Indoor optical wireless networks

Wireless networks offer the user increased mobility and flexibility, allowing information to be accessed or exchanged anywhere, without the need for a physical connection to a network. Early wireless radio LAN products operated in the unlicensed 900 MHz and 2.4 GHz Industrial-Scientific-Medical (ISM) bands. However, the bandwidths available at these frequencies are limited, and must be shared with other products on the market, such as cordless telephones, baby monitors and microwave ovens, which gives rise to the use of robust anti-interference spread spectrum techniques. More recently, wireless LAN products have been launched which operate in the 5GHz band, which does not have the same interference problems associated with the lower bands, and hence the system design can be optimised in terms of data rate and efficiency rather than coexisting with other products. However, even products operating in this band currently only offer data rates of around 10 megabits per second, equivalent to that of standard Ethernet. Such a data rate is barely sufficient for the applications today, let alone the advanced multi-media applications of the future. In addition to this, although the use of ISM bands is license free, not all countries throughout the world recognise and permit unlicensed use in such bands, which makes the goal of designing one product for a global market difficult to achieve in practice.