Shilin Xiao

Data Gathering with Compressive Sensing in Wireless Sensor Networks: A Random Walk Based Approach

In this paper, we study the problem of data gathering with compressive sensing (CS) in wireless sensor networks (WSNs). Unlike the conventional approaches, which require uniform sampling in the traditional CS theory, we propose a random walk algorithm for data gathering in WSNs. However, such an approach will conform to path constraints in networks and result in the non-uniform selection of measurements. It is still unknown whether such a non-uniform method can be used for CS to recover sparse signals in WSNs. In this paper, from the perspectives of CS theory and graph theory, we provide mathematical foundations to allow random measurements to be collected in a random walk based manner. We find that the random matrix constructed from our random walk algorithm can satisfy the expansion property of expander graphs. The theoretical analysis shows that a k-sparse signal can be recovered using `1 minimization decoding algorithm when it takes m = O(k log(n=k)) independent random walks with the length of each walk t = O(n=k) in a random geometric network with n nodes. We also carry out simulations to demonstrate the effectiveness of the proposed scheme. Simulation results show that our proposed scheme can significantly reduce communication cost compared to the conventional schemes using dense random projections and sparse random projections, indicating that our scheme can be a more practical alternative for data gathering applications in WSNs.

Direct observation of lateral photovoltaic effect in nano-metal-films

Lateral photovoltaic effect (LPE) observed on the metal films is unusual because it violates a principle that the LPEs are always observed on the surface of a semiconductor. Compared with early studies, we have realized an obvious metal film LPE in a metal-semiconductor (MS) structure. By further arguing with experimental results, this work also intensively elucidates many features of LPE which the early models never touched upon. All the data and analyses in this study indicate that metal side LPE in MS structure has some natural superiorities to the semiconductor side LPE and may open many exciting opportunities for realizing multifunctional devices.

Capacity and Delay Analysis for Data Gathering with Compressive Sensing in Wireless Sensor Networks

Compressive sensing (CS) provides a new paradigm for efficient data gathering in wireless sensor networks (WSNs). In this paper, with the assumption that sensor data is sparse we apply the theory of CS to data gathering for a WSN where n nodes are randomly deployed. We investigate the fundamental limitation of data gathering with CS for both single-sink and multi-sink random networks under protocol interference model, in terms of capacity and delay. For the single-sink case, we present a simple scheme for data gathering with CS and derive the bounds of the data gathering capacity. We show that the proposed scheme can achieve the capacity Θ(\frac{nW}{M}) and the delay Θ(M\sqrtfrac{nlog n}), where W is the data rate on each link and M is the number of random projections required for reconstructing a snapshot. The results show that the proposed scheme can achieve a capacity gain of Θ (\frac{n}{M}) over the baseline transmission scheme and the delay can also be reduced by a factor of Θ(\fracsqrt{n\log n}{M}). For the multi-sink case, we consider the scenario where n_d sinks are present in the network and each sink collects one random projection from n_s randomly selected source nodes. We construct a simple architecture for multi-session data gathering with CS. We show that the per-session capacity of data gathering with CS is Θ(\frac{n\sqrt{n}W}{M n_d \sqrt{n_s \log n}}) and the per-session delay is Θ(M\sqrtfrac{{n}{log n}}). Finally, we validate our theoretical results for the scaling laws of the capacity in both single-sink and multi-sink networks through simulations.

Compatible TDM/WDM PON Using a Single Tunable Optical Filter for Both Downstream Wavelength Selection and Upstream Wavelength Generation

We propose a hybrid time-division multiplexing/wavelength-division multiplexing passive optical network (TDM/WDM-PON) architecture compatible with the traditional TDM-PON configuration using a power splitter in the remote node. A tunable optical filter (TOF) is used to select the downstream wavelength in each optical network unit. Meanwhile, the TOF plays a second role of seeding a reflective semiconductor optical amplifier (RSOA) so as to construct a tunable fiber-ring laser as colorless upstream source. A stable performance is observed for the upstream laser source tuned from 1535 to 1565 nm and with a modulation data rate of 1.25 Gb/s. The upstream wavelength has a offset with the central wavelength of the TOF when the RSOA is biased at its saturation region, which mitigates the Rayleigh backscattering and back reflection-induced crosstalk in single-fiber bidirectional PON systems.

