基于k阶马尔可夫链的单播网络丢包层析成像

该文针对时域相关的网络链路丢包估计问题,提出一种基于k阶马尔可夫链的单播网络丢包层析成像方法。该方法首先引入k阶马尔可夫链描述网络链路丢包过程,然后用最大伪似然方法估计k阶马尔可夫链链路丢包模型的状态转移概率。当k足够大时,该文方法可以根据单播端到端测量数据,准确地估计出网络链路上每个数据包丢失的概率。ns-2仿真验证了该文方法的有效性。     

高清视频联网系统中一种新的丢包率分析方法

为了提高系统性能并最大限度降低算法实现复杂度,本文提出了一种新的高清视频联网系统中丢包率的更优近似分析方法,重点研究包长度对丢包率的影响。首先使用马尔可夫链模型估算数据包的误码率,进而得出数据包网络时延的概率分布,最后计算出基于包长度的丢包率的理论表达式。仿真结果表明,通过减小发包大小可以有效降低丢包率,同时基于包长度的丢包率的理论分析方法可以有效地运用到高清视频联网系统的分析研究中。     

Performance analysis of wireless multi-user VoIP system with adaptive modulation and coding

In this paper, we propose a new framework to analyze performance considering finite-length queuing and adaptive modulation and coding for multi-user Voice over IP (VoIP) services in wireless communication systems. We formulate an uplink VoIP system as a two-dimensional discrete-time Markov chain (DTMC) based on a Markov modulated Poisson process traffic model for VoIP services and modulation and coding scheme (MCS)-level set transition reflecting users’ channel variations. We extend the transition modeling of the MCS-level for a single-user to the transition modeling of the MCS-level set for multiple users. Since the users can have various MCS combinations in the case of a multi-user system, the MCS-level set transitions are more complicated than the MCS-level transitions of the single-user case. Throughout our DTMC formulation, we present various performance metrics, such as average queue-length, average throughput, packet dropping probability, packet loss probability, and so on. By using the results of the packet loss probability, we can find an optimum packet error rate value that minimizes the total packet loss probability.     

Queueing analysis of delay constrained voice traffic in a packetswitching system

Unlike data traffic, the voice packet stream from a node has very high correlation between consecutive packets. In addition, in order for the speech to be properly reconstructed, a delay constraint must be satisfied. A queueing model that accurately predicts packet loss probabilities for such a system is presented. Analytical results are obtained from an embedded bivariate Markov chain and are validated by a simulation program. Based on this model, the impact of the delay constraint, talkspurt detection thresholds, and packet size on packet loss are studied. Two schemes, named `instant' and `random', for discarding late packets are considered. Simulation results show that better performance can be obtained by using the latter scheme     

多速率系统呼叫级和分组级的损失率分析

对提供多速率实时VBR业务的系统中呼叫级和分组级的主要性能指标的分析计算进行了深入研究,从多维Markov链的全局平衡条件出发,提出了一种计算在部分共享策略下各业务在线连接数的联合概率分布的方法,在此基础上可算出呼叫损失概率和分组丢失率,仿真结果表明了其准确性。     

Modeling Packet Delay in Multiplexed Video Traffic

In this paper a Markov chain based characterization of a single video source is used to model multiplexed video traffic and the resulting packet delay. The multiplexed video stream of statistically identical sources is represented using a reduced order approximation of the superposed Markov generator matrix. It is shown that inadequate spectral content in the single source generator matrix is manifested as an underestimate of the packet delay probabilities for the multiplexed stream. A new method for simplifying the generator matrix for the multiplexed video stream that amply models its spectral content is given. The simulated and calculated results using the aforementioned model are shown be in good agreement.     

A cross layer approach based on queuing and adaptive modulation for MIMO systems

A cross layer approach based on queuing and adaptive modulation for MIMO systems has been presented. To realize the system, an adaptive modulation scheme using MIMO systems combined with finite-length queuing at the data link layer has been designed. A finite state Markov chain for MIMO channels has been constructed to persue the queuing analysis. The packet loss rate, the average throughput, and the average spectral efficiency have been computed. Furthermore, the packet error rate for adaptive modulation to minimize the packet loss rate and maximize the average throughput is extracted. The obtained results present the advantages of using the proposed cross layer architecture.     

