Matthew D. Higgins

Recent developments in indoor optical wireless [Optical wireless communications]

An overview of the developments in optical wireless systems viewed from the traditional communications viewpoint of transmitter, channel and receiver is presented. The trends in modulation formats that match information to the optical wireless channel are considered. This is followed by the discussion of recent transmitter and receiver innovations, particularly the utilisation of diversity transceivers. As a preliminary to the following treatment, the nature and modelling of the optical wireless channel are introduced, with particular emphasis on its unique features in terms of transmitted power constraints and non-negativity. From the examination of modulation formats, on-off-keying remains the format of choice for basic binary transmission, whereas

Forward Error Correction for Molecular Communications

Communication between nanoscale devices is an area of considerable importance as it is essential that future devices be able to form nanonetworks and realise their full potential. Molecular communication is a method based on diffusion, inspired by biological systems and useful over transmission distances in the nm to m range. The propagation of messenger molecules via diffusion implies that there is thus a probability that they can either arrive outside of their required time slot or ultimately, not arrive at all. Therefore, in this paper, the use of a error correcting codes is considered as a method of enhancing the performance of future nanonetworks. Using a simple block code, it is shown that it is possible to deliver a coding gain of ∼ 1.7dB at transmission distances of 1 m. Nevertheless, energy is required for the coding and decoding and as such this paper also considers the code in this context. It is shown that these simple error correction codes can deliver a benefit in terms of energy usage for transmission distances of upwards of 25 m for receivers of a 5 m radius.

Comparison of Three Receiver Designs for Optical Wireless Communications using White LEDs

Three visible light optical wireless communication systems using asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and white light emitting diodes (LEDs) are compared. The LEDs considered have a larger modulation bandwidth for the blue optical frequencies than for the rest of the transmitted optical spectrum. It is shown that for typical parameter values, a novel diversity combining receiver has slightly greater capacity than a system optimized for reception of blue light only, and that both have greater capacity than a system designed to receive the entire visible light spectrum.

Error correction coding for molecular communications

The emerging field of communications between nanoscale devices is one of considerable importance since it is essential that nanonetworks are formed to realize the potential of such devices. Molecular communication is a method based on diffusion, inspired by biological systems and useful over distances in the nm to μm range. Messenger molecules propagate via diffusion and there is thus a probability that they do not arrive at the receiver or are delayed so as to be delivered in the wrong communication time slot. In this paper, the use of error correction codes is considered to improve the transmission performance of molecular communications. Using a simple block code, it is possible to deliver a coding gain of ~1.6 dB. Nevertheless, energy is required for the coding and decoding when employing the code and this paper also considers this for the first time. It is shown that simple error correction delivers a benefit in terms of energy consumption for distances upwards of approximately 10 μm to 20 μm.

A Genetic Algorithm Method for Optical Wireless Channel Control

A genetic algorithm controlled multispot transmitter is proposed as an alternative approach to optimizing the power distribution for single element receivers in fully diffuse mobile indoor optical wireless communication systems. By specifically tailoring the algorithm, it is shown that by dynamically altering the intensity of individual diffusion spots, a consistent power distribution, with negligible impact on bandwidth and rms delay spread, can be created in multiple rooms independent of reflectivity characteristics and user movement patterns. This advantageous adaptability removes the need for bespoke system design, aiming instead for the use of a more cost effective, optimal transmitter and receiver capable of deployment in multiple scenarios and applications. From the simulations conducted it is deduced, that implementing a receiver with a FOV=55deg in conjunction with either of two notable algorithms, the dynamic range of the rooms, referenced against the peak received power, can be reduced by up to 26% when empty, and furthermore to within 12% of this optimized case when user movement perturbs the channel.

Comparison of Channel Coding Schemes for Molecular Communications Systems

Future applications for nano-machines, such as drug-delivery and health monitoring, will require robust communications and nanonetworking capabilities. This is likely to be enabled via the use of molecules, as opposed to electromagnetic waves, acting as the information carrier. To enhance the reliability of the transmitted data, Euclidean geometry low density parity check (EG-LDPC) and cyclic Reed-Muller (C-RM) codes are considered for use within a molecular communication system for the first time. These codes are compared against the Hamming code to show that an s = 4 LDPC (integer s ≥ 2) has a superior coding gain of 7.26 dBs. Furthermore, the critical distance and energy cost for a coded system are also taken into account as two other performance metrics. It is shown that when considering the case of nano-to nano-machines communication, a Hamming code with m = 4, (integer m ≥ 2) is better for a system operating between 10-6 and 10-3 bit error rate (BER) levels. Below these BERs,s = 2 LDPC codes are superior, exhibiting the lowest energy cost. For communication between nano-to macro-machines, and macro-to nano-machines, s = 3 LDPC and s = 2 LDPC are the best options respectively.

