Weizhi Zhang

Asynchronous indoor positioning system based on visible light communications

Abstract. Indoor positioning has become an attractive research topic within the past two decades. However, no satisfying solution has been found with consideration of both accuracy and system complexity. Recently, research on visible light communications (VLC) offer new opportunities in realizing accurate indoor positioning with relatively simple system configuration. An indoor positioning system based on VLC technology is introduced, with no synchronization requirement on the transmitters. Simulation results show that, with over 95% confidence, the target receiver can be located with an accuracy of 5.9 cm, assuming indirect sunlight exposure and proper installation of light-emitting diode bulbs.

Comparison of VLC-based indoor positioning techniques

Indoor positioning based on visible light communication (VLC) technology has become a very popular research topic recently. This paper provides an overview of different VLC based indoor positioning techniques and their performance. Three schemes of location estimation together with their mechanisms are introduced. We then present a detailed comparison on their performances in terms of accuracy, space dimension and complexity. We further discuss a couple of factors that would affect the performance of each of these positioning systems, including multipath reflections and synchronization. Finally, conclusions and future prospects of research are addressed.

VLC-based indoor positioning system with tracking capability using Kalman and particle filters

An indoor navigation system based on visible light communication (VLC) technology is proposed in this paper. Indoor positioning is realized by a received-signal-strength(RSS)-based method using modulated light-emitting-diodes (LEDs). In addition to the simple positioning, we use Kalman and particle filters to give the system tracking capability. Simulation results show that particle filtering converges to the true track faster than Kalman filtering, at the price of higher computational complexity.

Three-dimensional light positioning algorithm with filtering techniques for indoor environments

This paper introduces an indoor positioning system based on visible light communication technology with three-dimensional positioning capability. Light-emitting diodes are employed as transmitters, with photo- diodes as receivers to obtain the received signal strength (RSS) information. Based on the trilateration technique, the proposed algorithm is able to calculate horizontal coordinates of the receiver with RSS informa- tion, after which the height of the receiver is estimated. The system does not require other measurements such as time-of-arrival or angle-of-arrival, thus system design and costs are simplified and minimized. Basic framed slotted ALOHA is applied as the channel access method to enable asynchronous transmissions. In addition, Kalman and particle filters are used in order to realize target tracking. Results show that both filters help to increase the positioning accuracy and the particle filter exhibits a better performance than the Kalman filter, with a higher computational complexity.

Combined Deterministic and Modified Monte Carlo Method for Calculating Impulse Responses of Indoor Optical Wireless Channels

Because of the importance of calculating an accurate impulse response of an indoor optical wireless room environment that includes sufficient orders of multipath reflections from reflecting surfaces of the room, several different algorithms exist to solve the problem of calculating impulse responses accurately and in a reasonable amount of computing time. Deterministic approaches that divide the reflecting surfaces into small elements give the best accuracy but they require high computing time. Modified Monte Carlo methods provide a very fast approach of calculating impulse responses but the calculated impulse responses contain variance or, in other words, they are not as temporally smooth when compared to deterministic approaches. In this paper, we have taken a combined approach where we calculate the contribution of first reflections to the total impulse response by a deterministic method, and then the contributions of second and rest of the reflections to the total impulse response are calculated by the Modified Monte Carlo method. This carries the advantage of both of these approaches. Moreover, the algorithm can be easily implemented for parallel computation similar to the Modified Monte Carlo method to utilize the full power of modern multicore computer processors.

Three dimensional indoor positioning based on visible light with Gaussian mixture sigma-point particle filter technique

Over the past decade, location based services (LBS) have found their wide applications in indoor environments, such as large shopping malls, hospitals, warehouses, airports, etc. Current technologies provide wide choices of available solutions, which include Radio-frequency identification (RFID), Ultra wideband (UWB), wireless local area network (WLAN) and Bluetooth. With the rapid development of light-emitting-diodes (LED) technology, visible light communications (VLC) also bring a practical approach to LBS. As visible light has a better immunity against multipath effect than radio waves, higher positioning accuracy is achieved. LEDs are utilized both for illumination and positioning purpose to realize relatively lower infrastructure cost. In this paper, an indoor positioning system using VLC is proposed, with LEDs as transmitters and photo diodes as receivers. The algorithm for estimation is based on received-signalstrength (RSS) information collected from photo diodes and trilateration technique. By appropriately making use of the characteristics of receiver movements and the property of trilateration, estimation on three-dimensional (3-D) coordinates is attained. Filtering technique is applied to enable tracking capability of the algorithm, and a higher accuracy is reached compare to raw estimates. Gaussian mixture Sigma-point particle filter (GM-SPPF) is proposed for this 3-D system, which introduces the notion of Gaussian Mixture Model (GMM). The number of particles in the filter is reduced by approximating the probability distribution with Gaussian components.

