A MAC protocol for full exploitation of directional antennas in ad-hoc wireless networks

Directional antennas in ad hoc networks offer many benefits compared with classical omnidirectional antennas. The most important include significant increase of spatial reuse, coverage range and subsequently network capacity as a whole. On the other hand, the use of directional antennas requires new approach in the design of a MAC protocol to fully exploit these benefits. Unfortunately, directional transmissions increase the hidden terminal problem, the problem of deafness and the problem of determination of neighbors' location. In this paper we propose a new MAC protocol that deals effectively with these problems while it exploits in an efficient way the advantages of the directional antennas. We evaluate our work through simulation study. Numerical results show that our protocol offers significant improvement compared to the performance of omni transmissions

CDR-MAC: A protocol for full exploitation of directional antennas in ad hoc wireless networks

In this paper, we propose a new Medium Access Control (MAC) protocol for full exploitation of directional antennas in wireless networks. The protocol introduces a circular directional transmission of the Request To Send (RTS) control packet, spreading around a station information about the intended communication. The stations that receive the directional RTS, using a simple scheme of tracking the neighbors' directions, defer their transmission toward the beams that could harm the ongoing communication. In this way, the proposed protocol takes advantage of the benefits of directional transmissions as the increase of spatial reuse and of coverage range. Additionally, it reduces the hidden-terminal problem, as well as the deafness problem, two main factors for the decrease of the efficiency of directional transmissions in ad hoc networks. The performance evaluation of the protocol shows that it offers a significant improvement in static, as well as mobile, scenarios, as compared to the performance of the proposed protocols that use omnidirectional or directional transmissions

Handling asymmetry in gain in directional antenna equipped ad hoc networks

The deployment of traditional higher layer protocols (especially the IEEE 802.11 MAC protocol at the MAC layer) with directional antennae could lead to problems from an increased number of collisions; this effect is primarily seen due to three specific effects: (i) an increase in the number of hidden terminals; (ii) the problem of deafness and, (iii) a difficulty in determining the locations of neighbors. In this work we propose a new MAC protocol that incorporates circular RTS and CTS transmissions. We show that the circular transmission of the control messages helps avoid collisions of both DATA and ACK packets from hidden terminals. Our protocol intelligently determines the directions in which the control messages ought to be transmitted so as to eliminate redundant transmissions in any given direction. We perform extensive simulations and analyze the obtained results in order to compare our scheme with previously proposed protocols that have been proposed for use in directional antenna equipped ad hoc networks. Our simulation results clearly demonstrate the benefits of incorporating both circular RTS and CTS messages in terms of the achieved aggregate throughput. © 2005 IEEE

It is Better to Give than to Receive - Implications of Cooperation in a Real Environment

Abstract. Thanks to the immense potential cooperative communications displays, extensive investigations have been directed to examine its performance by means of both analysis and simulation. In this paper 1, an implementation approach has for the first time been pursued to demonstrate the viability of realizing cooperation at the MAC layer in a real environment. The paper further describes the technical challenges encountered, details the corresponding solution proposed, and shares the experience gained. The experimental measurements in a medium size (i.e., 10 stations) testbed are then reported, which not only helps develop a deeper understanding of the protocol behavior, but also confirms that a cooperative MAC protocol delivers superior performance.

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Queue-Sharing Multiple Access

Queue-Sharing Multiple Access (QSMA) is introduced and analyzed. The new channel-access method  consists of establishing  and maintaining a distributed transmission queue among nodes sharing a common channel  and results in   a sequence of queue cycles, with each cycle having one or multiple  queue turns with collision-free transmissions from  nodes that have joined the transmission queue, followed by a joining period for the current cycle.   Nodes can take advantage of carrier sensing to improve the efficiency with which nodes join and use the shared transmission queue. The throughput of  ALOHA with priority ACK's,  CSMA with priority ACK's,  CSMA/CD with priority ACK's, TDMA with a fixed schedule, and QSMA with and without carrier sensing is compared analytically and by simulation in ns-3.  The results show that QSMA is more efficient  than TDMA with the simplicity of CSMA or ALOHA