Jaafar M. H. Elmirghani

Line strip spot-diffusing transmitter configuration for optical wireless systems influenced by background noise and multipath dispersion

In this letter, we propose and evaluate a novel optical wireless configuration that employs a multibeam transmitter in conjunction with a narrow field-of-view direction diversity receiver. Such a configuration overcomes the drawbacks and combines the advantages of both types of optical wireless links, including line-of-sight and diffuse transmission. A multibeam transmitter placed on the communication floor was adopted to produce multiple diffusing spots on the middle of the ceiling in the form of a line strip. The design goal is to reduce the effect of intersymbol interference and to improve the signal-to-noise ratio (SNR) when the system operates under the constraints of background noise and multipath dispersion. Simulation results show that our line strip multibeam transmitter (LSMT) with only three branches diversity gives about 23 dB SNR improvement over the conventional system. The results also show that the multipath dispersion, which induces pulse spread, is significantly reduced when the LSMT with diversity detection is used.

Analysis of diffuse optical wireless channels employing spot-diffusing techniques, diversity receivers, and combining schemes

In this letter, the performance of an indoor optical wireless spot-diffusing system using various multibeam transmitter configurations, in association with direction diversity and combining techniques, is assessed and compared under the impact of multipath dispersion and ambient light noise through theoretical analysis and computer simulation. Computer simulation for three different multibeam transmitter configurations and a conventional diffuse transmitter is carried out. Diversity receiver and wide field-of-view (FOV) receiver configurations are evaluated in conjunction with the proposed configurations. For the diversity-detection case, a receiver comprising an array of narrow FOV detectors (three and seven segments) oriented in different directions is used to maximize the collected signals and minimize noise. A novel line-strip multibeam system (LSMS) is investigated with single and diversity receiver configurations, and is compared with other spot-diffusing methods. Combining schemes, including selection combining, maximum ratio combining, and equal gain combining are employed for the presented configurations. Our results indicate that the performance improvement obtained through the use of LSMS with a three-direction diversity receiver is about 20 dB signal-to-noise ratio enhancement over the conventional diffuse system, and 26 dB when combining techniques are used. Root mean square delay-spread performance for the proposed configurations, at different positions on the communication floor, are also evaluated and compared.

Optimization of a triangular PFDR antenna in a fully diffuse OW system influenced by background noise and multipath propagation

Optical wireless (OW) systems are generally impaired by multipath propagation and directional interference in the form of background noise. We present original results for a fully diffuse OW system that employs a novel triangular pyramidal fly-eye diversity receiver (PFDR). The received pulse shapes are evaluated at various locations on the communication floor and the background noise collected on the three faces of the pyramid is determined. It is demonstrated that, through optimization of the PFDR field-of-view, the directional background interference can be reduced and that the received pulse shape can be improved. The computed error probability shows a marked improvement when our optimized PFDR antenna is used instead of the conventional photodetector used in traditional diffuse optical wireless systems.

High-speed ultra-wide band in-car wireless channel measurements

Among the different wireless solutions, ultra-wide band (UWB) is a promising technology for in-car communications because of its high data rates. To optimise the UWB radio system design, knowledge of the propagation channel within the car is required. The performance of a high-speed 480 Mbps UWB radio system is studied within a real in-car environment measured under mobility. A comprehensive set of measurements is presented, including several possible non-line of sight scenarios while the vehicle is stationary and mobile, for open- and closed-window environments and with/without occupants. These measurements are used to characterise the in-car channel and evaluate the performance of a typical UWB radio system in this setting.

Characterization of mobile spot diffusing optical wireless systems with diversity receiver

Channel characteristics of mobile nondirected diffuse optical wireless communication under the constraints of multipath dispersion and ambient light noise have received little attention to date. This paper presents an original study of transmitter motion and diversity receivers and their effects on the system performance for both conventional diffuse systems (CDS) and line strip multispot diffusing systems (LSMS). Under these conditions, simulation results show that high-received signal power can be obtained by using a LSMS in conjunction with a composite receiver consisting of seven branches. Furthermore, under ambient noise corruption, LSMS provides signal-to-noise ratio (SNR) improvements of more than 30 dB over the conventional nondirected diffuse system at the worst communication link. Moreover, we evaluate the effect of path loss on the proposed system and it is confirmed that the path loss is reduced by more than 6 dB over the CDS.

