Participatory location fingerprinting through stationary crowd in a public or commercial indoor environment

The training phase of indoor location fingerprinting has been traditionally performed by dedicated surveyors in a manner that is time and labour intensive. Crowdsourcing process is more efficient, but is impractical in public or commercial buildings because it requires occasional location fix provided explicitly by the participant, the availability of an indoor map for correlating the traces, and the existence of landmarks throughout the area. Here, we address these issues for the first time in this context by leveraging the existence of stationary crowd that have timetabled roles, such as desk-bound employees, lecturers and students. We propose a scalable and effortless positioning system in the context of a public/commercial building by using Wi-Fi sensor readings from its stationary occupants' smartphones combined with their timetabling information. Most significantly, the entropy concept of information theory is utilised to differentiate between good and spurious measurements in a manner that does not rely on the existence of known trusted users. Our analysis and experimental results show that, regardless of such participants' unpredictable behaviour, including not following their timetabling information, hiding their location or purposefully generating wrong data, our entropy-based filtering approach ensures the creation of a radio-map incrementally from their measurements. Its effectiveness is validated experimentally with two well-known machine learning algorithms

Analysis of WLAN's received signal strength indication for indoor location fingerprinting

An indoor positioning system that uses a location fingerprinting technique based on the received signal strength of a wireless local area network is an enabler for indoor location-aware computing. Data analysis of the received signal strength indication is very essential for understanding the underlying location-dependent features and patterns of location fingerprints. This knowledge can assist a system designer in accurately modeling a positioning system, improving positioning performance, and efficiently designing such a system. This study investigates extensively through measurements, the features of the received signal strength indication reported by IEEE 802.11b/g wireless network interface cards. The results of the statistical data analysis help in identifying a number of phenomena that affect the precision and accuracy of indoor positioning systems. © 2011 Elsevier B.V. All rights reserved

Analysis of adaptive multi-hop time synchronization in large wireless sensor networks

Gordon, SD ORCiD: 0000-0003-4090-1199Time synchronization in wireless sensor networks is important for sensing services that require clock accuracy but use sensors without accurate hardware clocks. Pairwise synchronization is a common technique for two nodes to synchronize their clocks; a leading protocol that extends it across a larger network is AMTS. The challenge with AMTS and other protocols is that synchronization may incur significant communication overhead and more importantly reduce battery lifetime. Although AMTS has been analyzed with small networks, in this paper we analyze its performance in chain, grid and tree topology networks, identifying the trade off between synchronization period and energy consumptio

Analysis of adaptive multi-hop time synchronization in large wireless sensor networks

Time synchronization in wireless sensor networks is important for sensing services that require clock accuracy but use sensors without accurate hardware clocks. Pairwise synchronization is a common technique for two nodes to synchronize their clocks; a leading protocol that extends it across a larger network is AMTS. The challenge with AMTS and other protocols is that synchronization may incur significant communication overhead and more importantly reduce battery lifetime. Although AMTS has been analyzed with small networks, in this paper we analyze its performance in chain, grid and tree topology networks, identifying the trade off between synchronization period and energy consumptio

iACK: Implicit acknowledgements to improve multicast reliability in wireless sensor networks

Reliability in IP-multicast forwarding becomes useful while operating in lossy environment of wireless sensor networks. RPL is a protocol for forming a multicast tree in sensor networks for multicast data forwarding. Trickle multicast uses RPL to provide reliability, however it has a high overhead and delay, especially when a radio duty cycle is used on the sensors. Stateless Multicast Forwarding (SMRF) optimizes for the radio duty cycle, reducing delay but also reducing reliability. This paper proposes iACK, a retransmission scheme on top of SMRF that uses implicit acknowledgements present in wireless broadcast to determine which packets a node should retransmit. We have implemented iACK in ContikiOS. Results show that iACK delay is about 5 times less than Trickle (and close to SMRF), and packet delivery ratio is about 80% (compared to between 20% and 60% for Trickle and SMRF). With a slight increase in memory requirements, iACK offers a valuable tradeoff compared to existing protocols