A directional hidden terminal problem in ad hoc network MAC protocols with smart antennas and its solutions

M. Sekido, M. Takata, M. Bandai, T. Watanabe
2005 GLOBECOM '05. IEEE Global Telecommunications Conference, 2005.  
Smart antennas are expected to enhance scalability in ad hoc networks. This paper describes the evaluations of three directional MAC protocols, DMAC, MMAC, and SWAMP, as well as the IEEE 802.11 DCF omni-directional protocol in a multihop transmission environment. These evaluations address the problem that performance strongly depends on the route topology between the source and destination, referred to as the directional hidden terminal problem. After analyzing this problem, we propose three
more » ... level solutions. The MAC solutions are NAV indicators, i.e. HCTS, BRTS, and RCTS, which indicate on-going communications to a directional hidden terminal to set NAV. Based on simulated results, we show that all the proposed MAC solutions could improve the throughput performance. A. IEEE 802.11 DCF This is a popular and widely used MAC protocol that uses an omni-directional antenna and communicates in the order of RTS/CTS/DATA/ACK. In addition to a physical carrier sense, a virtual carrier sense is also used to ameliorate the hidden terminal problem. B. SWAMP Smart antennas based wider-range access MAC protocol consists of two access modes, omni-directional area communication access mode (OC-mode) and extend area communication access mode (EC-mode). OC-mode is selected when the destination terminal is located within the omni-directional transmission range or when the transmitter has no knowledge about the receiver node. A communication pair exchanges RTS/CTS/SOF (start of frame)/DATA/ACK. RTS/CTS/SOF are transmitted using an omni-directional beam and DATA/ACK are transmitted using a directional beam. Through the RTS/CTS/SOF exchange, the communication peer's position information is acquired and the position information is relayed to the neighborhood. The neighbor terminal that receives RTS/CTS/SOF temporarily suspends its communication activities, while Omni-NAV, which is shorter than the conventional NAV, is active. On the other hand, EC-mode is selected when the destination terminal is located out of the transmitter's omnidirectional range and in the twice of the omni-directional range. The beam direction is controlled by the terminal position information acquired from the neighborhood by the OCmode. Then, RTS/CTS/DATA/ACK are transmitted using a directional beam. By transmitting RTS using a higher gain directional beam, EC mode can directly communicate with the two-hop position terminals. C. DMAC In DMAC, communication pair exchanges RTS/CTS/DATA/ACK transmitted using a directional beam. The neighboring terminal that receives the RTS/CTS sets NAV, temporarily suspends communication to the RTS/CTS transmitting terminal. During this time, it is possible to communicate towards area in which NAV is not set. The communication area depends on the distance of the directional beam used. In DMAC, the position information acquisition method required for directional control is not shown. This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE GLOBECOM 2005 proceedings. 0-7803-9415-
doi:10.1109/glocom.2005.1578227 dblp:conf/globecom/SekidoTBW05 fatcat:urhi5bpjyzch3boxdmkzbtns5a