Ad Hoc网络中一种具有优先控制的自适应协同MAC协议

ARQ(Auto Repeat reQuest)机制通常用来在传输失败后重传数据,但是在深衰落信道下,源节点多次重传有可能导致系统性能持续变坏,作为未来无线通信的重要技术,协同通信能够大大提高链路的可靠性,可以有效解决上述问题。本文针对Ad Hoc网络,提出了一种基于优先控制的自适应协同MAC(Media Access Control)协议。此协议采用ARQ机制,根据瞬时信道情况,自适应地选择信道质量更好的中继节点来重传数据,并且在优化的退避算法和中继选择算法的控制下,赋予中继节点相对源节点更高的优先级,协议中还在传统RTS/CTS分组交互基础上加入了新的握手交互机制,使得协议的性能进一步提升。本文还对经典二维Markov模型进行了改进,加入了协同机制并提出中继节点冲突模型,对所提协议进行了建模并推导出了吞吐量性能表达式。仿真结果表明,本文所提协议相对IEEE 80211 DCF协议和传统采用ARQ机制的协同MAC协议有着更好的性能。
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利用LDPC编译码构建无线密钥协商协议的研究

基于无线信道特征的密钥生成过程中,为了降低通信双方生成的密钥不一致率常采取的措施是密钥协商。通常的密钥协商过程是在BSC信道下进行密钥协商,但是协商的效率较低。为了提高密钥协商的效率,本文提出一种在等效信道下基于LDPC编译码的协议机制。在此协议机制中,无线信道下采用Mathur[1][2]等人提出的Level-Crossing算法（LCA）提取密钥的过程构成了本协议中的等效信道,该机制对LCA提取后的密钥协商信息进行建模,推导了等效信道的最佳似然比,并据此采用LDPC码简单的加权比特翻转等译码算法[3-5]来有效进行密钥协商。将等效信道下LDPC码加权比特译码算法用于协商过程的性能和BSC信道下协商后的性能进行仿真,在SNR大于6db的前提下,仿真结果表明:1）在相同低门限的条件下,和LCA算法生成的初始密钥相比较,利用LDPC码比特翻转译码等算法在等效信道下和在BSC信道下协商后的密钥不一致率比初始密钥不一致率降低1至2个数量级;2）在等效信道下利用简单加权比特翻转译码算法进行密钥协商后的密钥不一致率比BSC信道下协商后的密钥不一致率降低大约1个数量级。      

Exploiting cooperative relays to enhance the performance of energy-harvesting systems over Nakagami-<Emphasis Type="Italic">m</Emphasis> fading channels

This paper investigates a time-switching energy-harvesting system in which a source communicates with a destination via energy-constrained amplify-and-forward relays. To exploit the benefit of using multiple relays, we propose a relay scheduling called consecutive relay selection (CRS), which allows all relays to assist the source-to-destination communication, to improve the transmission efficiency of the time-switching policy. The partial relay selection (PRS) is examined for performance comparison. The selected relay in the PRS protocol is considered in two cases: in one, it is selected based on the first-hop channel gains (PRS-1 protocol), and in the other, it is selected based on the second-hop channel gains (PRS-2 protocol). For performance evaluation, the analytical expressions of the outage probability and throughput for Nakagami-m fading channel are derived. Our results show that the CRS protocol outperforms the PRS protocol in terms of throughput, the PRS-1 protocol achieves better performance than the PRS-2 protocol. Moreover, we discuss the effects of various key system parameters on system performance, such as the energy-harvesting ratio, source transmission rate, and locations of relays, to provide insights into the various design choices.     

On the synergy between adaptive physical layer and multiple-access control for integrated voice and data services in a cellular wireless network

We propose a novel design to exploit the synergy between the multiple-access control (MAC) layer and the physical layer of a cellular wireless system with integrated voice and data services. As in a traditional design, the physical layer (channel encoder and modulator) is responsible for providing error protection for transmitting the packets over the hostile radio channel, while the MAC layer is responsible for allocating the precious bandwidth to the contending users for voice or data connections. However, a distinctive feature of our proposed design is that in the physical layer, a variable-rate adaptive channel encoder is employed to dynamically adjust the amount of forward error correction according to the time-varying wireless channel state such that the MAC layer, which is a reservation-based time-division multiple-access protocol, is able to make informed decisions as to bandwidth allocation. Specifically, based on the channel state information provided by the physical layer, the MAC protocol gives higher priority to users with better channel states. This novel synergistic mechanism between the two protocol layers can utilize the system bandwidth more effectively. The multiple-access performance of the proposed scheme is compared with two baseline systems. The first baseline system consists of the same reservation-based MAC protocol but with a traditional fixed-rate physical layer. The second system consists of the same reservation-based MAC protocol and the same channel adaptive physical layer, but without interaction between the two layers. All three protocols have a request queue, which stores the previous requests that survive the contention but are not allocated information slots. Our extensive simulation results demonstrate that significant performance gains are achieved through the exploitation of the synergy between the two protocol layers.     

