IBOC TECHNOLOGY

IBOC TECHNOLOGYPresented by: vishal kumarRoll no-774th semester ECEIn Band On Channel Technology For Digital Radio

CONTENTSIntroductionWorking principle of HD Radio Why Digital Radio?Benefits of Digital Audio BroadcastingWhat is IBOCBlock diagramIBOC modes of operationIBOC implementation TechniquesEureka 147Why delay in adoption?

INTRODUCTIONDigital radio, also called digital audio broadcasting (DAB), is transmission and reception of radio signals in the digital domain, as opposed to the traditional analogue transmission/reception by AM and FM systems.Digital radio is similar to hooking up the digital output from a CD player directly to a radio transmitter. At the other end is a digital-to-analogue converter (DAC), which converts the digital signal back into analogue mode so that it can be heard on the audio system as it was recorded.In practice, the CD player is hooked up to a control board, which, in turn, routes the signal as part of the feed to the radio stations transmitter.The signal is either impressed onto a signal carrier and transmitted via uplink to a satellite or transmitted across the land.In both the cases, the signal is received and converted into analogue by a specialized DAC within the radios tuner circuit.Currently, digital radio broadcasts are available in select countries, including the UK , Germany and Canada.

WORKING PRINCIPLE OF HD RADIO

1- Analog and Digital audio broadcast simultaneously created.2- Digital audio Compression3- Digital Broadcast Antenna for transmission of compressed digital signal and analog audio simultaneously.4- Interference: digital signal is less prone to signal dropout and reflections unlike analog signal 5- In Car HD Radio System

Why Digital Radio?

The main advantage of digital radio is that it doesnt have the usual distortion associated with analogue radio such as hissing, popping and phasing.It is immune to distortion from multipath, adjacent stations.User get a new array of data-rich services including traffic information, sports score and weather updates, stock prices, etc..The data is displayed on the LCD in the form of text, images and video. Thus multimedia radio becomes reality.Transmission and Reception as digital domain.CD quality AudioHooking up the digital output from a CD player directly to a radio transmitter. Efficient use of the limited radio frequency spectrum available &Easy-to-use receivers

Benefits of Digital Audio Broadcasting

Rugged, reliable delivery to fixed, portable and mobile receivers for interference- free receptionHigh-quality digital audioFlexibility and choice of programs for Listener Added-value system features such as RDS and multimedia

What is IBOC?In Band On Channel (IBOC) is a hybrid method of transmitting digital , analog radio signals broadcast simultaneously on the same frequency.By utilizing additional digital subcarriers or sidebands, digital information is multiplexed on an AM or FM analog, thus avoiding re-allocation of the broadcast bands. However, by putting RF energy outside of the normally- defined channel, interference to adjacent channel stations is increased when using digital sidebands.

IBOC does allow for multiple program channels, though this can entail taking some existing subcarriers off the air to make additional bandwidth available in the modulation baseband. On FM, this could eventually mean removing stereo. On AM, IBOC is incompatible with analog stereo, and any additional channels are limited to highly-compressed voice, such as traffic and weather. Eventually, stations can go from mode(both analog and digital) to all digital, by eliminating the baseband monophonic audio.

Basics of IBOC The IBOC technology is used to transmit CD-quality audio signals to radio receivers along with such data as station, song and artist identification, stock and news information and local traffic and weather updates.

The broadcasters can use the existing radio spectrum to transmit AM and FM analogue simultaneously with higher quality digital signals.

The system employs multiple digital signaling techniques, such as redundant sidebands, blend, first adjacent cancellation and code and power combining.

To compress the audio data and increase transmission without losing sound quality, it uses the PAC audio-compression technology.

IBOC: a new systemThe IBOC technology allows digital audio broadcasting without the need for new spectrum allocations for the digital signal.The IBOC system will be compatible with existing tuners as it utilizes the existing AM and FM bands by attaching a digital side band signal to the standard analogue signal.For digital compression, the IBOC uses a perceptual audio coder (PAC) developed by Lucent Technology.The USADR AM IBOC DAB system basically comprises the codec, forward error correction(FEC) coding, and interleaving section, modem and blender.

Block diagram of the IBOC DAB transmitter

IBOC modes of operation

Hybrid mode : In this mode the digital signal isinserted within a 69.041 kHzbandwidth, 129.361 kHz oneither side of the analog FM signal. Each sideband is approximately 23 dB below thetotal power in the FM signal.

hybrid IBOC waveform Low-level digital sidebands are added to each side of the analogue signal. The bandwidth is limited to 200 kHz from the centre frequency. Restricting the digital sub-carriers to 70kHz. This minimizes interferenceto the analogue host and adjacent channels without exceeding the existing spectral mask. This bandwidth is wide enough to support a robust, hybrid IBOC service with virtual CD-quality audio that mirrors the coverage of existing analogue radio stations.

