Simulation results showthat the proposed PDCA strategy significantly improvesthe forced call termination rate and interference ratewhile keeping the blocking rate at an acceptable level.     

Class-Based Service Connectivity Using Multi-level Bandwidth Adaptation in Multimedia Wireless Networks

Due to the fact that quality of service requirements are not very strict for all traffic types, more calls of higher priority can be accommodated by reducing some bandwidth allocation for the bandwidth adaptive calls. The bandwidth adaptation to accept a higher priority call is more than that of a lower priority call. Therefore, the multi-level bandwidth adaptation technique improves the overall forced call termination probability as well as provides priority of the traffic classes in terms of call blocking probability without reducing the bandwidth utilization. We propose a novel bandwidth adaptation model that releases multi-level of bandwidth from the existing multimedia traffic calls. The amount of released bandwidth is decided based on the priority of the requesting traffic calls and the number of existing bandwidth adaptive calls. This prioritization of traffic classes does not reduce the bandwidth utilization. Moreover, our scheme reduces the overall forced call termination probability significantly. The proposed scheme is modeled using the Markov Chain. The numerical results show that the proposed scheme is able to provide negligible handover call dropping probability as well as significantly reduced new call blocking probability of higher priority calls without increasing the overall forced call termination probability.     

Multibeam cellular communication systems with dynamic channel assignment across multiple sectors

In cellular communication systems, directional multibeam antennas at cell sites can be used to reduce cochannel interference, increase frequency reuse and improve system capacity. When combined with dynamic channel assignment (DCA), additional improvement is possible. We propose a multibeam scheme using dynamic channel assignment across multiple sectors. A cell is divided into several sectors, each of which is covered by several directional beams. Specific channels are allocated to each sector as in fixed channel assignment (FCA). A channel of a sector is dynamically assigned to a wireless user who communicates through one of the several beams of the sector. The assignment is made so that constraints on the allowable cochannel interference are satisfied. Limitations due to cochannel interference are analyzed. A tractable analytical model for the proposed scheme is developed using multidimensional birth–death processes. Theoretical traffic performance characteristics such as call blocking probability, forced termination probability, handoff activity, carried traffic and channel rearrangement rate are determined. With the proposed scheme, call blocking probability can be reduced significantly for a fixed offered traffic. Alternatively, system capacity can be increased while blocking probability is maintained below the required level. Smaller forced termination probability is obtainable in comparison with corresponding FCA schemes.     

Prioritized e‐mail servicing to reduce non‐spam delay and loss: A performance analysis

This paper proposes a prioritized e‐mail servicing on e‐mail servers to reduce the delay and loss of non‐spam e‐mails due to queuing. Using a prioritized two‐queue scheme, non‐spam e‐mails are queued in a fast queue and given higher service priority than spam e‐mails that are queued in a slow queue. Four prioritized e‐mail service strategies for the two‐queue scheme are proposed and analyzed. We modeled these four strategies using discrete‐time Markov chain analysis under different e‐mail traffic loads and service capacities. Non‐spam e‐mails can be delivered within a small delay, even under heavy e‐mail loadings and high spam‐to‐non‐spam a priori. Results from our analysis of the two‐queue scheme show that it gives non‐spam delay and loss probability two orders of magnitude smaller than the typical single‐queue approach during heavy spam traffic. Moreover, prioritized e‐mail servicing protects e‐mail servers from spam attacks. Copyright © 2007 John Wiley & Sons, Ltd.     

An innovative channel management strategy for highly reliable handoff in cellular networks

In this paper, we have resolved the problem of forced call termination that occurs when mobile traffic is concentrated on a hot‐spot cell in cellular networks. Enhanced Channel Management Scheme (ECMS) is an innovative way to increase the flexibility of channel usage over non‐uniform traffic distribution. ECMS exploits mobile hosts initiated or active in overlapping areas between cells. The scheme consists of three phases to monitor the status of channels on each base station and to make a channel reservation using the availability list maintained for the candidate‐MH selection. When the traffic load in a cell is intolerably high, ECMS invokes the load‐balancing procedure to distribute its traffic to adjacent cells. The reserved channels are used to support the safe and fast handoff. From the simulation, we observed that ECMS outperformed other compatible channel assignment schemes such as directed handoff schemes in blocking probability and channel utilization. Copyright © 2002 John Wiley & Sons, Ltd.     

Traffic model and performance analysis for cellular mobile radio telephone systems with prioritized and nonprioritized handoff procedures

A traffic model and analysis for cellular mobile radio telephone systems with handoff are described. Three schemes for call traffic handling are considered. One is nonprioritized and two are priority oriented. Fixed channel assignment is considered. In the nonprioritized scheme the base stations make no distinction between new call attempts and handoff attempts. Attempts which find all channels occupied are cleared. In the first priority scheme considered, a fixed number of channels in each cell are reserved exclusively for handoff calls. The second priority scheme employs a similar channel assignment strategy, but, additionally, the queueing of handoff attempts is allowed. Appropriate analytical models and criteria are developed and used to derive performance characteristics. These show, for example, blocking probability, forced termination probability, and fraction of new calls not completed, as functions of pertinent system parameters. General formulas are given and specific numerical results for nominal system parameters are presented.     

