Indoor optical wireless is, inherently, a cellular system [79, 80]. Each room, or section of a room, will have within it a base station linked to the backbone network [81]. It can also be assumed that every environment that a base station resides within , will be different. The advantages of OW such as high speed communications may be beneficial to scenarios in the workplace, but each workplace will have a different topology of furniture and seating arrangements. The low cost appeal of OW will allow systems to be deployed in residential environments, where, for example in living rooms and bedrooms, the type of furnishing and flooring is also unique. The immunity to RF interference may appeal to heavy industrial users, where there is no furniture but sparsely open plan factories or warehouses with reflective surfaces, such as concrete and steel for example, that are not normally found elsewhere. From a channel perspective, it is therefore reasonable to assume that no two environments are identical.
This argument can be carried through to the channel noise sources. The typical lighting found in office environments, although possibly similar from office to office, is certainly different to the ones found in residences. Some offices have many windows, whilst some do not, making sunlight different in each location. Industrial applications may be purely illuminated with artificial light. These channel variability challenges are enough on their own if one considers the environment to be static. Realistically, this cannot be assumed, as OW systems are about connecting users in a flexible way. Even if the users moved slowly, or assumptions were made about their typical behaviours, the channel can still change with simple actions like rearranging the furniture or substituting carpet for wooden flooring.
Furthermore, it needs to be assumed that there are multiple end users within each unique envi- ronment. Each of these users has upon them a battery powered portable device such a mobile phone or laptop. Historically, with work from standards bodies such as the IrDA, each of the devices is most likely very similar, or conform to some minimum technical specification of op- erational requirement. Furthermore, from a marketing point of view, the standards agencies or the parties with financial interest in the devices, try and make them as cheap as possible, and attempt to put them in as many devices as possible.
This leads to somewhat challenging system design requirements, of how to make a single, mass producible and cheap receiver design operate in an infinite number of channel scenarios, whilst still being able to market the device as user friendly. The system element not mentioned so far, is that of the transmitter. The transmitter stands alone as something that can be flexibly designed. The transmitter should be cost effective, or good value of money, but it does not have to be disposably cheap as with the receiver. The transmitter should be power efficient, but not necessarily low power, as it is connected to the backbone network, so potentially near a power plug. Finally the transmitter should be unobtrusive, but does not have to be small. The transmitter, is therefore one possible avenue of research that could lead to a solution to this system design challenge.
In the case of all the aforementioned receiver techniques proposed, each one has their respective merits in mitigating certain channel factors such as bandwidth or received power limitations. However, given the cellular nature of OW, one has to weigh the added complexity, cost and physical size of each receiver within the cell against the benefits they entail. There is an argu- ment with economies of scale, such that the larger the uptake, the lower the cost of each unit. The argument, however can also be debated the other way, if one considers that the cost and complexity overhead of the entire system will be influenced more, by the number of users or
receivers present in a cell, than by the single base station.
The aim of this work, is to prove, in principle, the conceptual idea, that a genetic algorithm ap- proach, can be used to optimise several OW channel characteristics. It is intended to show that the channel can be itself, designed, accounting for environmental and user movement induced channel variability. Much of the motivation for this work comes from a personal experience in receiver design, whereby it was never known how much power or bandwidth to expect from the channel, for each application at hand, such that, the choice of appropriate receiver design or topology to implement and develop, was always a difficult decision. The work will in general, focus purely on the algorithm and the effects of its use on the channel. A small amount of re- ceiver analysis is performed, but only to the extent of physical parameters that affect the channel response such as FOV. It is not the intent of this work to develop a bespoke system with the highest bit rate, SNR or focus exclusively on some other system performance characteristic, but rather, assume as wide a range of variables as possible, proving the method has a high degree of flexibility.
To the best of the author’s knowledge, GAs have not been applied in this way, with this focus, on indoor optical wireless communication systems, and it will be shown that their use will bring benefits to the research area. It should also be stated that the method and results presented here are not mutually exclusive, baring the one exception of computer generated holograms, with other research ideas currently being undertaken elsewhere, and this work is not shown to be a solution, but be part of the solution. It is hoped that the benefits of this work, are taken further by others, particularly the receiver designers who may be able to match an algorithm of their own, with their complementary receiver designs, potentially fulfilling the system design requirements. Furthermore, like any new idea, there are trade-offs, and they will be fully de- tailed. Emphasis will also be placed on critical self analysis of the results and on the validity and conditions for which they hold true.