IBOC Technology For Digital Radio

Rameesah Nisar15mmc010

Mtech –ECESMVDU, Katra

Digital Radio

• Digital radio, also called digital audio broadcasting (DAB).

• Digital radio is similar to hooking up the digital output from a CD player directly to a radio transmitter.

Digital Radio (contd..)

• At the other end is a digital-to-analogue converter (DAC), which converts the digital signal back into analogue mode.

• Currently, digital radio broadcasts are available in select countries, including the UK , Germany and Canada.

Advantages of Digital Radio

• It doesn’t have the usual distortion associated with analog signal (e.g. hissing, popping & phasing).

• Immune to distortion from multipath , adjacent stations.

• User gets a new array of data- rich services including traffic information, sports score &weather updates, etc.

• Efficient use of the limited radio frequency spectrum available & easy-to-use receivers.

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.

IBOC: a new system

• In Band On Channel .• Compatible with the current analog radio formats.• Utilizes the existing AM and FM bands by attaching

a digital side-band signal to the standard analog signal.

• For digital compression, the IBOC uses a perpetual audio coder (PAC).

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.

IBOC modes of operation(Contd..)

• Extended hybrid mode:

This mode includes the hybrid mode and additional digital signal 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 nominal power of the FM analog carrier.

Extended hybrid mode (cont..)

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.

• This method requires very good linearity from the PA part.

• 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.

High Level Combining Option

• 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 coupler.

• Such an injector offers a loss of about 10 dB on the IBOC path

Eureka 147: The digital radio system in use

• Uses at much higher frequenciesthan 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 .

iBiquity Digital Corp

• iBiquity Digital Corp. has developed a fully digital IBOC system that permits a smooth evolution from the current analogue FM.

• 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 Station’s broadcasting range is only equal

to the range of a terrestrial broadcasting tower so doesn’t cover a wider area as would satellite radio.

• IBOC licensing, and service rules have not been adopted yet.

• Cost of equipment is quite high.

CONCLUSION• FM 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 [1] Russell Mohn, “A Three Transistor Discrete FM Transmitter,” ELEN

4314 Communications 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] “The Future of Radio”. The Swedish Radio and TV Authority, 2008.[4] E. F. Louis, Principles of Electronic Communication Systems. McGraw-

Hill, 2008.[5] C. W. Kelly, “Digital HD Radio AM/FM Implementation Issues”, USA.[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, “HD-Radio: Real World Results in Asia”, USA.

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