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Digital Audio Broadcasting is a standard digital radio broadcast developed by EUREKA as a research project for the European Union (Eureka 147). The DAB receiver is designed for both home use and portable audio broadcasting for terrestrial and satellite, which also allows data entry. Uses the radio spectrum frequency Band III and Band L The technology was primarily developed in the 1980s, although the project began in 1987 and ended in 2000. More than 285 million people around the world can receive more than 550 different DAB services. The UK was the first country to implement DAB service, part of the BBC and commercial radio in London in 2001 and then nationally.
In February 2007 it released an updated version called DAB +, which is not compatible with previous receiver equipment. DAB + is about two times more efficient than DAB using the AAC + audio codec. Besides the quality of reception is more robust in the DAB + in the DAB because the first includes the error correction coding Reed-Solomon.
The development and diffusion of the DAB is in charge of WorldDMB, which also promotes Digital Multimedia Broadcasting (DMB).
History
The first DAB services will start on September 1995 in the UK by the BBC and in Sweden by Sveriges Radio. Subsequently, several German states have implemented the DAB.
Operation
The transmission of digital radio works combined two technologies to produce a digital radio transmission system efficient and very reliable.
First is the MUSICAM compression system, which is then normalized called MPEG-1 Audio Layer 2 or MP2, a coding system that works discarding sounds that will be perceived by the human ear. When two signals very close in frequency and one of them is stronger than the other, the signal is normally lower level is masked and can not hear it. In addition, the ear has a noise threshold below which you do not hear the sounds. What we do with this system is to remove everything that the ear will not perceive. In this way manages to reduce the bandwidth needed to transmit. The system is very similar to MP3 but requires less processing power than this.
In reality, continuously transmits a "container" of information, where one side sends the information content and configuration, to allow the receiver to know very quickly what was ordered and select any of the contents (programs ). On the other hand, the container is sent audio programs and additional services, and within each audio program can enter data associated with that program, as can be, for example, a weather map when you are informed about the weather .
The gross capacity of the multiplex information is 2'3 Mbit / s, but in reality we have is a container with 864 boxes, that are filling with the programs and data are output continuously.
The second technology is COFDM (Coded Orthogonal Frequency Division Multiplex). It is a frequency division multiplex in which we made orthogonal encoding. On the one hand, the encoding introduces redundancy to detect and correct transmission errors and, moreover, the system uses time diversity, diversity in space and frequency diversity. Time diversity is achieved by interleaving in time of all information, so that if there is any disturbance, having the information distributed is possible to recover better. With frequency diversity, using an exact mathematical relationship, the signal is divided MUSICAM carrier frequencies 1536 and got that information is distributed intermittently across the spectrum of the channel and look less affected by disturbances, and the diversity get space that can be sent from different emitting centers and they all contribute positively, creating a single frequency network, and also the reflections of the signal contribute positively to the receiver.
Interferences that disrupt the FM signal reception, typically caused by buildings or mountains, are eliminated through COFDM technology. This means that the same frequency can be used throughout a country without the need to retune the receiver when you're traveling (single frequency network).
A digital radio multiplex consists of 2,300,000 bits, which are used to transport audio, data and system protection against transmission errors. Of these, about 1,200,000 bits are used for audio and data service. For a day, a number of bits can be assigned to cover each service.
Each multiplex can carry a mixture of stereo or mono broadcasts and data services. The number of programs depends on the quality required for each of them. Services vary throughout the day depending on the schedule.
Analog or Digital
The analogue radio is known, both AM and FM. In this case, the radio wave carrying the original sound, the music or the voice of an announcer, which may be subject to atmospheric disturbances or other electrical equipment. Analog signals can also be blocked or distorted by terrain or large buildings.
With the FM signal, a short-range microwave, but better audio quality than AM-requires a large number of frequencies, generally different, covering a large area. This affects the electromagnetic spectrum is used inefficiently and that when a person moves more than a few tens of kilometers have to retune the radio to follow the program that was listening.
Digital Radio allows more efficient use of the electromagnetic spectrum offers issuers a wider band to include additional services. Digital Radio signal is converted into "bits" that are carried by radio waves so as to resist interference. The sound is almost perfect. With Digital Radio, the space used in the electromagnetic spectrum can be optimized through a single frequency network, through which all use the same frequency transmitters to broadcast the same signal Digital Radio. This means no tune to change if you move from one place to another.
Receiver
To receive digital radio services will need a receiver specifically designed for this purpose. And household appliances that are designed for cars are available in countries that have adopted the Digital Radio. Companies such as Arcam, Cymbol, Tag Mac Laren and Panasonic have launched digital radio equipment and many other manufacturers and are preparing. Clarion, Grundig, Kenwood, JVC, Pioneer and Sony have for sale digital radios for cars.
[edit] Types of existing receivers
HiFi Components: The first digital radios have been released are Hi-Fi components or separate devices can be connected in legacy systems. These tuners are of two types: DAB Tuners exclusively or combined systems for DAB and FM / AM tradition. All appliances, no matter what tuning ability, have a built-in screen for displaying information relating to the broadcast program.
Car Receivers: These consist of a drive compatible with DAB CD with traditional radio receiver included in a box (similar to the car CD) that can be installed under seats or in the trunk of the car.
Digital audio cards for PCs: These tuners can not only listen to radio programs but allow access to new information services. In the future, the DAB will transmit fax sheets or website.
