Making transmission schedules immune to topology changes inmulti-hop packet radio networks

Transmissions scheduling is a key design problem in packet radio networks, relevant to TDMA and CDMA systems. A large number of topology-dependent scheduling algorithms are available, in which changes of topology inevitably require recomputation of transmission schedules. The need for constant adaptation of schedules to mobile topologies entails significant, sometime insurmountable, problems. These are the protocol overhead due to schedule recomputation, performance penalty due to suspension of transmissions during schedule reorganization, exchange of control message and new schedule broadcast. Furthermore, if topology changes faster than the rate at which new schedules can be recomputed and distributed, the network can suffer a catastrophic failure. The authors propose a robust scheduling protocol which is unique in providing a topology transparent solution to scheduled access in multi-hop mobile radio networks. The proposed solution adds the main advantages of random access protocols to scheduled access. Similarly to random access it is robust in the presence of mobile nodes. Unlike random access, however, it does not suffer from inherent instability, and performance deterioration due to packet collisions. Unlike current scheduled access protocols, the transmission schedules of the proposed solution are independent of topology changes, and channel access is inherently fair and traffic adaptive     

A topology transparent link activation protocol for mobile CDMAradio networks

A topology transparent protocol for link activation in mobile CDMA networks is presented. The protocol resolves primary and secondary conflicts, and can easily be adapted to TDMA link activation, as well. The proposed protocol guarantees that each link will be successfully activated at least once in a frame without the need to adjust transmission schedules in mobile environments. Compared to other protocols with guaranteed delivery, the overhead due to the recomputation of transmission schedules is eliminated and, accordingly, transmissions need not be suspended for schedule reorganization. Furthermore, contrary to previously known protocols that adapt to mobility by schedule recomputation, the proposed solution is not subject to a potential catastrophic failure when the rate of topology changes exceeds the rate at which schedules can be readjusted. We prove the correctness and evaluate the efficiency of the new protocol by analytical methods     

Performance analysis of adaptive MAC protocol in VANETs considering the potential impact on throughput and transmission delays

The existing adaptive multichannel medium access control (MAC) protocols in vehicular ad hoc networks can adjust themselves according to different vehicular traffic densities. These protocols can increase throughput and guarantee a bounded transmission delay for real‐time safety applications. However, the optimized control channel interval is computed based on the maximum throughput while ignoring the strict safety packet transmission delay requirements. In this paper, we analyze the effects of the throughput and strict safety packet transmission delay with adaptive multichannel MAC protocols, such as connectivity‐aware MAC (CA MAC), adaptive multi‐priority distributed MAC (APDM), multi‐priority supported p‐persistent MAC (MP MAC), and variable control channel interval MAC (VCI) protocols. The performance and analysis results show that: (a) under a low data rate condition, CA MAC does not guarantee a strict safety packet transmission delay; (b) APDM not only satisfies the safety packet transmission requirement, but also provides the lowest safety packet transmission delay; (c) under a high data rate condition, we suggest APDM for use as an adaptive MAC protocol because it allows for high throughput for nonsafety packets and preserves low safety packet transmission delay; (d) under a low data rate condition with various data packet sizes, we suggest MP MAC for high throughput, which satisfies the safety packet transmission requirement; and (e) under low vehicle density and low data rate conditions, VCI can support high throughput. A balance between transmission delay and throughput must be considered to improve the optimal efficiency, reliability, and adaptability.     

Immediate neighbor scheduling (INS): An adaptive protocol for mobile ad hoc networks using direct-sequence spread-spectrum modulation

We investigate a new approach for scheduling transmissions in a mobile ad hoc network employing direct-sequence spread-spectrum (DSSS). Multiple-access interference may be better tolerated in these systems, allowing higher levels of spatial reuse and a reduction in the overhead required to schedule transmissions. We present a protocol which leverages these features of DSSS to support greater end-to-end throughput and terminal mobility rates. A protocol extension allows terminals to adjust protocol overhead in order to preserve network connectivity in sparse networks. For each transmission, terminals use a combination of common and transmitter-oriented spreading sequences in a format which allows for discovery of nearby terminals and adaptation of transmission rates to maximize throughput. The protocol does not operate over an artificial network graph, nor does it require an initialization phase or two-way exchange of information during a transmission slot. Through simulations, we evaluate the performance of the transmission scheduling protocol in a variety of static and mobile scenarios. For comparison, we also simulate a centralized transmission scheduling protocol with perfect knowledge of topology.     

