Collaborative Adaptive Optical Wireless System in Realistic Indoor Environment

In this paper, we propose and evaluate a collaborative mobile optical wireless (OW) system that employs a collaborative adaptive beam clustering method (CABCM) in conjunction with an imaging receiver. Three cases involving two, three and five receivers are considered. A collaborative maximum ratio combining scheme is used to collaboratively distribute the transmit power among the diffusing spots. Our ultimate goal is to increase the received optical power and improve the signal-to-noise ratio (SNR) at each coexisting receiver when the system operates in a multiuser scenario under the constraints of background noise, multipath dispersion, mobility and shadowing typical in a real indoor environment. Our proposed system (collaborative adaptive beam clustering method) is evaluated at 30 Mbit/s to enable comparison with previous work, and is also assessed at higher bit rates: 2.5 Gbit/s and 5 Gbit/s. Simulation results show that the mobile CABCM system offers a significant performance improvement including a reduction in the background noise (BN) effect, a strong received power, reduction in delay spread, and improvement in the SNR over multiuser line strip multibeam system (LSMS). However, the performance degrades gradually with increase in the number of users

MIMO MC-CDMA systems over indoor optical wireless communication channels

Optical wireless communication systems offer a number of advantages over their radio frequency counterparts. The advantages include freedom from fading, freedom from spectrum regulations and abundant bandwidth. The main limitations of optical wireless systems include background noise attributed to natural and artificial light sources and multipath propagation. The former degrades the signal to noise ratio while the latter limits the maximum achievable data rate. This thesis investigates the use of transmit power adaptation in the design of optical wireless spot-diffusing systems to increase the power associated with the main impulse response components, resulting in a compact impulse response and a system that is able to achieve higher data rates. The work also investigates the use of imaging diversity receivers that can reject the background noise components received in directions not associated with the signal. The two techniques help improve the optical wireless system performance. The multibeam transmitter and the multi-detector angle diversity receiver or imaging receiver form a multiple input multiple output (MIMO) system. The work also investigates additional methods that can improve the performance such as transmitter beam angle adaptation, and improved modulation and coding in the form of multi-carrier code division multiple access (MC-CDMA). Furthermore, the work investigates the robustness of a link design that adopts the combination of these methods in a realistic environment with full mobility.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Mobile optical wireless system using fast beam Angle, delay and power adaptation with angle diversity receivers

In this paper, we introduce a novel fast angle and power adaptation method in optical wireless (OW) systems. The fast angle and power adaptive line strip multibeam system (FAPA-LSMS) can identify the optimum spots distribution based on a divide and conquer (D&C) algorithm and can achieve a signal-to-noise ratio (SNR) performance comparable to that obtained using the normal APA-LSMS. This results in a significant reduction in the system adaptation time by a factor of 20. The proposed FAPA system makes use of delay adaptation to minimize the delay spread at the receiver. A significant reduction in the delay spread by a factor of 50 can be achieved compared to the non-adaptive LSMS. The proposed system improves the SNR by 50 dB over a conventional diffuse system

Collaborative Multibeam Transmitter and Imaging Receiver in Realistic Environment

In this paper, we propose a collaborative mobile optical wireless (OW) system that employs a collaborative adaptive beam clustering method (CABCM) in conjunction with an imaging receiver. Collaborative maximum ratio combining (MRCColl) scheme is used to collaboratively distribute the transmit power among diffusing spots. The main goal is to increase the received optical power and improve the signal-to-noise ratio (SNR) at each coexisting receiver when the system operates in a multiuser scenario under the constraints of background noise, multipath dispersion and mobility. Our proposed system (collaborative adaptive beam clustering method) is evaluated at 30 Mbit/s to enable comparison with previous work, and is also assessed at higher bit rates: 2.5 Gbit/s and 5 Gbit/s. Simulation results show that at a bit rate of 30 Mbit/s, a significant SNR improvement of 39 dB is achieved when a CABCM system replaces a multiuser line strip multibeam system (LSMS) at a 6 m transmitter-receiver horizontal separation. The results also show that the proposed system can achieve a 22 dB SNR when the system operates at 2.5 Gbit/s in a two-user scenario

Delay Adaptation Method for Relay Assisted Optical Wireless Systems

In this paper, we investigate optical wireless repeaters as relay terminals between a transmitter and a user in an Infrared Optical Wireless Communication (IROWC) system. A delay adaptation method is introduced to solve the problem of irregular signal arrival time from different relay terminals. Three different relay terminal deployment scenarios were investigated in a typical two-phase relay IROWC system with the proposed delay adaptation method. The simulation results indicate that the proposed system has better impulse response compared to the conventional system and that the root-mean-square delay spread of the relay system with the delay adaptation method is on average 30% less than the conventional system