Performance evaluation of a triangular pyramidal fly-eye diversity detector for optical wireless communications

Background noise and multipath propagation are the major impairments in indoor optical wireless links. They can introduce heavy distortion in the received optical signal and can degrade the system performance. An investigation into the optical wireless system performance has been carried out for two configurations: a hybrid system, and a diffuse system with a single detector and a triangular pyramidal fly-eye diversity receiver (PFDR). Original results for both systems that employ a PFDR antenna, under different fields of view (FOVs), are presented. The design goal is to reduce the effect of signal spread and improve the signal-to-noise ratio when the system operates under the constraints of background noise and multipath dispersion. It is demonstrated that through PFDR FOV optimization the directional background interference can be reduced and the received pulse shape improved.

Performance of impulse radio direct sequence ultra-wideband system with variable-length spreading sequences

An adaptive transmission scheme using variable-length spreading sequences (VLSS) is proposed. The system is based on an impulse direct sequence ultra-wideband (DS-UWB) approach for wireless communication where the number of active users is variable. In contrast to the conventional DS-UWB system, which employs a fixed length spreading code, the proposed system changes the length of spreading code according to the system load adaptively, which is proven to be able to reduce the inter-chip interference, inter-symbol interference and multiple-access interference and thus improve the system performance in terms of bit error rate. The proposed system is simulated in multipath channels with a high level of multipath fragments, modelled by the standard IEEE 802.15.3a indoor channel model 1 (CM1) and channel model 2 (CM2). Numerical results demonstrate that when RAKE receivers are employed, the proposed VLSS DS-UWB system outperforms the conventional system by appropriately allocating the spreading sequences.

Performance of a slotted MAC protocol for WDM metropolitan access ring networks under self-similar traffic

This article proposes a WDM slotted-ring network architecture. Used as a metropolitan access network, it is shown through theoretical predictions and simulation results how a simple MAC protocol can be implemented to achieve fairness between access nodes and efficient bandwidth utilization. In the paper it is shown that the MAC protocol efficiency grows with the number of nodes in the network - a very attractive feature in the metropolitan market. Simple theoretical equations allow for easy provisioning of the network size and scalability. These were validated by discrete-event simulations using realistic traffic sources. The original set of simulation results using a source-stripping scheme are then compared with an improved implementation where destination-stripping is used. Finally, the impact of receiver collision is studied and a solution to this problem is presented.

Analysis of optical wireless links employing a beam clustering method and diversity receivers

High-speed nondirected optical wireless (OW) transmission is greatly desired for freedom of user mobility. In a mobile infrared wireless environment, it is difficult to maintain a signal-to-noise ratio (SNR) sufficient to support low error probability using the conventional diffuse optical wireless systems. We propose a novel beam clustering method (BCM) based on a line strip multibeam transmitter system (LSMS) combined with a diversity receiver and examine its performance under adverse conditions such as multipath dispersion and background noise. The BCM consists of three sets of spots aimed at different directions. BCM design, multipath dispersion, ambient light interference, and diversity receiver design are discussed. We investigate and compare the impact of user mobility on the performance of OW links for both BCM and conventional diffuse system (CDS). Simulation results for the BCM link characteristics are presented and comparison is made with CDS. Our results indicate that at the worst conventional communication link, BCM can substantially reduce the signal delay spread by nearly a factor of six and increase the SNR by more than 30 dB over the CDS.

A Metro WDM Multi-ring Network with Variable Packet Size

This paper proposes two metro Wavelength Division Multiplexing (WDM) ring network architectures for variable size packet traffic. Firstly, it presents the network architectures and describes their medium access control (MAC) protocol. Secondly, it evaluates and compares the performance of the modified and original architectures, presenting results for throughput, queuing delay, packet dropping probability and global delay. Finally, it analyses and explains the results.