GEO卫星移动通信系统信道分配策略研究

根据移动终端越区切换的物理过程,结合GEO系统的特点,建立移动终端运动的数学模型,将地面移动通信系统的无优先权、预留信道和排队方案3种信道分配方案应用于GEO系统,进行仿真分析。仿真结果表明,预留信道方案虽然能够降低切换呼损率,但却增加了初始呼叫呼损率;排队混合方案在取得与预留信道方案同样的切换呼损率时,可以获得更低的初始呼叫呼损率,排队混合方案优于预留信道方案。     

机会频谱接入系统的切换请求排队机制及性能分析

针对非实时业务的特点,该文提出了机会频谱接入系统的两种切换请求排队方案,并采用二维Markov模型对其性能进行了建模分析,得到了呼叫阻塞率、强制中断率、信道利用率等系统性能关键参数的解析结果。数值结果分析表明,提出的两种切换请求排队方案是降低系统强制中断率的有效方法,且可克服切换信道预留机制阻塞率高、信道利用率低的缺点,信道利用率最多可提高26%。仿真实验验证了理论分析的正确性。     

A MAC Protocol for New and Handoff Calls with Finite Population

A MAC protocol for new and handoff calls with a finite populationof users, rather than with an infinite user population as indynamic channel reservation scheme (DCRS), is considered. Similarto DCRS, we divide the wireless channels into shared channels andreserved channels. The handoff calls access any available channelwith probability of one, while the new calls access a sharedchannel with probability of one and access a reserved channel witha request probability. We propose three simpler formulae than thatused in the existing DCRS in setting the request probability. Inaddition, the handoff calls in our proposed protocol are allowedto queue in a finite buffer. To evaluate the system performance, amathematical model based on queuing theory, rather than asimulation method used in DCRS, is developed. It is a generalmodel that can be adopted for any types of request probabilitiesincluding DCRS. Suggestions of how to get the optimum values ofthe design parameters are also given.     

Performance analysis of a preemptive and priority reservation handoff scheme for integrated service-based wireless mobile networks

We propose an analytical model for integrated real-time and non-real-time services in a wireless mobile network with priority reservation and preemptive priority handoff schemes. We categorize the service calls into four different types, namely, real-time and non-real-time service originating calls, and real-time and non real-time handoff service request calls. Accordingly, the channels in each cell are divided into three parts: one is for real-time service calls only, the second is for non-real-time service calls only, and the last one is for overflow of handoff requests that cannot be served in the first two parts. In the third group, several channels are reserved exclusively for real-time service handoffs so that higher priority can be given to them. In addition, a realtime service handoff request has the right to preempt non-real-time service in the preemptive priority handoff scheme if no free channels are available, while the interrupted non-real-time service call returns to its handoff request queue. The system is modeled using a multidimensional Markov chain and a numerical analysis is presented to estimate blocking probabilities of originating calls, forced termination probability, and average transmission delay. This scheme is also simulated under different call holding time and cell dwell time distributions. It is observed that the simulation results closely match the analytical model. Our scheme significantly reduces the forced termination probability of real-time service calls. The probability of packet loss of non-real-time transmission is shown to be negligibly small, as a non-real-time service handoff request in waiting can be transferred from the queue of the current base station to another one.     

Fractional channel reservation in mobile communication systems

A fractional channel reservation scheme is proposed. In conventional channel reservation schemes, the number of channels reserved for handoff calls has always been an integer. The proposed fractional channel reservation algorithm can be used to finely control the communication service quality. By varying the number of reserved channels for handoff calls by fractions of one     

Performance Evaluation and Resource Management of Hierarchical MACRO-/MICRO Cellular Networks using MOSEL-2

