Reducing false wake-up in contention-based wake-up control of wireless LANs

This paper studies the potential problem and performance when tightly integrating a low power wake-up radio (WuR) and a power-hungry wireless LAN (WLAN) module for energy efficient channel access. In this model, a WuR monitors the channel, performs carrier sense, and activates its co-located WLAN module when the channel becomes ready for transmission. Different from previous methods, the node that will be activated is not decided in advance, but decided by distributed contention. Because of the wake-up latency of WLAN modules, multiple nodes may be falsely activated, except the node that will actually transmit. This is called a false wake-up problem and it is solved from three aspects in this work: (i) resetting backoff counter of each node in a way as if it is frozen in a wake-up period, (ii) reducing false wake-up time by immediately putting a WLAN module into sleep once a false wake-up is inferred, and (iii) reducing false wake-up probability by adjusting contention window. Analysis shows that false wake-ups, instead of collisions, become the dominant energy overhead. Extensive simulations confirm that the proposed method (WuR-ESOC) effectively reduces energy overhead, by up to 60% compared with state-of-the-arts, achieving a better tradeoff between throughput and energy consumption

Improving performance of pedestrian positioning by using vehicular communication signals

Pedestrian-to-vehicle communications, where pedestrian devices transmit their position information to nearby vehicles to indicate their presence, help to reduce pedestrian accidents. Satellite-based systems are widely used for pedestrian positioning, but have much degraded performance in urban canyon, where satellite signals are often obstructed by roadside buildings. In this paper, we propose a pedestrian positioning method, which leverages vehicular communication signals and uses vehicles as anchors. The performance of pedestrian positioning is improved from three aspects: (i) Channel state information instead of RSSI is used to estimate pedestrian-vehicle distance with higher precision. (ii) Only signals with line-of-sight path are used, and the property of distance error is considered. (iii) Fast mobility of vehicles is used to get diverse measurements, and Kalman filter is applied to smooth positioning results. Extensive evaluations, via trace-based simulation, confirm that (i) Fixing rate of positions can be much improved. (ii) Horizontal positioning error can be greatly reduced, nearly by one order compared with off-the-shelf receivers, by almost half compared with RSSI-based method, and can be reduced further to about 80cm when vehicle transmission period is 100ms and Kalman filter is applied. Generally, positioning performance increases with the number of available vehicles and their transmission frequency

Energy-Efficient Data Collection Method for Sensor Networks by Integrating Asymmetric Communication and Wake-Up Radio

In large-scale wireless sensor networks (WSNs), nodes close to sink nodes consume energy more quickly than other nodes due to packet forwarding. A mobile sink is a good solution to this issue, although it causes two new problems to nodes: (i) overhead of updating routing information; and (ii) increased operating time due to aperiodic query. To solve these problems, this paper proposes an energy-efficient data collection method, Sink-based Centralized transmission Scheduling (SC-Sched), by integrating asymmetric communication and wake-up radio. Specifically, each node is equipped with a low-power wake-up receiver. The sink node determines transmission scheduling, and transmits a wake-up message using a large transmission power, directly activating a pair of nodes simultaneously which will communicate with a normal transmission power. This paper further investigates how to deal with frame loss caused by fading and how to mitigate the impact of the wake-up latency of communication modules. Simulation evaluations confirm that using multiple channels effectively reduces data collection time and SC-Sched works well with a mobile sink. Compared with the conventional duty-cycling method, SC-Sched greatly reduces total energy consumption and improves the network lifetime by 7.47 times in a WSN with 4 data collection points and 300 sensor nodes

Association Control for Wireless LANs: Pursuing Throughput Maximization and Energy Efficiency

