Wireless lans with smart antennas /

Smart antenna systems not only enable users to have high quality links but also increase network throughput by allowing spatial reuse of wireless channels by the use of directional transmission. However performance of smart antenna systems is limited because of the increased hidden terminal problem and deafness of nodes. In this work, we have proposed the Angular MAC (ANMAC) protocol that avoids both problems through medium access tables in the nodes that keep track of the locations of the destination nodes as well as all communicating neighbors. We present detailed performance analysis of ANMAC considering different topologies and traffic scenarios, and we show that SDMA cannot be fully exploited without a smart scheduler. We have also proposed ANMAC with Location based Scheduling (ANMAC-LS) and compared its performance with other smart antenna approaches and omni 802.11 MAC. We prove the efficacy of location based scheduling in wireless networks with smart antennas, and we also show the effects of antenna orientation on throughput, using realistic antenna patterns and the ANMAC protocol. We have also analyzed the effect of contention window size on the performance of the network. By adjusting the contention window according to channel conditions, we can always get the maximum network throughput. We propose an updating algorithm for contention window, and we have analyzed the results both analytically and through simulations

Routing in heterogeneous wireless ad hoc networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.Includes bibliographical references (p. 135-146).Wireless ad hoc networks are used in several applications ranging from infrastructure monitoring to providing Internet connectivity to remote locations. A common assumption about these networks is that the devices that form the network are homogeneous in their capabilities. However in reality, the networks can be heterogeneous in the capabilities of the devices. The main contribution of this thesis is the identification of issues for efficient communication in heterogeneous networks and the proposed solutions to these issues. The first part of the thesis deals with the issues of unambiguous classification of devices and device identification in ad hoc networks. A taxonomical approach is developed, which allows devices with wide range of capabilities to be classified on the basis of their functionality. Once classified, devices are characterized on the basis of different attributes. An IPv6 identification scheme and two routing services based on this scheme that allow object-object communication are developed. The identification scheme is extended to a multi-addressing scheme for wireless ad hoc networks. These two issues and the developed solutions are applicable to a broad range of heterogeneous networks. The second part of the thesis deals with heterogeneous networks consisting of omnidirectional and directional antennas. A new MAC protocol for directional antennas, request-to-pause-directional-MAC (RTP-DMAC) protocol is developed that solves the deafness issue, which is common in networks with directional antennas. Three new routing metrics, which are extensions to the expected number of transmissions (ETX) metric are developed. The first metric, ETX1, reduces the route length by increasing the transmission power. The routing and MAC layers assume the presence of bidirectional links for their proper operation. However networks with omnidirectional and directional antennas have unidirectional links. The other two metrics, unidirectional-ETX (U-ETX) and unidirectional-ETX1 (U-ETX1), increase the transmission power of the directional nodes so that the unidirectional links appear as bidirectional links at the MAC and the routing layers. The performance of these metrics in different scenarios is evaluated.by Sivaram M.S.L. Cheekiralla.Ph.D