Simultaneous query for wireless sensor networks: A power based solution

We study the problem of supporting simultaneous query in WSNs. For such networks, the network efficiency can be significantly improved if the poller can obtain information via a simultaneous query. Two fundamental cases of such queries are studied in this paper: counting and identifying active neighboring nodes. We propose two mechanisms, Power based counting (Poc) and Power based identification (Poid), which achieve the goals by allowing neighbors to respond simultaneously to a poller. A key observation that motivates our design is that the power of a superposed signal increases with the number of component signals under the condition that the component signals are synchronized precisely. However, such high precision of synchronization is rather difficult to achieve in WSNs. To address this challenge, we design delicate delay compensation methods to reduce the phase offset of each component signal. Moreover, we propose a novel probabilistic estimation technique to overcome the hardware limitations on the observed received power. Poid currently works only in sparse networks though, we discuss and analyze the time complexity of applying Poid in dense networks. Experimental results show that the average accuracy of Poc and Poid is above 95 and 91 percent, respectively. In addition, our methods achieve substantially lower energy consumption and estimation delay compared with the state-of-the-art solutions.