A mobility-transparent deterministic broadcast mechanism for ad hocnetworks

Broadcast (distributing a message from a source node to all other nodes) is a fundamental problem in distributed computing. Several solutions for solving this problem in mobile wireless networks are available, in which mobility is dealt with either by the use of randomized retransmissions or, in the case of deterministic delivery protocols, by using conflict-free transmission schedules. Randomized solutions can be used only when unbounded delays can be tolerated. Deterministic conflict-free solutions require schedule recomputation when topology changes, thus becoming unstable when the topology rate of change exceeds the schedule recomputation rate. The deterministic broadcast protocols we introduce in this paper overcome the above limitations by using a novel mobility-transparent schedule, thus providing a delivery (time) guarantee without the need to recompute the schedules when topology changes. We show that the proposed protocol is simple and easy to implement, and that it is optimal in networks in which assumptions on the maximum number of the neighbors of a node can be made     

移动Ad HOc网络中的公平按需多址接入协议

基于快速、有效竞争预约接入、无冲突轮询传输的思想和带冲突预防的冲突分解策略,本文提出了适于移动Ad Hoc网络的公平按需多址接入(FODA)协议.该协议在分群结构的基础上,利用公平冲突预防算法预约信道资源获得轮询服务,从而完全消除了载波侦听方式下多跳无线网络业务传输中的隐藏终端和暴露终端问题.另外,公平冲突预防算法解决了节点竞争接入时的冲突问题和不公平现象.最后,仿真结果表明,与带冲突避免的载波侦听多址接入(CSMA/CA)和轮询协议相比,FODA协议可以提供较高的信道吞吐量、较低的平均消息丢弃率和平均消息时延.     

An in-band signaling protocol for optical packet switching networks

Advances in optical networking reveal that all optical networks offering a multigigabit rate per wavelength will soon become economical as the underlying backbone in wide-area networks, in which the optical switch plays a central role. One of the central issues is the design of efficient signaling protocols which can support diversified traffic types, in particular the bursty IP traffic. This paper introduces a novel signaling protocol called the sampling probe algorithm (or SPA) to be used in a class of optical packet switching systems based on wavelength division multiplexing (WDM). The proposed scheme takes a drastically different approach from all existing signaling protocols. The salient features are 1) the pretransmission coordination is using an in-band signaling protocol, and thus does not require separate control channel(s) for transmission coordination; 2) the protocol is based on a reservation (connection) scheme which is capable of supporting multimedia traffic; 3) a gated service is adopted in which each successful reservation allows multiple packets (train of packets) to be transmitted, which can significantly reduce the per packet overhead; 4) the scheduling algorithm is adaptive by allowing flexible assignment of bandwidth on-demand; 5) the channel status gathering is done in a distributed fashion, and uses a passive listening mechanism, which itself does not interfere with packet transmissions. The results demonstrate that the proposed in-band signaling protocol can achieve high throughput and stability under heavy traffic condition.     

一种新的有效支持智能天线应用的多址接入协议

本文研究将智能天线应用于分组无线网络中,提出了支持智能天线应用的自适应时隙分配多址接入协议(ASAMA).该协议采用时分双工(TDD)方式,每一帧开始时用户节点依次发送训练序列,基站的智能天线据此计算出各用户节点的空间特征(Spatial Signature).基于波束形成的信干噪比最大化准则,设计了逐点优化与全局优化两种不同复杂度的时隙分配算法.由基站对上下行业务的时隙进行动态分配,在保证通信质量的前提下,使每个时隙容纳多个数据分组,以充分实现信道的空分复用(SDMA).对该协议的信道利用率进行了近似分析,并利用仿真方法考察其性能.结果表明,ASAMA协议能有效支持智能天线应用并具有很高的信道利用率与良好的时延性能.     