A prioritized handoff dynamic channel allocation strategy for PCS

An analytical method is developed to calculate the blocking probability (p_b), the probability of handoff failure (p_h ), the forced termination probability (p_ft), and the probability that a call is not completed (p_nc) for the no priority (NPS) and reserved channel (RCS) schemes for handoff, using fixed channel allocation (FCA) in a microcellular system. Based only on the knowledge of the new call arrival rate, a method of assessing the handoff arrival rate for any kind of traffic is derived. The analytical method is valid for uniform and nonuniform traffic distributions and is verified by computer simulations. An extension (generalization) to the nonuniform compact pattern allocation algorithm is presented as an application of this analysis. Based on this extended concept, a modified version of a dynamic channel allocation strategy (DCA) called compact pattern with maximized channel borrowing (CPMCB) is presented. With modifications, it is shown that CPMCB is a self-adaptive prioritized handoff DCA strategy with enhanced performance that can be exploited in a personal communications service (PCS) environment leading either to a reduction in infrastructure or to an increase in capacity and grade of service. The effect of user mobility on the grade of service is also considered using CPMCB     

基于排队理论的信道分配算法研究

针对蜂窝移动通信系统,基于排队理论提出了一种信道分配方案。该方案将信道分为2部分:语音信道和数据保护信道。预留数据保护信道用于补偿数据丢包率,同时对语音业务设置FIFO排队缓冲器,切换呼叫优先占用缓冲器以确保切换优先。当语音信道空闲时,数据业务可以占用语音信道,一旦有语音呼叫请求到来且无可用语音信道,数据业务应释放占用的语音信道,在数据缓存器中排队等待。仿真结果表明该方案不仅降低了新增呼叫阻塞率和切换掉话率,而且提升了数据业务的性能。     

NACR: A New Adaptive Channel Reservation in Cellular Communication Systems

Future Personal Communication Networks (PCN) will employ microcells and picocells to support a higher capacity, thus increasing the frequency of handoff calls. Forced call terminations due to handoff call blocking are generally more objectionable than new call blocking. The proposed guard channel schemes for radio channel allocation in cellular networks reduce handoff call blocking probability at the expense of increases in new call blocking probability by giving resource access priority to handoff calls over new calls in call admission control. Under uniform traffic assumptions, it has been shown that a fixed number of guard channels leads to good performance results. In a more realistic system, non-uniform traffic conditions should be considered. In this case, the achieved call blocking probability may deviate significantly from the desired objective. In this paper, we propose a new adaptive guard channel scheme: New Adaptive Channel Reservation (NACR). In NACR, for a given period of time, a given number of channels are guarded in each cell for handoff traffic. An approximate analytical model of NACR is presented. Tabu search method has been implemented in order to optimize the grade of service. Discrete event simulations of NACR were run. The effectiveness of the proposed method is emphasized on a complex configuration.     

蜂窝移动通信系统中一种热点业务分配算法

基于提出的最优组合业务量预测模型,对下一时刻的业务量进行预测,从而确定蜂窝系统中业务分布情况,据此将蜂窝小区分成冷点区域和热点区域,并提出一种优化的混合信道分配(OHCA)方案,分析并给出了该方案中动静信道比的定量关系。仿真结果证实了该最优组合预测模型较单一预测方法降低了预测误差、提高了预测精度,同时该优化分配算法较固定信道分配(FCA)和动态信道分配(DCA)方案,有较小的呼阻率和较高的频谱利用率,该策略可用来有效处理热点业务问题,有较好的应用前景。     

系统服务等级约束下提高认知无线网络可达业务负荷的研究

针对现有方案在系统服务等级约束下可能会降低认知无线网络可达业务负荷的问题,提出了一种新的频谱共享机制以提高系统服务等级约束下具有异构业务的认知无线网络可达业务负荷.该机制的主要思想是根据实时业务和非实时业务的不同延时特性,分别引入剥夺优先权和缓冲队列,进而同时减小异构次用户呼叫的强制中断概率和阻塞概率.仿真结果表明,所提机制能有效提高系统服务等级约束下认知无线网络的可达业务负荷.     