A media access and feedback protocol for reliable multicast over wireless channel

A link level reliable multicast requires a channel access protocol to resolve the collision of feedback messages sent by multicast data receivers. Several deterministic media access control protocols have been proposed to attain high reliability, but with large delay. Besides, there are also protocols which can only give probabilistic guarantee about reliability, but have the least delay. In this paper, we propose a virtual token-based channel access and feedback protocol (VTCAF) for link level reliable multicasting. The VTCAF protocol introduces a virtual (implicit) token passing mechanism based on carrier sensing to avoid the collision between feedback messages. The delay performance is improved in VTCAF protocol by reducing the number of feedback messages. Besides, the VTCAF protocol is parametric in nature and can easily trade off reliability with the delay as per the requirement of the underlying application. Such a cross layer design approach would be useful for a variety of multicast applications which require reliable communication with different levels of reliability and delay performance. We have analyzed our protocol to evaluate various performance parameters at different packet loss rate and compared its performance with those of others. Our protocol has also been simulated using Castalia network simulator to evaluate the same performance parameters. Simulation and analytical results together show that the VTCAF protocol is able to considerably reduce average access delay while ensuring very high reliability at the same time.     

基于载波监听的Ad Hoc网络双信道接入协议研究

双信道接入协议在解决隐终端和暴露终端问题上具有独特的优势.基于报文监听的Ad Hoc网络双信道接入协议无法消除数据报文的冲突.本文对基于载波监听的Ad Hoc网络双信道接入协议进行了研究,提出了DCMA载波监听信道接入协议.其中DCMA_CSBI通过载波监听和BI控制报文完全解决了隐终端和暴露终端问题.文章通过仿真对DCMA协议的性能进行了分析和比较.分析结果表明DCMA_CSBI是一种非常高效实用的Ad Hoc网络双信道接入协议,载波监听对Ad Hoc网络信道接入协议而言是至关重要的.     

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。     

A hybrid reservation-based MAC protocol for underwater acoustic sensor networks

Due to the characteristics of underwater acoustic channel, such as long propagation delay and low available bandwidth, media access control (MAC) protocol designed for the underwater acoustic sensor network (UWASN) is quite different from that for the terrestrial wireless sensor network. However, for the contention-based MAC protocols, the packet transmission time is long because of the long preamble in real acoustic modems, which increase the packet collisions. And the competition phase lasts for long time when many nodes are competing for the channel to access. For the schedule-based MAC protocols, the delay is too long, especially in a UWASN with low traffic load. In order to resolve these problems, a hybrid reservation-based MAC (HRMAC) protocol is proposed for UWASNs in this paper. In the proposed HRMAC protocol, the nodes reserve the channel by declaring and spectrum spreading technology is used to reduce the collision of the control packets. Many nodes with data packets to be transmitted can reserve the channel simultaneously, and nodes with reserved channel transmit their data in a given order. The performance analysis shows that the proposed HRMAC protocol can improve the channel efficiency greatly. Simulation results also show that the proposed HRMAC protocol achieves better performance, namely higher network throughput, lower packet drop ratio, smaller end-to-end delay, less overhead of control packets and lower energy overhead, compared to existing typical MAC protocols for the UWASNs.     

A New Digital Sense Multiple Access (DSMA) Protocol for High-Speed Wireless Networks

In this paper, we propose a new digital sensemultiple access with delayed transmission (DSMA/DT)protocol for reverse channel in high-speed wirelessnetworks. The new protocol is motivated by theobservation that the existing DSMA protocol does not yieldsatisfactory throughput for long round-trip propagationand processing delay, which occurs in outdoor high-speedenvironments or when the receiver hardware requires long signal processing time. The newDSMA/DT protocol is intended to reduce the performanceimpacts of the round-trip delay. Look-ahead busy/idleflag, seizure queueing, and reserved time slots are also devised for the new protocol. Whilerequiring at most two additional status bits on theforward channel and no additional hardware capability,these features further enhance the protocol performance and enable constant-bit-rate service withlittle added complexity in control. The channelthroughput of the DSMA/DT protocol and the optionalfeatures are analyzed. Closed-form expressions for thethroughput are obtained. For non-negligible round-tripdelay relative to packet transmission time, ournumerical results show that the new protocol improvesthe throughput by as much as 60% when compared to theexisting DSMA protocol. For superior performance andsimplicity, the DSMA/DT protocol will be appropriate foruse in high-speed wireless networks.     

