On the way to digital radio:
With Digital audio broadcasting the reception of terrestrial radio on stationary, mobile, and portable receivers reaches a completely new standard.The DAB system is designed to provide reliable, high quality stereophonic sound and broadcasting for reception by stationary, mobile or portable receivers, using a simple non directional antenna. The system does not add noise and distortions to the signals as it happens with FM/AM.
An important step towards DAB was the development of MUSICAM (Masking Pattern Adapted Universal Sub-band Integrated Coding And Multiplexing) for signal coding .In the past the large bandwidth required to digitize audio signals has prevented the use of digital broadcasting techniques. Now days, the MUSICAM coding method allows high data reduction rates without affecting the radio quality. The method uses irrelevance and redundancy knowledge about psychoacoustics properties of the human ear. With MUSICAM high audio quality can be perceived with data rates down 192 k-bit/s per stereo channel, compared to 1411 k-bit/s of CDs that use an uncompressed technique.
Until now analogue radio signals such as FM or AW have been subject to numerous kinds of interference on their way from the transmitter to radio. These problems were caused by mountains, high rise buildings and whether conditions.
DAB however uses these effects as reflectors creating multi-path reception conditions to optimize receiver sensitivity. Since DAB always selects the strongest regional transmitter automatically you will be at the focal point of incoming radio signals.
Not just CD quality audio to mobile and stationary receivers, digital audio broadcasting also gives opportunity to receive completely new services from program providers. In future radio program will be audible as well as visible to users. The user will be able to store all kinds of information transmitted via digital audio broadcasting in their receiver’s access it when desired. The programmed services in DAB will comprise sound, graphics, images and text.
Technical terms for DAB
COFDM: Coded Orthogonal Frequency Division Multiplexing .It is digital broadcasting process which enables the gathering of several programs in multiplexed .A signal is divided into 1536 signals, carried simultaneously .The signal are sent at right angle to each other that they do not interference with other, for better quality. DAB: Digital Audio Broadcasting. Digital system for broadcasting will remove the FM band. Contradictory to the traditional radio broadcasting system the DAB technology benefits from multi media possibilities, which enables the broadcasting texts pictures or videos in addition to audio programs.
OUTPUT: -Amount of data per time unit necessary to broadcast of a program or service, concerning DAB, output necessary for programs depends upon the quality required; classical music requires higher output than news program.
EUREKA 147: Eureka 147 is an international consortium of broadcasters, network operators, consumer electronics, industries and research industries. It is a technical body, which initiates technical projects for digital audio broadcasting system. This project developed a new digital transmission system, which received ITU recognition standard. This technology is used in band –3 and L-band.
BANDWIDTH: Range of frequencies within program is broadcast, for FM broadcasting the fixed bandwidth is .3MHz per program .For DAB the bandwidth is 1.536 MHz (in case DAB, each radio is given a variable part of this bandwidth).
MULTIPLEXER: A networking local device where several programs from a radio studios are combined. The multiplexer makes it single flow of DAB data and send it to the transmitter
MUSICAM: Masking Pattern Adapted Universal Sub–band Integrated Coding And Multiplexing. A flexible bit rate reduction standard for high quality audio .The process uses a psycho-acoustic effect. For human ear certain sound are masked by other according to the frequency and the volume. MUSICAM eliminates this masking sound that cannot be heard.
PAD: Program Associated Data. This term designates all the information associated to a radio program such as dates of concert, word of song, the name of speaker etc…
Multiple Path Reception: - The signal of a radio program can meet several obstacles and be reflected by mountains, buildings, cars etc. In this case the signal comes from different places (multiple path) at the different times. In FM broadcasting this phenomenon creates distortions .DAB, on the contrary, uses defects and combines the different signals to optimize the quality.
SFN: - Single Frequency Network. Synchronized broadcasting network compose of several transmitter that operates at the same time on the same frequency.
Data casting: - Data service that can be broadcast via DAB independently from radio programs.
