一种改进的无线信道分配策略分析

随着GSM／GPRS移动接入网的广泛应用．有效的信道分配策略在保证网络服务质量中的重要性开始凸现。针对GSM／GPRS网络存在无线资源使用率和信道利用率低的局限性,在GSM／GPRS网络现有的资源分配策略基础上,提出一种改进的资源分配策略。数值结果表明,该新策略能很好地降低语音呼叫阻塞率,减少GPRS包平均传输时间。提高信道利用率．     

一种新的基于多业务的移动通信系统切换策略

针对目前移动通信系统大部分信道切换策略中新呼叫阻塞率高的问题,提出了一种新的呼叫延迟切换策略,该策略是让即将占用最后一个空闲信道的新呼叫短暂延迟后再占用空闲信道,切换呼叫则直接占用空闲信道,缩短了信道被全部占用的时间,增加了新呼叫和切换呼叫占用信道的机会。该策略同时考虑了数据业务之间的优先级,只有当高优先级数据队列中的数据包为空时,低优先级队列中的数据包才能够占用信道。给出了切换呼叫掉话率、新呼叫阻塞率及数据包掉包率的理论公式。与预留信道策略和可移动边界策略的对比表明,新策略既提高了新呼叫进入系统的概率,又有效降低了切换呼叫的掉话率,同时也减少了高优先级数据的掉包率。     

一种基于TCRA的低轨星座通信系统的强占预留信道策略

在基于时间信道预留算法的基础上,提出了一种改进的低轨星座通信系统信道分配策略——强占预留信道策略。讨论了策略的基本原理,并通过仿真,比较分析了该策略与 TCRA 和固定信道预留策略对系统新呼叫阻塞概率、切换失败概率和服务等级的影响。仿真结果表明,与 TCRA 策略相比,该策略有效降低了新呼叫阻塞,同时为网络提供更好的 QoS 保证。     

LEO卫星中模拟实时通信量确保保护信道的分配

由于LEO（Low Earth Orbit）卫星网络中不断变化的点波束小区实时通信量负载无法估计,提出了一种根据系统仿真过程中当前通信量状态优化动态保护信道算法（ODGCS）。该分配策略引入呼叫间隔时间和切换呼叫中断间隔时间来获悉系统的实时性能状态,由仿真中通信量状态预测当前系统切换呼叫的中断概率,根据比较计算的呼叫中断概率和预先设定的QoS（Quality of Service）值,动态调整预留给切换呼叫使用的保护信道数。仿真结果表明,与传统的静态预留保护信道的算法相比,该算法能有效提高LEO卫星系统的性能稳定性。在负载较轻时,ODGCS算法保证切换呼叫QoS的同时,降低了新呼叫阻塞概率。     

IEEE802.16中基于自适应信道预留的呼叫接入策略

呼叫接入控制（CAC）在宽带无线接入（BWA）服务质量（QoS）中起着非常重要的作用。对无线城域网中IEEE802.16复杂的QoS定义,该文提出了一种在IEEE802.16中基于自适应资源预留的呼叫接入控制策略（AR-CAC）。该策略根据UGS负载和信道利用率为其自适应预留信道,同时考虑了IEEE802.16业务的带宽特性。仿真结果表明,该策略在硬切换呼叫切换失败概率不变的情况下降低了高优先级服务的呼叫阻塞率,同时增大了系统的吞吐量。     

WLAN与蜂窝混合网络有效的信道切换策略

针对无线局域网WLAN(Wireless Local Area Network)与蜂窝混合网络,提出一种具有抢占蜂窝网络信道的切换策略。当使用蜂窝信道的终端移入WLAN覆盖区域时,只有在该终端所使用的信道被抢占时,该机制才进行垂直切换以减少因切换造成的时延与丢包;建立了该切换策略的三维马尔可夫模型,分析了WLAN网络的终端数、蜂窝信道的利用率、信道接入请求阻塞率、信道抢占率与信道被抢占率的性能。详细的仿真结果证明了提出的模型的有效性,当WLAN覆盖面积比例为0.2时,信道抢占概率最大;当终端移动速度达到100km/h时,信道被抢占的概率是移动速度为20km/h的3倍;提出的信道切换策略与随机切换策略相比,显著地降低了业务的丢包率与传输时延。     

基于预留信道机制的CR频谱切换描述及改进

利用IEEE 802.22标准草案中的预留信道机制,分析和描述认知无线电的3种基本频谱切换方案。针对预留信道机制以牺牲新呼阻塞率换取较低切换阻塞率的不足,提出对新呼用户进行排队缓冲的方法,并利用二维马尔可夫模型和排队理论,给出其状态转移图。仿真结果表明,该方法在保证切换性能的条件下,能有效降低新呼阻塞率,并使GoA值大幅下降。     

GEO卫星通信系统中MF-TDMA信道分配算法研究

提出了GEO卫星通信系统中MF-TDMA信道分配算法C-BFD。与传统信道资源分配算法相比,C-BFD采用了基于优先组合的方式,利用用户信道请求大小以及信道结构的特点,通过分配过程中对用户信道请求进行组合并优先分配,来减少时隙碎片的产生。仿真结果表明,该算法能够有效降低系统阻塞率以及信道碎片对系统资源利用率的负面影响。     

蜂窝网中基于分布式约束满足算法的改进信道分配

随着蜂窝网业务需求的不断增长,如何利用有限的信道资源在各小区间进行复用,以便既能避免移动用户之间的干扰,又能满足所有移动用户的话务请求,使蜂窝系统容量大大增加,已成为一项重要研究课题。此类问题属于NP-hard的信道分配问题(Channel Assignment Problem,CAP),将CAP问题形式化为分布式约束满足问题(DC-SP),然后提出基于改进现有的信道分配策略,以获得更高的信道利用率、较令人满意的系统服务质量,尽可能满足所有用户的话务请求。将利用尽可能简单、搜寻时间短的算法,并将现有的benchmark问题进行仿真。实验表明,该方案对有效改进信道分配问题,充分利用有限的信道资源,降低系统的阻塞率,有着较好的应用前景。     