Combined CATV and very-high-speed data transmission over a 1550-nm wavelength indoor optical wireless link

We report details of an experimental demonstration involving a 15 meter pointed indoor optical wireless link in the 1550-nm wavelength range, that is comprised of a uni-directional Cable Television (CATV) signal and a bi-directional link comprised of two 10 Gbps data links. Four port wavelength division mux-demuxes have been used on both ends of the link. The CATV transmission system is connected to port 1 of the mux-demux. CATV signal consists of both analog and digital parts, and its bandwidth is 1 GHz. The laser is directly modulated by the CATV signal, and at the receiver end, the optical signal is demodulated and fed to a TV. Port 2 of the mux-demux is left unused. Ports 3 and 4 are used for the 10 Gbps links. A bit error rate tester has been used to generate the 10 Gbps signals that are converted to optical wavelengths by enhanced Small Form Factor Pluggable (SFP+) modules at both ends of the setup. Collimators are used at both ends to transmit the combined optical signal that is the output of the mux and to receive the optical signal by focusing it onto a single-mode fiber as the input of the demux. We present results on the CATV portion of the setup and the bit-error-rate performance of the two 10 Gbps links. This experiment shows the feasibility of using pointed optical links in datacenters as secondary links to alleviate the loads of highly utilized wired connections and improve the overall throughput performance of datacenters.

Effects of source spatial partial coherence on temporal fade statistics of irradiance flux in free-space optical links through atmospheric turbulence

The temporal covariance function of irradiance-flux fluctua-tions for Gaussian Schell-model (GSM) beams propagating in atmospheric turbulence is theoretically formulated by making use of the method of effective beam parameters. Based on this formulation, new expressions for the root-mean-square (RMS) bandwidth of the irradiance-flux temporal spectrum due to GSM beams passing through atmospheric turbulence are derived. With the help of these expressions, the temporal fade statistics of the irradiance flux in free-space optical (FSO) communication systems, using spatially partially coherent sources, impaired by atmospheric turbulence are further calculated. Results show that with a given receiver aperture size, the use of a spatially partially coherent source can reduce both the fractional fade time and average fade duration of the received light signal; however, when atmospheric turbulence grows strong, the reduction in the fractional fade time becomes insignificant for both large and small receiver apertures and in the average fade duration turns inconsiderable for small receiver apertures. It is also illustrated that if the receiver aperture size is fixed, changing the transverse correlation length of the source from a larger value to a smaller one can reduce the average fade frequency of the received light signal only when a threshold parameter in decibels greater than the critical threshold level is specified.

Cable television transmission over a 1550-nm infrared indoor optical wireless link

Abstract. We experimentally demonstrate transmission of cable television (CATV) radio frequency signals over a pointed indoor optical wireless link. The length of the optical link was 15 m. Collimators used at both the transmitter and the receiver sides required good alignment before sufficient optical power could be received. The system was placed at a height of 2 m, which is more than average human height, so human movements throughout the room did not obstruct the link. The optical wireless propagation path was almost lossless. The originality in this experimental demonstration is the transmission of full range of CATV signals compared to other works in this area. This experiment of radio over free-space optics showed that point-to-point indoor optical wireless links can be utilized as an alternative means for transmission of multimedia data.

Gaussian mixture sigma-point particle filter for optical indoor navigation system

With the fast growing and popularization of smart computing devices, there is a rise in demand for accurate and reliable indoor positioning. Recently, systems using visible light communications (VLC) technology have been considered as candidates for indoor positioning applications. A number of researchers have reported that VLC-based positioning systems could achieve position estimation accuracy in the order of centimeter. This paper proposes an Indoors navigation environment, based on visible light communications (VLC) technology. Light-emitting-diodes (LEDs), which are essentially semiconductor devices, can be easily modulated and used as transmitters within the proposed system. Positioning is realized by collecting received-signal-strength (RSS) information on the receiver side, following which least square estimation is performed to obtain the receiver position. To enable tracking of user’s trajectory and reduce the effect of wild values in raw measurements, different filters are employed. In this paper, by computer simulations we have shown that Gaussian mixture Sigma-point particle filter (GM-SPPF) outperforms other filters such as basic Kalman filter and sequential importance-resampling particle filter (SIR-PF), at a reasonable computational cost.