有效提高无线局域网信道可用带宽的MAC机制

802.11 WLAN基础架构BSS（基础服务集）的DCF模式下,有两个因素严重影响可用带宽.一是随着竞争站点数增加,信道竞争开销增大,利用率下降;二是AP（接入点）在竞争信道中并无优势,上下行带宽严重不对称,降低了实际利用率.针对这两个问题提出一种新的MAC机制,首先通过在AP端统计MAC地址来估计竞争站点数,然后根据数学模型计算AP和站点上下行比例控制下的最优初始竞争窗值,通过广播设置以获取信道最大利用率.     

MAC intelligence for adaptive multimedia in 802.11 networks

Services in wireless networks must be capable of receiving information about the network and adaptively tune their transport parameters to the underlying networking conditions and technologies. A central problem in wireless transports is obtaining reliable metrics of congestion. How can lower layers assist transports and what is the performance tradeoff with pure peer-to-peer end-to-end solutions? We design and evaluate a lower layer assistance architecture. We focus on adding minimal intelligence to lower layers, according to the end-to-end principle. We find that we can adequately solve the measurement problem by minimal medium access control (MAC) assistance and describe an architecture that can aid transports over wireless links. The MAC-assisted solution is scalable to large number of flows, where the performance of pure end-to-end transports deteriorates rapidly. An improvement factor of 30-50 is exhibited in our experiments. We argue that including this minimal additional functionality in the MAC is sufficient for transports. It is also necessary when compared with end-to-end techniques.     

自适应p-持续CSMA/CD介质访问控制策略

针对IEEE802．3局域网介质随机访问协议l-持续CSMA／CD，在同一个冲突域内，它的性能在重荷载下有明显缺陷的问题，本文分析了p-持续CSMA／CD协议，提出了一种新的关于概率p的自适应算法。该算法基于对网络流量的分析，在OSI物理层通过信道信息量的在线实时检测，根据反馈控制的原理，在数据链路层动态地调整控制输入参数p，从而控制站点发送分组数据帧的行为，使信道处于最佳的传输状态，提高信道的效率。     

An adaptive opportunistic retransmission control scheme environment-aware-based for wireless multimedia Mesh networks

In this paper, we propose an aware-based adaptive opportunistic retransmission control scheme for wireless multimedia Mesh networks. The proposed scheme provides maximum retransmission count optimization based on environment-aware to improve packet relay probability. The scheme discriminates the types of packet loss in wireless link by means of environment information and selects the retransmission count by taking the IEEE 802.11 wireless channel characteristics into consideration. Furthermore, the maximum retransmission count of MAC is adjusted adaptively. Extensive simulations demonstrate that the proposed scheme significantly reduces packet collision probability and packet loss rate, and thus improves network throughput.     

A new scheme to achieve weighted fairness for WLAN supporting multimedia services

This work presents a new scheme which exploits differentiations of both inter frame space (IFS) and contention window (CW) to achieve weighted fairness for two classes of services under enhanced distributed channel access (EDCA) mode in an 802.11e WLAN. Given the arbitration IFSs (AIFSs), the proposed scheme can properly set the corresponding CWs such that the ratio of the two classes' successful transmission probabilities can attain a pre-defined weighted-fairness goal. Additionally, the throughput and delay of the two classes of services are derived. The simulation results compare well with the analytical results. Also, the analytical results illustrate that the proposed scheme can achieve a fairness index very close to 1 and attain a greater aggregate throughput with lower collision probability than the CW differentiation scheme presented in A. Banchs and X. Perez (2002), for a specified weighted-fairness goal.     

一种基于全双工的节能型无线局域网MAC协议

提出了一种基于同时同频全双工的节能型无线局域网MAC协议,对该协议进行网络仿真,并从网络吞吐量、能量消耗等方面与传统的无线局域网MAC协议进行比较。从仿真结果可以看出,基于同时同频全双工的MAC协议的性能较传统半双工无线局域网MAC协议有较大改善,而且在达到同等性能的条件下所提出的MAC协议比FD-MAC消耗的能量更少。     

一种应用于WLAN的混合双工MAC协议

全双工通信技术可以提高链路容量和频谱利用率,会给现有无线局域网(WLAN)带来极大的变革。该文针对传统半双工WLAN向全双工WLAN发展的过程中多种双工站点共存的问题,提出一种混合双工媒体接入控制(MAC)协议(HYD-MAC)。该协议合理设计了请求发送/清除发送(RTS/CTS)帧,并根据网络隐藏节点状况和站点全双工能力,自适应地选择最佳的传输模式,包括同步全双工、异步全双工、条件半双工以及半双工等4种模式。给出了HYD-MAC协议在4种传输模式下的链路建立与数据传输流程,分析了HYD-MAC的饱和吞吐量和介质访问时延等网络性能。仿真结果表明,所提的HYD-MAC的性能优于传统半双工DCF协议,特别在帧长较长、站点数较少、数据传输速率较低时,HYD-MAC的性能提升效果更加明显;与经典的全双工协议相比,HYD-MAC协议通过牺牲极少的吞吐量和时延性能,可以同时满足全双工、半双工以及混合双工网络的通信需求。     

