IEEE 802.11 MAC protocol has been the standard for Wireless LANs and is also implemented in many simulation software for mobile ad hoc networks. However, IEEE 802.11 MAC has been shown to be quite inefficient in the multihop mobile environments. Besides the well-known hidden terminal problem and the exposed terminal problem, there also exists the receiver blocking problem which may result in link/routing failures and unfairness among multiple flows. Moreover, the contention and interference from the upstream and downstream nodes seriously decrease the packet delivery ratio of multihop flows. All these problems could lead to the “explosion” of control packets and poor throughput performance.
    To achieve the desired protocol behavior, a dual-channel approach for DATA and control packets, separately. DATA is transmitted over the data channel. RTS and CTS are transmitted over the control channel. Negative CTS (NCTS) is used to solve the receiver blocking problem and is also transmitted in the control channel. An outband receiver based busy tone is used to solve the hidden terminal problem. ACK is unnecessary here because our protocol can guarantee that there is no collision to DATA packets. To deal with wireless channel errors, a NACK signal which is a continuing busy tone signal when the receiver determines that the received DATA packet is corrupted. The sender will not misinterpret this NACK signal since there are no other receivers in its sensing range and hence no interfering NACK signals. It will conclude that the transmission is successful if no NACK signal is sensed.
    DUCHA adopts the same transmission power and capture threshold CPThresh in both control and DATA channels. And the transmission power level for correct receiving RXThresh is also the same for the two channels so that the two channels have the same transmission and sensing range. The newly designed message exchange sequence provides a comprehensive solution to all the aforementioned problems. Simulations demonstrate that DUCHA scheme provides a much more stable link layer, greatly improves the spatial reuse, and works well in reducing the packet collisions. It improves the throughput by 7% to 20% for one-hop flows and by 2-5 times for multihop flows under heavy traffic comparing to the IEEE 802.11 MAC.

Reference Paper: DUCHA: A New Dual-channel MAC Protocol for Multihop Ad Hoc Networks

Author’s Name: Hongqiang Zhai, Jianfeng Wang, and Yuguang Fang

Source: IEEE

Year: 2006

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