Abstract—Directional antennas are introduced to improve the performance of IEEE 802.11-based wireless networks by allowing stations equipped with directional antennas to beam the data in a specific direction. Since IEEE 802.11 has been developed with omni antennas in mind, deploying IEEE 802.11 in a directional antenna environment leads stations to be conservative in blocking their own transmissions in favor of the ongoing transmissions. This conservative behavior conflicts with the main directional anten-nas ’ objective of increasing the spatial reuse channel by supporting simultaneous transmissions. In this paper, we analytically show that an IEEE 802.11 station with directional antenna is conserva-tive in terms of assessing channel availability, with as much as 60% of unnecessary blocking assessments. This percentage increases up to 90 % in case we allow the station to alter the way it accesses its media access control (MAC) data queue. Motivated with this analysis, we design and evaluate two enhancement schemes for IEEE 802.11 networks when using directional antennas. The first enhancement is to augment the IEEE 802.11 protocol with addi-tional information (location of the stations) that gives a station the flexibility to transmit data while there are ongoing transmissions in its vicinity. The second enhancement, using the augmented protocol, alters the way the IEEE 802.11 accesses its data queue. Simulation shows improvement in network throughput of up to 40 % in the case of applying the first enhancement and up to 60% in the case of applying the second enhancement. Index Terms—Capture effect, carrier sense, directional an-tenna, IEEE 802.11, network protocol, spatial reuse, wireless communication. I.

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This paper investigates the benefits and impacts of using directional antennas for multicast communications in ad hoc networks. In terms of signal reception, directional antennas have shown considerable improvement in the performance of all aspects over omni-directional antennas, especially over dense networks with heavy traffic load. In addition, we have found that transmitting multicast packets directionally to known neighboring group members or forwarders can help reduce the average end-to-end packet delay and increase the overall throughput. However, directional transmission of unacknowledged data transfers may result in lower performance in terms of packet delivery ratio than omni-directional transmission in any carrier sensing MAC protocols under moderate load due to the effect from the hidden terminal problem. Both analytical results and simulation results, as well as an acknowledgment mechanism to improve the successful delivery rate of multicast data packets, are presented. I.

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