Acoustic-enabled Low Latency Indoor Localization Based On Smart Mobile Devices

Indoor localization is the key enabled technique for location based services.After years of innovative researches,there are now many available localization approaches.Among these localization techniques,acoustic-based indoor localization methods attract much attention for their cost-effective deployment and high-precision localization accuracy.Developing low-latency acoustic-based indoor localization techniques can not only improve user experience but also enables tracking,which could facilitate lots of interesting applications such as tracking and routing.Therefore,researching on low-latency localization techniques is invaluable.However,in dynamic channels where the transceiver distance,type of devices,and motion states are changeable,current asynchronous localization techniques suffer from high latency in obtaining a location fix.The reasons behind high latency are:1.Latency caused by unreliable signal detection under dynamic channels.The unreliable signal detection could lead to false signal detection,miss detection,or large detection errors and thus are filtered out.Therefore,it would need much time to gathering enough beacons for localization,leading to high localization latency.The near-far effect and device diversity problem are the major cause for the unreliable signal detection.2.Latency caused by the time duration of the beacon messages.To obtain a location fix,a target must capture multiple beacon messages.In state-of-the-art asynchronous localization schemes,the beacon messages needs to encode some compulsory information for localization.Due to the low transmission rate,it cause a long time to deliver those compulsory information,making the duration of the beacon messages longer and leading to high latency in localization.In conquering the above high-latency problem in asynchronous localization techniques,we have made in-depth study.We have proposed a normalized signal detection algorithm and a loose orthogonal modulation technique.We verify the above loose orthogonal modulation in a communication system.In the localization techniques,we flexibly utilize the loose orthogonality condition to reduce localization latency.Specifically,by reducing the time to obtain enough beacon messages and compress the duration of a single beacon message,we successfully reduce the latency in the localization systems.Our work innovates in the following aspects:1.To handle the unreliable signal detection under dynamic channels,we propose a simple yet effective normalization method,which utilizes the mean value of several preceding correlation results to normalize the current one.To reduce the latency,we propose a loose orthogonality modulation technique in which two signals are deemed orthogonal if the ratio between the cross-correlation and auto-correlation is below a certain threshold.The above signal detection algorithm and the loose orthogonal modulation technique lay the foundation for our aerial acoustic communication system and localization system.2.We propose a long-range,high-throughput aerial acoustic communication system based on the loose orthogonal modulation technique.In the aerial acoustic communication system,we utilize the loose orthogonal modulation technique to significantly improve the link rate without compromising the communication range.We incorporate the normalized signal detection method and a light-weight rate adaptation mechanism,making the communication system achieve significantly low BER even under long distances.Experiments results present that our proposed method can achieve less than 3% BER under a distance of20 m.3.We propose an orthogonal scheduling and virtual anchors based localization technique,which reduces the latency problem and overcomes the shortcomings of infrastructurebased localization systems that cannot adapt to environment changes.In the proposed technique,we devise an concept of orthogonal scheduling,by which we schedule the orthogonal beacon messages concurrently on distributed anchors,and thereby reducing the latency in obtain sufficient beacon messages.In addition,we incorporate the crowd-sourcing technique which utilizes the stationary clients in the place-of-interest to help locating other targets,eliminating the deployment efforts and making the localization system resilient to environment dynamics.Results show that the proposed approach can reduce the latency from 2 s to0.3 s and achieve a 90% tracking error of 0.5 m.4.We propose a loose orthogonal modulation based localization technique,overcoming the high latency problem and achieving real-time tracking.In this localization technique,we propose a orthogonal chirp spread spectrum modulation scheme which compresses the time duration of the beacon messages and thus reduce the localization latency.In the proposed localization technique,we make several improves.We insert multiple Doppler carriers in the beacon message;we propose a new particle filter model to fuse the observed timestamps and motion states which allows location updates under one scheduling,making it feasible for mobile target tracking.Results reveal a minimal latency of 0.2 s,and a 90% tracking error of 0.49 m.All in all,we have proposed a normalized signal detection algorithm and a loose orthogonal modulation technique for acoustic-enabled mobile devices based low latency indoor localization methods.We verify the above algorithms in an aerial acoustic communication system and utilize these algorithm to reduce the latency in the localization systems.