A weighted fairness guarantee scheme based on node cooperation for multimedia WLAN mesh networks

In this paper, we focus on weighted fairness in multimedia WLAN mesh networks. Based on the analysis of the fairness problem of IEEE 802.11e Enhanced Distributed Channel Access (EDCA) scheme in WLAN mesh networks, we propose a weighted fairness guarantee scheme (WFGS), which provides weighted fairness for multimedia flows with different QoS requirements through node cooperation. WFGS piggybacks extra field in RTS/CTS frames to declare the channel occupation ratio of each flow. Accordingly, the transmitters can get the neighboring flows’ channel occupation ratio via overhearing the RTS/CTS frames from its neighbors, and cooperatively adjust the contention window size to achieve weighted fairness among the flows. Also, to reliably reserve transmissions, an adaptive power control based RTS/CTS handshake mechanism is introduced. Simulation results show that compared with EDCA scheme, WFGS can effectively resolve the collisions induced by the carrier interference and thereby guarantee both the short-term and long-term weighted fairness among multimedia flows.     

ARDCH：适于多媒体传感器网络的自适应周期分簇机制

分析了多媒体传感器网络节点部署特点以及多媒体信息位置相关性特点,提出了一种基于剩余能量与传输距离的自适应周期簇头竞争机制(ARDCH,adaptive round distributed cluster head),综合考虑通信代价及剩余能量选取簇头,同时根据剩余能量来动态调节簇头的工作周期,以此均衡网络中节点的能量消耗.此外采用多信道簇间通信,避免簇间干扰,与已有的几个分簇协议相比,显著地延长了网络的生存周期,更适于多媒体传感器网络.     

An OFDMA-based joint reservation and cooperation MAC protocol for the next generation WLAN

Wireless Networks - The rapidly increasing use of mobile devices and the explosive growth of wireless traffic demands continuously drive the development of wireless networks. IEEE 802.11ax, as the...     

An adaptive coding scheme for time-varying channels

An adaptive coding scheme for digital communication over time-varying channels is presented. The scheme is based on a finite-state Markov channel model. Emphasis is on the adaptation of the error protection to the actual channel state. The throughput gains that are achieved by the adaptive scheme relative to the conventional nonadaptive coding methods are demonstrated by several examples. Of special interest is the use of punctured convolutional codes with maximum-likelihood Viterbi algorithm to enable adaptive encoding and decoding without modifying the basic structure of the encoder and the decoder     

An adaptive network prefetch scheme

In this paper, we present an adaptive prefetch scheme for network use, in which we download files that will very likely be requested in the near future, based on the user access history and the network conditions. Our prefetch scheme consists of two parts: a prediction module and a threshold module. In the prediction module, we estimate the probability with which each file will be requested in the near future. In the threshold module, we compute the prefetch threshold for each related server, the idea being that the access probability is compared to the prefetch threshold. An important contribution of this paper is that we derive a formula for the prefetch threshold to determine its value dynamically based on system load, capacity, and the cost of time and system resources to the user. We also show that by prefetching those files whose access probability is greater than or equal to its server's prefetch threshold, a lower average cost can always be achieved. As an example, we present a prediction algorithm for web browsing. Simulations of this prediction algorithm show that, by using access information from the client, we can achieve high successful prediction rates, while using that from the server generally results in more hits     

支持TDD的无线局域网MAC协议

本文在分析无线局域网媒体接入控制（MAC）协议的基础上,提出支持时分双工（TDD）的MAC协议：EDCF-TDD。IEEE802．11增强型分布式协调功能（EDCF）只支持单工通信,即数据帧只能由发送方传送到接收方。EDCF-TDD利用IEEE802．11点协调功能（PCF）提供的数据帧格式,可以实现数据帧的双向传输。EDCF-TDD更适合传输对称的实时业务和面向连接的TCP业务,而且与IEEE802．11完全兼容。仿真结果表明：EDCF-TDD可以提高吞吐量和实现时延、时延抖动和丢组率分级;理论分析结果基本准确。     

An adaptive ISMA-DS/CDMA MAC protocol for third-generation mobilecommunications systems

