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Collision due to the hidden terminals in contention-based medium access control protocols is one of the main reasons of the poor end-to-end performance of wireless networks. In this paper, we present a novel approach for MAC protocol improvements for 802.11-based multi-hop ad-hoc wireless networks to reduce unnecessary collisions, resulting in performance enhancement. Our main idea is to reduce unnecessary collisions by introducing a new time interval, named CAI (Collision Avoidance Interval) for the node in the carrier sensing zone[6]. Specifically, in the context of 802.11, the four-way handshake is specified as a collision avoidance medium access protocol and the protocol behavior for the node in the carrier sensing zone is required to be modified when it senses a signal for CTS, such that the node defers transmitting a frame during CAI, unlike during EIFS in the 802.11 specification. We carry in-depth analysis of the protocol behavior and have conducted a comprehensive simulation to study the performance improvements. The simulation results show that the end-to-end performance is greatly increased and the number of dropped frames due to collision is significantly reduced as much as one half, and so is the throughput cost. Keywords: Ad-hoc wireless networks, IEEE 802.11, MAC, Collision, CAI (Collision Avoidance Interval) [ABSTRACT FROM AUTHOR]

In DCF of 802.11-based multi-hop wireless networks, a channel access sequence of 4-way handshake with RTS-CTS-DATA-ACK is used to forward a single packet. For multi-hop packet forwarding, multiple channel accesses with this 4-way handshake are required, and this might entail multiple collisions, which, in turn, results in poor end-to-end performance. To eliminate the overhead of these multiple channel accesses and, as a result, to reduce the possible number of collisions, the DCMA (Data-driven Cut-through Medium Access) protocol has been proposed[5]. We name the scheme used in the DCMA protocol the forward cut-through scheme. In this paper, we propose BCTMA (Bi-directional Cut-Through Medium Access)protocol for high performance 802.11-based multi-hop wireless networks by combining both forward and backward cut-through schemes. We have implemented BCTMAprotocol in ns-2[9]. We conducted a comprehensive simulation to study the performance improvements. The simulation results indicate that the performance is significantly improved and the number of dropped packets due to collisions can be significantly reduced as much as a half. Keywords: Forward cut-through scheme, Backward cut-through scheme, BCTMA (Bi-directional Cut-Through Medium Access) protocol, DCF (Distributed Coordination Function), Wireless multi-hop networks, IEEE 802.11 [ABSTRACT FROM AUTHOR]

The IEEE 802.15.3 standard does not specify how to schedule CTA (Channel Time Allocation)s in CTAP (Channel Time Allocation Period) of a superframe. In this paper, we propose a novel scheduling algorithm for channel time allocation of 802.15.3-based HR-WPAN (High Rate Wireless Personal Area Networks), named WFCTA (Weighted Fair Channel Time Allocation). The proposed WFCTA inherently has properties which are necessary for various QoS provisioning, because it is based on TDMA, applied by WFQ algorithm. We explain and compare four implementation cases of WFCTA. We also analyze its worst-case performance in terms of both link utilization and fairness and verify it by simulation. Keywords: IEEE 802.15.3, HR-PAN, WFQ (Weighted Fair Queueing), superframe, beacon, CTAP (Channel Time Allocation Period), CTA (Channel Time Allocation) [ABSTRACT FROM AUTHOR]