一种适应时变信道的多用户多信道自适应协议

在认知网络中,具有强时变性的信道状态、用户状态影响着系统性能。为了提高系统吞吐量,实现用户最大通信速率,如何将时变的信道、用户状态和链路自适应调制与编码匹配是一个亟待解决的问题。针对此,提出了一种匹配检验分配协议（matching-check allocation protocol,MAP）。该协议联合链路自适应包错误率与通信速率,旨在实现信道状态、用户状态与传输模式匹配的同时最大化系统总通信速率。为了评估频谱分配协议在多用户多信道联合目标优化等复杂网络复杂指标下的性能,利用离散时间排队模型分析非授权用户行为,构建了一种通用的、适用性强的协议评估框架,得到了平均队长、平均吞吐量、平均时延、平均拒绝量等综合性能指标。在该框架下,将MAP与最大速率分配协议、公平随机分配协议进行比较。数据结果表明了MAP优于对比协议,也表明了协议评估框架能够评估不同的频谱分配协议,证明了MAP与协议评估框架的有效性。

     

Combination of repetition-coded PPM with SR-ARQ for wirelessinfra-red communication

An efficient combination of repetitive coded L-PPM with an ARQ protocol is presented which can estimate the channel state and adjust the link transmission rate. The protocol operation is modelled as a Markov chain and analysis results indicate the enhanced performance of the proposed scheme under adverse channel conditions     

A Distributed Mechanism for Power Saving in IEEE 802.11 Wireless LANs

The finite battery power of mobile computers represents one of the greatest limitations to the utility of portable computers. Furthermore, portable computers often need to perform power consuming activities, such as transmitting and receiving data by means of a random-access, wireless channel. The amount of power consumed to transfer the data on the wireless channel is negatively affected by the channel congestion level, and significantly depends on the MAC protocol adopted. This paper illustrates the design and the performance evaluation of a new mechanism that, by controlling the accesses to the shared transmission channel of a wireless LAN, leads each station to an optimal Power Consumption level. Specifically, we considered the Standard IEEE 802.11 Distributed Coordination Function (DCF) access scheme for WLANs. For this protocol we analytically derived the optimal average Power Consumption levels required for a frame transmission. By exploiting these analytical results, we define a Power Save, Distributed Contention Control (PS-DCC) mechanism that can be adopted to enhance the performance of the Standard IEEE 802.11 DCF protocol from a power saving standpoint. The performance of an IEEE 802.11 network enhanced with the PS-DCC mechanism has been investigated by simulation. Results show that the enhanced protocol closely approximates the optimal power consumption level, and provides a channel utilization close to the theoretical upper bound for the IEEE 802.11 protocol capacity. In addition, even in low load situations, the enhanced protocol does not introduce additional overheads with respect to the standard protocol.     

A TRAFFIC OVERSTOCK RESLOVE SCHEME IN WLAN

A new Multiple Access Control （MAC） protocol-User Adaptive Scheduling Multiple Access （UASMA） protocol is proposed in this paper. It can well schedule the packet transmission according to the exact number of active Mobile Terminals （MTs） determined by selforganizing algorithm and adjust the number of packets sent by one node in one frame properly. UASMA protocol employs a special frame structure, which makes it possible to allocate channel resource to uplink and downlink traffic according to their respective service requirements. The proposed concept of referenced-frame-length can ensure the frame length varies in a certain range, and consequently increase the utilization efficiency of the channel greatly. Meanwhile, UASMA protocol uses an efficient collision resolution algorithm to guarantee that active MTs can access the channel rapidly. Finally, the performance of UASMA protocol is evaluated by simulation and it is also compared with carrier sense multiple access, rounding-poll and UPMA protocols. The results show that the UASMA has better performance than others.     

Performance of a wireless access protocol on correlatedRayleigh-fading channels with capture

The throughput performance of a wireless media access protocol taking into account the effect of correlated channel fading, capture, and propagation delay is analyzed. For efficient access on the uplink (mobile-to-base-station link), the protocol makes use of the uplink channel status information which is conveyed to the mobiles through a busy/idle flag broadcast on the downlink (base-station-to-mobile link). A first-order Markov model is used to describe the correlation in the packet success/failure process on a Rayleigh-fading channel. The analytical results obtained through the first-order Markov approximation of the channel are compared to those obtained from an independent and identically distributed (i.i.d.) channel model. The Markovian-fading channel model is shown to provide better performance results than the i.i.d. channel model. Simulations show that a first-order Markov approximation of the Rayleigh-fading process is quite accurate. An enhanced version of the access protocol to take advantage of the memory in the fading channel behavior is proposed and analyzed. The effect of retransmission of erroneous data packets and propagation delay on the throughput is also analyzed. It is shown that the access protocol with an error detect (ED) feature is efficient in slow fading (e.g., pedestrian user speeds), whereas a retransmission protocol is more efficient in fast fading (e.g., vehicular user speeds)     

