Wake up after transmissions and reduced channel contention to alleviate the hidden terminal problem in preamble sampling WSNs
The hidden terminal problem is a well-known problem in wireless networks that degrades the network performance due to collisions between nodes unable to sense each other. Preamble sampling WSNs are more sensitive to that problem than wireless local area networks due to the high vulnerability time caused by the long preamble transmission. This is specially important when the traffic load is high, for instance due to event detection and query dissemination or in regions closer to the sink. Typical mechanisms to reduce the negative effects of hidden terminals, like the use of RTS/CTS messages, cannot alleviate the problem in preamble sampling WSNs as the long preamble is still needed, thus not reducing the high vulnerability time. To alleviate the hidden terminal problem in this kind of networks the LWT-MAC, a new preamble sampling MAC protocol, is presented. The LWT-MAC protocol adapts to the sporadic increases in the network load by waking up sensor nodes at the end of a transmission. At the same time, it reduces the channel contention by implementing a non-aggressive retransmission procedure. In this work, the ability of the LWT-MAC protocol to reduce hidden terminal problems is evaluated and compared to the basic preamble sampling technique. Results show that the LWT-MAC protocol is able to significantly lighten the hidden terminal problem, thus improving the overall system performance.