基于M/G/1/K排队模型的IEEE802.11e EDCA性能研究

该文利用二维Markov链分析方法,提出了一种新的IEEE802.11e EDCA网络分析模型,该模型引入了空闲状态和不同接入等级的仲裁帧间隔(AIFS)的使用;利用Markov链状态转移图的Z域信号传递函数推导了MAC层平均服务时间的概率分布;结合M/G/1/K排队模型分析了增强分布式信道接入(EDCA)在非饱和和饱和负载下的性能。经过访真实验结果与数值分析结果的对比,验证了分析模型的准确性。分析结果表明:EDCA接入机制只为不同优先级业务提供QoS区分;不同优先级业务信道接入的不公平性是EDCA接入机制的特点。     

Joint Antenna Selection and Robust Beamforming Design in Multi-cell Distributed Antenna System

Most of studies on Distributed Antenna System （DAS） focus on maximizing the sum capacity and perfect channel state information at transmitter （CSIT）. However, CSI is inevitable imperfect in practical wireless networks. Based on the sources of error, there are two models. One assumes error lies in a bounded region, the other assumes random error. Accordingly, we propose two joint antenna selection （AS） and robust- beamforming schemes aiming to minimize the total transmit power at antenna nodes subject to quality of service （QoS） guarantee for all the mobile users （MUs） in multicell DAS. This problem is mathematically intractable. For the bounded error model, we cast it into a semidefinite program （SDP） using semidefinite relaxation （SDR） and S-procedure. For the second, we first design outage constrained robust beamforming and then formulate it as an SDP based on the Bernstein-type inequality, which we generalize it to the multi-cell DAS. Simulation results verify the effectiveness of the proposed methods.     

STUDY OF RADIO DEVICES ON 2.4GHZ SM BAND IN PHYSICAL PHASE

In the unlicensed 2.4GHz ISM band, there is not only IEEE 802.11 wireless systems being used, but also some other devices, such as residential microwave oven, Bluetooth devices, and cordless phone. All these devices that are not used for the data communications cause unintentional interference that will degrade the WI-FI system. In this paper, the transmission powers for common RF devices are measured and the SIR （signal-to-interference ratio） of different interferers to Wi-Fi is also studied. With this information, the effect of different interference on WI-Ft signal can hence be quantified. Furthermore, the ability of the interference avoidance protocols, which is built into the AP, to address interference problems caused by that device is determined.     

Dynamic Per-flow Queuing to Reduce Competitions Among Large Number of Flows

Per-flow queuing is believed to be able to guarantee advanced Quality of service （QoS） for each flow at high speed routers. With the dramatic increase for both llnk speed and number of traffic flows, per-flow queuing confronts a great challenge, since millions of queues need to be maintained for implementation in a traditional sense. In this paper, setting only a small number of physical queues, we propose a Dynamic per-flow queuing （DPFQ） mechanism that achievesthe same performance as per-flow queuing at a cost of an additional Binary content addressable memory （BCAM）. The proposed mechanism works due to the fact that the number of simultaneous active flows at a mini-time scale in the router buffer is much smaller than that of in-progress flows. In DPFQ, a physical queue is created on demand when a new flow comes, and released when the flow temporarily pauses or finishes. A small BCAM is occupied to map flows to queues, so as to guarantee that only the packets from the same flow are buffered in any assigned queue. Through analysis and simulation we show that using a small number of physical queues, DPFQ achieves both low operation delay and power consumption.     

Performance Analysis of Capture Effect in High Speed Wireless Networks

The influence of capture effect on the high speed wireless networks is investigated in this paper. A new garkov chain model considering capture effect for the binary exponential back-off scheme in the MAC layer has been proposed. A new throughput model used in the IEEE 802.11 networks is proposed Based on this new Markov chain model, and then we analyzed throughput impacted by the capture effect under different transmission speeds. The performance analysis shows the capture effect has more impact on the throughput of high speed wireless networks than that on the low speed wireless networks.     