An inhibit sense multiple access-direct sequence/code division multiple access (ISMA-DS/CDMA) medium access control protocol for a packet transmission mobile radio network is presented. The main feature of this protocol is its ability to retain the inherent flexibility of random access protocols while at the same time reducing to some extent the randomness in the access in order to increase the system capacity. In this framework, the protocol is presented together with some adaptive mechanisms that improve the protocol performance by means of regulating the access and varying the transmission bit rate according to the channel load that is broadcast by the base station. As a result, an adaptive bit rate algorithm is presented that reaches a throughput value close to the theoretical maximum     

An integrated adaptive bandwidth-management framework for QoS-sensitive multimedia cellular networks

Bandwidth is an extremely valuable and scarce resource in a wireless network. Therefore, efficient bandwidth management is necessary in order to provide high-quality service to users in a multimedia wireless/mobile network. In this paper, we propose new online bandwidth-management algorithms for bandwidth reservation, call admission, bandwidth migration, and call-preemption strategies. These techniques are combined in an integrated framework that is able to balance the traffic load among cells accommodating heterogeneous multimedia services while ensuring efficient bandwidth utilization. In addition, our online framework to adaptively control bandwidth is a cell-oriented approach that has low complexity, which makes it practical for real cellular networks. Simulation results indicate the superior performance of our bandwidth-management framework to strike the appropriate performance balance between contradictory quality-of-service requirements.     

An adaptive load balancing scheme for web servers

This paper describes an overload control scheme for web servers which integrates admission control and load balancing. The admission control mechanism adaptively determines the client request acceptance rate to meet the web servers' performance requirements while the load balancing or client request distribution mechanism determines the fraction of requests to be assigned to each web server. The scheme requires no prior knowledge of the relative speeds of the web servers, nor the work required to process each incoming request. Copyright © 2002 John Wiley & Sons, Ltd.     

AN ADAPTIVE FEC SCHEME FOR Ka-BAND SATELLITE COMMUNICATIONS

Rain attenuation is the major problem for Ka-band satellite communications, and the fading due to rain can be well described by a lognormally distributed, first-order autoregressive model. Forward Error-control Coding (FEC) techniques can be used to reduce the effect of the rain attenuation, but the use of FEC causes a reduction in the bandwidth efficiency. In order to increase the bandwidth efficiency as well as maintain high link availability, an Adaptive Forward Error-control Coding (AFEC) scheme with rain fading prediction is proposed and analyzed in this paper. The results show that AFEC offers a good trade-off between link availability and bandwidth efficiency.     

Virtual reservation scheme for supporting CBR multimedia services with strict QoS performance over WLAN and wireless mesh

Carrier sense multiple access and its variants have been widely used in mobile ad hoc networks. However, most existing access mechanisms cannot guarantee quality of service for real‐time traffic. In this paper, we present a novel approach to guarantee the performance of real‐time applications such as voice and video that require periodic access to the wireless local area network (WLAN) channel. Our approach can work either with distributed coordination function or enhanced distributed coordination function, and includes distributed reservations of time slots between the stations sharing the WLAN without the need to send any signaling or control messages. Stations can access the wireless medium only if they are able to complete the frame transmission without interruption to the reserved slots of existing real‐time sessions. Simulation results indicate that the proposed mechanism provides high channel utilization, and bounded delays and jitter for real‐time traffic. Copyright © 2009 John Wiley & Sons, Ltd.     

基于宽带多媒体卫星网络的MAC协议

提出了一种基于MF-TDMA的宽带卫星MAC协议联合随机预约接入协议(CRRAP)。协议采用随机预约和捎带预约结合,按需分配和自由分配结合来实现的。仿真结果表明,相对于现有的方法,CRRAP减少了高信道负荷下的时延,提高了吞吐性能,并具有较高的信道利用率。     

Joint optimization and threshold structure dynamic programming with enhanced priority scheme for adaptive VANET MAC

Nodes in vehicular ad-hoc network (VANET) are highly mobile, traversing in unpredictable and varying environment. Therefore, contention window size and transmission power should adapt according to the high mobility transmission environment. In this paper, we propose an adaptive VANET medium access control (MAC) layer with joint optimization for VANET (MACVS) which aims at minimizing average delay and maximizing packet success rate. An adaptive joint optimization with proposed threshold structure dynamic programming, with closed loop feedback control system, is designed to optimize contention window size and transmission power. Adaptive optimization is done based on road traffic conditions and transmission reliable distance range (depicted by interference and noise), by monitoring the continuous change and threshold of received signal strength to interference and noise ratio. Mathematical expressions have been developed for the MACVS optimization framework, and the produced analytical results show good agreement with the simulation results. Simulations with different arrival rates and urban map of city center show that the proposed MACVS with low complexity joint optimization effectively reduces end-to-end delay while achieving high packet success rate under various network traffic condition.