The paper presents a performance evaluation and resource management of hierarchical MACRO-/MICRO cellular networks using the new Modeling and Evaluation Language (MOSEL-2). MOSEL-2 with new constructs has the ability to find the performance and reliability modeling and evaluation of systems with exponential and non-exponential distributions. A MACRO/MICRO cell structure is solved numerically and mathematically in this paper to handle the handoff calls. Additionally, a simulation program is written to validate these results. In order to reduce the loss probability, a guard channels are introduced at the MICRO cell and channel reservation at the MACRO cell. Additionally, the concept of queuing is introduced where there is a possibility for the handoff calls from both MACRO and MICRO layers to be queued when all the resources are occupied. MOSEL-2 is used to find the numerical solution for this problem with both exponential and general exponential (GE) distribution. The performance analysis show the efficiency of the proposed scheme to manage the handoff calls and the ability of the suggested scheme to reduce the blocking probability of handover calls and the loss probability as the main objective is to block the new connection rather than terminating the ongoing connection as well as balancing the load all over the whole network. It is shown in this paper that there are a set of important factors that affect the performance, such as: reservation policy, channel allocation, handover ratio, capacity of the queue and the variation of the inter-arrival times. These factors are discussed via some important performance measures, such as: new call blocking probability, blocking probability of handover calls, loss probability, utilization and the average delay of the queue.     

基于信道借用和信号预测的切换方法

随着业务需求的日益增长,蜂窝也越变越小,移动蜂窝通信环境中的切换成为日益重要的问题。在CDMA蜂窝系统中使用软切换,为了解决切换时的信道短缺问题,提出了许多解决方法。该文中提出了称为基于信道借用和信号预测的切换算法。当切换请求到达蜂窝时,如果没有空闲信道,就将从参与软切换的静止呼叫借用一信道,并将借用的信道分配给移动呼叫的切换请求.如果没有信道可借用,就将切换请求放入队列中,使用信号预测的方法来确定队列中的优先级。并将此切换方式的性能与其它切换方式进行了比较。     

Adaptive channel reservation scheme for soft handoff in DS-CDMAcellular systems

Soft handoff techniques in direct-sequence code-division multiple-access (DS-CDMA) systems provide mobile calls with seamless connections between adjacent cells. Channel reservation schemes are used to give high priority to more important soft handoff attempts over new call attempts. However, since the number of soft handoff attempts varies according to environmental conditions, fixed reservation schemes for handoff attempts can be inefficient. An adaptive channel reservation scheme is herein proposed to control the size of reservation capacity according to varying the number of soft handoff attempts. The proposed scheme also includes a balancing procedure between soft handoff failure and new call blocking to maximize the system capacity. To evaluate the performance of the proposed scheme, a Markovian model is developed that considers the interference-limited capacity effect of DS-CDMA systems. The analytical result shows that the proposed scheme yields a considerable enhancement in terms of new call blocking and soft handoff failure probabilities when compared with the conventional fixed channel reservation scheme     

Channel assignment for initial and handoff calls to improve the call-completion probability

The paper focuses on how to assign channels for initial and handoff calls. Previous schemes give priority to handoff calls by queuing handoff calls, reserving some channels for handoff calls, or subrating existing calls for handoff calls. We queue both initial and handoff calls. We take this idea from derivations of the optimal value for an approximation to the call-completion probability. Our goal is to have higher call-completion probability and still keep forced-termination probability low. We propose four schemes: SFTT (single-queue, FIFO, timeout, average timeout), SPTT (single-queue, priority, timeout, average timeout), DFTS (dual-queues, FIFO, timeout, statistical TDM), and DPTS (dual-queues, priority, timeout, statistical TDM). The four schemes, along with the NPS and FIFO schemes, were simulated and compared. For the SFTT scheme, we also simulated different average timeouts for initial calls. All four proposed schemes have better call-completion probabilities than the NPS and FIFO schemes. Call-completion probabilities can be improved by implementing a priority scheme which serves the waiting call with the least remaining time first. The implementation of statistical multiplexing also has the effect of increasing call-completion probability when the average new-call arrival rates are high. However, both the priority scheme and statistical multiplexing may increase forced-termination probability.     