A Novel Event Model for Performance Analysis of IEEE 802.11 DCF

After considering the memory effect among series events occurring on the channel, we propose a novel event model to analyze the channel status more precisely. The memory effect is caused by the backoff freezing regulation of IEEE 802.11 Distributed coordination function （DCF）, which has been ignored before and thus resulted in the inaccurate evaluation of the network performance. Based on our new event model, the network performance of IEEE 802.11 DCF, including throughput, packet delay distribution and energy efficiency is analyzed. Simulation results show that our model is highly accurate.     

A 55 nm CMOS △∑fractional-N frequency synthesizer for WLAN transceivers with low noise filters

A fully integrated ΔΣ fractional-N frequency synthesizer fabricated in a 55 nm CMOS technology is presented for the application of IEEE 802.11b/g wireless local area network(WLAN) transceivers.A low noise filter,occupying a small die area,whose power supply is given by a high PSRR and low noise LDO regulator,is integrated on chip.The proposed synthesizer needs no off-chip components and occupies an area of 0.72 mm2 excluding PAD.Measurement results show that in all channels,the phase noise of the synthesizer achieves -99 dBc/Hz and -119 dBc/Hz in band and out of band respectively with a reference frequency of 40 MHz and a loop bandwidth of 200 kHz.The integrated RMS phase error is no more than 0.6°.The proposed synthesizer consumes a total power of 15.6 mW.     

Performance Analysis of the IEEE 802.15.3 CSMA/CA in Unsaturated Traffic Conditions

In IEEE 802.15.3 the traffic communicated by Carrier sense multi access/Collision avoidance （CSiVIA/CA） mechanism are unsaturated in most cases that are different in IEEE 802.11. This paper presented an extension analytical model based on the Bianchi model in IEEE 802.11 considering unsaturated traffic conditions in error-prone channel. By using this model we analyzed the throughput, frame discard probability and average frame delay performance of IEEE 802.15.3 CSMA/CA. This model is validated through extensive simulation results. Effects of unsaturated situation and channel error condition on the performance were analyzed.     

Queuing Scheme for Improved Downlink Throughput on WLANs

A transmission queuing scheme is described that increases downlink throughput on wireless local area networks (WLANs) while also increasing the total throughput. When the amount of uplink traffic increases on a WLAN, the carrier sense multiple access with collision avoidance (CSMA/CA) protocol, which is the prescribed scheme for IEEE 802.11 WLAN channel access, may substantially reduce the rate of downlink data frame transmission. This results in severe throughput degradation for mobile stations with downlink traffic. The proposed scheme comprises a transmission control function based on consecutive transmission, as described in the IEEE 802.11e standard, and a dynamic queue prioritization algorithm. Simulation results demonstrate that the proposed scheme increases the maximum total throughput for uplink and downlink traffic by 17% compared with the conventional distributed coordination function (DCF) scheme and that it reduces the difference between uplink and downlink throughput. In an environment where transmission errors occur, the difference in throughput is reduced by about 50% compared with the conventional schemes.     

Saturation Throughput Analysis of the IEEE 802.11e EDCA Network with Contention Free Burst Under Fading Channel

The 802.11 WLAN legacy standard cannot provide Quality of Service (QoS) support for multimedia applications because the 802.11 was initially developed for Best Effort services. Hence, the 802.11e amendment was published in order to provide the QoS support to WLANs. One of the most important functions in 802.11e is the contention based channel access mechanism called Enhanced Distributed Channel Access (EDCA), which provides a priority scheme by differentiating the Arbitration Inter Frame Space (AIFS), initial window size and Transmission OPportunity limit (TXOPlimit). In this paper, we propose a novel analytical model for the performance analysis of the IEEE 802.11e EDCA network with Contention Free Burst under fading channel and saturated traffic conditions. This new model captures all of the major QoS specific features, namely AIFS, minimum contention window size, maximum contention window size, virtual collision and TXOPlimit. So, we have analyzed the saturation system throughput of the basic access method of the IEEE 802.11e EDCA network.     

