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Wireless sensor networks (WSNs) are increasingly used in environmental monitoring applications. They are designed to operate for several months by featuring low activity cycles in order to save energy. In this paper, we propose a Medium Access Control (MAC) protocol for such WSNs with very low duty-cycles of 1% and less. Nodes are activated randomly and use a history of previous successful frame exchanges to decide their next activation time. We study the choice of the history size, and we compare the performance of our protocol with other protocols from the literature. We show by simulations and real experiments that with a limited history size of only six entries, our protocol achieves better performance than other protocols from the literature, while keeping the advantages of fully asynchronous protocols.

Wireless sensor networks (WSNs) are increasingly used in environmental monitoring applications. They are designed to operate for several months by featuring low activity cycles in order to save energy. In this paper, we propose a Medium Access Control (MAC) protocol for suchWSNs with very low duty-cycles of 1% and less. Nodes are activated randomly and use a history of previous successful frame exchanges to decide their next activation time. We study the choice of the history size, and we compare the performance of our protocol with other protocols from the literature. We show by simulations and real experiments that with a limited history size of only six entries, our protocol achieves better performance than other protocols from the literature, while keeping the advantages of fully asynchronous protocols.

In this paper the problem of maximum lifetime routing is investigated in asynchronous duty-cycled wireless sensor networks. To model this problem, a new energy balance based asynchronous MAC protocol is proposed called K-Persistent FRTS-RCTS, which stands for K-Persistent flooding of RTS and random sending of CTS. In this protocol, each transmitter in order to send a data packet, first transmits at most K packets of RTS to its neighbors by flooding, but if the transmitter does not receive any CTS packets, it transmits the RTS packet directly to the sink. The CTS packet is sent to the transmitter either by one of the waking neighbors via a uniform random mechanism or by the sink node in response to the received RTS packet. It is shown that by using K-Persistent FRTS-RCTS MAC, the problem is formulated as a mixed integer nonlinear programming problem. In this problem, the optimization variables consist of the maximum number of RTS flooding requests ( K) as the integer values and the flow rate of information on any route and the duty cycle of nodes both as the real values. To assess the performance of the proposed method, it is compared to the same maximum lifetime routing problem under the 1-Persistent FRTS-RCTS and the well-known X-MAC protocols. Evaluation results indicate that K-Persistent FRTS-RCTS MAC outperforms two mentioned MAC protocols in terms of both network lifetime and topology changes. [ABSTRACT FROM AUTHOR]

Multi-user multiple-input multiple-output (MIMO) technology makes it possible for wireless nodes to successfully receive multiple packets from simultaneous transmitters in wireless networks. As it can provide more transmission opportunities without causing collisions, the network throughput performance can be dramatically improved. In this paper, we propose an asynchronous medium access control (MAC) protocol, which enables senders to independently start their transmissions if the access point (AP) can receive more simultaneous packets up to its multi-packet reception capability. This asynchronous protocol makes the multi-user MIMO channel more efficiently used, especially in wireless networks where transmission durations are dynamically varying due to different packet sizes and transmission rates. Through our performance analysis and extensive simulations, we show that the proposed asynchronous MAC protocol achieves significantly higher uplink throughput performance in multi-user MIMO wireless networks. [ABSTRACT FROM AUTHOR]