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CHOWDHURY, KAUSHIK ROYMULTI-CHANNEL MEDIUM ACCESS PROTOCOLS FOR WIRELESS NETWORKS
MS, University of Cincinnati, 2006, Engineering : Computer Science
As wireless technology becomes increasingly pervasive, there is a need for decentralized medium access control (MAC) protocols that satisfy user requirements at an acceptable cost of complexity and energ consumption. Hardware improvements have provided for multi-channel transceivers and leveraging this benefit necessitates further work in higher layer protocols. As devices get smaller leading to large networks formed of tiny sensor motes, the allocation of available channels without a central authority and their subsequent arbitration is a challenging task. In our work, we address this by first devising a channel allocation protocol (DCA) that ensures interference-free communication. We then propose a multi-channel MAC, C-MAC that enables energy efficient data transfer without tradeoffs in latency or throughput, and allows nodes to remain in their low-power sleep period for the maximum possible time. Apart from sensor networks, we have also analyzed the case for wireless local area networks (WLANs) that are the default providers of community and enterprise level internet connectivity. A judicious choice of the operational channel based on current network conditions can greatly improve performance in randomly deployed or hotspot areas. Our analytical estimation of interference allows each access point (AP) to independently arrive at the best channel, thus resulting in fewer re-transmissions due to neighboring traffic. For all the proposed schemes, a thorough performance evaluation has been undertaken and results reveal major improvement in performance for both WLAN and sensor networks, thus proving the viability of multi-channel communication models.

Committee:

Dr. Dharma Agrawal (Advisor)

Keywords:

Graph coloring,; Medium Access Control,; Multi-channel,; Sensor networks,; Wireless LAN.;

JAIN, VIVEKON-DEMAND MEDIUM ACCESS IN HETEROGENEOUS MULTIHOP WIRELESS NETWORKS
PhD, University of Cincinnati, 2007, Engineering : Computer Science and Engineering
Recent years have witnessed an extensive proliferation of wireless technology in every domain of day-to-day life. Examples include mobile phones, broadband communication, wireless LAN, wireless enabled PDAs, cordless phones, garage-door openers and the list continues. Advancements in radio technology, antenna technology, low power computational digital signal processing (DSP) and micro-electro-mechanical systems (MEMS) are instrumental in reducing the size and cost of wireless devices. A wireless network consists of wireless devices forming an infrastructure-based or a peer-to-peer network. A network can be a single-hop or multihop network. Single-hop networks are already in existence and have been substantially investigated. This dissertation thus focuses on multihop wrireless networks, where the intermediate wireless devices also act as routers. Depending on their functionality, multihop wireless networks can be categorized into ad hoc, mesh and sensor networks. A mobile ad hoc network (MANET) aims at provding a mobile network with connectivity similar to a wired network without the need for any infrastructure support. A wireless mesh network (WMN) typically extends the infrastructure based single hop wireless network and has become a new paradigm for providing last mile broadband access. A wireless sensor network (WSN) is similar to an ad hoc network, providing a cheap alternative to monitoring applications. Each of these multihop wireless networks has their own set of challenges with respect to operation and implementation. The first part of this dissertation focuses on developing on-demand medium access control (MAC) protocols for multiple beam smart antennas (MBSAs) in ad hoc and mesh environments. MBSA has the unique capability of simultaneously initiating packet transmissions or receptions in multiple beams. Thus, compared to traditional omnidirectional antennas, MBSA can better utilize the spatial bandwidth, thereby increasing the capacity of wireless networks. We have performed both simulation and analytical studies to evaluate the proposed protocols for MBSA in ad hoc environments. To the best of our knowledge, this is the first attempt to analyze and develop on-demand protocols for multiple beam smart antennas. We have also proposed a cost-effective mesh network architecture employing heterogeneous antenna technologies and hybrid MAC protocol. The second part of this dissertation focuses on designing energy-efficient and reliable medium access mechanisms for wireless sensor networks. Sensor motes are battery-operated, hence protocols designed for them have to be innately energy-efficient. Also, depending on the application, reliability and latency might be important parameters. Taking into account all these design considerations, we have proposed dual-radio architecture. A low-energy wakeup radio is used to transmit and receive wakeup tones, while another transceiver is used for data communication. We have demonstrated the superior performance of our protocol using extensive simulation and analytical studies. We have also proposed a wireless sensor network testbed for quantifying reliability of wireless channels. The setup can be used to quantify reliability of wireless channels in terms of packet error rate, received signal strength and overall latency of the system. On the basis of our studies, we have provided deployment guidelines and medium access strategies for wireless sensor networks.

Committee:

Dr. Dharma Agrawal (Advisor)

Subjects:

Computer Science

Keywords:

Ad hoc Network; Concurrent Packet Reception; Deafness; Differentiated Service Classes; Medium Access Control; Mesh Network; Multihop Wireless Network; Multiple Beam Smart Antenna; Sensor Network

JAIN, NITINMULTICHANNEL CSMA PROTOCOLS FOR AD HOC NETWORKS
MS, University of Cincinnati, 2001, Engineering : Computer Science and Engineering
An ad hoc network is a collection of wireless mobile nodes dynamically forming a network without the use of any existing stationary network infrastructure. The network can be multi-hop and mobile; there is no central controller and packet transmissions are typically unsynchronized. The efficiency of the medium access control (MAC) protocol to coordinate the access to the shared radio medium is critical. Carrier sense multiple access (CSMA) protocols are typically used. However, their efficiency is limited when the load and the level of contention is high. This thesis proposes use of multichannel CSMA protocols to reduce contention on the wireless medium. Though the aggregate capacity with a multichannel scheme is the same as a single channel, contention per channel is now lower and thus channel access is more efficient. We show that only a handful of channels provide optimum performance as with too many channels per-channel bandwidth is too low that affects performance adversely. Since the number of channels are much lower than the number of nodes, effective channel selection schemes are needed. We propose a receiver-based channel selection (RBCS) scheme that selects channel based on interference levels on different channels at the receiver. We implement this technique as an extension of IEEE standard 802.11 MAC protocol (which is a single channel protocol) on a network simulator. We show that it provides superior delay performance at high loads compared to single channel, as well as other, previously studied, channel selection schemes, such as selcting a random free channel or selecting channel based on sender-side signal power. As a final contribution, we study the effect of multichannel CSMA protocols for multipath routing on ad hoc networks. With use of single channel CSMA, ''route coupling'' can exist for multipath routes. This means that routes can form in radio neighborhood, and their transmissions can interfere with each other, preventing multiple routes to be used concurrently. Thus, the load balancing advantages of multiple paths are lost. We show that the use of multichannel CSMA protocols as above can remarkably improve the effectiveness of the multipath routing by providing more diversity.

Committee:

Dr. Samir R. Das (Advisor)

Subjects:

Computer Science

Keywords:

Ad Hoc Networks; medium access control; multichannel MAC; wireless networks; channel selection techniques