Fig. 3: FM hybrid IBOC power spectral density

Extended hybrid mode:This mode includes the hybrid mode and additional digital signals are inserted closer to the analog signal, utilizing a 27.617 kHz bandwidth, 101.744 kHz on either side of the analog FM signal. The total power of the digital sidebands is 20dB below the nominalpower of the FM analog carrier.

IBOC implementation Technique The requirement for FM-to-IBOC isolation is also somewhat difficult to achieve in practice because of the power ratio between FM and IBOC(100:1).

In a combiner that has to deal with a 1:1 power combining ratio, a 26 dB isolation seems to be fine.

There are a few techniques used to combine FM and IBOC signals.

Low Level Combining Option

Low level combining relies essentially on a common amplification technique which means that both the host FM and the IBOC signals are amplified in the same Power Amplifier(PA).This method requires very good linearity from the PA part.Most PAs cannot handle common mode amplification at rated output power; they have to be operated in the most linear portion of their transfer curve which results in a substantial back-off(around 6-10 dB).As IBOC adds about 1% to the total channel power, its power contribution is negligible so the power rating of the antenna is normally not an issue.16

High Level Combining Option

17

High level combining is based on the use of distinct power amplifiers for the Host FM and the IBOC signals.This technique uses an IBOC Power injector which is basically an inverted directional couplerIts power ratio is selected to minimize the loss on the host path, typically 0.5 dB.Such an injector offers a loss of about 10 dB on the IBOC path18

Uses at much higher frequencies than standard 88-108Mhz FM band and 0.525-1.705MHz AM band.UK utilizes Band III (174-240 MHz)Canada uses L-Band (1452-1492MHz)The eureka system broadcasts multiple stations and services over a single frequency in something called a multiplex.The bandwidth within the multiplex is allotted to stations as needed.Stereo programming is typically broadcast at 192kilobits.Eureka 147: The digital radio system in use

A small screen attached to the digital receivers displays text and pictures. Text, data and images can be diffused at the scale of a country or a region.

iBiquity Digital CorpiBiquity Digital Corp. has developed a fully digital IBOC system that permits a smooth evolution from the current analogue FM. The system delivers digital audio and data services to mobile, portable and fixed receivers from terrestrial transmitters in the existing VHF radio band. The broadcasters may continue to transmit analogue FM simultaneously with the new, higher-quality and more robust digital signals. This approach allows broadcasters to shift from analogue to digital radio while maintaining their current frequency allocations.

Why delay in adoption?Low power FM stations are prone to interference.An HD Stations broadcasting range is only equal to the range of a terrestrial broadcasting tower so doesnt cover a wider area as would satellite radio. IBOC licensing, and service rules have not been adopted yet.Cost of equipment is quite high. 21

CONCLUSIONFM transmission is an area of communication that is always moving with technological advancements. As the new digital radios become more available, dramatic improvements will be heard by listeners. Careful design of the new transmissions systems will pay off with reduced costs and improved performance and reliability. HD Radio FM is both robust and efficient in the difficult mobile environment, SDR provides flexibility and Cognitive Radio will definitely define a whole new level of FM transmission.

REFERENCES

23 [1] Russell Mohn, A Three Transistor Discrete FM Transmitter, ELEN 4314Communications Circuits - Design Project, pp. 1, April 2007.

[2] FM broadcasting in the United States Ibiquity /ATTC/ Dynasat FM IBOC Test Data Report, Aug 2001

[3] T.U.M Swarna kumara et al., A Mini Project on Simple FM-Transmitter.

[4] E. F. Louis, Principles of Electronic Communication Systems. McGraw-Hill, 2008

[5] The Future of Radio. The Swedish Radio and TV Authority, 2008.

[6] Holm, Steve (2007). "Lydkvalitetet i DAB digitalradio". Digitale Utgivelser ved UiO. Retrieved 2009-01-03. (Norwegian).[7] C. Renee, An Industrial White Paper: HD Radio[8] C. W. Kelly, Digital HD Radio AM/FM Implementation Issues, USA.

[9] C. W. Kelly, HD-Radio: Real World Results in Asia, USA.

4/12/201624

www.facebook.com/ashik.askTHANK YOU