多媒体卫星通信系统中的时隙分配方法

论文针对VoIP实时通信业务,根据其对延迟性能的需求,分析了时隙分配对延迟性能的影响,并对其进行了建模分析.结果表明,与传统的时隙位置连续分配相比,时隙均匀分配能显著提高业务的延迟性能.文中给出了MF-TDMA的通信系统中,提高延迟性能的解决方案,分析了两种业务下时隙均匀分配和时隙连续分配的延迟性能和丢包率.     

EASA：一种分簇Ad Hoc网络高效自适应TDMA时隙分配算法

 提出一种适合于分簇Ad Hoc网络的高效自适应TDMA时隙分配算法EASA. EASA采用动态调整帧长以及根据簇内节点MAC层缓存队列长度进行自适应的时隙分配,解决了传统TDMA时隙分配算法中低传输速率节点占用不必要时隙的问题. 多个场景的实验结果表明,与传统TDMA时隙分配算法以及802.11相比,EASA可以大大提高网络吞吐量,很好的提高网络整体性能.     

一种利用信道侦听的动态TDMA协议

针对TDMA网络节点间业务量不均匀时,会造成信道资源严重浪费的情况,提出了一种利用信道侦听的CS-TDMA协议。该协议在TDMA协议的基础上,节点通过接收到各节点的数据包数量估算相应节点的业务量大小。当某节点时隙剩余时,向其统计中业务量最大的一个节点发送ATS信息,通知该节点占用剩余时隙发送数据,直至时隙结束。仿真结果表明,CS-TDMA协议较TDMA协议在传输时延、吞吐量、数据接收率上均有所提高,尤其在节点间业务量大小不均匀时,时延性能提升更加明显。     

单兵作战系统中信息监听冲突消除技术研究

针对当前单兵作战系统通信网络中所采用的固定分配TDMA算法不能适应大型战场环境和自组织运行需求的问题,提出一种基于消费算法和二叉树时隙分配算法的动态时隙分配TDMA算法,即C-TDMA算法,通过多组载波监听消除接入冲突,在保证延时的基础上使用消费算法控制节点分组发送量,提高信道接入公平性,同时通过二叉树时隙分配算法支持网络分布式运行。仿真结果表明,对于负载较重、传输混合业务且时延敏感的单兵作战系统网络,该算法可以消除接入冲突,提高信道吞吐率。     

基于TDMA支持实时应用的多跳时隙预留协议

提出一种基于时分多址接入(TDMA)的多跳时隙预留的协议(TMSR)以支持Ad Hoc网络中的实时应用,协议中节点为实时数据包的多跳转发预留信道时隙,通过超帧把数据包从源节点传输到远端的目的节点。通过NS2对提出的协议性能进行评估,重点分析了静态和移动环境下该协议的平均端到端时延和平均吞吐量,同时,在单跳仿真场景中,对TMSR协议与ETDMA进行对比,仿真结果表明随着数据流量的增加,TMSR提供了比E-TDMA更好的数据包吞吐量和时延性能。在多跳仿真场景中,采用TMSR协议的节点间的平均端到端的时延满足了实时应用的端到端多跳时延要求。     

一种基于固定TDMA的无冲突动态时隙分配算法

本文提出了一种适用于Adhoc网络的动态时隙分配TDMA算法——IP-TDMA算法,该算法以一种新颖的方式在固定TDMA的基础上叠加了优先级竞争机制,既有最差性能保障,又有较高信道利用率。通过采用一种特殊的帧结构,P-TDMA算法还可以避免信令分组的碰撞,是一种有效而又可靠的广播动态时隙分配TDMA算法。仿真结果表明,无论在吞吐量还是迟延方面,P-TDMA算法都比固定TDMA表现出更好的性能。     

JTIDS 的时隙分配技术研究

JTIDS 采用 TDMA 的工作方式,时隙分配技术至关重要,讨论了该系统中的时隙结构、分配形式、分配方式和访问模式,指出了它与一般通信系统的区别,并提出了预分配和工作过程中按需分配相结合的时隙分配步骤。最后,介绍了一种同类系统 TIS 的主要特点。     

TDMA动态时隙分配在EOC上的应用

为提高EOC、EPON等一对多通道的使用效率通常采用TDMA方式，采用动态时隙分配能实现动态带宽分配，提高通道的使用效率，减少时隙无数据传输时的浪费，提高EOC系统的QoS性能。     

WCDMA与GSM系统在设计规划中的不同

引言 GSM系统是目前全球覆盖范围最广的第二代无线网络,它采用TDMA(时分多址)接入方式,即在一个载频信道内,按相同的时间间隔划分成每帧若干时隙的固定循环周期,每个时隙承载一个业务用户信息和必要的信令.这样,一个载频信道由若干个用户按时间顺序依次占用,以不同时隙作为区分不同用户的方式.     

