The recent advances in antenna technology have made smart beamforming antennas attractive candidates to be deployed in multi-hop wireless networks. Beamforming antennas can increase the spatial reuse of the channel and consequently the network capacity. Due to practical and economical considerations, deploying beamforming antennas in the whole network is sometimes infeasible. In this paper, we focus on multi-hop wireless networks with heterogeneous antenna capabilities. We study the problem of optimal antenna placement to maximize the total network throughput. We first introduce an antenna-aware conflict graph using the notion of virtual links. With the objective of minimizing the size of the maximum clique, we formulate our problem as a mixed-integer linear programming problem. Moreover, we propose a beamforming antenna placement heuristic algorithm for the partial deployment of beamforming antennas to upgrade existing wireless networks originally equipped with traditional omni-directional antennas. Our numerical results show that the proposed algorithm produces near-optimal results in a small fraction of time.

Beamforming antennas promise a significant increase in the spatial reuse of the wireless medium when deployed in multihop wireless networks. However, existing directional Medium Access Control (MAC) protocols with the default binary exponential backoff mechanism are not capable of fully exploiting the offered potential. In this paper, we discuss various issues involved in the design of MAC protocols specific for beamforming antennas. Based on our discussion, we argue that the traditional binary exponential backoff mechanism limits the possible spatial reuse and aggravates some beamforming-related problems such as deafness and head-of-line blocking. To grasp the transmission opportunities offered by beamforming antennas, we design an Opportunistic Directional MAC (OPDMAC) protocol for multihop wireless networks. The OPDMAC protocol employs a novel backoff mechanism in which the node is not forced to undergo idle backoff after a transmission failure but can rather take the opportunity of transmitting other outstanding packets in other directions. This mechanism minimizes the idle waiting time and increases the channel utilization significantly and thereby enables OPDMAC to enhance the spatial reusability of the wireless medium and reduce the impact of the deafness problem without additional overhead. Through extensive simulations, we demonstrate that OPDMAC enhances the performance in terms of throughput, delay, packet delivery ratio, and fairness. To further improve its performance, we discuss and evaluate the benefits of carefully choosing some protocol parameters instead of using the default values commonly used by other directional MAC protocols.

Utilizing smart beamforming antennas in contention-based wireless mesh networks has proven to provide a significant increase in the network capacity. Nevertheless, their effectiveness in providing additional QoS guarantees is still under-explored. In this paper, we develop a framework for analyzing conflicts on wireless links considering both the physical interference and the operation of the underlying directional MAC protocol. Based on a novel taxonomy, we classify the link conflicts into several categories and propose a novel colored conflict graph abstraction to model the network interference pattern in the presence of contention-based directional MAC protocols. Using the proposed colored conflict graph, we derive a closed form expression for the probability of successful transmission over a wireless link given that all the bandwidth requirements are satisfied. Based on our analysis, we formulate the bandwidth-guaranteed routing problem as an optimization problem. Since the problem is NP-hard, we present a heuristic algorithm for joint routing and admission control to find single-path bandwidth-guaranteed routes. Using extensive simulations, we demonstrate the accuracy of our conflict analysis and the ability of the proposed algorithm to provide QoS guarantees along with efficient channel utilization.

Recently, the use of directional antennas in multi-hop wireless networks has received increasing attention in the research community due to their potential benefits and numerous advantages over omni-directional antennas. However, the majority of existing work has focused on homogeneous wireless networks where all the nodes are equipped with the same beamforming antennas. In this work, we focus on multi-hop wireless networks with heterogeneous antennas capabilities, a scenario that is expected to prevail in next generation wireless networks. We address the fundamental question: Given a specific network topology with heterogeneous antennas, what are the theoretical capacity bounds of such network? For that purpose, we formulate the problem as an optimization problem and compute the upper and lower bounds. Our results show that the capacity of heterogeneous multi-hop wireless networks can be significantly increased even with small fraction of directional nodes.