Distributed space-time-coded protocols for exploiting cooperative diversity in wireless networks

We develop and analyze space-time coded cooperative diversity protocols for combating multipath fading across multiple protocol layers in a wireless network. The protocols exploit spatial diversity available among a collection of distributed terminals that relay messages for one another in such a manner that the destination terminal can average the fading, even though it is unknown a priori which terminals will be involved. In particular, a source initiates transmission to its destination, and many relays potentially receive the transmission. Those terminals that can fully decode the transmission utilize a space-time code to cooperatively relay to the destination. We demonstrate that these protocols achieve full spatial diversity in the number of cooperating terminals, not just the number of decoding relays, and can be used effectively for higher spectral efficiencies than repetition-based schemes. We discuss issues related to space-time code design for these protocols, emphasizing codes that readily allow for appealing distributed versions.     

MATS: multichannel time-spread scheduling in mobile ad hoc networks

Wireless mobile ad hoc networks (MANETs) have received considerable attention in the last few years. Most research works focus on single-channel MANETs with a single power-level in order to simplify the network design and analysis. How to take advantage of multiple channels and multiple power levels in MANETs poses a serious challenging problem. Recently, a few multichannel transmission protocols such as collision-avoidance transmission scheduling (CATS) have been proposed to harvest the advantage of high transmission efficiency when multiple channels are deployed. Although such protocols do provide ways to coordinate the use of multiple channels, there exist some serious problems such as the throughput fast drop-off under heavy traffic loads. In this paper, we propose a new protocol, namely, multichannel time-spread scheduling (MATS), which attempts to tackle these problems. In MATS, nodes with transmission requests are divided into three groups, which carry out channel reservations in parallel and can simultaneously support unicasting, multicasting and broadcasting at the link level. MATS ensures successful and collision-free data transmissions using the reserved channels and allows multicasting and broadcasting high priorities over unicasting. Both theoretical analysis and extensive simulation studies are carried out which show that the performance of MATS under high traffic loads significantly outperforms the existing schemes.     

Design and performance evaluation of a MAC protocol for wireless local area networks

We propose and analyze, from a performance viewpoint, a Medium Access Control (MAC) protocol for Wireless Local Area Networks (WLANs). The protocol, named Prioritized-Access with Centralized-Control (PACC), supports integrated traffics by guaranteeing an almost complete utilization of network resources. The proposed protocol combines random access for signalling, with collision-free access to the transmission channel. The transmission channel is assumed to be slotted, with slots grouped into frames. Access to transmission slots is controlled by a centralized scheduler which manages a multiclass queue containing the users' requests to access the transmission channel. Three classes of users are assumed: voice traffic (voice), data traffic with real-time constraints (high-priority data), and classical data traffic (low-priority data). A priority mechanism ensures that speech users have the highest priority in accessing the idle slots, since speech packets have a more demanding delay constraint. The remaining channel bandwidth is shared fairly among the high-priority data terminals. The low-priority data terminals use the slots left empty by the other classes. Specifically, access to transmission slots is controlled by the centralized scheduler by managing a transmission cycle for each class of terminals. The voice-terminals cycle has a constant length equal to one frame, while the lengths of the data-terminals cycles are random variables which depend on the number of active voice and data terminals. In this paper we show that the proposed scheme can support the same maximum number of voice terminals as an ideal scheduler, while guaranteeing an almost complete utilization of network capacity. In addition, via a performance analysis, we verify that by limiting the number of real-time data terminals in the network this class of traffic can be statistically guaranteed access delays in the order of 200–300 msec. Hence, the QoS the network gives to the real-time data terminals makes this service suitable for real-time applications such as alarms or low bit rate video. This revised version was published online in June 2006 with corrections to the Cover Date.     

Improving protocol robustness in ad hoc networks through cooperative packet caching and shortest multipath routing

A mobile ad hoc network is an autonomous system of infrastructure-less, multihop, wireless mobile nodes. Reactive routing protocols perform well in this environment due to their ability to cope quickly against topological changes. This paper proposes a new routing protocol named CHAMP (caching and multiple path) routing protocol. CHAMP uses cooperative packet caching and shortest multipath routing to reduce packet loss due to frequent route failures. We show through extensive simulation results that these two techniques yield significant improvement in terms of packet delivery, end-to-end delay and routing overhead. We also show that existing protocol optimizations employed to reduce packet loss due to frequent route failures, namely local repair in AODV and packet salvaging in DSR, are not effective at high mobility rates and high network traffic.     