Multi-user indoor optical wireless communication system channel control using a genetic algorithm

A genetic algorithm controlled multispot transmitter is demonstrated that is capable of optimising the received power distribution for randomly aligned single element receivers in multiple fully diffuse optical wireless communications systems with multiple mobile users. Using a genetic algorithm to control the intensity of individual diffusion spots, system deployment environment changes, user movement and user alignment can be compensating for, with negligible impact on the bandwidth and root mean square delay spread. It is shown that the dynamic range, referenced against the peak received power, can be reduced up to 27% for empty environments and up to 26% when the users are moving. Furthermore, the effect of user movement, that can perturb the channel up to 8%, can be reduced to within 5% of the optimised case. Compared to alternative bespoke designs that are capable of mitigating optical wireless channel drawbacks, this method provides the possibility of cost-effectiveness for mass-produced receivers in applications where end-user friendliness and mobility are paramount.

Relay Analysis in Molecular Communications With Time-Dependent Concentration

Molecular communications (MC) is a promising paradigm which enables nano-machines to communicate with each other. Due to the severe attenuation of molecule concentrations, there tends to be more errors when the receiver becomes farther from the transmitter. To solve this problem, relaying schemes need to be implemented to achieve reliable communications. In this letter, time-dependent molecular concentrations are utilised as the information carrier, which will be influenced by the noise and channel memory. The emission process is also considered. The relay node (RN) can decode messages, and forward them by sending either the same or a different kind of molecules as the transmitter. The performance is evaluated by deriving theoretical expressions as well as through simulations. Results show that the relaying scheme will bring significant benefits to the communication reliability.

Optical Wireless for Intravehicle Communications: A Channel Viability Analysis

This paper provides an initial analysis into the viability of implementing an optical wireless system for intravehicle communications. Based on the use of a simple linearly scalable infrared light-emitting-diode transmitter, the results for received power, bandwidth, and root-mean-square (RMS) delay spread are shown at more than 3000 locations within a sports utility vehicle. Several of these locations, including the rear passenger seats, backs of the driver and front passenger seats, and the dashboard, are highlighted as having advantageous channel characteristics for the deployment of mobile communications equipment, audio-visual (AV) displays, computer consoles, or human-vehicle interface devices such as air conditioning or window controllers. Within the vehicle, received powers of up to 49 μW with associated bandwidths ≥ 300 MHz and negligible RMS delay spread can be achieved at several locations. The analysis presented, as the first of its type, will provide the foundations for a larger investigation into intravehicular communications, including the optimization of transmitter-receiver configurations and the advancements of upper layer protocols that can exploit specific channel characteristics for high-end-user quality of service.

Performance of SW-ARQ in bacterial quorum communications

Bacteria communicate with one another by exchanging specific chemical signals called autoinducers. This process, also called quorum sensing, enables a cluster of bacteria to regulate their gene expression and behaviour collectively and synchronously, such as bioluminescence, virulence, sporulation and conjugation. Bacteria assess their population density by detecting the concentration of autoinducers. In Vibrio fischeri, which is a heterotrophic Gram-negative marine bacterium, quorum sensing relies on the synthesis, accumulation and subsequent sensing of a signalling molecule (3-oxo-C6-HSL, an N-acyl homoserine lactone or AHL). In this work, a data link layer protocol for a bacterial communication paradigm based on diffusion is introduced, considering two populations of bacteria as the transmitter node and the receiver node, instead of employing two individual bacteria. Moreover, some initial results are provided, which concern the application of the Stop-N-Wait Automatic Repeat reQuest (SW-ARQ) schemes to the proposed model. The performances of the system are later evaluated, in terms of the transmission time, frame error rate, energy consumption and transmission efficiency.