Predictive schemes for handoff prioritization in cellular networksbased on mobile positioning

We propose and evaluate new schemes for channel reservation motivated by the rapidly evolving technology of mobile positioning. The schemes, called predictive channel reservation (PCR), work by sending reservation requests to neighboring cells based on extrapolating the motion of mobile stations (MSs). A number of design enhancements are incorporated to minimize the effect of false reservations and to improve the throughput of the cellular system. These enhancements include: (1) reservation pooling; (2) queuing of reservation requests; (3) hybrid approach for integrating guard channels (GCs); and (4) using a threshold distance (TD) to control the timing of reservation requests. The design enhancements have produced a set of highly efficient schemes that achieve significant reduction in handoff blocking rates while only incurring remarkably small increases in the new call blocking rates. The PCR approach has also been used to solve the MINBLOCK optimization problem and has given significant improvement over the fractional guard channel (FGC) protocol. Detailed performance results of the different variations of the PCR scheme and comparisons with conventional channel reservation schemes are presented. An analytical Markov model for the hybrid predictive version of the scheme is developed and its applicability and numerical results are discussed     

Performance analysis of channel-borrowing handoff scheme based onuser mobility in CDMA cellular systems

Code-division multiple-access (CDMA) cellular systems use soft handoff. Although the capacity of CDMA systems is interference-limited in nature, channel shortages may occur because soft handoff uses several channels simultaneously. To cope with this problem, we propose an improved handoff method that borrows channels from stationary calls participating in soft handoff and allocates the borrowed channels to handoff requests by moving calls when a channel shortage occurs. Borrowing from stationary calls is possible because these calls do not undergo fast-fading and do not require receiver diversity. The proposed method is designed to avoid increased interference resulting from channel borrowing. The proposed channel-burrowing handoff scheme is analyzed in a situation involving both moving and stationary calls. A comparison is made between the performances of the typical IS-95-based handoff scheme and the proposed scheme. Numerical results show that the proposed scheme is better than the IS-95 scheme in view of the handoff refused probability, the handoff queuing delay, and total interference     

Dynamic channel reservation based on mobility in wireless ATMnetworks

We present a dynamic channel reservation scheme to improve the utilization of wireless network resources while guaranteeing the required QoS of handoff calls. The wireless channels are dynamically reserved by using the request probability determined by the mobility characteristics and channel occupancy to guarantee acceptable quality of handoff calls and keep the new call blocking probability as low as possible     

A Dynamic Reservation-Based Call Admission Control Algorithm for Wireless Networks Using the Concept of Influence Curve

In this paper a dynamic channel reservation and call admission control scheme is proposed to provide QoS guarantees in a mobile wireless network using the concept of influence curve. The basic idea behind the proposed scheme is that a moving user, in addition to its requirements in the current cell, exerts some influence on the channel allocation in neighboring cells. Such an influence is related to the moving pattern of the users and is calculated statistically. Furthermore we developed a general analytical model to calculate the corresponding blocking probabilities for wireless networks with multiple platforms, which removes the commonly used assumption that new calls and handoff calls have same channel holding time. The numerical results demonstrate that our scheme outperforms traditional channel reservation schemes and can effectively adapt to the real time network conditions.     

A mathematical model for wireless channel allocation and handoff schemes

A mathematical model for analytical study on complete and partial channel allocation schemes is presented in this paper. Expression for the queue length distribution has been analytically derived. The mathematical model can be used for analysis of multiple call categories like new calls, handoff calls, delay tolerant or delay sensitive calls. This adaptive mathematical model can be utilized to design optimal channel allocation algorithms, or even test the already established resource allocation schemes for provisioning of Quality-of-Service to enable the usage of real time mobile applications. Most existing studies depend upon simulation experiments to investigate the performance of their proposed algorithms, but the mathematical model presented here can really help to evaluate such proposals from an analytical perspective.     

Performance evaluation of hierarchical cellular CDMA networks with soft handoff queueing

We consider hierarchical cellular code-division multiple-access networks supporting soft handoff, where users with different mobility are assigned to different layers, i.e., microcells in the lower layer are used to carry slow users, whereas macrocells in the upper layer are for fast users, and handoff queues are provided for handoff calls that cannot obtain the required channel immediately, so that forced termination probability can be reduced. According to whether handoff queues are provided in microcells and/or macrocells, four different call admission control schemes are proposed and studied. We derive the mathematical model of the considered system with multidimensional birth-death process and utilize Gauss-Seidel iterative method to find the steady-state probability distribution and thus the performance measures of interest: new call blocking probability, handoff failure probability, and forced termination probability. Analytical results show that providing handoff queues in both microcells and macrocells can achieve largest performance improvement. Furthermore, handoff queue size greater than a threshold is shown to have little effect on performance measures of interest. Last but not least, the studied two-tier system is compared with a one-tier counterpart. It is shown that the two-tier system performs better in terms of average number of handoffs per fast call.     