Hi Fi Systems: The second generation of digital radio tuners will be included in the new Hi-Fi systems. The arrival of DAB means that its components (CD and digital radio) will be compatible.
Portable Receivers: Now are the size of a cell phone and the average price around 30 euros.
In February 2007 it released an updated version called DAB +, which is not compatible with previous receiver equipment. DAB + is about two times more efficient than DAB using the AAC + audio codec. Besides the quality of reception is more robust in the DAB + in the DAB because the first includes the error correction coding Reed-Solomon.
The development and diffusion of the DAB is in charge of WorldDMB, which also promotes Digital Multimedia Broadcasting (DMB).
History
The first DAB services will start on September 1995 in the UK by the BBC and in Sweden by Sveriges Radio. Subsequently, several German states have implemented the DAB.
Operation
The transmission of digital radio works combined two technologies to produce a digital radio transmission system efficient and very reliable.
First is the MUSICAM compression system, which is then normalized called MPEG-1 Audio Layer 2 or MP2, a coding system that works discarding sounds that will be perceived by the human ear. When two signals very close in frequency and one of them is stronger than the other, the signal is normally lower level is masked and can not hear it. In addition, the ear has a noise threshold below which you do not hear the sounds. What we do with this system is to remove everything that the ear will not perceive. In this way manages to reduce the bandwidth needed to transmit. The system is very similar to MP3 but requires less processing power than this.
In reality, continuously transmits a "container" of information, where one side sends the information content and configuration, to allow the receiver to know very quickly what was ordered and select any of the contents (programs ). On the other hand, the container is sent audio programs and additional services, and within each audio program can enter data associated with that program, as can be, for example, a weather map when you are informed about the weather .
The gross capacity of the multiplex information is 2'3 Mbit / s, but in reality we have is a container with 864 boxes, that are filling with the programs and data are output continuously.
The second technology is COFDM (Coded Orthogonal Frequency Division Multiplex). It is a frequency division multiplex in which we made orthogonal encoding. On the one hand, the encoding introduces redundancy to detect and correct transmission errors and, moreover, the system uses time diversity, diversity in space and frequency diversity. Time diversity is achieved by interleaving in time of all information, so that if there is any disturbance, having the information distributed is possible to recover better. With frequency diversity, using an exact mathematical relationship, the signal is divided MUSICAM carrier frequencies 1536 and got that information is distributed intermittently across the spectrum of the channel and look less affected by disturbances, and the diversity get space that can be sent from different emitting centers and they all contribute positively, creating a single frequency network, and also the reflections of the signal contribute positively to the receiver.
Interferences that disrupt the FM signal reception, typically caused by buildings or mountains, are eliminated through COFDM technology. This means that the same frequency can be used throughout a country without the need to retune the receiver when you're traveling (single frequency network).
A digital radio multiplex consists of 2,300,000 bits, which are used to transport audio, data and system protection against transmission errors. Of these, about 1,200,000 bits are used for audio and data service. For a day, a number of bits can be assigned to cover each service.
Each multiplex can carry a mixture of stereo or mono broadcasts and data services. The number of programs depends on the quality required for each of them. Services vary throughout the day depending on the schedule.
Analog or Digital
The analogue radio is known, both AM and FM. In this case, the radio wave carrying the original sound, the music or the voice of an announcer, which may be subject to atmospheric disturbances or other electrical equipment. Analog signals can also be blocked or distorted by terrain or large buildings.
With the FM signal, a short-range microwave, but better audio quality than AM-requires a large number of frequencies, generally different, covering a large area. This affects the electromagnetic spectrum is used inefficiently and that when a person moves more than a few tens of kilometers have to retune the radio to follow the program that was listening.
Digital Radio allows more efficient use of the electromagnetic spectrum offers issuers a wider band to include additional services. Digital Radio signal is converted into "bits" that are carried by radio waves so as to resist interference. The sound is almost perfect. With Digital Radio, the space used in the electromagnetic spectrum can be optimized through a single frequency network, through which all use the same frequency transmitters to broadcast the same signal Digital Radio. This means no tune to change if you move from one place to another.
Receiver
To receive digital radio services will need a receiver specifically designed for this purpose. And household appliances that are designed for cars are available in countries that have adopted the Digital Radio. Companies such as Arcam, Cymbol, Tag Mac Laren and Panasonic have launched digital radio equipment and many other manufacturers and are preparing. Clarion, Grundig, Kenwood, JVC, Pioneer and Sony have for sale digital radios for cars.
[edit] Types of existing receivers
HiFi Components: The first digital radios have been released are Hi-Fi components or separate devices can be connected in legacy systems. These tuners are of two types: DAB Tuners exclusively or combined systems for DAB and FM / AM tradition. All appliances, no matter what tuning ability, have a built-in screen for displaying information relating to the broadcast program.
Car Receivers: These consist of a drive compatible with DAB CD with traditional radio receiver included in a box (similar to the car CD) that can be installed under seats or in the trunk of the car.
Digital audio cards for PCs: These tuners can not only listen to radio programs but allow access to new information services. In the future, the DAB will transmit fax sheets or website.
Hi Fi Systems: The second generation of digital radio tuners will be included in the new Hi-Fi systems. The arrival of DAB means that its components (CD and digital radio) will be compatible.
Portable Receivers: Now are the size of a cell phone and the average price around 30 euros.