Performance Analysis of an Enhanced PRMA-HS Protocol for LEO Satellite Communication

The packet reservation multiple access with hindering state （PRMA-HS） is a protocol suitable for LEO satellite mobile communication. Although working well with light system payload （amount of user terminals）, the protocol imposes high channel congestion on system with heavy payload, thus degrades the system＇s quality of service. To controlling the channel congestion, a scheme of enhanced PRMA-HS protocol is proposed, which aims to reduce the collision of voice packets by adopting a mechanism of access control. Through theoretic analysis, the system＇s mathematic model is presented and the packet drop probability of the scheme is deduced. To testify the performance of the scheme, a simulation is performed and the results support our analysis.     

Performance evaluation of a reservation TDMA protocol for voice/data transmissions in a LEO satellite communication system

In this paper, the capability is investigated of a reservation TDMA‐based protocol to support constant bit rate and best‐effort traffics in Low Earth Orbit (LEO) satellite communication systems under typical propagation conditions. Differently from several previous papers on the same subject, we focus here on a communication channel affected by multipath fading and characterized by a high round trip delay. In our protocol, a higher priority is given to constant bit rate terminals with respect to best‐effort data terminals. The performance for constant bit rate and best‐effort terminals was derived by means of a suitable analytical approach and computer simulations. The results shown herein permits to evaluate the influence of the channel propagation conditions on the system performance. Moreover, they highlight that the reservation TDMA protocol exhibits a good behaviour for the communication channel under consideration and in comparison with a recent protocol based on the classical PRMA scheme. Copyright © 2003 John Wiley & Sons, Ltd.     

A Multiaccess Protocol for Multihop Radio Networks

We describe an adaptive multiaccess channel protocol for use in radio networks with an arbitrary distribution of stationary hidden nodes, which provides the nodes with controlled, collision-free access to the channel. The protocol can be considered to belong to the BRAM [5] protocol family, but differs in significant ways from BRAM. In this paper we describe the tenets of the protocol, then develop the protocol, and finally develop analytic expressions for its expected throughput and delay performance. Given these delay-throughput expressions, we show how protocol "delay" optimization can be achieved by dynamic adjustment of a protocol parameter as the network traffic load changes.     

适用于水下物联网的混合地理路由协议设计

该文针对水下物联网(IoUT)数据传输问题设计了一种混合地理路由协议。海洋环境的复杂性严重地限制了IoUT水下物联网节点间的数据传输性能,因此需要一个高效的路由协议以对抗复杂的信道环境。无状态几何路由(G-STAR)是一种采用贪婪转发模式的地理路由协议,在大多数3维物联网情景中能够找到合适的数据传输路径,然而水下环境中存在诸多不利因素制约了G-STAR的性能。对此,该文提出一个混合G-STAR(Hybrid G-STAR, H-G-STAR)协议,在保有G-STAR优势的基础上对协议在水下环境中的适应性进行了针对性设计。通过增加基于信道监听的无协作转发策略,在节点数量足够时自发地选择信道状况最佳的路径进行路由,由此避开贪婪转发在水下环境中可能遭遇的极端劣化信道。仿真结果显示H-G-STAR协议相较于基准G-STAR协议有着更好的路由性能,并且在物理层能够取得更低的误比特率(BER),在水下节点的网络拓扑中更为适用。     

Modeling and analysis of WAP performance over wireless links

In this paper, an analytical model for studying the performance behavior of wireless application protocol (WAP) over wireless links is proposed. A Rayleigh fading channel model is used to characterize the behavior of the wireless channel. Mathematical expressions that represent the performance of WAP as a function of the protocol and the channel parameters are derived. Computer simulation results are presented to validate the analytical results. It is shown that WAP performs better in a bursty error environment than in a random error environment. The goodput of WAP can be improved by increasing the WAP packet group size, but the significance of the improvement depends on the underlying channel condition.     

An MAC protocol supporting multiple traffic over mobile ad hoc networks

This letter presents the design and performance of a multi-channel MAC protocol that supports multiple traffics for IEEE 802.11 mobile ad-hoc networks.The dynamic channel selection scheme by receiver decision is implemented and the number of the data channel is independent of the network topology.The priority for real-time traffic is assured by the proposed adaptive back off algorithm and different IFS.The protocol is evaluated by simulation and the results have shown that it can support multiple traffics and the performance is better than the performance that IEEE 802.11 standard provides.