A vast number of broadcasting protocols have been developed for wireless networks. However, most of these protocols assume a single-radio single-channel network model. Employing multiple channels can effectively improve the network capacity in wireless mesh networks. This paper considers minimum cost broadcast (MCB) problem in multi-radio multi-channel wireless mesh networks. We first present the multi-radio multi-channel network model, and then formulate the MCB problem using an integer linear programming model. Our model considers two cases of MCB. In the first case, there already exists a channel assignment in the network, and the formulation minimizes the broadcast cost and reduces interference amongst the adjacent neighbors. In the second case, each node has a set of available channels to be selected. We jointly consider channel assignment and the MCB problem. The joint channel assignment and MCB formulation fully exploits the channel diversity, and also further reduces interference in the network. We propose corresponding centralized and distributed heuristic algorithms to minimize the number of broadcast transmissions with full reliability. In our heuristic algorithms, each node participates in the broadcasting if chosen to maintain the network connectivity or to achieve maximum coverage. Extensive numerical results are presented to demonstrate the performance.

Wireless mesh networks (WMNs) have recently emerged as a promising broadband access infrastructure for next-generation wireless networking. Several approaches that exploit directional antennas have been proposed in the literature to increase the performance of WMNs. In this paper, we study the interference optimization multicast problem in WMNs where nodes are equipped with directional antennas. Interference can make a significant impact on the performance of multi-hop wireless networks. Directional transmissions can greatly reduce radio interference, increase spatial reuse, and enable more efficient MAC designs. We first present the definition of interference with directional transmissions that are suitable for designing multicast algorithms, and formulate minimum interference multicast problems using a linear programming model. We then propose a heuristic algorithm to solve the problem. Our model and algorithm are good for both single multicast session and multiple multicast sessions. Multicast routing found by our interference-aware algorithm tends to have less channel collisions.

Achieving efficient bandwidth utilization in multi-channel sensor networks is a challenging research problem. In this paper, we present a cognitive load balance algorithm for single-hop multi-channel sensor networks. Based on the load distribution of all base stations, our algorithm dynamically alternates the communication channels. As a result, the extra load from over-loaded channels is directed to under-loaded channels with a computed switch probability. In this paper, we also prove that a high throughput can be achieved if the load is balanced. The performance of the load balance algorithm is evaluated through both theoretical analysis and simulation study.

In this paper, we propose a novel access point (AP) selection algorithm to maximize the system throughput while considering user fairness. The main idea is that when a new-coming user enters an overlapping area of a wireless local area network (WLAN), it first estimates the system throughput as if it were associated with each of the APs involved. Then it chooses the AP that can achieve the highest system throughput. For existing users that locate in the overlapping area, they may also need to change the AP association due to the dynamic nature of traffic load. To enable the fairness among users, each user is guaranteed the minimum transmission opportunity. Another significant contribution of this paper is that we find that load-balancing based approaches could not achieve the maximum throughput for multi-rate WLANs, although load-balancing has been considered as an effective approach to improve the network throughput for single-rate WLANs. In-depth theoretical analysis and extensive simulations are performed to verify the throughput optimization and user fairness.

One approach for information dissemination in large-scale communication systems is using epidemic protocols. Current epidemic protocols, however, adopt a constant fanout policy, which does not enable end users to control the information dissemination process. For distributed applications that need to compute a global function within a pre-determined response time, better procedures to control the information dissemination process have to be developed. In this paper, we introduce two distributed adaptive epidemic protocols using a dynamic fanout scheme. They are named Round-Based dynamic fanout (RBdf) and Cluster-Based dynamic fanout (CBdf). In RBdf, the network topology is flat and each node transmits a message with a varied fanout every round. In CBdf, the network topology is hierarchical, and the fanout values in every cluster differ within the same round. The main objectives are to ensure that peers receive messages within a bounded latency and that the system message overhead is a bounded value. The performance of the proposed protocols are verified through both theoretical and simulation studies.

