MAC Protocol Design and Optimization for Multi-Hop Ultra-Wideband Networks

Ultra-wideband (UWB) communication is a promising enabling technology for future broadband wireless services. A simple, scalable, distributed, efficient medium access control (MAC) protocol is of critical importance to utilize the large bandwidth UWB channels and enable numerous new applications and services cost-effectively. In this paper, by investigating the characteristics of UWB communications, we propose a Distributed, EXclusive region (DEX) based MAC protocol. The proposed DEX protocol capitalizes on the spatial multiplexing gain of UWB networks by reserving exclusive regions (ER) surrounding the sender and receiver for data and acknowledgment (ACK) transmissions, so that users can efficiently and fairly share network resources in a distributed and asynchronous manner. We further quantify the network performance bounds and derive the optimal ER size to maximize the expected network transport throughput for a dense, multi-hop UWB network. Extensive simulation results demonstrate the efficiency and effectiveness of the DEX protocol. This work explores how to effectively utilize the wireless spatial capacity of distributed, multi-hop wireless networks by optimizing protocol parameters, instead of depending on more complicated control messages.     

带有广义反馈的多址接入中继信道的可达速率区域的研究

多址接入中继信道是含有多个接入节点、1个中继节点和1个目的接收节点的无线多用户信道,同时考虑接入节点之间能够接收彼此含噪的广义反馈信息,此种模型存在于接入节点之间协作通信能力较差的多跳无线网络和无线传感器网络。论文给出了带有此种广义反馈的离散无记忆多址接入中继信道的可达速率区域,并将这一结果推广到高斯信道。提出一个新的编码方案,主要基于速率划分和译码前传策略,并通过采用分组Markov叠加编码建立各接入源节点之间以及源节点和中继节点之间的协作通信,在可达性证明中还采用规则编码和反向译码策略。结果表明,在离散无记忆信道环境下可达速率区域相比较以往结果更具一般性,在高斯信道环境下可达速率区域被扩展。     

Obstacle-Free Geocasting Protocols for Single/Multi-Destination Short Message Services in Ad Hoc Networks

Mobile ad hoc networks (MANET) comprise mobile hosts in a network bereft of base stations and characterized by a highly dynamic network topology. The MANET environment contains unpredictable obstacles, such as mountains, lakes, buildings, or regions without any hosts, impeding or blocking message relay. This study proposes geocasting protocols for sending short message from a source host to single or multiple geocasting regions in ad hoc networks. The proposed protocols keep messages away from unpredictable obstacles and create a small flooding region. Experimental results show that a source host can send a short message to all hosts located in single or multiple geographical areas with a high success rate and low flooding overhead.     

A survey of geocast routing protocols

Geocasting is the delivery of a message to nodes within a geographical region. With geocast, new services and applications are feasible, such as finding friends who are nearby, geographic advertising, and accident or wrong-way driver warning on a motorway. In this article we present a survey on geocast routing protocols. The protocols mainly differ in whether they are based on flooding, directed flooding, or on routing without flooding, and whether they are suitable for ad hoc networks or for infrastructure networks. Based on these criteria we propose a classification of geocast protocols. Our protocol comparison includes message and memory complexity, robustness, and the ability to deliver geocast packets in partially partitioned networks. Finally, we present simulations to compare the approaches based on flooding, directed flooding, and routing without flooding.     

Contention aware mobility prediction routing for intermittently connected mobile networks

This paper introduces a novel multi-copy routing protocol, called predict and forward (PF), for delay tolerant networks, which aims to explore the possibility of using mobile nodes as message carriers for end-to-end delivery of the messages. With PF, the message forwarding decision is made by manipulating the probability distribution of future inter-contact and contact durations based on the network status, including wireless link condition and nodal buffer availability. In particular, PF is based on the observations that the node mobility behavior is semi-deterministic and could be predicted once there is sufficient mobility history information. We implemented the proposed protocol and compared it with a number of existing encounter-based routing approaches in terms of delivery delay, delivery ratio, and the number of transmissions required for message delivery. The simulation results show that PF outperforms all the counterpart multi-copy encounter-based routing protocols considered in the study.     

Active caching: a transmission method to guarantee desired communication reliability in wireless sensor networks

Due to the high packet loss rate during multi-hop transmissions in wireless sensor networks, more reliable endto- end data transmission is desirable. Because wireless sensor network applications require various levels of communication reliability (CR), the end-to-end data transmission should satisfy the desired CR of the applications. In this letter, we propose a flexible loss recovery mechanism for sensor network applications with various CRs. The proposed scheme caches data packets at intermediate nodes over routing paths computed by CR to retransmit lost packets during multi-hop transmissions. Because the proposed scheme presents a tradeoff between end-to-end delays and memory requirements dependent on CR, it can be used flexibly in various sensor network applications.     