BeamMAC: A new paradigm for medium access in wireless networks

Medium access using the distributed coordination function of IEEE 802.11 is not efficient in wireless multihop networks if the devices are equipped with beamforming antennas. This paper proposes a distributed MAC protocol that goes completely away from the spatial reservation scheme of 802.11. It facilitates the use of beamforming antennas by following an announcement-objection scheme: a potential sender must “simulate” a transmission on a signaling channel before it can access the traffic channel. Based on this simulation, each receiving device estimates the expected interference and objects to the transmission if necessary. This paradigm overcomes the drawback of 802.11-based approaches that neighboring devices are silenced irrespective of whether or not they disturb signal reception. It benefits from a tight interaction of the MAC and physical layer.     

IEEE802.11e EDCA和CFB下饱和吞吐量分析

IEEE802.11eMAC草案规范对IEEE802.11无线局域网标准在QOS方面加以了补充。IEEE802.11e采用2种协调机制基于控制的综合协调可控信道接入方式HCCA和基于竞争的增强型分布式信道接入方式EDCA。主要评估EDCA和竞争空闲脉冲(contention-freeburst)CFB相结合时,在系统负载过载的情况下,改变性能参数后系统饱和吞吐量的变化,并分析系统性能参数对饱和吞吐量的影响,从而达到系统参数优化的作用。     

一种基于预测式公平队列调度算法的802.11e MAC层机制

在共享媒体的通信系统中,队列调度的公平性是很重要的。该文在研究了IEEE WLAN已有的各种队列调度算法的基础上,提出了一种预测式公平队列调度算法 (Predict Fair Queuing, PFQ),并结合IEEE 802.11e的EDCF(Enhanced Distributed Coordination Function)机制提出一种基于PFQ的新的MAC层协议P-EDCF(PFQ-based EDCF)。该协议通过引进PFQ算法来修改EDCF的优先级控制方式,提供一种公平、高效的接入机制。仿真结果表明,该机制很好地改善了EDCF的性能,为各种类型业务提供了公平的服务。     

Analytical modeling of bidirectional multi‐channel IEEE 802.11 MAC protocols

This paper presents an analytical approach to model the bi‐directional multi‐channel IEEE 802.11 MAC protocols (Bi‐MCMAC) for ad hoc networks. Extensive simulation work has been done for the performance evaluation of IEEE 802.11 MAC protocols. Since simulation has several limitations, this work is primarily based on the analytical approach. The objective of this paper is to show analytically the performance advantages of Bi‐MCMAC protocol over the classical IEEE 802.11 MAC protocol. The distributed coordination function (DCF) mode of medium access control (MAC) is considered in the modeling. Two different channel scheduling strategies, namely, random channel selection and fastest channel first selection strategy are also presented in the presence of multiple channels with different transmission rates. M/G/1 queue is used to model the protocols, and stochastic reward nets (SRNs) are employed as a modeling technique as it readily captures the synchronization between events in the DCF mode of access. The average system throughput, mean delay, and server utilization of each MAC protocol are evaluated using the SRN formalism. We also validate our analytical model by comparison with simulation results. The results obtained through the analytical modeling approach illustrate the performance advantages of Bi‐MCMAC protocols with the fastest channel first scheduling strategy over the classical IEEE 802.11 protocol for TCP traffic in wireless ad hoc networks. Copyright © 2010 John Wiley & Sons, Ltd.     