HIGH-PERFORMANCE BROADCAST AND MULTICAST PROTOCOLS FOR MULTI-RADIO MULTI-CHANNEL WIRELESS MESH NETWORKS Jun Wang Old Dominion University, 2009 Director: Dr. Min Song Recently, wireless mesh networks (WMNs) have attracted much attention. A vast amount of unicast, multicast and broadcast protocols has been developed for WMNs or mobile ad hoc networks (MANETs). First of all, broadcast and multicast in wireless networks are fundamentally different from the way in which wired networks function due to the wellknown wireless broadcast/multicast advantage. Moreover, most broadcast and multicast protocols in wireless networks assume a single-radio single-channel and single-rate network model, or a generalized physical model, which does not take into account the impact of interference. This dissertation focuses on high-performance broadcast and multicast protocols designed for multi-radio multi-channel (MRMC) WMNs. MRMC increases the capacity of the network from different aspects. Multi-radio allows mesh nodes to simultaneously send and receive through different radios to its neighbors. Multi-channel allows channels to be reused across the network, which expands the available spectrum and reduces the interference. Unlike MANETs, WMNs are assumed to be static or with minimal mobility. Therefore, the main design goal in WMNs is to achieve high throughput rather than to maintain connectivity. The capacity of WMNs is constrained by the interference caused by the neighbor nodes. One direct design objective is to minimize or reduce the interference in broadcast and multicast. This dissertation presents a set of broadcast and multicast protocols and mathematical formulations to achieve the design goal in MRMC WMNs. First, the broadcast problem is addressed with full consideration of both inter-node and intra-node interference to achieve efficient broadcast. The interference-aware broadcast protocol simultaneously achieves full reliability, minimum broadcast or multicast latency, minimum redundant transmissions, and high throughput. With an MRMC WMN model, new link and channel quality metrics are defined and are suitable for the design of broadcast and multicast protocols. Second, the minimum cost broadcast problem (MCBP), or minimum number of transmissions problem, is studied for MRMC WMNs. Minimum cost broadcast potentially allows more effective and efficient schedule algorithms to be designed. The proposed protocol with joint consideration of channel assignment reduces the interference to improve the throughput in the MCBP. Minimum cost broadcast in MRMC WMNs is very different from that in the single radio single channel scenario. The channel assignment in MRMC WMNs is used to assign multiple radios of every node to different channels. It determines the actual network connectivity since adjacent nodes have to be assigned to a common channel. Transmission on different channels makes different groups of neighboring nodes, and leads to different interference. Moreover, the selection of channels by the forward nodes impacts on the number of radios needed for broadcasting. Finally, the interference optimization multicast problem in WMNs with directional antennas is discussed. Directional transmissions can greatly reduce radio interference and increase spatial reuse. The interference with directional transmissions is defined for multicast algorithm design. Multicast routing found by the interference-aware algorithm tends to have fewer channel collisions. The research work presented in this dissertation concludes that (1) new and practical link and channel metrics are required for designing broadcast and multicast in MRMC WMNs; (2) a small number of radios is sufficient to significantly improve throughput of broadcast and multicast in WMNs; (3) the number of channels has more impact on almost all performance metrics, such as the throughput, the number of transmission, and interference, in WMNs.

A vast number of broadcasting protocols have been developed for wireless networks. To the best of our knowledge, however, most of these protocols assume a single-radio single channel network model and/or a generalized physical model, which does not take into account the impact of interference. In this paper, we present a Distributed Interference-aware Broadcasting (DIB) protocol for multi-radio multi-channel mesh networks. The protocol has two phases. In the first phase, each node constructs a local structure by removing bad links and channels. In the second phase, a high-performance broadcasting tree is built by using message passing procedures. Our research distinguishes itself in a number of ways. First, a multi-radio multi-channel mesh network model is used. Second, comprehensive link and channel quality metrics are defined to fully take into account interferences. Third, four design principles have been identified in the tree building process to combat inter-node and intra-node interferences. Finally, a comprehensive performance metric, called power, is defined which includes reliability, receiving redundancy, latency, and goodput. Analytical and simulation studies verify that the DIB protocol is able to achieve 100% reliability, less broadcasting redundancy, low broadcasting latency, and high goodput.

With the ability of simultaneous transmissions, multi-channel multi-interface wireless mesh networks (WMNs) have emerged with great potential in the improvement of network throughput and fairness. However, most proposed channel assignment algorithms for WMNs made an assumption that the network interface cards (NICs) are evenly assigned to the mesh routers. In this paper, we investigate the problems of NIC assignment and bandwidth allocation to minimize the infrastructure cost, and meanwhile guarantee the application requirements. We argue evenly assigning NICs to all routers is neither a necessary condition nor an effective solution, since not only the interference but also the traffic flows are important factors that will affect the parallel use of the bandwidth. One of the principal challenges addressing these problems is their interactive impact on the optimization of network throughput. By analyzing all kinds of constraints for traffic, NIC and performance, we formally define a problem space that addresses the relationships between different assignment and allocation problems. Furthermore, we demonstrate that a hard NIC assignment and bandwidth allocation problem can be decomposed and formulated into a well-defined single or multiple-phase problem. In addition to the linear programming (LP) solutions, we propose novel efficient heuristics for on-line decisions for the situation whenever the network architecture changes and needs recompute the system performance in real-time. We show through extensive simulations that the heuristic algorithms can achieve close to optimal solution and outperform the equal NIC assignment method with even a smaller number of NICs. 2008 Elsevier B.V. All rights reserved.