The DAB system is intrinsically a multimedia one: it manages end-to-end digital information, and then contents are not confined to audio program. The room is offered to services to information and data related or independent of the audio programs. The DAB system can be used for nation wide regional or local coverage. That generally implies the use of a distribution infrastructure to feed the transmission sites with the DAB bouquet. When satellite distribution is used (to offer nation wide availability of programs) it becomes easy to use the nation wide available programs to feed various broadcasts systems like DAB and FM.
Dab Task, Definition, Requirements:
There are different task of DAB, theyare as follows:
High quality transmission process.
- Error free signal transmission with better audio quality and minimum use of bandwidth.
- Transparent radio channel.
- In future, there should be possibilities to include multi-channel surround sound or freely assignable data transmission.
- New system should last at least 50 years; a lot of room for future developments.
There is perfect reception with portable radios, no special antennas are needed.
Transmission capacity:
- DAB is useful for both regional and local areas
- At least 6 stereo programs through the country, also additional local programs.
Sufficient Capacity For Additional Information:
High performance data channels for additional information, traffic information, control signals, program identification, and radio text information could be generated in the receivers with speech synthesis.Dynamic range control (DRC) system dynamic range control signal is added with the program listeners can select the sound dynamics they wish (e.g. for home or car environment)
Transmission sites :
Whatever the nature of the primary distribution network(leased lines, satellite link , microwave link ) the availability of a common distribution transport frame any where (specially if satellite transport is used), makes easy the progressive deployment of DAB transmitters sites and the operation of AM and FM ones .
AM and FM transmission sites:
In such sites, both audio signal and additional data need to be extracted from the transport frame to supply various transmission equipment (exciter, RDS encoder). A FM DAB receiver (SDX700) has been designed in collaboration with the French company SODIELEC , to allow reception per extraction and decoding ,at the receiving end of the primary distribution network
FM DAB Receiver
An ETI cleaner perform the regeneration of a pure of a pure DAB transport frame, restricted to the pure DAB components.
A component processor, which extracts then, decodes the non-DAB streams.
As a result SDX700 is able to deliver to AM and FM sites up to 4 audio signals (either in analogue or linear digital form) to supply FM exciters, 4 services channels by the way of RS-232 lines and 4*4 binary commands. That make possible to manage from the service provider studios, the transmitter sides features like substitution of national audio with regional contents, delivery of dynamic RDS data, etc.
DAB Transmission:
In the DAB transmission sites the pure DAB ETI signal delivered by the FM DAB receiver supply the COFDM exciter, which realizes the DAB modulation .in that case the FM DAB receiver can be considered as a transparent telecom modem. In particularly, it does not affect the ETI timing information (time stamps) require to establish a Single Frequency DAB Network (SFN).
Receiver:
The future DAB receiver will consists of a tuner, loudspeaker, graphics screen, processor and large memory. A user-friendly interface will make it obedient
to your fingertips. There will be all types of receivers from home and car receivers, to walkman-like portable receivers with optional display.
Thanks to the ISO frequency programs, the receiver needs to be set only once. It will be possible to selects programs according to preferred category
news, sports, classic and rock music . All radio programs are identical by the station name rather than difficult to remember frequency. The name appears on the display of the DAB receiver and one can push simple ‘up’ and ‘down’ to scan through all the programs that are on the air to find the desired program. More sophisticated sets will have large LCD screen listing all the stations that are on the air, making the selection easier.
Digital radio can be received with a telescopic or disk antenna on a car and with a whip or throw-out antenna on a portable radio. The antenna will be smaller than being used currently, as it will use shorter wavelength for DAB than for VHF-FM. Broadcasters can provide extra data along with the radio program (classic music or news). One can ask one’s DAB receiver s that the request.
Over 285 mullion people around the world can now receive more 585 DAB services. However, in order to listen to these services you need a digital radio receiver, which are all identified by the DAB logo, which is displayed on them.
DAB receiver has been on the market since summer 1998. Nevertheless there
now exits DAB car radios, hi-fi units, pc cards and software as well as portable receivers and other exciting developments and prototypes such as the DAB palm top receiver.
In fact it will be possible to listen DAB n every setting or location –whether it be in the office, at home, in car or taking the dog for a walk. Also displayed is the DAB equipment developed for professional use by the manufactures such as ITIS and Philips. Individual manufacture web sites can facilities further information on specific products.
