Different Aspects of Hidden Terminal Problems in Wireless Ad Hoc Network: Problems and Solutions

• Main Authors: Yen-Da Chen, 陳彥達
• Other Authors: Kuei-Ping Shih
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/18781404899162419795

博士 === 淡江大學 === 資訊工程學系博士班 === 95 === Hidden terminal problem is a notorious problem in contention-based MAC protocol for multihop wireless ad hoc networks. RTS/CTS exchange is the well-know solution to hidden terminal problem. However, hidden terminal problem still happens in some particular situations. For example, in IEEE 802.11 ad hoc network, for two mobile hosts (MHs) hidden from each other, RTS frames are also possible to collide with each other, even that their backoff counters are different. The situation will be getting worse in high traffic load or in a dense network. On the other hand, power control is a common and popular mechanism used to save energy for MHs in wireless ad hoc networks. Unfortunately, hidden terminal problem is very likely to happen if the exactly power is used to transmit between the sender and the receiver. In addition, on TDMA-based mobile ad hoc networks, if an MH selects an unsuitable slot to send, the hidden terminal problem will occur as well. As a result, the major focus of this dissertation is to solve hidden terminal problem for the three environments: 1) IEEE 802.11-based wireless ad hoc networks, 2) power-control-based wireless ad hoc networks, and 3) TDMA-based mobile ad hoc networks. In IEEE 802.11-based wireless ad hoc networks, RTS collisions not only result in the following CTS or ACK collisions, but also induce false blocking problem, even dead locks of transmissions. In the dissertation, an improvement mechanism protocol is also devised, which only uses a single channel and one transceiver to reduce RTS collisions. This improvement mechanism provides a type of fast collision detection and decreases the probability of RTS collisions, which is benefit for RTS/CTS exchange scheme. Meanwhile, this improvement mechanism can reduce the retransmission cost and have lower control overhead than that of IEEE 802.11 DCF. Power control mechanism which can save power consumption of station and prolong the network lifetime is a common technology in power-control-based wireless ad hoc networks. However, collisions are very likely to happen if exact power level is used. Thus, the dissertation identifies a power control induced hidden terminal problem and takes the interference range into consideration to propose a collision avoidance power control MAC scheme which uses the appropriate power to exchange packets, instead of the exact power in order to resist the interference of other stations for avoiding interference due to the reduced power in power control mechanism. On TDMA-based mobile ad hoc networks, if an MH depending on one-hop neighboring information may select an unsuitable slot to send, the hidden terminal problem will occur as well. In this dissertation, a Slot Inhibited Policies is proposed to determine which slots are valid to use in a communication link. As mentioned above, hidden terminal problem is a serious and important issue in multihop wireless ad hoc networks. Although RTS/CTS exchange mechanism is used for avoiding hidden terminal problem, hidden terminal problem may still happen in IEEE 802.11-based, power-control-based, or TDMA-based ad hoc networks. Consequently, this dissertation proposes some mechanisms to avoid the hidden terminal problems in these three particular situations. In the future, we will study and focus on another famous problem, exposed terminal problem, to improve the network performance. Thus, the protocols will be more effective and practical for real situations.