<Emphasis Type="BoldItalic">LAMA/CA</Emphasis>: A Load-Adaptive MAC Protocol for Short Packets

An efficient Media Access Control (MAC) protocol for wireless Internet access is developed in this study. The proposed access protocol exploits the fact that very often the Internet access messages, such as HTTP download requests, are based on short packets. In addition, whenever the user is able to access to multiple overlapping base stations (e.g., in WiMAX access networks, or in 3GPP cellular networks), the proposed protocol enables the user to select the least loaded base station. Consequently, the user gets a better quality of service, while load balancing is achieved by preferring links that are less loaded over congested links. The key idea is to adjust the access probability to the load on the local link, and to use a different access protocol for short messages. Delay insensitive and long messages are transmitted using a Request To Send (RTS) and Clear To Send (CTS) mechanism, in a similar way to IEEE 802.11, over hops that are able to support this protocol type, while short and delay-sensitive messages are transmitted using another method, that offers a reduced call delivery delay, as well as better channel utilization. Whenever the message length drops below a certain threshold (evaluated in this study), the overhead of transmitting an RTS and CTS messages becomes too large. The analysis in this study shows that this threshold is load-dependent. Whenever the message length drops below this load-dependent threshold, this study proposes to use a protocol which is more efficient for short messages transmissions, such as HTTP download requests, Short Message Service (SMS) messages, and signaling messages. The proposed MAC protocol is especially suitable for 3G and beyond cellular networks. Whenever there are number of channels that can be possibly used to deliver a message, it enables to select the least loaded channel among several channels.     

A Reed-Solomon Based Method to Improve Message Delivery in Delay Tolerant Networks

Delay and Disruption Tolerant Networks are made up of mobile wireless nodes which may experience major message delivery restrictions. Such restrictions are the result of intermittent connectivity and scattered topology. Within these networks, messages can be detained for long periods of time or never be delivered. Existing solutions that purport improved message delivery rates modify routing protocols to perform integrity verification with each hop, resulting in routing overhead and, very often, unnecessary processing costs. This article proposes a scheme, named EMCOD, which decreases message delivery delay, while minimally increasing the processing overheads. To achieve this, EMCOD uses data encoding and interleaving to create messages. The original data is reassembled from some of the messages received, without the need to wait for all messages to be received. In scenarios subject to long delays and/or significant packet loss rates, it is possible to reduce original data recovery times by more than 50%. The processing overhead resulting from the encoding procedures is offset by the data recovery capabilities, which effectively decreases network overheads by more than 60%, in the same scenarios. EMCOD modifies the Bundle Layer, without interfering with the remaining layers, making it possible to route the messages through nodes that do not implement the proposed scheme.     

Performance Modeling for Relay Cooperation in Delay Tolerant Networks

Delay tolerant networks (DTNs) rely on the mobility of nodes and sequences of their contacts to compensate for lack of continuous connectivity and thus enable messages to be delivered from end to end in a “store-carry-forward” way, where multiple relay nodes are usually employed in the message delivery process. In this paper, we focus on such relay cooperation and analytically explore its impact on the delivery performance in DTNs. Specifically, we first develop a continuous time Markov chain-based theoretical framework to model the complicated message delivery process in delay tolerant networks adopting the two-hop relay algorithm. We then derive closed-form expressions for both the expected delivery delay and the corresponding expected delivery cost, where the important relay behaviors of forwarding traffic for itself or for other nodes are carefully incorporated into the analysis.     

车载网络中基于区域覆盖的机会传递算法研究

The highly mobility of vehicles, intermit-tent communication between the vehicles and the requirements of real time applications are some of the main challenges of multi-hop message delivery in Vehicular Ad Hoc Networks(VANETs).There are also additional challenges, especially when the des-tination for the message delivery is a moving vehi-cle. In this paper, we propose a novel multi-hop message delivery method, called the Coverage Area-based oPportunistic message forwarding algorithm (CAP). The main idea of CAP is to cover the poten-tial area of a moving target vehicle as much as pos-sible with the reachable area of the required deliver-y messages, so that the message can be delivered successfully. Because the success ratio and overhead of the multi-hop message delivery are two important but incompatible parameters in CAP, two tunings are discussed in the algorithm in order to maintain the balance of the two parameters. The simulation results show that compared with other reference ap-proaches, CAP provides an efficient message deliv-ery with a higher success ratio and a shorter mes-sage delay.     