Analysis of Cognitive Radio Spectrum Access with Optimal Channel Reservation

A Markov chain analysis for spectrum access in licensed bands for cognitive radios is presented and forced termination probability, blocking probability and traffic throughput are derived. In addition, a channel reservation scheme for cognitive radio spectrum handoff is proposed. This scheme allows the tradeoff between forced termination and blocking according to QoS requirements. Numerical results show that the proposed scheme can greatly reduce forced termination probability at a slight increase in blocking probability     

Analysis of a hybrid cutoff priority scheme for multiple classes of traffic in multimedia wireless networks

In this paper, we propose and analyze the performance of a new handoff scheme called hybrid cutoff priority scheme for wireless networks carrying multimedia traffic. The unique characteristics of this scheme include support for N classes of traffic, each may have different QoS requirements in terms of number of channels needed, holding time of the connection and cutoff priority. The proposed scheme can handle finite buffering for both new calls and handoffs. Futhermore, we take into consideration the departure of new calls due to caller impatience and the dropping of queued handoff calls due to unavailability of channels during the handoff period. The performance indices adopted in the evaluation using the Stochastic Petri Net (SPN) model include new call and handoff blocking probabilities, call forced termination probability, and channel utilization for each type of traffic. Impact on the performance measures by various system parameters such as queue length, traffic input and QoS of different traffic has also been studied. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparison of two novel heuristic dynamic channel allocation techniques in cellular systems

Dynamic channel assignment (DCA) has been discussed in the literature as a way to achieve improved resource management in cellular networks. In the simplest dynamic allocation scheme, all channels are kept in a central pool and are used on a call-by-call basis. DCA is therefore a complex real time operation and various heuristic methods have been devised as mechanisms to give a fast and reliable solution to this problem. This paper examines the implementation of a DCA model using two approaches from the field of evolutionary computation. The first is the so called genetic algorithm (GA) and the second is the combinatorial evolution strategy (CES). Computer simulations evaluate and compare these proposed heuristic DCA schemes concerning their application to a cellular model for both uniform and non-uniform traffic load conditions. © 1998 John Wiley & Sons, Ltd.     

Design aspects of satellite–cellular hybrid wireless systems

In this paper we investigate various issues related to the design of satellite–cellular hybrid systems. First, we review the fundamental problems of channel partitioning and call admission/assignment. Second, we study the impact of different frequency reuse constraints, in both layers, on the optimum channel partitioning. Third, we investigate, analytically and via simulation, the effect of reducing the cell size. We emphasize the blocking‐forced termination probabilities trade‐off for pure cellular and satellite–cellular hybrid systems. Accordingly, an optimization problem with respect to the cell size is formulated. Finally, we search for the optimum dynamic call re‐assignment policy that improves the system capacity at the expense of the complexity associated with tearing down a connection in one system and setting‐up an alternative one in the other system. For a small hybrid system, we characterized the optimum re‐assignment policies that minimize the blocking probability, dropping probability, and a weighted cost function of these probabilities. Copyright © 2002 John Wiley & Sons, Ltd.     

Non‐preemptive Queueing Model of Spectrum Handoff Scheme Based on Prioritized Data Traffic in Cognitive Wireless Networks

In this study, a non‐preemptive M/G/1 queueing model of a spectrum handoff scheme for cognitive wireless networks is proposed. Because spectrum handoff gives secondary users an opportunity to carry on their transmissions, it is crucially important to determine the actions of primary users. In our queueing model, prioritized data traffic is utilized to meet the requirements of the secondary users. These users’ packets are categorized into three different priority classes: urgent, real‐time, and non‐real time. Urgent data packets have the highest priority, while non‐real time data packets have the lowest priority. Riverbed (OPNET) Modeler simulation software was used to simulate both reactive and proactive decision spectrum handoff schemes. The simulation results were consistent with the analytical results obtained under different load and traffic conditions. This study also revealed that the cumulative number of handoffs can be drastically decreased by exploiting priority classes and utilizing a decent spectrum handoff strategy, such as a reactive or proactive decision‐based strategy.     

Performance analysis and overflowed traffic characterization in multiservice hierarchical wireless networks

A cellular hierarchical network with heterogeneous traffic is considered, where calls with shorter (longer) average call-holding time are assigned to the associated lower (upper) layer. The main contribution of this paper is that an efficient and reasonably accurate analytical method is proposed to calculate performance measures of interest, i.e., new call-blocking probability and forced termination probability for conversational services, new call-blocking probability, forced termination probability, and the average number of assigned time slots for streaming services. In particular, a simple two-state MMPP/sup (1,2,...,K)/, that takes into account not only the dependence among overflowed calls of the same class but also the correlation among overflowed calls of different classes, is used to approximate overflowed traffic to reduce computational complexity and improve accuracy. The methods with the multiclass overflowed traffic being approximated as independent Poisson processes and interrupted Poisson processes are also conducted for comparison. Importantly, it is shown via simulation results that the proposed model generates more accurate results than those obtained with the other two approximation methods. Last but not least, the effect of nonuniform traffic density on performance measures is studied via simulation. It is shown that the nonuniform traffic density may have a significant impact on the performance.