International audienceBecause the access points (APs) and the stations (STAs) of a community access network are deployed at the users' desired places, the APs and STAs tend to concentrate in certain areas. A concentration of STAs often results in the AP(s) and STAs in that particular area suffering from severe congestion. A concentration of APs, on the other hand, may cause energy wastage. While a number of association control schemes are proposed to alleviate congestion in WLANs, the existing schemes do not necessarily maximize throughput and do not consider energy consumption. In this paper, we analytically formulate the network throughput as the multiplication of the success probability, frame transmission rate, and channel air-time ratio. The second and third components can easily be monitored and controlled based on measurements of local link and channel condition using the off-the-shelf WLAN devices. On the other hand, the first component, success probability is a function of the number of contending nodes that is extremely difficult to monitor in overlapping WLANs. Due to this reason, we extend our theoretical study and show that success probability can be indirectly maximized by controlling air-time ratio. Finally, we propose an association control scheme that aims at maximizing throughput and reducing energy consumption by taking account of the multiplication of frame transmission rate and air-time ratio. The proposed scheme is evaluated by computer simulations and testbed experiments conducted under real-world complex scenarios with UDP and TCP traffic. Both the simulations and actual implementations confirm the correctness of the theoretical work and the effectiveness of the proposed scheme

Energy Efficient Downlink Transmission in Wireless LANs by Using Low-Power Wake-Up Radio

In the downlink of a wireless LAN, power-save mode is a typical method to reduce power consumption. However, it usually causes large delay. Recently, remote wake-up control via a low-power wake-up radio (WuR) has been introduced to activate a node to instantly receive packets from an access point (AP). But link quality is not taken into account and protocol overhead of wake-up per node is relatively large. To solve these problems, in this paper, a broadcast-based wake-up control framework is proposed, and a low-power WuR is used to receive traffic indication map from an AP, monitor link quality, and perform carrier sense. Among the nodes which have packets buffered at the AP, only those whose SNR is above a threshold will be activated, contending via a proper contention window to receive packets from the AP. Optimal SNR threshold, deduced by theoretical analysis, helps to reduce transmission collisions and false wake-ups (caused by wake-up latency) and improve transmission rate. Extensive simulations confirm that the proposed method (i) effectively reduces power consumption of nodes compared with other methods, (ii) has less delay than power-save mode in times of light traffic, and (iii) achieves higher throughput than other methods in the saturation state

CCN-Based Inter-Vehicle Communication for Efficient Collection of Road and Traffic Information

Recently, inter-vehicle communication, which helps to avoid collision accidents (by driving safety support system) and facilitate self-driving (by dissemination of road and traffic information), has attracted much attention. In this paper, in order to efficiently collect road/traffic information in the request/response manner, first a basic method, Content-centric network (CCN) for Vehicular network (CV), is proposed, which applies CCN cache function to inter-vehicle communication. Content naming and routing, which take vehicle mobility into account, are investigated. On this basis, the CV method is extended (called ECV) to avoid the cache miss problem caused by vehicle movement, and is further enhanced (called ECV+) to more efficiently exploit cache buffer in vehicles, caching content according to a probability decided by a channel usage rate. Extensive evaluations on the network simulator Scenargie, with a realistic open street map, confirm that the CV method and its extensions (ECV, ECV+) effectively reduce the average number of hops of data packets (by up to 47%, 63%, and 83%, respectively) and greatly improve the content acquisition success rate (by up to 356%, 444%, and 689%, respectively), compared to the method without a cache mechanism

Packet distribution for complex wireless access route using IEEE802.11/802.16 and its field trial

Abstrak The diversification of wireless communication usagehas been proceeding rapidly with the diffusion of cellular phones,WiFi and WiMAX. In the emerging wireless communicationenvironments, diverse wireless systems coexist. On the otherhand, there is increasing concern that the growing use ofwireless systems will exhaust the finite wireless resources. Tosolve this problem, we aim to optimize the utilization of wirelessresources by combining communications among multiple wirelessinterfaces. In this paper, we propose a packet distribution forcomplex access route combining IEEE802.11/802.16 wireless linksin parallel and tandem, and show its performance in field trial.The proposed method improves delay and throughput in thenetwork by taking full advantages of wireless media diversity.4 Halama