无线局域网络模型建立与性能分析

基于EDCA接入方式分析了无线局域网传输协议,IEEES02.1le标准为各个服务类别制定了不同的信道竞争参数数值,使得无线局域网具备了业务区分能力;通过对无线局域网传输协议EDCA接入方式进行建模,分析队列在接入过程中的竞争行为,进而准确估计各个队列的接入延迟;并以每个缓存队列以M/G/1/K排队模型为基础进行定量分析,结果表明,该模型能够准确地描述资源竞争情况,接入延迟计算法方法可根据不同系统参数精确地计算接入延迟性能。     

VANET/LTE-Advanced异构网络中基于协议序列-IEEE 802.11p的信道接入机制

摘要：提出了VANET/LTE-Advanced异构网络架构,并重新规划信道使用及接入模式,提高车载设备之间通信的有效性,增强公平性并兼顾自由度。以车辆间通信为研究对象,深入剖析并比较IEEE 802.11p MAC协议,基于协议序列信道接入机制,提出基于协议序列-IEEE 802.11p的信道接入算法,将“基于调度”与“基于竞争”的信道接入结合,完善IEEE 802.11p MAC层协议。仿真结果表明,基于协议序列-IEEE 802.11p的信道接入机制与UI模式及IEEE 802.11p模式相比,实现了用户平均吞吐量和平均数据分组发送时延性能的权衡,具有理论价值和实用价值。     

Performance analysis of IEEE 802.11ah wireless local area network under the restricted access window‐based mechanism

IEEE 802.11ah is an approved amendment to IEEE 802.11 wireless local area network (WLAN) standard to support growing demand for machine‐to‐machine (M2M) applications. To enable an efficient scheme for accessing the channel by a large number of stations (STAs) within the coverage of an access point, 802.11ah has developed a novel mechanism known as Restrictred Access Window (RAW). Here, a group of STAs attempts channel access during their designated RAW slot by following the carrier sense multiple access‐collission avoidance (CSMA‐CA)‐based enhanced distributed channel access (EDCA) mechanism. In this paper, we develop an analytical model for finding the nonsaturation/saturation throughput of 802.11ah WLAN under the RAW‐based channel access mechanism. We describe an analytical model for finding the average frame delay as well. The impact of the number of STAs and number of groups on network throughput and average delay are presented. We establish that the RAW mechanism can improve the throughput while the average frame delay gets reduced. The analytical results are validated by extensive simulation studies.     

Variable Persistence Sensing Schemes for Opportunistic Spectrum Access

Cognition technologies can significantly enhance spectrum utilization through secondary usage. Secondary users （SUs） search for spectrum holes which are not used by Primary users （PUs） and communicate through them. The design and analysis of simple opportunistic spectrum access schemes for maximizing utilization efficiency and minimizing delay of SUs under limited sensing bandwidth and energy is still at infancy. In this work, we consider PU＇s frequency occupancy patterns and propose three simple variable persistence sensing schemes for maximum exploitation of idle spectrum chunks by SUs, and perform their theoretical analysis. Numerical case studies are presented to verify the theoretical analysis and illustrate the performance of the schemes proposed.     

Performance Analysis of Regular Low-Density Erasure Codes

We propose a simple method for calculating the thresholds of regular low-density erasure codes under erasure recovery algorithm. Based on this conclusion, we prove that among （l, r）-regular low-density erasure codes, （3, r）-regular codes perform best, for the given integer l ≥ 3 and any rate R with 1/4 〈R 〈 1. Numerical results show the correctness of this conclusion.     

A Non-Cyclic Prefixed SFBC-SCFDE System Based on a Recursive Algorithm of Joint Channel Estimation and Data Detection

We propose a non-cyclic prefixed Single carrier frequency-domain equalization （SCFDE） system with Space-frequency block codes （SFBC）. The transmitted signals in proposed system are composed of Singlecarrier （SC） information sequences derived from SFBC and training sequences, both of which have been placed in an alternate order without any Cyclic prefix （CP） before each SC information sequence. Furthermore, a recursire algorithm of Joint channel estimation and data detection （recursive-JCEDD） is proposed for system receiver. Simulation results show that the proposed non-cyclic prefixed SFBC-SCFDE system based on the recursive-JCEDD algorithm has better Bit error rate （BER） performance than traditional cyclic prefixed SFBC-SCFDE, Space-time block-coded SCFDE （STBC-SCFDE） and STBC-OFDM systems with some common channel estimation algorithms.