The first cordless link in home entertainment equipment was to provide remote control. Initially the medium was ultrasonic sound, but that soon gave way to infra-red light, modulated by being chopped into pulses, each command having its own unique pulse train. Later infrared cordless headphones made their appearance, powered by on-board batteries. Then came IR sound systems, with loudspeakers needing no more than a mains connection.
Infra-red coupling systems, with their line-of-sight limitations, are constricted in terms of reliability and carrying capacity. About ten years ago an RF wireless system, Bluetooth, was introduced, initially for the mobile phone industry, to transfer data and voice signals between devices within a few metres of each other. It quickly grew into a very versatile ‘cable substitute’, with many applications in the computer, communications and home-electronics fields, and it continues to expand.
Bluetooth is a digital system, conveying data at a maximum rate of 1Mbits/sec; net of ‘housekeeping’ and error-protection data, a throughput of 721kbit/sec is possible. Bluetooth operates in the 2•4GHz ISM band at three alternative power levels, chosen to suit the application: Class 3, 1mW output, has an across-desk range of 1m, and is seldom used; Class 2, 2.5mW level, is most common for indoor and in-car applications with about 10m reach; while Class 1 has 100mW power and a clear-space range of 100m. This is useful for home/office use because it can penetrate walls within reason. Generally used for point-topoint communications, point-tomultipoint operation is also possible here. Each type of application for Bluetooth has a different profile, a specific electronic protocol which should ensure compatibility between different manufacturers’ products and minimise conflicts.
Bluetooth has many applications in computing – cordless keyboards and printers are examples, along with wireless access to the net from a laptop PC in a Bluetooth ‘hotspot’ in a home, office, hotel, airport or motorway service area. It’s also widely used in sophisticated handsfree mobile phone operation, and is incorporated in some in-car sat-nav systems. In the home-entertainment business stereo headsets and speakers are linked to amplifiers, iPods etc. by Bluetooth, and it’s used with camcorders and still cameras for wireless coupling to a computer, cellphone or other device. New applications for this versatile technology are being found all the time.
WLAN (Wireless Local Area Network) is also starting to feature in some high-end consumer electronics products. Based on (and sometimes called) 802•11, an IEEE specification, this is a fast (potentially up to 540Mbit/sec) cordless coupling system which can – alongside its primary role of providing broadband Internet access and home/office PC networking – be the basis of a residential gateway, interfacing with external glass-fibre or copper data highways, and storing, co-ordinating and routing multimedia content in both directions. WLAN-equipped electronic cameras facilitate easy uploading of images in a Wi-Fi hotspot in a public place on holiday, for instance, or downloading of music into an MP3 player in a retail or leisure environment.
Quite different is the emerging Zigbee system, viewed favourably in many quarters because of its ‘green’ energy-conserving credentials. Similar to Bluetooth in its operation, but slower and simpler, it has a maximum data rate of 250kbits/sec and 30 to 50m range at 2•4GHz transmission frequency. It can be used for remote control of home audio/video equipment, lighting and appliances; security monitoring; and in cordless PC peripherals. Zigbee has several proprietary competitors in the home-automation field.
Analogue wireless devices
While the digital systems described above are suited to control data and voice applications, convenience and economy require analogue solutions in other cases. FM transmitters (now legal in low-power form in the UK) facilitate easy playback of music through a stereo radio receiver in a car or at home: from MP3 devices, iPods, mobile phones, games, laptop PCs, etc. Tuneable – in some cases automatically – to any vacant spot in the VHF broadcast band, they cost £30 or more and come from makers like Belkin and Griffin.