THERE ARE FOLLOWING DAB RECEIVERS:
CLARION DAB 9475R: Clarion’s DAB 9475r was the first ever all in one car radio which fits into a standard mounting frame. The car radio was launched in August 1998. GRUNDIC WKC 5300: In 1195 Grundic was one of the first manufactures along with Bosch-Blaupunkt to introduce DAB ready car radio. These is the first DAB products included data terminals ad the accompanying screen.
JVC KT-DB 1500 DAB Tuner: The features of this receiver is that up/down Ensemble Search, manual frequency tuning, up/down DAB service select, primary/secondary service select, 18 DAB service preset, label indication.
Panasonic DAB in car radio system: This is Panasonic DAB in car radio system complete with navigation screen, boot box, head unit and aerial .It was displayed at the exhibition Berlin.
Sony X1 100 DABS: -The Sony X1 100 DAB system boot box can be linked to the CDX C90R unit for a complete in-car radio system. The head unit comes with full CD and MD control and comes equipped with two remote the unique The boot box also come equipped with a special antenna as a part of the packet
The features of the receiver are as follows:
1. Dual band receiver
(band 3 and band 1).
2. Optical digital output.
3. Analog and Digital selector.
4. Sampling rate converter.
5. High gain active antenna supplied.
MobiLe reception of DAB:
Multi path reception and Doppler effect mostly cause interference during mobile reception. Multi-path reception means that directly received signal and portion of that signal reflected from the buildings and hills overlap at the receiving antenna, causing frequency-dependent interference. In the Doppler effect, movement of vehicles causes slight frequency shifts, leading to time dependent interference.
DAB uses up to 1536 carrier frequencies (distributed over 1.5 MHz band) rather than just a single carrier frequency. This means interference affects only some of the carriers, and the majority of carriers are received always noise free.
The information bits are transmitted in groups, called as “symbols”. As direct and reflected signal components reach the receiver at different time, inter-symbol interference occurs i.e. symbols adjacent in time overlap due to signal components arriving at different time. To prevent this disruptive inter-symbol interference, the symbol duration is lengthening by a guard interval at the DAB transmitter. Since it delays use of signal until the interference caused by overlaps
For each useful bit, 1, 1/3, 4 bits are transmitted. This extensive redundancy makes it possible to reconstruct the transmitted bit sequence in the receiver, even if part of it is disrupted during transmission. This process is called forward error correction (FEC).
In the receiver error can be concealed at the audio reproduction stage, so that residual transmission errors, which could not be corrected, do not disruptive noise.
DAB networks are usually common block frequency networks, i.e. all the transmitters in the network are operated on the same frequency. If the guard interval is long enough, the receiver cannot tell whether time-delayed incoming signal components are from another transmitter. On the margin of transmitter service area, reception gaps and a more uniform pattern of the received field strength may be achieved. In places where problem would never the less arise, for example, in a valley or the radio shadow of a high-rise building, additional gap filters can be installed. Common frequency networks make DAB more frequency-effective than VHF-FM.
FM – DAB:
Necessity FM-DAB implementation In 1997 the decision was taken to replace the “MVR 128 (by Globcast in French)“ by a system able to provide simultaneously FM and DAB transmission networks. This system has been called FMDAB system. DAB transport solution was able to full fill the following FM radio distribution requirements: -
- To provide a universal and professional system to complexly fit the Radio and operator expectations.
- To provide a high audio quality.
- To send programming associated data mainly to control the regional switching to convey the RDS (Radio Data Service) existing data.
- To be highly cost effective and multiplexing capability.
The first implementation of FM DAB commercial network started by the end of 1998 and lasts one year. At the beginning of 1999 a set of 10 radio France programs was multiplexed over a digital satellite distribution link, which feed all the radio France analog FM transmitters. At the same time and from the satellite link feed, the radio France multiplexed was broadcast over DAB in the French cities.
