Within the short span of a decade, Wi-Fi hotspots have revolutionized Internet service provisioning. With the increasing popularity and rising demand for more public Wi-Fi hotspots, network service providers are facing a daunting task. Wi-Fi hotspots typically require extensive wired infrastructure to access the backhaul network, which is often expensive and time consuming to provide in such situations. wireless mesh networks (WMNs) offer an easy and economical alternative for providing broadband wireless Internet connectivity and could be called the web-in-the-sky. In place of an underlying wired backbone, a WMN forms a wireless backhaul network, thus obviating the need for extensive cabling. They are based on multihop communication paradigms that dynamically form a connected network. However, multihop wireless communication is severely plagued by many limitations such as low throughput and limited capacity. In this article we point out key challenges that are impeding the rapid progress of this upcoming technology. We systematically examine each layer of the network and discuss the feasibility of some state-of-the-art technologies/protocols for adequately addressing these challenges. We also provide broader and deeper insight to many other issues that are of paramount importance for the successful deployment and wider acceptance of WMNs.

Wireless Mesh Networks: Current Challenges and Future Directions of Web-In-The-Sky

The beamforming antenna technology is a promising solution to many challenges facing wireless ad hoc networks. Beamforming antennas have the ability to increase the spatial reuse, improve the transmission reliability, extend the transmission range and/or save the power consumption. If they are effectively used, they can significantly improve the network capacity, lifetime, connectivity and security. However, traditional Medium Access Control (MAC) protocols fail to exploit the potential benefits due to the unique characteristics of wireless ad hoc networks with beamforming antennas. To that end, numerous MAC protocols have been designed over the years to harness the offered potential. In this paper, we survey the literature on MAC protocols proposed for wireless ad hoc networks with beamforming antennas during the last decade. We discuss the main beamforming-related challenges facing the medium access control in ad hoc networks. We present taxonomy of the MAC protocols proposed in the literature based on their mode of operation and the mechanisms used to address the challenges. In addition, we provide a qualitative comparison of the protocols highlighting their features, benefits and requirements. Finally, we provide directions for possible future work.

A Survey On MAC Protocols for Wireless Adhoc Networks with Beamforming Antennas

The paper presents a detailed discussion of various issues involved in designing a medium access control (MAC) protocol for multihop wireless networks with nodes employing multiple beam smart antennas. Multiple beam smart antennas can form several beams simultaneously and can initiate concurrent transmissions or receptions .in them, thereby increasing the throughput of the bottleneck nodes. Traditional on-demand MAC protocols for omnidirectional and single beam directional antennas based on the IEEE 802.11 distributed coordination function (DCF) mechanism cannot take advantage of this unique capability of multiple beam antennas as they do not facilitate concurrent transmissions or receptions by a node. This paper introduces a novel protocol, hybrid MAC (HMAC), which enables concurrent packet reception (CPR) and concurrent packet transmission (CPT) at a node equipped with multiple beam antennas and is backward compatible with IEEE 802.11 DCF. Simulation results show the superior performance of HMAC in most ad hoc scenarios. Moreover, in some sample topologies, the throughput of HMAC is close to the theoretical maximum. The paper also presents a wireless mesh network architecture with heterogeneous antenna technologies and illustrates the advantages of employing multiple beam smart antennas and HMAC in such networks.

On-Demand Medium Access in Multihop Wireless Networks with Multiple Beam Smart Antennas

Described herein are techniques for distributed key management (DKM) in cooperation with Trusted Platform Modules (TPMs). The use of TPMs strengthens the storage and processing security surrounding management of distributed keys. DKM-managed secret keys are not persistently stored in clear form. In effect, the TPMs of participating DKM nodes provide security for DKM keys, and a DKM key, once decrypted with a TPM, is available to be used from memory for ordinary cryptographic operations to encrypt and decrypt user data. TPM public keys can be used to determine the set of trusted nodes to which TPM-encrypted secret keys can be distributed.

Key management using trusted platform modules

ECGK: An efficient clustering scheme for group key management in MANETs

This paper introduces a novel cross layer medium access control protocol for multiple beam antennas to fully utilize their multiple-beam-forming capability. Our protocol, explicit synchronization via intelligent feedback (ESIF), uses feedback from neighboring nodes to synchronize data communication at multiple beams. ESIF exploits routing information to guarantee long-term fairness and minimize the energy and latency overheads. Unlike previous works on directional antennas that discuss range extension, we focus on optimal spatial reuse. Simulation results demonstrate that ESIF outperforms other on-demand access schemes based on IEEE 802.11 DCF for multiple beam antennas

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A cross layer MAC with explicit synchronization through intelligent feedback for multiple beam antennas

Distributed key management for dynamic groups in MANETs

Multiple beam antennas can receive (or transmit) data on multiple beams simultaneously. The aim of this paper is to show the limitations of using IEEE 802.11 distributed coordination function (DCF) based schemes for medium access control (MAC) in such antennas. We provide four different variants of IEEE 802.11 DCF based on-demand protocols to study this phenomenon. Our simulation results and analyses emphasize the need to develop a novel MAC protocol to fully exploit the capabilities of multiple beam antennas. We further provide some embryonic guidelines for the development of such a protocol

IEEE 802.11 DCF based MAC protocols for multiple beam antennas and their limitations

Most existing solutions to group security in mobile ad hoc networks (MANETs) rely on a multicast core based tree (CBT) for key distribution. Such solutions, although suitable for systems with low mobility and static characteristics, are highly unsuitable for dynamic and sparse groups with changing neighborhoods. Also, tree based solutions are prone to a man-in-the-middle attack which might lead to network partitioning. Moreover, a group controller is required to control the key generation process. In this paper, we propose an entirely decentralized key generation mechanism. Using our approach, keys can be established between group members with absolutely no prior communication, as long as the group members are known. The solution relies on threshold cryptography and introduces a novel concept of node-group-key (NGK) mapping. Analytical and simulation results show appreciable performance enhancements.

Anurag Gupta

Papers

On-Demand Medium Access in Multihop Wireless Networks with Multiple Beam Smart Antennas

A cross layer MAC with explicit synchronization through intelligent feedback for multiple beam antennas

Distributed key management for dynamic groups in MANETs

IEEE 802.11 DCF based MAC protocols for multiple beam antennas and their limitations

Totally distributed key management for dynamic groups in MANETs