A protocol for adaptive transmission in direct-sequence spread-spectrum packet radio networks

Wireless communication channels may change greatly from one transmission to the next, due to variations in propagation loss and interference. The use of fixed transmission parameters for such channels results in wasted energy when channel conditions are good. Adaptation of the power, code rate, and symbol rate reduces energy consumption and interference caused to other systems. Such adaptation requires information about the characteristics of the channel, which is more difficult to obtain in a packet radio network (PRN) or other mobile ad hoc network than in a typical cellular communication system. We develop methods for providing partial information about the channel state from three statistics that are derived by different subsystems in the receiving terminals of a direct-sequence spread-spectrum PRN. We present and evaluate a protocol that uses this information to adapt the transmission parameters in response to changes in interference and propagation conditions in the network. The performance of the new adaptive-transmission protocol is compared with a system with fixed transmission parameters and with an adaptive protocol that is furnished with perfect knowledge of the channel state at the completion of each transmission.     

Towards Robust Multi-Layer Traffic Engineering: Optimization of Congestion Control and Routing

In the Internet today, traffic engineering is performed assuming that the offered traffic is inelastic. In reality, end hosts adapt their sending rates to network congestion, and network operators adapt the routing to the measured traffic. This raises the question of whether the joint system of congestion control (transport layer) and routing (network layer) is stable and optimal. Using the established optimization models for TCP and traffic engineering as a basis, we find the joint system can be stabilized and often maximizes aggregate user utility. We prove that both stability and optimality of the joint system can be guaranteed for sufficiently elastic traffic simply by tuning the cost function used for traffic engineering. Then, we present a new algorithm that adapts on a smaller timescale to changes in traffic distribution and is more robust to large traffic bursts. Uniting the network and transport layers in a multi-layer approach, this algorithm, distributed adaptive traffic engineering (DATE), jointly optimizes the goals of end users and network operators and reacts quickly to avoid bottlenecks. Simulations demonstrate that DATE converges quickly     

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.     

CROMA – An Enhanced Slotted MAC Protocol for MANETs

TDMA based MAC protocols can provide a very good utilization of the shared radio resources, especially at high input loads, in synchronized mobile ad hoc networks (MANETs). Global positioning systems like GPS or GALLILEO should provide a very good timing accuracy for synchronization of nodes. This paper presents a new medium access protocol for mobile ad hoc networks, called CROMA. CROMA is collision-free and receiver-oriented. It operates in a slotted environment, in a dynamic and distributed way. In this protocol, receivers act as local base stations and can manage one or several communications on a single slot. Thus, sophisticated functions are allowed at higher layers. Moreover, the hidden terminal as well as the exposed terminal problems are handled by CROMA. A theoretical analysis and extensive simulations show that CROMA can reach very high throughputs.     

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.     

Adaptive load distribution approach based on congestion control scheme in ad-hoc networks

The ‘load distribution’ proposition in mobile ad-hoc networks (MANETs) is accomplishing great stimulation. This is because of the phenomenal facets it possesses including advanced network resilience, reliability and performance. Though there are other leading network layer routing protocols, but they radically utilise single-path communication paradigm, which is why they fail in achieving efficient load distribution in a network. Via this paper, we propose an efficient cross-layer adaptive load distribution approach to capitalise network’s channel utilisation and to rapidly adapt to dynamic wireless channel characteristic changes. The proposed method modifies the load balanced congestion adaptive routing (LBCAR) protocol and is developed using dynamic load distribution technique, by pioneering (i) novel parameters, which report for the availability of route pertaining to minimum traffic load and better link lifetime and also adapt according to varying available network resources; (ii) an absolute dynamic method to lessen the redundant route oscillations which further reduces the routing instabilities. The simulation results demonstrate the usefulness of the proposed method and yields better results in comparison to LBCAR and standard instead of dynamic ource outing, it is dynamic source routing (DSR) protocol.     

Distributed paging and registration in wireless networks

The success of current and future wireless networks depends on their ability to provide connections to mobile terminals anywhere and at any time. It is therefore of crucial importance that wireless networks are able to quickly and efficiently locate mobile users at the time of an incoming call, which is achieved in current networks through a combination of paging and registration. In this article we present novel distributed paging and registration procedures that are naturally suited to future distributed wireless network architectures. In addition, the distributed nature of these strategies allows us to effectively balance the paging and registration traffic and the required signal processing throughout the network and alleviate any potential overloads of individual base stations.