Today the FM transmitter distributing system based on FM DAB is established. 4 multiplexed of national radio programs are broadcast over the FMDAB network. It means that about 25 radio programs feed more than 1500 FM and AM transmitters
IMPLEMENTATION RESULTS: -
It provides a “Universal and Professional System “ which complexly fit the radio and operators exceptions
It provides a high quality of audio signal over several networks and offer sufficient additional data to face the various operational situations in regions.
It is fully DAB compliant, allowing to smoothly increasing the DAB coverage in France with additional investments limited to the transmitters themselves.
It saves operational cost as it share costly satellite link between several programs and services (AM, FM, DAB).
Studios and network equipment are homogeneous, the maintained activates, and the spare parts stock, the measurement equipment and the operator training are optimized.
The regional re-multiplexing needed to build DAB regional ensembles easily performed
AM, FM and DAB: a distribution network
In such networks at least 3 categories of sites are involved: the Services Providers ones (where contents are produced), the Ensemble Provider one (where DAB multiplex is assembled) and the Transmitters ones (where DAB multiplex is modulated and radiated).
A collection network is organized to bring service providers contributions to the ensemble operator and a further primary distribution network is deployed to transport DAB multiplexed to the transmitter sites. In practice the topology of the broadcast network is far more complex: due to regional inserts, several multiplexes may be present in the network, constituting at least 2 layers, focused on national coverage and regional coverage.
Practically large number of situations is encountered in the primary distribution .
The transport multiplexed issued by the main ensemble multiplexer can be used on FM and DAB transmission sites, but it can be also be used on regional multiplexing site, where it acts as the tributary to the regional DAB multiplex.
Service Provider Sites: -
Radio broadcasters (service provider) no longer produced a single simple audio program, but generally operate several programs dedicates to one or several networks and en-riched with various additional side information. Conscious of this context, ITIS has developed a complete range of source equipment, able to full fill the needs. Following its customer needs IT IS has defined and designed, called source encoder able:
- To encode one audio program.
- To offer a PAD physical input for data cancerous to the audio programs.
- To offer physical input, for complementary information by the way of RS-232 physical ports
- To transmit signaling or management information using files played repetitively.
Service multiplexer:
In many situation service(s) providers deliver more than one audio program on the collection network. Then a service multiplexer (SMUX) is needed to group all the components inside the serve provider, studios and to deliver them a single transport link. The view of such service multiplexer system as shown in figure
The IT IS equipment family offers a cascaded bus (STAR BUS) allowing to daisy chain (in cascaded, the output of first is given to next input) source equipment .the service multiplexer constitutes the whole multiplex that embeds the service provider contributions to feed the collection network. Various output modules are available to adapt the service multiplex to the physical telecom link.
The service-multiplexed system can be secured either by duplication of the source or service multiplexed equipment. If supplied, time and frequency reference signals are used to synchronize the whole system. An external station running management software and communicating with the system through Ethernet LAN.
Network operator site : -
In the network operator sites the objective is to coolest the contribution of various service providers to perform their assembly to produce the broadcast multiplexed. Using a common transport frame, all the inputs became syntactically similar can include one or more service providers contributions. In the context, so called Ensemble multiplexer has to as versatile as possible: large scalability of its inputs, versatile telecom adapter input modules, comprehensive manegment system are the keywords of these platform and of course of the IT IS “D-EMUX”
Ensemble multiplexer. Ensemble multiplexer. System used basic bricks having two inputs and one output to constitute a multiplexing system offering ”h”inputs and one output. Each of them is equipped with a module relevant with the telecom link.
Ensemble Multiplier system : D-EMUX is able to perform both multiplexing and re-multiplexing functions: both primary service providers multiplexed and already constituted Ensemble one, can be processed to constitute the output Ensemble multiplex. As in the case of service multiplexer, D-EMUX system can be secured by equipment duplication, and time and frequency reference signal can be used to synchronize the whole system. D-EMUX system is supervised by an external station running management software and connected through an Ethernet LAN.