Although directional antennas can increase the spatial reuse in wireless ad hoc networks, the directional carrier sense multiple access/collision avoidance (CSMA/CA) protocols encounter unprecedented challenges that can offset this potential benefit. One critical problem is known as deafness that occurs when a transmitter repeatedly fails to communicate with its intended receiver because the receiver is beamformed towards another direction. The deafness problem has not yet been analytically studied since existing analytical models for directional CSMA/CA ignore the effect of deafness. In this study, the authors develop an analytical framework for directional CSMA/CA, which is the first analytical model to consider the problem of deafness as a source of transmission failures in multi-hop wireless networks with directional antennas. They also propose a deafness index to quantify the negative impact of deafness. Using their framework, the authors study the tradeoff between spatial reuse and deafness when a directional CSMA/CA protocol is employed. Their results demonstrate that decreasing the antenna beamwidth increases the saturation throughput up to a certain limit corresponding to an optimum beamwidth. However, by further lowering the beamwidth, the negative impact of deafness offsets the benefits of spatial reuse and results in a steep decrease in the saturation throughput. These results prove analytically that deafness is a critical problem if left unaddressed.

The demand for QoS has made its support an essential component in today's wireless networks. The use of directional antennas in multi-hop wireless networks is known to provide substantial increase in the utilization of the wireless medium. However its effectiveness in providing QoS assured routing is unexplored. In this paper, we study the problem of bandwidth guaranteed routing in contention-based wireless mesh networks with directional antennas. We present a detailed analysis for the interference pattern of such networks taking into account the challenges imposed by the use of directional antennas such as deafness. Based upon this analysis, we formulate the QoS routing problem as an optimization problem. We then present a routing and admission control heuristic to solve the problem. Our simulation results demonstrate the effectiveness of our routing scheme and the necessity of admission control for QoS support.

Directional antennas in multihop wireless networks offer a potential increase in the spatial reuse of the wireless channel. However, existing directional MAC protocols are not capable of fully exploiting this essential benefit. In this paper, we propose OPDMAC which is an opportunistic directional MAC protocol that is motivated by the possibility of achieving higher spatial reuse. The proposed protocol is novel in its backoff mechanism with directional antennas. If a node is forced to backoff due to a missing CTS or acknowledgement in one direction, OPDMAC explores transmission opportunity in other directions. This minimizes the idle wait time of the wireless channel and increase the channel utilization. In addition, OPDMAC is found to decrease the effect of deafness without additional control overhead. Our simulation results show that OPDMAC outperforms existing directional MAC protocols in terms of throughput, delay and fairness.

The access link contention can severely constrain the end- to-end throughput of the path between a source and destination mobile node connected through the backbone of the wireless mesh network (WMN). In this paper, we propose an integrated routing system for WMN that includes both the backbone paths and the ad-hoc paths formed as a result of direct communication among mobile nodes without going through the backbone. In our proposed routing system, an alternative ad-hoc path can be used only when the primary backbone path is severely constrained due to access links contention. We propose a scheme that allows the source mobile node to evaluate the throughput of the backbone and ad-hoc paths, and select one path for communicating with the destination. We implemented the proposed routing system in OPNET simulator, and evaluated the performance of our scheme under variety of conditions. Simulation results show that the alternative ad-hoc path is effective in delivering higher throughput when backbone path is severely constrained.

is identified as a key driver of next-generation network technology under communication paradigms for 2020 initiative. The future's pervasive computing environments need all their components to become autonomous by managing their own evolution and configuration changes without explicit user or administrator action. Since there is no current routing protocol which always performs well for all kinds of possible environments and requirements, new innovative routing paradigms must be designed to best fit the next generation networks. In this paper, we present our vision of routing in Autonomic communication. More specifically, we discuss the main design issues for the new routing paradigms. Moreover, some research directions and challenges are also addressed.