Minimizing Broadcast Latency and Redundancy in Ad Hoc Networks

Network wide broadcasting is a fundamental operation in ad hoc networks. In broadcasting, a source node sends a message to all the other nodes in the network. In this paper, we consider the problem of collision-free broadcasting in ad hoc networks. Our objective is to minimize the latency and the number of transmissions in the broadcast. We show that minimum latency broadcasting is NP-complete for ad hoc networks. We also present a simple distributed collision-free broadcasting algorithm for broadcasting a message. For networks with bounded node transmission ranges, our algorithm simultaneously guarantees that the latency and the number of transmissions are within $O(1)$ times their respective optimal values. Our algorithm and analysis extend to the case when multiple messages are broadcast from multiple sources. Experimental studies indicate that our algorithms perform much better in practice than the analytical guarantees provided for the worst case.      

Throughput and delay analysis of multi-channel wireless infrastructure networks

Wireless infrastructure networks (WINs) provide ubiquitous connectivity to mobile nodes in metro areas. The nodes in such backbone networks are often equipped with multiple transceivers to allow for concurrent transmissions in multiple orthogonal channels. In this study, we develop an analytical model for the estimation of the delay and throughput performance of wireless infrastructure networks employing slotted ALOHA channel access and slotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) over multiple channels. The analytical model, which takes into account the correlation due to multi-hop transmissions, approximates the performance observed through simulations accurately.     

Regional Gossip Routing for Wireless Ad Hoc Networks

Many routing protocols have been proposed for wireless ad hoc networks, and most of them are based on some variants of flooding. Thus many routing messages are propagated through the network unnecessarily despite various optimizations. Gossip based routing method has been used and re-investigated to reduce the number of messages in both wired networks and wireless ad hoc networks. However, the global gossiping still generates many unnecessary messages in the area that could be far away from the line between sender node and receiver node. We propose a regional gossip approach, where only the nodes within some region forward a message with some probability, to reduce the overhead of the route discovery in the network. We show how to set the forwarding probability based on the region and the network density both by theoretical analysis and by extensive simulations. Our simulations show that the number of messages generated using this approach is much less than the simple global gossiping method, which already saves many messages compared with global flooding. We expect that the improvement should be even more significant in larger networks.     

Efficient Scheduling Algorithms for Real-Time Service on WDM Optical Networks

One of the important issues in the design of future generation high-speed networks is the provision of real-time services to different types of traffic with various time constraints. In this paper we study the problem of providing real-time service to hard and soft real-time messages in Wavelength-Division-Multiplexing (WDM) optical networks. We propose a set of scheduling algorithms which prioritize and manage message transmissions in single-hop WDM passive star networks based on specific message time constraints. In particular, we develop time-based priority schemes for scheduling message transmissions in order to increase the real-time performance of a WDM network topology. We formulated an analytical model and conducted extensive discrete-event simulations to evaluate the performance of the proposed algorithms. We compared their performances with that of the state-of-the-art WDM scheduling algorithms which typically do not consider the time constraint of the transmitted messages. This study suggests that when scheduling real-time messages in WDM networks, one has to consider not only the problem of resources allocation in the network but also the problem of sequencing messages based on their time constraints.     

Network condition and application‐based data adaptive intelligent message routing in vehicular network

Recent advances in intelligent transportation systems enable a broad range of potential applications that significantly improve the vehicle and road safety and facilitate the efficient dissemination of information among the vehicles. To assist the vehicle traffic, message broadcasting is a widely adopted technique for road safety. But efficient message broadcasting is a significant issue, especially in a high network density due to the broadcast storm problem. To solve this issue, several methods are proposed to eliminate the redundant transmission of safety packets. However, they lack in restricting the broadcasting region of safety messages, and the transmissions of safety packets outside the dangerous region, and force the vehicles to unnecessary detours. This paper proposes an adaptive multimode routing protocol, network condition, and application‐based data adaptive intelligent message routing in vehicular network (NetCLEVER) that supports 2 modes of operation such as message broadcasting and intelligent routing. In message broadcasting mode, the NetCLEVER decides the dangerous region of the network by considering the changes of neighbor vehicles velocity, instead of current vehicle velocity, because a vehicle decision in velocity is interdependent with the preceding vehicles. In intelligent routing mode, the NetCLEVER exploits the cuckoo search optimization in routing by taking into account multiple routing factors such as the road topology of intersections and traffic signals and their impact on link stability, which improves the reliability of routing packets significantly. The performance evaluation illustrates that the proposed NetCLEVER improves reliable wireless communication as well as road safety in vehicular ad hoc networks.     

