Research On Multiple Access And Transmission Concurrency For Low Power Wireless Networks

The unprecedented proliferation of Io T devices in the last decade has been led by multiple wireless technologies,each offering convenience in different aspects of our daily lives.However,wireless technologies are victims of their own success: spectrum sharing among wireless devices and technologies has led to a severe wireless coexistence problem.Although there have been many efforts made to address this problem,they still suffer from the following two weaknesses: first,existing methods usually involve frequent control information exchanges and link measurements,which leads to particularly high communication overhead and therefore unstuitable for the energy limited Io T devices.Second,existing methods achieve collision avoidance by sacrificing channel efficiency and therefore leads to low throughput.In summary,the target of this paper is exploring how to fully utilize the channels and enhance network throughput in the scenario where a large number of low-power Io T devices co-exist in the same space.The contribution of this paper can be summarized as follows:(i)Research on clock synchronization for low power ZigBee devices.To deal with the high energy consumption problem caused by frequent timestamps exchange,this paper proposes an environment-aware energy-efficient and high precision clock synchronization method,named Dual Sync.By smartly utilizing of the temperature and voltage information,Dual Sync makes it possible to simultaneously achieve high synchronization accuracy and low cost.We evaluate the performance of Dual Sync across various scenarios and compare it with state-ofart approaches.The experimental results illustrate the superior performance of Dual Sync in terms of both accuracy and energy efficiency.(ii)Research on cross-technology interference identification.Accurate interference identification is profitable for wireless co-existance technologies.This paper proposes Cross Find,a practical system which is able to identify different interferences based only on the time-domain RSSI sequence provided by the CC2420 radio of the ZigBee nodes.Specifically,we carefully study and extract short-term features of the interferences purely from the time-domain RSSI sequence and design a K-means based approach to efficiently identify the interferences.We examine the performance of Cross Find under controlled interference and office environments.The evaluation results show that,the identification accuracy of Cross Find keeps higher than 85% under all circumstance.(iii)Research on corss-technology interference resolution.Operating in unlicensed ISM bands,ZigBee devices often yield poor throughput and packet reception ratio due to the interference from ever increasing wireless devices in 2.4 GHz band.Although there have been many efforts made for interference avoidance,they come at the cost of miscellaneous overhead,which oppositely hurts channel utilization.Our empirical results show that,a specific interference is likely to have different influence on different outbound links of a ZigBee sender,which indicates the chance of simultaneous transmissions.Based on this insight,we propose Smoggy-Link,a practical protocol to exploit the potential concurrency for adaptive ZigBee transmissions under harsh interference.Smoggy-Link maintains an accurate link model to describe and trace the relationship between interference and link quality of the sender's outbound links.With such a link model,Smoggy-Link can obtain fine-grained spatiotemporal link information through a low-cost interference identification method.The link information is further utilized for adaptive link selection and intelligent transmission schedule.We implement and evaluate a prototype of our approach with Tiny OS and Telos B motes.The evaluation results show that Smoggy-Link has consistent improvements in both throughput and packet reception ratio under interference from various interferer.(iv)Research on parallel decoding for backscatter communication.Existing parallel decoding mechanisms assume that signals of the tags are highly stable,and hence may not perform optimally in the naturally dynamic backscatter systems.This paper introduces Flip Tracer,a practical system that achieves highly reliable parallel decoding even in hostile channel conditions.Flip Tracer is designed with a key insight: although the collided signal is time-varying and irregular,transitions between signals' combined states follow highly stable probabilities,which offers important clues for identifying the collided signals,and provides us with an opportunity to decode the collided signals without relying on stable signals.Motivated by this observation,we propose a graphical model,called one-flip-graph(OFG),to capture the transition pattern of collided signals,and design a reliable approach to construct the OFG in a manner robust to the diversity in backscatter systems.Then Flip Tracer can resolve the collided signals by tracking the OFG.We have implemented Flip Tracer and evaluated its performance with extensive experiments across a wide variety of scenarios.Our experimental results have shown that Flip Tracer achieves a maximum aggregated throughput that approaches 2 Mbps,which is 6× higher than the state-of-the-art...