一种新的无线传感网络的时隙分配策略

时隙分配是时分多址(TDMA)接入的核心。TMDA将时间划分为若干个固定时隙,使2个干扰的节点在不同时隙内传输数据,进而降低接入碰撞率。为此,提出基于分布式TDMA的时隙分配算法。该算法以Drand算法为基础,对其进行改进。利用路由信息分配时隙,降低通信时延和传输的消息数。仿真结果表明,与Drand算法相比,提出的算法传输时延降低了约8%,传输的消息数约下降了24%。     

Delay and throughput characteristics of TH, CDMA, TDMA, and hybridnetworks for multipath faded data transmission channels

The new concepts of adaptive time hopping and variable frame code division (CDMA) multiple access are introduced. By a unified analysis, the probabilities of bit and packet errors in multipath fading environment for five time division (TDMA), code division, and time hopping (TH) related multiaccess networks are obtained; namely, TDMA, CDMA, CDMA/TDMA, Adaptive CDMA/TH, and variable frame CDMA/TDMA networks. The delay and useful throughputs of the five systems are also evaluated for data and voice traffic. All systems compared have the same channel power and bandwidth and support the same traffic. Though implementation issues are not covered, CDMA systems are put at a disadvantage (compared to cellular-type FDMA networks, for example) by ignoring such inherent advantages as voice silence utilizations and automatic frequency reuse. Nontheless, two CDMA systems outperform TDMA systems at low and medium input traffics     

Bandwidth guaranteed call admission in TDMA/CDMA ad hoc wireless networks

This paper first studied the timeslot assignment problem in time division multiple access/code division multiple access (TDMA/CDMA) wireless ad hoc networks. Given a path P, we prove that a timeslot assignment providing one unit of bandwidth on P can be found in O(P) time if such an assignment exists. The results have been extended to the case that P can provide two units of bandwidth. Based on the timeslot assignment for the special cases, an efficient slot assignment algorithm with O(P²k) is proposed for general cases, where k is the number of slots in a TDMA frame. Then, the timeslot assignment algorithm is integrated into a quality of service (QoS) call admission scheme for QoS call requests. Extensive simulations are conducted and the results have demonstrated the superior performance of our method.     

Performance evaluation of a satellite-switched variable-frame TDMA system

In satellite-switched time-division multiple access (SS/TDMA) systems, the demand assignment control is a suitable scheme for the bursty packets to enhance the capacity efficiency. In the system, by applying the demand assignment scheme, the minimum transmission time could be achieved by the efficient time slot assignment algorithm. According to a given traffic matrix, the minimum transmission time cannot exceed the fixed TDMA frame duration. The spare time may be left at the end of the TDMA frame as the growth space for the future needs. To increase the system efficiency, the spare time could be reduced. In this paper, a demand assignment protocol with a variable frame is proposed for the system. The Markov chain model is applied to analyze the system performance on throughput, balking probability and packet delay. Performance comparison with the previous presented protocol, the proposed protocol could show a simple control technique and the efficient performance results in the system. It is a suitable candidate to be employed in the satellite networks to provide communication between the satellite and earth stations.     

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.     

Reduced‐frame TDMA protocols for wireless sensor networks

Time‐division multiple‐access (TDMA) is a common medium access control paradigm in wireless sensor networks. However, in its traditional form, the TDMA‐based protocols suffer from low channel utilization and high message delay because of a long frame length needed to provide collision‐free transmissions, which is particularly damaging in dense wireless sensor networks. In this paper, we investigate the performance and the energy efficiency of a class of TDMA‐based protocols, called reduced‐frame TDMA, where every TDMA slot is augmented with a short time period dedicated for carrier sense multiple access‐based contention resolution mechanism. Because of their ability to dynamically resolve collisions caused by conflicting slot assignments, the reduced‐frame TDMA protocols can be configured with any frame length, independently of node density. In addition, we present a distributed heuristic slot assignment algorithm that minimizes interslot interference in the presence of limited number of slots per frame. The simulation results indicate that the reduced‐frame TDMA protocols significantly reduce the message delay and increase the maximum throughput without incurring significant penalty in energy efficiency compared with the traditional TDMA scheme. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance Evaluation of the Networks with Wi-Fi based TDMA Coexisting with CSMA/CA

The wireless technology is widely used in industries with timing stringent tasks. However, it lacks of the consideration of the co-channel interference when designing and estimating the performance of the media access strategies. Thus, it is hard to guarantee the real-time and reliable packet transmissions. In this study, we first propose a Wi-Fi based TDMA access scheme to provide the stringent timing and reliability guarantees under the coexistence with the CSMA/CA scheme. Then, we theoretically analyze the delay of the Wi-Fi TDMA scheme and the throughput of the CSMA/CA scheme considering mutual interferences. The effectiveness of the proposed Wi-Fi TDMA scheme is demonstrated by numerous simulation results since the results show that the retransmission times and the average access delay of the TDMA station are small when varying the CSMA/CA packet length, TDMA packet length, TDMA slot length and TDMA duty cycle. The simulation results also show that the analysis TDMA delays are almost the same with the simulation ones which indicate the accuracy of our theoretical analysis models. Additionally, numerous simulations have been done to show the impact of the Wi-Fi TDMA scheme on the typical CSMA/CA scheme by varying the TDMA frame length and the TDMA duty cycle under centralized and distributed slot assignment strategies.