Flooding-Based Geocasting Protocols for Mobile Ad Hoc Networks

Geocasting is a variation on the notion of multicasting. A geographical area is associated with each geocast, and the geocast is delivered to the nodes within the specified geographical area. Thus, geocasting may be used for sending a message that is likely to be of interest to everyone in a specified area. In this paper, we propose three geocasting protocols for ad hoc networks, obtained as variations of a multicast flooding algorithm, and then evaluate these approaches by means of simulations. Proposed geocasting algorithms attempt to utilize physical location information to decrease the overhead of geocast delivery.     

Impact of Bloom Filter on Infection Rate in Epidemic Forwarding for ICNs

Mobile ad hoc routing protocols fails in intermittently connected networks (ICN) (i.e. characterized by short-range communication and absence of connected path from source to destination). However, Epidemic routing techniques ensures eventual message delivery from source to destination even where there is never a connected path or when a network partition exists at the origin of message. Epidemic Routing uses random pair-wise messages exchanges between nodes with goals to maximize message delivery rate, minimize message latency, and the total resources consumed in message delivery. Epidemic routing uses summary vector to avoid useless transmission and redundancy. Further,to make summery vector efficient, epidemic routing can use bloom filter to significantly reduce the useless transmissions associated with the summary vector. However, the challenge for epidemic routing remains opens is to optimal design of summary vector size for finite buffer while keeping the benefits of infinite buffer space. This paper proposes an improved scheme of Bloom filter (named it modified bloom filter MBLF), which is tailored according to epidemic routing. We performed simulation to support our clam and observed that delivery ratio of MBLF with epidemic routing is 19 % higher then the traditional bloom filter. In this paper, we have proposed a bloom filter based epidemic forwarding for ICNs.     

Energy-efficient information routing in sensor networks for robotic target tracking

Target tracking problems have been studied for both robots and sensor networks. However, existing robotic target tracking algorithms require the tracker to have access to information-rich sensors, and may have difficulty recovering when the target is out of the tracker??s sensing range. In this paper, we present a target tracking algorithm that combines an extremely simple mobile robot with a networked collection of wireless sensor nodes, each of which is equipped with an unreliable, limited-range, boolean sensor for detecting the target. The tracker maintains close proximity to the target using only information sensed by the network, and can effectively recover from temporarily losing track of the target. We present two algorithms that manage message delivery on this network. The first, which is appropriate for memoryless sensor nodes, is based on dynamic adjustments to the time-to-live (TTL) of transmitted messages. The second, for more capable sensor nodes, makes message delivery decisions on-the-fly based on geometric considerations driven by the messages?? content. We present an implementation along with simulation results. The results show that our system achieves both good tracking precision and low energy consumption.     

Virtual Surrounding Face Geocasting in Wireless Ad Hoc and Sensor Networks

Geocasting in wireless sensor and ad hoc networks means delivering a message from a source node to all the nodes in a given geographical region. The objectives of a geocasting protocol are two-fold: guaranteed message delivery and low transmission cost. Most of the existing protocols do not guarantee message delivery, and those that do, incur high transmission costs.      

Performance Modeling and Analysis of a Class of ARQ Protocols in Multi-Hop Wireless Networks

This paper models and analyzes the performances of a class of ARQ (automatic repeat request) protocols in a multi-hop wireless data network. The performance metric here is the number of transmissions required for successful delivery of a packet over a multi-hop path. By using a discrete-time Markov model, the distribution for the total required number of transmissions is modeled as phase type distribution. The effects of different network parameters-such as packet error rate in each hop, maximum number of allowable retransmissions at each hop and retransmission probability at each hop-on the required total number of transmissions are investigated. The novelty of this model is that the probability mass function (pmf) for the number of transmissions required for successful end-to-end delivery of a packet can be easily obtained under different hop-level error control policies. Using the pmf, the tradeoff between transmission energy and percentage of data delivery (i.e., reliability) in a multi-hop path can be analyzed. The analytical model is validated by simulations. While the proposed analytical framework is general enough to capture the impact of any MAC (medium access control) mechanism at each hop, we specifically present typical performance results under IEEE 802.11 DCF (distributed coordination function) MAC