一种滞后控制的马尔可夫链计算方法

提出了一种带有滞后控制结构的马尔可夫链状态概率及应用中相关性能参数的数学计算方法。根据马尔可夫归一化特性,分解马尔可夫链状态图,先计算整体简化状态,再计算局部状态,最后推导出整个马尔可夫链状态概率的计算公式。带滞后控制结构的马尔可夫链在各个领域都有非常广泛的应用,以它在低轨道卫星通信中信道资源的分配模型为例,通过比较模拟仿真的各个性能参数值和计算所得参数值,验证了提出的马尔可夫链分解计算方法的正确性。     

低复杂度的图像信源-信道联合译码算法

该文提出将图像编码后残留冗余的马尔可夫场模型分解为4个方向的马尔可夫链,并结合简化的模型及低密度奇偶校验码(LDPC)译码的软输出进行信源-信道联合译码。将分解后信源中多个方向上同时存在的相关性看作一种特殊的天然信道编码方式,利用前向-后向算法、和积算法以及信道译码软输出分别对信源符号进行串行和并行的译码。仿真实验表明,与传统利用马尔可夫场模型的联合译码算法相比,该联合译码算法降低了复杂度,同时提高了重建图像的峰值信噪比。     

GPRS在 GSM无线网络中的应用技术研究(上)

首先简要介绍GPRS的基本工作原理和系统构造方法，然后详细分析GPRS在GSM无线网络中应用的关键技术，涉及GPRS移动台的控制机理、GPRS的逻辑信道及网络工作模式、GPRS编码方案及相应的C／I要求、GPRS的话务模型、GPRS的业务信道设置方法、GPRS的频率规划、GPRS对GSM网络容量的影响和GPRS对GSM网络质量的影响等各方面的技术。     

蜂窝网越区切换方案的研究

论文对无信道预约优先的模型、具有信道预约优先的模型、信道预约优先和排队优先相结合的切换模型，以及支持话音和数据多业务的切换模型等几种典型的越区切换模型进行了研究概括。分别对其系统模型进行描述，用马尔可夫进行数学建模。最后，研究了支持多业务的具有复合优先权的越区切换策略，比较了现有文献的特点，提出了今后的工作方向。     

随机预约式一点多址通信系统性能分析

采用稳定点分析方法对一点多址通信系统的随机预约信道进行了理论分析,计算出预约信道的吞吐量。用马尔可夫链理论,对通信系统的数据信号的通信量和信道利用率进行了分析,给出了计算结果.     

一种基于信道预测的FGS视频信源信道联合编码新方法

提出一种基于信道预测的无线FGS视频信源信道联合编码的新方法。该方法利用马尔可夫链对无线信道进行预测，针对FGS分级编码视频流的优先级差异，提供非均匀FEC信道编码保护，根据信道预测的结果，调整视频传输的时隙位置，优化信道编码效率，使得视频在无线传输过程中所需要的数据量最小，同时满足用户的失真要求。实验结果证明了该方法的有效性。     

多带UWB优先级竞争接入饱和吞吐量优化方法

采用二维马尔可夫链模型,计入了超帧中的标记期和硬预留,对系统中的同一优先级竞争接入站点在差错信道下的饱和吞吐量进行研究。分析表明,信道质量较差时短帧比长帧的系统饱和吞吐量大。理论计算结果与NS2软件仿真结果在误差范围内相一致。差错信道条件下存在最优传输帧长,为优化链路控制,提高系统吞吐量提供了理论依据。     

相关衰落信道下的一种层间联合自适应SR-ARQ传输机制

传统自适应传输机制在相关慢衰落信道下有较差的系统性能.针对相关衰落信道,提出了一种层间联合自适应传输机制.利用有限状态马尔可夫链来描述相关衰落信道,同时通过构建一个多状态马尔可夫系统模型来分析系统吞吐性能,并对调制方式和传输分组大小进行优化.另外,推导了系统平均吞吐性能的表达式.仿真结果显示所提出的自适应传输机制在相关衰落信道上能获得更好的系统性能.     

基于IEEE 802.11的多信道多址接入协议性能分析

 本文对一种基于IEEE 802.11 DCF协议多信道多址接入方案的性能进行了分析,在该接入方案中,节点在公共的控制信道上预约数据信道,随后在预约成功的数据信道上,进行数据分组的传输.本文采用马尔科夫链构建了控制信道的预约模型,给出了多信道吞吐量的理论分析算法.最后,通过仿真验证了理论分析结果与仿真结果的一致性,并给出了信道吞吐量与信道数、数据分组长度、节点密度、信道切换时延等参数之间的数值关系.     

基于IEEE 802.11的多信道多址接人协议性能分析

本文对一种基于IEEE802.11 DCF协议多信道多址接入方案的性能进行了分析,在该接入方案中,节点在公共的控制信道上预约数据信道,随后在预约成功的数据信道上,进行数据分组的传输.本文采用马尔科夫链构建了控制信道的预约模型,给出了多信道吞吐量的理论分析算法.最后,通过仿真验证了理论分析结果与仿真结果的一致性,并给出了信道吞吐量与信道数、数据分组长度、节点密度、信道切换时延等参数之间的数值关系.     

