Sunday, February 20, 2011

Understanding Digital Radio


Digital radio has several meanings.
1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting (DAB) system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as mp2, and transmitted using a digital modulation scheme. The aim is to increase the number of radio programs in a given spectrum, to improve the audio quality, to eliminate fading problems in mobile environments, to allow additional datacasting services, and to decrease the transmission power or the number of transmitters required to cover a region. However, analog radio programs and equipment, especially for the FM broadcasting system, still dominate the market.
2. An older and more wide definition, that still is used in communication engineering literature, is wireless digital transmission technologies, i.e. microwave and radio frequency communication standards where analog information signals as well as digital data is carried by a digital signal, by means of a digital modulation method. This definition includes broadcasting systems such at digital TV and digital radio broadcasting, but also two-way digital radio standards such as the second generation (2G) cell-phones and later, short-range communication such as digital cordless phones, wireless computer networks, digital micro-wave radio links, deep space communication systems such as communications to and from the two Voyager space probes, etcetera.
3. A less common definition is radio receiver and transmitter implementations that are based on digital signal processing, but may transmit or receive analog radio transmission standards, for example FM radio. This may reduce noise and distortion induced in the electronics. It also allows software radio implementations, where the transmission technology is changed just by selecting another piece of software. In most cases, this would however increase the energy consumption of the receiver equipment.

One-way digital radio (digital broadcasting systems)

[edit]One-way digital radio standards

One-way standards are those used for audio and video broadcasting, and sometimes also datacasting, as opposed to those used for two-way communication. Digital radio broadcasting standards may provide terrestrial or satellite radio service. Digital radio broadcasting systems are typically designed for handheld mobile devices, just like mobile-TV systems, but as opposed to other digital TV systems which typically require a fixed directional antenna. Some digital radio systems provide in-band on-channel (IBOC) solutions that may coexist with or simulcast with analog AM or FM transmissions, while others are designed for designated radio frequency bands. The latter allows one wideband radio signal to carry a multiplexconsisting of several radio-channels of variable bitrate as well as data services and other forms of media. Some digital broadcasting systems allow single-frequency network (SFN), where all terrestrial transmitters in a region sending the same multiplex of radio programs may use the same frequency channel without self-interference problems, further improving the system spectral efficiency.
While digital broadcasting offers many potential benefits, its introduction has been hindered by a lack of global agreement on standards. The Eureka 147 standard (DAB) for digital radio is the most commonly used and is coordinated by the World DMB Forum, which represents more than 30 countries. This standard of digital radio technology was defined in the late 1980s, and is now being introduced in many countries. Commercial DAB receivers began to be sold in 1999 and, by 2006, 500 million people were in the coverage area of DAB broadcasts, although by this time sales had only taken off in the UK and Denmark. In 2006 there are approximately 1,000 DAB stations in operation.[1] There have been criticisms of the Eureka 147 standard and so a new 'DAB+' standard has been proposed.
To date the following standards have been defined for one-way digital radio:

[edit]Digital audio broadcasting systems

[edit]Digital television broadcasting (DTV) systems



source: wikipedia

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Posted by RJ Aamir at 9:55 PM

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