Performance of a nonblocking space-division packet switch in a timevariant nonuniform traffic environment

The authors study the performance of a nonblocking space-division packet switch, given that the traffic intensities at the switch not only are nonuniform but also change as a function of time. A finite-state Markov chain is used as an underlying process to govern the time variation of traffic for the entire switch. The packet arrivals at each input form an independent Bernoulli process modulated by the underlying Markov chain. The output address of each packet is independently and randomly assigned with probability distributions, which are also modulated by the Markov chain. Provided that the traffic on each output is not dominated by individual inputs the service time of each output queue for sufficiently large switches can be characterized by an independent Markov modulated phase-type process. A matrix geometric solution for the resultant quasi-birth-death type queuing process is presented. The maximum throughput is obtained at the system saturation. The performance of the switch is numerically examined under various traffic conditions. A contention priority scheme to improve the switch performance is proposed     

Performance evaluation of input-buffered replicated banyan networks

Input-buffered replicated networks are considered for broadband switching applications. They are characterized by many design parameters such as the replication factor, the traffic management policy, and input buffer location and length. To show the influence of these parameters on switching performance, an analytical model is defined based on a Markov chain representation of the input buffer. This model is suitable for application to input buffered architecture having different routing network choices. The results, expressed in terms of throughput, packet delay, and packet loss probability, outline the performance improvements with respect to other well-known networks with input buffers, such as banyan and crossbar, reached through the flexibility offered by this architectural solution     

H ∞ Control with Limited Communication for Networked Control Systems

In this paper, the H _∞ control problem is studied for discrete time systems with limited communication network. The communication limitation includes signal quantization, random packet loss, which appear typically in a network environment. The random packet loss is modeled as a two-state Markov chain. Both the packet-loss dependent and independent H _∞ controllers are designed. The packet-loss dependent controller is applicable only to the network with accessible packet-loss information. However, the packet-loss independent controller is applicable to networks both with and without accessible packet-loss information. Finally, an example is provided to demonstrate the effectiveness and applicability of the proposed design approach.     

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.     

Performance analysis of the IEEE 802.11 MAC protocol for wireless LANs

Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co‐ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright © 2005 John Wiley & Sons, Ltd.     

Performance analysis of a random packet selection policy formulticast switching

This paper studies a random packet selection policy for multicast switching. An input packet generates a fixed number of primary copies plus a random number of secondary copies. Assuming a constant number of contending packets during a slot, the system is modeled as a discrete time birth process. A difference equation describing the dynamics of this process is derived, the solution of which gives a closed form expression for the distribution of the number of packets chosen. Then this result is extended to the steady state distribution through a Markov chain analysis. It is shown that the old packets have larger fanout than the fresh packets and the copy distribution of the mixed packets is determined. The packet and copy throughput taking into account the old packets have been obtained. We determined the mean packet delay as well as an upperbound for packet loss probabilities for finite buffer sizes. The asymptotic distribution of the number of packets is also given for large switch sizes under saturation by applying results from the renewal theory. Finally, simulations are done to determine the performance of the switch under mixed (unicast plus multicast) traffic     

New cross-Layer design approach to ad hoc networks under Rayleigh fading

We propose a new cross-layer design employing the predictability of Rayleigh channels to improve the performance of ad hoc networks. In addition, we propose a Markov model for Rayleigh channels and an innovative Markov model for IEEE 802.11 distributed coordination function. By combining these two models, we derive the theoretical expressions for network throughput, packet processing rate, packet loss probability, and average packet delay under Rayleigh channels. The simulation of the proposed cross-layer design is also carried out. It is shown that the new approach improves the network throughput, reduces unnecessary packet transmissions and therefore reduces packets lost. We also show that there is a close match between the analytical and the simulation results which confirms the validity of the analytical models.     

Accurate hidden markov modeling of packet losses in indoor 802.11 networks

This article presents an analysis of packet losses in IEEE 802.11 networks under indoor environment constraints, and shows how the Gilbert-Elliot model fails to represent packet losses in such networks. As an alternative, we propose a simple hidden Markov model (HMM) with a birth-death structure, which describes with sufficient accuracy the mean packet loss rate, variance, length of loss bursts, and process autocorrelation.     