OFDMA系统中的多业务接入控制算法

提出一种针对分析正交频分多址接入(OFDMA)系统的改进多业务接入控制算法。OFDMA系统为用户提供一定数量的子载波进行传输,通过压缩原信道带宽或传输速率,降低原信道上的业务服务质量,从而提高小区内可使用的信道数量。仿真结果表明,与传统信道预留算法相比,该算法可提高信道资源利用率,降低目标小区的切换呼叫阻塞率和新呼叫阻塞率。     

Performance analysis of wireless mobile networks with queueing priority and guard channels

The blocking probability of originating calls and forced termination probability of handoff calls are important criteria in performance evaluation of integrated wireless mobile communication networks. In this paper, we model call traffic in a single cell in an integrated voice/data wireless mobile network by a finite buffer queueing system with queueing priority and guard channels. We categorize calls into three types of service classes: originating voice calls, handoff voice calls and data calls. The arrival streams of calls are mutually independent Poisson processes, and channel holding times are exponentially distributed with different means. We describe the behavior of the system by a three‐dimensional continuous‐time Markov process and present the explicit expression for steady‐state distribution of queue lengths using a recursive approach. Furthermore, we calculate the blocking, forced termination probabilities and derive the Laplace–Stieltjes transform of the stationary distribution of actual waiting times and their arbitrary kth moment. Finally, we give some numerical results and discuss the optimization problem for the number of guard channels.     

LEO卫星通信系统中信道分配策略仿真

切换是LEO卫星移动通信系统中移动性管理的一个重要组成部分。LEO切换中的信道分配一般采用保护信道和各种排队方法相结合的策略。研究了多业务条件下LEO卫星通信系统越区切换中的信道分配策略，根据数据业务和话音业务的特点，提出了适用于LEO卫星通信系统的保护信道和强占优先相结合的信道分配策略。建立了一个简单而有效的LEO卫星通信系统切换模型，将新策略与传统的保护信道策略进行比较，仿真结果表明新策略以略微增加数据时延为代价换取了话音业务各项性能的极大改善。     

基于多业务的移动通信系统呼叫接入控制

针对在可移动边界保护信道方法中新呼叫堵塞率高的问题,提出一种呼叫接入控制策略。当切换呼叫的掉话率小于门限时,新呼叫以一定的概率使用为切换呼叫预留的保护信道。当高优先级数据等待队列中的数据包为空时,传输普通数据等待队列中的数据包。仿真结果表明,在对切换呼叫掉话率影响较小的前提下,该策略能够有效降低新呼叫的堵塞率和高优先级数据的掉包率。     

An adaptive call admission algorithm for cellular networks

In this paper, we first propose a new continuous action-set learning automaton and theoretically study its convergence properties and show that it converges to the optimal action. Then we give an adaptive and autonomous call admission algorithm for cellular mobile networks, which uses the proposed learning automaton to minimize the blocking probability of the new calls subject to the constraint on the dropping probability of the handoff calls. The simulation results show that the performance of the proposed algorithm is close to the performance of the limited fractional guard channel algorithm for which we need to know all the traffic parameters in advance.     

Dynamically adaptive channel reservation scheme for cellular networks

In personal communications networks (PCN) supporting network-wide handoffs, new and handoff requests compete for connection resources in both mobile and backbone networks. Forced call terminations due to handoff call blocking are generally more objectionable than new call blocking. In general, most of the previously proposed schemes for radio channel allocation in cellular networks reduce handoff call blocking probability substantially at the expense of increasing the new call blocking probability by giving higher priority to handoff calls over new calls in admission control. This reduces the total admitted traffic and results in inefficient utilization of wireless channels. The tradeoff between the new and handoff calls blocking probabilities should be defined on importance basis. In this paper, we propose a performance metric equation that makes a trade off between the two probabilities depending on the network preferences. Using this equation, we study the performance of various proposed channel reservation schemes. Also in this paper, a new dynamically adaptive channel reservation scheme (DACRS) is developed and compared with other schemes proposed in the literature. The DACRS assigns handoff-reserved channels to new calls depending on the locality principle in which the base station with the help of location estimation algorithms in the mobile location center predicts the position of the mobile terminal. Eventually, the DACRS is designed to improve channel utilization while satisfying the QoS of the calls. As will be shown analytically and through simulation, the DACRS outperforms current reservation schemes and results in more statistical gain, and powerful channel utilization.     

QoS-aware radio resource management scheme for CDMA cellular networks based on dynamic interference guard margin (IGM)

Efficient radio resource management (RRM) for CDMA-based cellular communication systems using the interference guard margin (IGM) scheme is investigated in this work. Two important concepts, i.e., the guard channel (GC) and the load curve (LC), are integrated to derive IGM. The resulting call admission control (CAC) scheme gives preferential treatment to higher priority handoff calls by pre-reserving a certain amount of resource in terms of IGM. A radio resource estimation (RRE) function is implemented in each base station (BS) to assist RRM module to adjust the level of IGM dynamically. RRE in each BS estimates the amount of IGM by considering traffic load in its current cell as well as traffic conditions in neighboring cells. A service model is adopted to support quality of service (QoS) demand of multiple services, which includes mobile terminal’s data rate, different levels of priorities, mobility and rate adaptivity characteristics. Simulations are conducted by OPNET to study performance of the proposed IGM scheme in terms of a defined cost function, new call blocking probability, handoff dropping probability and system utilization, under different traffic conditions.