In this paper, we first propose a redundant radix based number (RBN) representation for encoding the data to be transmitted in a wireless network. This RBN encoding uses three possible values - 0, 1 and @math , for each digit to be transmitted. We then propose to use silent periods (zero energy transmission) for transmitting the 0's in the RBN encoded data thus obtained. This is in contrast to most conventional communication strategies that utilize energy based transmission (EbT) schemes, where energy expenditure occurs for transmitting both 0 and 1 bit values. The binary to RBN conversion algorithm presented here offers a significant reduction in the number of non-zero bits in the resulting RBN encoded data. As a result, it provides a highly energy-efficient technique for data transmission with silent periods for transmitting 0's. We simulated our proposed technique with ideal radio device characteristics and also with parameters of various commercially available radio devices. Experimental results on various benchmark suites show that with ideal as well as some commercial device characteristics, our proposed transmission scheme requires 69 less energy on an average, compared to the energy based transmission schemes. This makes it very attractive for application scenarios where the devices are highly energy constrained. Finally, based on this transmission strategy, we have designed a MAC protocol that would support the communication of such RBN encoded data frames.
A wireless sensor network consists of many energy-autonomous microsensors distributed throughout an area of interest. Each node monitors its local environment, locally processing and storing the collected data so that other nodes can use it. To optimize power consumption, the Swiss Center for Electronics and Microtechnology has developed WiseNET, an ultralow-power platform for the implementation of wireless sensor networks that achieves low-power operation through a careful codesign approach. The WiseNET platform uses a codesign approach that combines a dedicated duty-cycled radio with WiseMAC, a low-power media access control protocol, and a complex system-on-chip sensor node to exploit the intimate relationship between MAC-layer performance and radio transceiver parameters. The WiseNET solution consumes about 100 times less power than comparable solutions. Wireless sensor networks (WSNs) are typically characterized by a limited energy supply at sensor nodes. Hence, energy efficiency is an important issue in the system design and operation of WSNs. In this paper, we introduce a novel communication paradigm that enables energy-efficient information delivery in wireless sensor networks. Compared with traditional communication strategies, the proposed scheme explores a new dimension - time, to deliver information efficiently. We refer to the strategy as Communication through Silence (CtS). We identify a key drawback of CtS - energy - throughput trade-off, and explore optimization mechanisms that can alleviate the trade-off. We then present several challenges that need to be overcome, primarily at the medium access control layer of the network protocol stack, in order to realize CtS effectively. We present a deterministic broadcast algorithm for the class of mobile ad hoc networks where the mobile nodes possess collision detection capabilities. The algorithm is based on a breadth-first traversal of the network, allows multiple transmissions in the same time slot and completes broadcast in O(n log n) time in the worst case. It is mobility resilient even for networks where topology changes are very frequent. The idea of this broadcast algorithm is then extended to develop a gossiping algorithm having O((n+D)Dlog n) worst case run time, where D is the diameter of the network graph, which is an improvement over the existing algorithms. Energy conservation is a major concern in wireless sensor networking. Conventionally in wireless communications, each bit transmitted by a node consumes one unit of energy. Some recent advances, however, explore silent time intervals between signal transmissions to convey information (Zhu and Sivakumar [1]). Such a scheme of Communication through Silence (CtS), while reducing energy consumption for sensor nodes, introduces long delay. In this paper, we propose Variable-Base Tacit Communication (VarBaTaC) to mitigate the delay introduced by CtS. We also develop three MAC protocols based on VarBaTaC for different environments. We then outline experiment designs for further investigations and point out some interesting future research directions. Wireless sensor networks are appealing to researchers due to their wide range of application potential in areas such as target detection and tracking, environmental monitoring, industrial process monitoring, and tactical systems. However, low sensing ranges result in dense networks and thus it becomes necessary to achieve an efficient medium-access protocol subject to power constraints. Various medium-access control (MAC) protocols with different objectives have been proposed for wireless sensor networks. In this article, we first outline the sensor network properties that are crucial for the design of MAC layer protocols. Then, we describe several MAC protocols proposed for sensor networks, emphasizing their strengths and weaknesses. Finally, we point out open research issues with regard to MAC layer design.