me

Research

High-rate, Non-intrusive Visual Codes within Regular Videos via ImplicitCode

Given the penetration of mobile devices equipped with cameras, there has been increasing interest in enabling user in- teraction via visual codes. Simple examples like QR Codes abound. Since many codes like QR Codes are visually intrusive, various mechanisms have been explored to design visual codes that can be hidden inside regular images or videos, though the capacity of these codes remains low to ensure invisibility. We argue, however, that high capacity while main- taining invisibility would enable a vast range of applications that embed rich contextual information in video screens. We propose ImplicitCode, a high-rate visual codes that can be hidden inside regular videos. Experiment results show that ImplicitCode can deliver a significant capacity boost, while maintaining a similar or better level of invisibility.This work is presented in UbiComp'15. [PDF]

RF-based Passive Activity Recognition

We consider the detection of activities of device-free entities from the analysis of RF-channel fluctuations induced by these very activities. In analogy to the definition of device-free radio-based localisation systems (DFL) we define device-free radio-based activity recognition systems (DFAR) as systems which recognise the activity of a person using analysis of radio signals while the person itself is not required to carry a wireless device.

We leverage various RF sources including WiFi, FM and SDR. Also we invesigate the ifferent parameters of implementation on the performance of system. Futhermore, we have succeeded in activity recogintion in many case studies including attention monitoring, gesture recogintion and speed estimation. These studies have been accepted by UbiComp'12 [PDF], CoSDEO@UbiComp'13 [PDF], IEEE Perasive Computing'14 [PDF], IEEE TMC'13[PDF], etc.

Details about this project can be found here: [LINK]

Rendezvous Protocols in Cognitive Radio Networks

In cognitive radio (CR) networks, “TTR”, a.k.a.time-to-rendezvous, is one of the most important metrics for evaluating the performance of a channel hopping (CH) rendezvous protocol, and it characterizes the rendezvous delay when two CRs perform channel hopping. Inspired by the neighbor discovery problem, we establish a design framework of creating a wake-up schedule whereby every CR follows the sequence-based (or random) CH protocol in the awake (or asleep) mode. Analytical and simulation results show that the hybrid CH protocols under this framework are able to achieve a greatly improved average TTR as well as a low upper-bound of TTR, without sacrificing the rendezvous diversity.This work is presented in ICC '15[PDF] and submitted to TPDS.

We also we present a systematic approach using group theory for designing CH protocols that guarantee the maximum number of rendezvous channels and the minimal time-to-rendezvous (TTR) in heterogeneous environments. We have submitted this work to TMC.

On Heterogeneous Duty Cycles for Neighbor Discovery in Wireless Sensor Networks

Neighbor discovery plays a crucial role in the formation of wireless sensor networks and mobile networks where the power of sensors (or mobile devices) is constrained. Due to the difficulty of clock synchronization, many asynchronous protocols based on wake-up scheduling have been developed over the years in order to enable timely neighbor discovery between neighboring sensors while saving energy. However, existing protocols are not fine-grained enough to support all heterogeneous battery duty cycles, which can lead to a more rapid deterioration of longterm battery health for those without support. We propose two neighbor discovery protocols, called Hedis and Todis, that optimize the duty cycle granularity of quorum and co-primality based protocols respectively, by enabling the finest-grained control of heterogeneous duty cycles. We compare the two optimal protocols via analytical and simulation results, which show that although the optimal co-primality based protocol (Todis) is simpler in its design, the optimal quorum based protocol (Hedis) has a better performance since it has a lower relative error rate and smaller discovery delay, while still allowing the sensor nodes to wake up at a more infrequent rate. We have submitted this work to TMC.