Markov-based channel characterization for tractable performance analysis in wireless packet networks

Finite-state Markov chain (FSMC) models have often been used to characterize the wireless channel. The fitting is typically performed by partitioning the range of the received signal-to-noise ratio (SNR) into a set of intervals (states). Different partitioning criteria have been proposed in the literature, but none of them was targeted to facilitating the analysis of the packet delay and loss performance over the wireless link. In this paper, we propose a new partitioning approach that results in an FSMC model with tractable queueing performance. Our approach utilizes Jake's level-crossing analysis, the distribution of the received SNR, and the elegant analytical structure of Mitra's producer-consumer fluid queueing model. An algorithm is provided for computing the various parameters of the model, which are then used in deriving closed-form expressions for the effective bandwidth (EB) subject to packet loss and delay constraints. Resource allocation based on the EB is key to improving the perceived capacity of the wireless medium. Numerical investigations are carried out to study the interactions among various key parameters, verify the adequacy of the analysis, and study the impact of error control parameters on the allocated bandwidth for guaranteed packet loss and delay performance.     

Hierarchical constellation for multi-resolution data transmission over block fading channels

We propose a new technique for multi-resolution video/image data transmission over block fading channels. The proposed scheme uses an adaptive scheduling protocol employing a retransmission strategy in conjunction with a hierarchical signal constellation (known also as nonuniform, asymmetric, multi-resolution constellation) to give different transmission priorities to different resolution levels. Transmission priorities are given in terms of average packet loss rate as well as average throughput. Basically, according to the transmission scheduling and channel state (acknowledgment signal) of the previous transmission, it dynamically selects packets from different resolution levels to transmit for the current transmission. The bits from the selected packets are assigned to different hierarchies of a hierarchical 4/16-quadrature amplitude modulation to transmit them with different error protections. The selection of packets for transmission and the assignment of these selected packets to different hierarchies of the hierarchical constellation are referred to as the scheduling protocol in our proposed scheme. We model this protocol by a finite state first order Markov chain and obtain the packet loss rate and the packet transmission rate over Nakagami-m block fading channel in closed-form. Some selected numerical results show that the proposed scheme can control the relative packet loss rate and the packet transmission rate of different resolution levels by varying the priority parameter (or equivalently, the asymmetry) of the hierarchical constellation and the maximum number of allowed retransmissions.     

Joint source/channel coding of statistically multiplexed real-timeservices on packet networks

The interaction of congestion control with the partitioning of source information into components of varying importance for variable-bit-rate packet voice and packet video is investigated. High-priority transport for the more important signal components results in substantially increased objective service quality. Using a Markov chain voice source model with simple PCM speech encoding and a priority queue, simulation results show a signal-to-noise ratio improvement of 45 dB with two priorities over an unprioritized system. Performance is sensitive to the fraction of traffic placed in each priority, and the optimal partition depends on network loss conditions. When this partition is optimized dynamically, quality degrades gracefully over a wide range of load values. Results with DCT encoded speech and video samples show similar behavior. Variations are investigated such as further partition of low-priority information into multiple priorities. A simulation with delay added to represent other network nodes shows general insensitivity to delay of network feedback information. A comparison is made between dropping packets on buffer overflow and timeout based on service requirements     

Predictive multicast polling for wireless networks with multipacket reception and queuing

In this paper, we propose the predictive multicast polling scheme for medium access control in wireless networks with multipacket reception capability. We concentrate on the case in which the packet arrival process is general and the maximum queue size is finite but larger than one. We derive both analytical results and simulation results. We use the theory of discrete-time Markov chain to analyze the evolution of the system state. In addition, we propose to use Markov reward processes to calculate the exact value of the network throughput. Furthermore, we obtain the average system size, the packet blocking probability, and the average packet delay. We show that our numerical results are consistent with simulation results. We also use simulation results to justify the usage of the proposed approach. Our study shows that the system performance can be significantly improved with a few additional buffers in the queues.     

具有多重码的预约Slotted ALOHA协议性能分析

本文对具有多重码的预约Slotted ALOHA协议进行了性能分析。它是基于帧的协议且在一个时隙内有多重码可用来传输分组信息。文中利用离散时间,离散状态和Markov链来分析一个小区上行链路的话音分组吞吐量和数据分组延时性能,并提出了两种改进碰撞解决的方法,得到了较好的系统特性。