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Sync module supervision & control
10 MHz 1pps RS alarms
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Integrated DAB multiplexer :
Multiplexed for Audio and Data programs ensemble and/or Service multiplexer, with integrated management of NPAD. It is totally compatible with ETI (Ensemble Transport Interface) (ETS 300 799) and DAB (ETS 300 401) standards designed by a DAB operator to meet concrete and specific requirements of DAB broadcasters.
The multiplrxer is user-friendly and easy to use software for management of the system. Software conception of the product allows remote maintenance and updating.
Modular conception provides a complete ability to meet the needs of the user and an adapted at a time. This is compatible with every MPEG encoders with X21 output; input is to X21 or G703 cards. Output of an ETI - NI or ETI NA 5376 or 5592 flows in G703/G704 card. There is possibility of n+1 and n+n redundancy with automatic commutation. This is a compact product: all functions in one unit
Functions :
- Multiplexing of the DAB flow from an input supplied by the source encoders is accepted by all output from 8 to 384 kb/s to 24 or 48 kHz sampling.
- Integrated NPAD insertion via TCP/ IP network (option).
- There is management of TDC (Transport Data Channels)
- There is possibility to order, the change of output for the encoders from the graphic interface of the multiplexer
- Possibility to remotely encode one or several audio channels forwarded via specific lines
- The time is set by automatically for the multiplexer by RS232 or NTP server
- There is management of MNSC (Management Network Service Channels) and TIST (Time Stamp Information) for synchronization of SFN (single Frequency Network ) transmitters.
- The software for local or remote management of the multiplexer is available via TPC/IP in a simple and user-friendly Windows interface.
- To complete configuration of the whole multiplex.
- There is configuration and time scheduling of the output of each encoder
- The selection of the language of the graphic interfaces such, as English or French are included in the basic configuration.
- There is secured access by password and log-in.
- The visualization of alarms directly on the graphic interface of the multiplexer
- Immediate and automatic sending of alert messages by e-mail or SMS
- Local or remote visualization of alarms and alerts reporting
- Automatic commutation to an MPEG file in case no signal is detected at the output of encoder
- Automatic commutation to a spare encoder in case of problem affecting the main encoder
- Automatic hardware commutation to a spare multiplexer in case no ETI flow is detected (option)
- Remote maintenance and updating of the multiplexer
CURRENT STATUS
Current feactures:All the parameters were defined as a part of Eureka EU 147 project in 1992
System description ready in 1993 after standard has been defines by ETSI (European Telecommunications Standard Institute)
After that Eureka partners can start development and manufacturing of chip sets and terminals.
Schedule: - 2010 simulcast operation with FM, 2010 DAB will replace FM in band 87.5 to 108 MHz, 2010 DAB will have a total bandwidth of 20.5 MHz, surround sound, new services
Currently DAB is its market introduction phase: several work groups test and trials, network planning, terminal, introduction strategy.
Currently, available frequency ranges for DAB are not get standard yet .
Taiwan and Australia have been launched operational or pilot Mexico and Paraguay among other countries have countries have expressed their advanced interest in DAB. A country progress report and coverage maps are also available on this site from the DAB Worldwide area.
ADVANTAGES OF DAB SYSTEM
According to listener viewpoint: 1.Constant excellent reception fromcarradios and portable radios (CD quality) with simple antenna.
2. No signal fading
3. No interference due to multi-path propagation
4. More user-friendly receivers (radio) no station finding is needed
5. Additional information of the program (speech of music identification, program identification, variable dynamic system)
6. Other information (traffic information, control system, data to certain groups)
7. Not compatible with FM – multi-standard radio are needed
BROADCASTER’S VIEWPOINT:
Same quality than the storage media have Single-frequency network.
More programs or services.
Greater program variety.
BENEFITS OF DAB
1. Wide choice of receiver
2. Lower transmission cost broadcasters:
3. Superior frequency economy: .
4. Pay radio services:
5. configuration flexibility:
6. Quick facts
7. CD sound quality
8. Easy program selection
9. Perfect reception:
10. Once receiver does all: .
11. Programmed associated data:
12. Information services:
13. Target music or data services: .
14. DAB a system designed for terrestrial or satellite reception:
15. Digital means more choice:
16. No charges
17. No more numbers to remember:
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