Performance evaluation of a reservation random access scheme for packetized wireless systems with call control and hand-off loading

We consider a packet switched wireless network where each cell's communication channel is shared among packet voice sources. In this paper, we present a method for the design and analysis of wireless cells using a reservation random access (RRA) scheme for packet access control. This scheme is integrated with a call admission control procedure. We model the state process of a single cell as a vector Markov chain. We compute the steady state distribution of the Markov chain. This result is used to calculate the packet dropping probability and the call blocking probability. By setting limits on maximum permissible levels for the call blocking probability and the packet dropping probability, we obtain the Erlang capacity of a single cell, with and without hand-off traffic. For an illustrative RRA scheme, the Erlang capacity of a single cell is shown to be about twice that attained by a comparable fixed assigned TDMA scheme. We show that a cellular network using this RRA scheme and which applies can be no blocking of hand-off calls, exhibits similar call capacity levels.This work is supported by a University of California MICRO and Pacific-Bell Grant No. 94-107.     

多业务移动通信系统中的呼叫接入控制

在多业务无线移动通信系统的呼叫接入控制中,不仅要考虑业务之间的优先级,同时也必须考虑切换呼叫的优先级。本文结合可移动边界算法和保护信道策略,提出了一种有效的多业务呼叫接入控制算法。为了方便地分析方案的性能,设计了一个二维的Markov链对方案的性能进行理论上的分析。通过数值分析结果表明,提出的算法同时保证了两种优先级,并提高了系统的性能。1     

Modeling of customer retrial phenomenon in cellular mobile networks

In the planning of modern cellular mobile communication systems, the impact of customer behavior has to be carefully taken into account. Two models dealing with the call retrial phenomenon are presented. The first model considers a base station with a finite customer population and repeated attempts. A Markov chain modeling is proposed, and an efficient recursive solution of the state probabilities is presented. The second model focuses on the use of the guard channel concept to prioritize the handover traffic. Again, the retrial phenomenon plays an important role. The influence of the repeated attempt effect on the quality of service experienced by the mobile customers is discussed by means of numerical results     

Call Admission Control in Satellite Networks under Rain Fading

A new call admission control scheme for satellite networks operating at frequencies above 10 GHz is proposed. The major factor impairing the link performance at these frequencies is rain attenuation, a physical phenomenon exhibiting both spatial and temporal variation. Exploiting the predictability of the satellite channel, a new call is accepted provided that there are sufficient resources for existing and new users to guarantee QoS. The performance of the proposed scheme is investigated using Markov chain analysis. Finally, the upper bound of the call blocking probability is determined.     

Enhancement to IEEE 802.11 Distributed Coordination Function to Reduce Packet Retransmissions Under Imperfect Channel Conditions

In this paper, we provide an extended model for analytical analysis of IEEE 802.11 wireless local area networks under noisy wireless channel. A reservation stage is introduced in the Markov chain model to reduce unnecessary retransmissions in the case of transmission failure due to channel error. A lot of work has been carried out to enhance the performance of 802.11 distributed coordination function in the error free channel. Throughput enhancement of 802.11 medium access control protocol under error prone channel was still missing in the available literature. Through the analysis result it is shown that the proposed method significantly improves the performance of the backoff algorithm when the reservation stage is employed in the Markov chain model. The analysis result is validated by using the network simulator tool ns-2. The proposed modifications can be employed in the Markov chain model of any backoff algorithm.     

VoIP capacity analysis in cognitive radio system

In this letter, we analyze a voice over IP (VoIP) capacity in a cognitive radio system. We formulate the system as a two-dimensional discrete time Markov chain (DTMC). The VoIP traffic and wireless channel in the cognitive radio system are described as a Markov modulated Poisson process (MMPP) model and a Markov channel model, respectively. We demonstrate various numerical and simulation results, such as packet dropping probability and VoIP capacity.     

Reconnection Analysis for a Cognitive Radio Network with Unreliable Sensing

In cognitive radio networks, an initiating secondary user senses a channel that is unused by a primary user and then makes use of the idle channel. An ongoing secondary user still needs to sense when a primary user accesses its channel and then either moves to another idle channel or moves to a buffer. In the latter case, the secondary user’s call waits in the buffer until either a channel becomes available or a predefined maximum waiting time expires. In this letter, an analysis of reconnection opportunity is presented for the queued secondary calls in the buffer in a cognitive radio network under unreliable sensing through developing a 3-D Markov process, where the unreliable sensing is modeled by different false alarm and misdetection events for both initiating and ongoing secondary users. A closed-form expression of the reconnection probability for an arbitrary secondary call in the buffer is obtained and the numerical computation is provided to highlight the analysis.     

Probabilistic call admission control in wireless multiservice networks

A new probabilistic call admission control scheme is proposed for multiservice wireless networks. The new scheme gradually suppresses the admission rate of the new calls and of the calls of each service class (SC) supported considering their priorities independently. The scheme is examined both for a single SC and for multiple SCs under general conditions. The analysis employs Markov chain theory and yields analytical expressions for the call blocking probabilities. The proposed analytical method was validated via simulations employing different distributions for the channel holding time; the simulations demonstrated the accuracy of the proposed framework.     

Performance Analysis of Fair Channel Sharing Policies in an Integrated Cellular Voice/Data Network

We study channel sharing in an integrated cellular voice/data network with a finite queue for data call requests that cannot be served immediately upon arrival. Using analytical techniques, a comparison of different fair channel sharing policies is made. As a main result, a closed-form expression is derived for the expected sojourn time (waiting time plus transfer time) of a data call, conditional on its size, indicating that the sojourn time is proportional to the call size. This attractive proportionality result establishes an additional fairness property for the channel sharing policies proposed in the paper. Additionally, as a valuable intermediate result, the conditional expected sojourn time of an admitted data call is obtained, given the system state at arrival, which may serve as an appreciated feedback information service to the data source. An extensive numerical study is included to compare the proposed policies and to obtain insight in the performance effects of the various system and policy parameters.