Energy and latency analysis for in-network computation with compressive sensing in wireless sensor networks

In this paper, we study data gathering with compressive sensing from the perspective of in-network computation in random networks, in which n nodes are uniformly and independently deployed in a unit square area. We formulate the problem of data gathering to compute multiround random linear function. We study the performance of in-network computation with compressive sensing in terms of energy consumption and latency in centralized and distributed fashions. For the centralized approach, we propose a tree-based protocol for computing multiround random linear function. The complexity of computation shows that the proposed protocol can save energy and reduce latency by a factor of Θ(√(n/log n)) for data gathering comparing with the traditional approach, respectively. For the distributed approach, we propose a gossip-based approach and study the performance of energy and latency through theoretical analysis. We show that our approach needs fewer transmissions than the scheme using randomized gossip.

Multiple access scheme based on block encoding time division multiplexing in an indoor positioning system using visible light

In view of the application of a visible light positioning system in a public indoor environment with numerous light emitting diodes (LEDs), a long delay is one of the main factors that limits the performance of the positioning systemwith a moving device. To solve this problem, a multiple access scheme based on block encoding time division multiplexing (TDM) is proposed in this paper. In our scheme, nine LEDs compose one block to reduce the system delay. Meanwhile, in order to reduce intercell interference, an extended binary coded decimal code is used to encode signals transmitted by LEDs. The feasibility and performance of the scheme is demonstrated by simulations. The results show that the proposed TDMscheme provides a better performance than the conventional TDM and is more applicable to the accurate positioning of a moving device.

A Sensitivity-Enhanced Refractive Index Sensor Using a Single-Mode Thin-Core Fiber Incorporating an Abrupt Taper

A sensitivity-enhanced fiber-optic refractive index (RI) sensor based on a tapered single-mode thin-core diameter fiber is proposed and experimentally demonstrated. The sensor head is formed by splicing a section of tapered thin-core diameter fiber (TCF) between two sections of single-mode fibers (SMFs). The cladding modes are excited at the first SMF-TCF interface, and then interfere with the core mode at the second interface, thus forming an inter-modal interferometer (IMI). An abrupt taper (tens of micrometers long) made by the electric-arc-heating method is utilized, and plays an important role in improving sensing sensitivity. The whole manufacture process only involves fiber splicing and tapering, and all the fabrication process can be achieved by a commercial fiber fusion splicer. Using glycerol and water mixture solution as an example, the experimental results show that the refractive index sensitivity is measured to be 0.591 nm for 1% change of surrounding RI. The proposed sensor structure features simple structure, low cost, easy fabrication, and high sensitivity.

Experimental Demonstration of Symmetric 100-Gb/s DML-Based TWDM-PON System

In this letter, first, the symmetric 100-Gb/s time and wavelength-division-multiplexed passive optical network system is experimentally demonstrated, based on the directly modulated lasers (DMLs) modulated by 25-Gb/s none-return-to-zero signals. A bypass delay interferometer (DI) is deployed in the optical line terminal to mitigate the signal distortion caused by the DML chirp and fiber chromatic dispersion. The experimental results show that with the DI, error free transmission is achieved over 25-km single mode fiber with a power budget of 42 dB, which could support 1:1024 splitting ratio. Moreover, the transmission performance of differential fiber length and burst-mode operation is also investigated.

Discrimination between strain and temperature by cascading single-mode thin-core diameter fibers

A simple fiber-optic sensor capable of discrimination between temperature and strain is proposed and experimentally demonstrated. The sensor head is formed by cascading two sections of single-mode thin-core diameter fibers (TCFs) that act as two different inter-modal interferometers (IMIs). Due to the different sensitivity responses of the two IMIs to strain and temperature, it is possible to discriminate temperature and strain by monitoring the resonant wavelength shifts. The experimental results indicate that the measured strain and temperature resolutions are 37.41 με and 0.732 °C within a strain range of 0-1333.3 με and a temperature range from 26.9 °C to 61.7 °C. The sensing sensitivities of strain and temperature are -1.03 pm/με and 30.74 pm/°C, respectively. The proposed sensor features the advantages of easy fabrication, low cost and high sensitivity, and it exhibits great potential in dual-parameter measurement.

Video-Service-Overlaid Wavelength-Division-Multiplexed Passive Optical Network

We propose and demonstrate a novel wavelength-division-multiplexed passive optical network (WDM-PON) with multicast overlay. By superimposing an inverse return-to-zero multicast signal onto a nonreturn-to-zero point-to-point signal, simultaneous transmission is realized for both services. At the optical network unit (ONU), only one photodiode is required to detect both signals. No complex receiver is demanded. Multicast control is realized through a switch for each wavelength at the optical line terminal. We successfully demonstrate the proposed WDM-PON.