Dynamic connection rerouting and wired‐resource reservation scheme on ATM‐based PCN

In this paper, we propose a connection rerouting and dynamic resource reservation scheme for fast inter-switch handoffs on ATM-based personal communications networks. The proposed rerouting and reservation scheme can reduce the delay in connection rerouting by reserving VPI/VCIs for possible inter-switch handoff calls in advance. It also improves the utilization of wired resources by reserving statistically the wired resources in separate ways according to the classes (i.e., real-time vs. non-real-time traffic) of possible inter-switch handoff calls. Our simulation results show that the proposed scheme can decrease the dropping rate of inter-switch handoff calls without the sacrifice of the blocking probability of new calls and, moreover, can flexibly cope with the time-variant environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Teletraffic performance evaluation of microcellular personalcommunication networks (PCN's) with prioritized handoff procedures

Evaluates four handoff priority-oriented channel allocation schemes. These give priority to handoff calls by reserving channels exclusively for handoff calls. The measurement-based handover channel adaptive reassignment scheme (MHAR-A) exclusively uses reserved handover channels for newly originated calls if a certain criterion is satisfied. All four schemes studied differ from the conventional guard channel-based handover priority-oriented channel allocation scheme. To study the schemes, a personal communication network (PCN) based on city street microcells is considered. A teletraffic simulation model accommodating a fast moving vehicle is developed, and the performance parameters are obtained. The performances of all four schemes are compared with the nonpriority scheme and the conventional guard channel-based handover priority-oriented channel allocation scheme. It was found that some of the channel allocation algorithms studied improved the teletraffic capacity over the nonpriority and the conventional guard case. Also, the probability of new call blocking and carried traffic was improved for three of the schemes when compared to the conventional guard scheme. The MHAR-A scheme did not perform up to expectation. Nevertheless, it can be used to finely control the communication service quality equivalent to the control obtained by varying the number of handoff channels in a fraction of one. Increasing the number of reserved handover channels in fraction of one can never be achieved in the conventional guard channel-based handover priority-oriented channel allocation scheme     

多载波蜂窝移动通信系统中的多业务切换算法

提出一种用于多载波蜂窝移动通信系统的子信道合并切换算法。采用多维Markov链对子信道合并切换算法进行系统建模分析,得到了呼叫阻塞率、切换阻塞率等关键系统性能参数的解析结果。与切换保护信道算法相比,子信道合并切换算法在对其他类型呼叫性能影响很小的前提下,改善了对带宽要求较高的业务的切换性能。该算法还可以与其他资源预留切换算法相结合,改善其性能。     

A Predictive Bandwidth Reservation Scheme Using Mobile Positioning and Road Topology Information

In cellular networks, an important practical issue is how to limit the handoff dropping probability efficiently. One possible approach is to perform dynamic bandwidth reservation based on mobility predictions. With the rapid advances in mobile positioning technology, and the widespread availability of digital road maps previously designed for navigational devices, we propose a predictive bandwidth reservation scheme built upon these timely opportunities. In contrast to the common practice of utilizing only incoming handoff predictions at each cell to compute the reservations, our scheme is more efficient as it innovatively utilizes both incoming and outgoing handoff predictions; it can meet the same target handoff dropping probability by blocking fewer new calls. The individual base stations are responsible for the computations, which are shown to be simple enough to be performed in real-time. We evaluate the scheme via simulation, along with five other schemes for comparison. Simulation results show that those schemes that rely on positioning information are significantly more efficient than those that do not. Our scheme's additional use of the road topology information further improves upon this advantage, bringing the efficiency closer to the bound set by a benchmark scheme that assumes perfect knowledge about future handoffs.     

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.