     

A Hybrid Adaptive Wireless Channel Access Protocol for Multimedia Personal Communication Systems

This paper proposes a new medium access protocol (MAC) protocol for futurewireless multimedia personal communication systems, denoted hybrid andadaptive multiple access control (HAMAC) protocol. The HAMAC protocolintegrates fixed assignment TDMA protocol, reservation-based protocols, andcontention-based protocols into a single wireless network so as tosimultaneously and efficiently support various classes of traffic such asconstant-bit-rate (CBR), variable-bit-rate (VBR), and available-bit-rate (ABR)traffic. In particular, the HAMAC protocol uses a novel preservationslot technique to overcome the packet contention overhead in packetreservation multiple access (PRMA) like protocols, while keeping mostisochronous service features of TDMA protocols to serve voice and CBR trafficstreams. A preservation slot is a very short slot which is used torepresent a CBR connection when the traffic in the CBR connection is in asilent period in which there is no meaningful data to transmit. Due to thevery short length of the preservation slot, it only takes minimalportion of the bandwidth pre-allocated to the CBR connection, so that theremaining bandwidth can be freed for other connections to use. When the CBRsource becomes active again, the preservation slot is replaced bynormal data slots without any reservation operation, extra delay, orsignificant bandwidth loss. Consequently, the guaranteed service andsimplified signaling features of TDMA protocols, together with the adaptivebandwidth allocation features of PRMA-like protocols, are both realized in theHAMAC protocol. We have analyzed the performance of the HAMAC protocol usingextensive simulations. The results show that the HAMAC protocol can achievevery low loss rates for various multimedia traffic with stringent quality ofservice (QoS) requirements and outperforms state-of-the-art PRMA-likeprotocols. As a result, the HAMAC protocol appears to be a good candidate forfuture generation multimedia personal communication systems.     

A Bandwidth Reservation Multiple Access Protocol for Wireless ATM Local Networks

A bandwidth reservation multiple access scheme(BRMA) is proposed to resolve contention and assignbandwidth among multiple users trying to gain access toa common channel such as in mobile users contending for resources in an ATM-based cellular networkor a wireless local area network (LAN) with shortpropagation delays. The protocol is best suited tosupport variable-bit-rate (VBR) traffic that exhibits high temporal fluctuations. Each mobile user isconnected end-to-end to another user over virtualchannels via the base station that is connected to thewired ATM B-ISDN network. The channel capacity is modeled as a time frame with a fixed duration.Each frame starts with minislots, to resolve contentionand reserve bandwidth, followed by data-transmissionslots. Every contending user places a request for data slots in one of the minislots. If therequest is granted by the base station through adownlink broadcast channel, the user then startstransmission in the assigned slot(s). The number ofassigned slots varies according to the required qualityof service (QoS), such as delay and packet lossprobability. A speech activity detector is utilized inorder to indicate the talkspurts to avoid wastingbandwidth. Due to its asynchronous nature, BRMA is ratherinsensitive to the burstiness of the traffic. Since theassignment of the minislots is deterministic, therequest channels are contention-free and the data channels are collision-free. Hence, in spite ofthe overhead (minislots) in each frame, BRMA provideshigher throughput than Packet Reservation MultipleAccess (PRMA) for the same QoS, especially for high-speed systems. A better delay performance is alsoachieved for data traffic compared to Slotted Alohareservation-type protocol PRMA. In addition, BRMAperforms better in terms of bandwidth efficiency thanthe conventional TDMA or the Dynamic TDMA, wherespeech activity detectors are very difficult toimplement.     

Frame‐based adaptive uplink scheduling algorithm in orthogonal frequency division multiple access‐based Worldwide Interoperability for Microwave Access networks

Because the orthogonal frequency division multiple access physical resource available for scheduling in Worldwide Interoperability for Microwave Access networks is frame by frame, an uplink scheduler located at the base station must efficiently allocate available resources to the subscriber stations in response to constant or bursty data traffic on a per‐frame basis. Available resources for real‐time and nonreal‐time traffics, called frame‐based adaptive bandwidth allocation and minimum guarantee and weight‐based bandwidth allocation, respectively, are proposed in this paper. Moreover, both short‐term and long‐term bandwidth predictions for traffic are incorporated so that the long‐term bandwidth prediction can have sustainable throughput requirement, and the short‐term bandwidth prediction can meet the objectives of low delay and jitter. For the scenarios studied, it shows that system performance of the proposed algorithm is better than the hybrid (earliest deadline first + weighted fair queuing + FIFO) algorithm in terms of packet delay, jitter, throughput, and fairness. Copyright © 2011 John Wiley & Sons, Ltd.