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Yomo H.,Kansai University | Abe K.,Advanced Technology Development Center | Ezure Y.,Advanced Technology Development Center | Ito T.,Advanced Technology Development Center | And 2 more authors.
2015 IEEE Global Communications Conference, GLOBECOM 2015

Wireless sensor and actuator networks (WSANs) are required to achieve both energy-efficiency and low-latency in order to prolong the network lifetime while being able to quickly respond to intermittently-transmitted control commands. These two requirements are in general in a relationship of trade-off when each node operates with well-known duty-cycling modes: nodes need to make their radio interfaces (IFs) frequently active in order to promptly detect the communication requests from the other nodes. One approach to break this inherent trade-off, which has been actively studied in recent literature, is the introduction of wake-up receiver that is installed into each node and used only for detecting the communication requests. The radio IF in each node is woken up only when needed through a wake-up message received by the wake-up receiver. While the effectiveness of this type of on-demand WSANs has been shown in several studies by theoretical analysis and computer simulations, its implementation and large-scale experimental investigations are missing. Therefore, in this paper, we first design and implement radio-on-demand sensor and actuator networks (ROD-SAN) including all protocols to realize on-demand WSANs, from the lowest layer of wake-up signaling to the application layer offering the functionalities of information monitoring and networked control. Then, we show experimental results obtained through our field trial in which 20 nodes are deployed in an outdoor area with the scale of 450m X 200m. The numerical results provide us with practical insights on the effectiveness as well as limitations of on-demand WSANs. © 2015 IEEE. Source

Tang S.,Adaptive Communications Research Laboratories
IEEE Transactions on Wireless Communications

In wireless LANs, the performance of CSMA/CA might be degraded by several problems: (i) severe collisions in the uplink, (ii) head-of-line problem caused by fading in the downlink, and (iii) serious unfairness between uplink and downlink. In this paper, a distributed multiuser scheduling (DMUS) scheme is proposed to simultaneously address these problems. In DMUS, a node (i) computes its normalized SNR (signal to noise ratio) as the ratio of its instantaneous SNR to its average SNR, and (ii) contends via a contention window (CW) for the channel to initiate its uplink or downlink transmission when its normalized SNR is greater than a threshold. The contribution is threefold: (i) All three problems are solved in a unified framework by applying multiuser diversity in both uplink and downlink. Fresh SNR is exploited for distributed scheduling meanwhile airtime fairness is retained. (ii) SNR threshold and CW are jointly optimized to maximize throughput, taking into account time-variant link quality, collision probability and protocol overhead. (iii) Network performance is theoretically analyzed. Extensive simulations confirm that DMUS greatly improves total throughput under almost all scenarios compared with both the contention-based CSMA/CA scheme and the contention-free PCF scheme. © 2014 IEEE. Source

Kondo Y.,Adaptive Communications Research Laboratories | Yomo H.,Kansai University | Tang S.,Adaptive Communications Research Laboratories | Iwai M.,NEC Communication Systems LTD. | And 3 more authors.
Computer Communications

This paper considers a radio-on-demand (ROD) wireless LAN (WLAN) in which access points (APs) are put into a sleep mode during idle periods and woken up by stations (STAs) upon communications demands. The on-demand wake-up is realized by a wake-up receiver which is equipped with each AP and is used to detect a wake-up signal transmitted by STA. In order to reduce the hardware installation cost at STA, we advocate to utilizing wireless LAN frames transmitted by each STA as a wake-up signal. We generate a wake-up signal based on frame length modulation (FLM) where each STA creates a series of WLAN frames with different length to which the information on wake-up ID is embedded. The simple and low-power wake-up receiver extracts the wake-up ID from the received frames. In this paper, we design and develop a prototype of the wake-up receiver and propose a wake-up protocol which defines a procedure to realize the on-demand AP wake-up in ROD WLAN. We evaluate system-level performance of ROD WLAN based on our prototype and our proposed wake-up protocol, and investigate appropriate settings of parameters for our proposed FLM to achieve the required system-level performance. Our numerical results confirm that the proposed wake-up protocol with FLM achieves smaller delay than a conventional AP employing passive scanning while maintaining small probability to be falsely woken up by continuous interference. © 2012 Elsevier B.V. All rights reserved. Source

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