M. I. Sakib Chowdhury

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.

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.

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.

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.

Interference analysis of interleaved and localized mapping schemes in OFDMA system with Carrier Frequency Offset

In this paper, we analyze the effect of Carrier Frequency Offset (CFO) of multiple users on the SINR of a single user in OFDMA based uplink communication receiver. We have computed an explicit SINR expression for two types of mapping strategies used in uplink OFDMA systems namely Interleaved Frequency Division Multiple Access (IFDMA) and Localized Frequency Division Multiple Access (LFDMA). SINR expressions in case of carrier frequency offset correction are also computed. Using simulations, we have compared the total average interference due to different values of CFOs of multiple users for both mapping schemes. Simulation results also show that the average value of Inter-Carrier Interference (ICI) for localized mapping is higher than interleaved mapping while the average value of Multiuser Interference (MUI) is higher for interleaved mapping. Moreover, the average MUI for localized mapping is minimum at the center of the band and it increases as we move towards the band edges. We also observe a flat response for ICI and MUI for interleaved mapping.

Human shadowing effect on indoor visible light communications channel characteristics

The shadowing effect caused by the human body can have a considerable influence on indoor visible light communications (VLC) channel characteristics. A shadowing ray tracing (SRT) algorithm to investigate the human shadowing channel characteristics is proposed. To validate the effectiveness of the SRT model, an extensive indoor human shadowing channel measurement has been presented. Both scenarios, the line-of-sight (LOS) and the non-line-of-sight (NLOS), have been measured. Theoretical results from the SRT model are validated against the measurement results for channel path loss. The results from measurements and simulations show that receiver rotations can mitigate human shadowing effect under the LOS scenario. Under the NLOS scenario, the VLC system becomes more sensitive to human shadowing when the distance between the LED and the receiver is large. Finally, more simulation results on the channel root mean square delay spread are also presented to analyze its relation with human shadowing distance to the receiver.

Multiband channel characteristics for indoor visible light communications

Abstract. We present a multiband ray tracing (MRT) algorithm to analyze the indoor multiband channel characteristics for visible light communications (VLC). As visible light spans a wide spectrum from 380 to 780 nm, spectral reflectivities of walls are wavelength dependent. This model is able to analyze the multiband channel in VLC and provide the channel information for implementing the wavelength division multiplexing VLC system. To validate the effectiveness of the MRT model, an extensive indoor measurement of the multipath channel characteristics has been presented. Effects of relative angles from lighting emitting diodes (LEDs) to receivers and the variation of receiver locations have been taken into consideration. Theoretical results from the MRT model are validated against the measurement results on the channel path loss of the typical wavelength at 420 nm. Furthermore, channel characteristics like the root mean square delay spread and the spectral response of the three typical wavelengths based on the red green blue (RGB) LEDs are analyzed by the MRT model simulation. Finally, comparisons of receiver positions, relative angle as well as field-of-view angles, for three wavelengths are considered.

An archipelago of high-bandwidth islands by optical wireless systems — A solution to the USA wireless airwaves spectrum crunch

We discuss the current problem of spectrum shortage and the idea of a viable solution employing indoor optical wireless links creating small high-bandwidth islands for each user effectively helping to combat this spectrum shortage.

Short-Range Optical Wireless: Theory and Applications

This book discusses the fundamental aspects of multiple-source Optical Wireless Applications, including Visible Light Communications (VLC). Moreover, the authors explore VLC performance in several conventional household layouts and investigate the impact of these layouts on VLC. Multiple sources increase multipath distortion. Multi-inputMulti-Output (MIMO) techniques will be included as they provide either reliability improvement or bandwidth efficiency increase. Based on these topics, the book further explores VLC performance in real applications, such as aircraft cabin wireless communications.