A vast amount of broadcasting protocols has been developed for wireless ad hoc networks. To the best of our knowledge, however, these protocols assume a single-radio single-channel and single-rate network model and/or a generalized physical model, which does not take into account the impact of interference. In this paper, we present a set of broadcasting protocols to simultaneously achieve 100% reliability, minimum broadcasting latency, and minimum redundant transmissions. Our research distinguishes itself in a number of ways. First, a multi-radio multi-channel and multi-rate mesh network model is used. Second, the broadcasting tree is constructed by using local information without the global network topological information. Third, a comprehensive link quality metric is defined to fully take into account the interference. The link quality information is also made available to broadcasting protocols. Fourth, three performance metrics that include reliability, latency, and redundancy are simultaneously considered. Simulations are conducted to evaluate the proposed protocols and compare the performance improvement to other protocols.

Current active queue management (AQM) and TCP protocol are designed and tuned to work well on wired networks where packet loss is mainly due to network congestion. In wireless networks, however, communication links suffer from significant transmission bit errors and handoff failures. As a result, the performance of TCP flows is significantly degraded. To mitigate this problem, we analyze existing AQM schemes and propose a rate-based exponential AQM (REAQM) scheme. The proposed REAQM scheme uses the input rate as a primary metric and queue length as the secondary metric. The objectives of REAQM are to stabilize networks with low packet loss, low packet delay, and high link utilization regardless the dynamic of network conditions. We prove the global asymptotic stability of the equilibrium based on Lyapunov theory. Simulation results suggest that REAQM is capable of performing well for TCP flows over both wired and wireless networks, and has comparable implementation complexity as other AQM schemes.

To avoid collisions in wireless networks, medium access control (MAC) protocols, such as Distributed Coordination Function (DCF), have been developed to assist each node to decide when and how to access the communication channel. Although DCF is widely used in 802.11 based wireless local area networks, its performance is limited because DCF does not take into account the traffic intensity and node density. In other word, DCF only knows collision occurs but does not know how severe of the collision. In this paper, we develop a novel traffic adaptive backoff (TAB) protocol. We use network allocation vector count to approximate the intensity of surrounding traffic and the density of the nodes. TAB protocol then chooses a random backoff time uniformly between a lower threshold and an upper threshold. Simulations results suggest that the TAB protocol improves network performance by achieving a better channel utilization and reducing the number of dropped packets.

Owing to limited bandwidth, high bit error rate, and bursty error in the wireless environment, the performance of the transmission control protocol (TCP) degrades greatly in wireless networks. Up to now, many researchers have contributed greatly to the wireless TCP field. However, in most of their works, the wireless TCP module usually works in the TCP layer and has no idea of the actual time of the packet transmission, which is determined by the Scheduler in the media access control (MAC) layer, and this will bring the inaccuracy to the local retransmission timeout and induce the redundant local retransmission. In this article, a coordinator is introduced into the base-station (BS), which can provide efficient cooperation between the TCP module and the scheduler module. On the bais of the performance analysis and simulation results, the proposed method is shown to eliminate redundant local retransmission, increase throughput, and improve TCP-level fairness in wireless networks. Moreover, this scheme is orthogonal to those existing wireless TCP schemes, thus it can give great compatibility to the current networks, and further enhance the performance of TCP under the condition that the performance improvement benefiting from the existing approaches will not be affected.

Current active queue management (AQM) and TCP are designed and tuned to work well for wired networks where packet loss is mainly due to network congestion. In wireless networks, however, communication links suffer from transmission bit errors and handoff failures. As a result, the performance of TCP flows is significantly degraded. To mitigate this problem, we propose a rate-based exponential AQM (REAQM) scheme. REAQM tries to stabilize the system and achieve low delay, low packet loss, and high link utilization regardless the dynamic of network conditions. Simulation results indicate that REAQM is capable of performing well for TCP flows over both wired and wireless links.

In mobile wireless sensor networks, sensors move in the monitored area at any direction and at any speed. Unlike many other networking hosts, sensor nodes do not have global addresses. Very often they are identified by using a location-based addressing scheme. Therefore, it is important to have the knowledge of the sensor location indicating where the data came from. In this paper, we design three mobility-pattern based localization update algorithms. Specifically, we divide sensor movements into three states, Pause, Linear, and Random. Each state adopts different localization update algorithms. Analytical and simulation results are provided to study the localization cost and location accuracy of the proposed localization-update algorithm in different mobility patterns. The analysis to these results indicates that the localization cost is minimized and the location accuracy is improved.

Fault tolerant algorithms are often designed under the t-out-of-n assumption, which is based on the assumption that all processes or components fail independently with equal probability. However, real systems may exhibit dependent failures. Cores and survivor sets are used to build an abstraction model for dependent process failures. Using this abstraction, we design an algorithm to solve consensus problem crash failures. Our algorithm uses the processes in all cores to broadcast messages. Each core reaches agreement separately and even simultaneously in some round with no failure in the core. In the worst-case, the decision can be made in the round that is equal to the size of the minimal core. Our algorithm guarantees that all processes eventually decide on the same value regardless the initial values. We prove the correctness of our algorithm and give the lower bound of the number of rounds to solve consensus problem.