IBOC TECHNOLOGY

CONTENTS Introduction Why Digital Radio? What is IBOC Block diagram IBOC modes of operation IBOC implementation Techniques Why delay in adoption? Advantages Disadvantages

INTRODUCTION Digital 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 station’s 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 radio’s tuner circuit. Currently, digital radio broadcasts are available in select countries, including the UK , Germany and Canada.

Why Digital Radio? The main advantage of digital radio is that it doesn’t 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.

Contd… To explain, in analogue radio, a large number of radio signals can exist in the atmosphere at any time. However each of them is being transmitted on a different radio frequency. Stations that share the same radio frequency are usually far apart so that they don’t interface with each other. In order to receive a station within its transmission range, all we have to do is tune the receiver to its frequency. The drawback of this analogue mode is that the signals in close proximity in terms of frequency can interfere with each other to some extent, depending on the modulation pattern of the radio station and the ability of the radio receiver to reject interfering adjacent signals.

What is IBOC? In-band on -channel (IBOC) is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency.

IBOC: a new system The 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 is inserted within a 69.041 kHz bandwidth, 129.361 kHz on either side of the analog FM signal. Each sideband is approximately 23 dB below the total power in the FM signal.

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 nominal power of the FM analog carrier.

All Digital mode: This mode replaces the analog signal with additional digital signals and also includes the digital signals of the Hybrid and Extended Hybrid Modes. The total power of the digital sidebands is 10dB below the nominal power of the replaced 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 PA’s 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.

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 Its 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 path

Why delay in adoption? Low power FM stations are prone to interference. IBOC licensing, and service rules have not been adopted yet. Cost is high.

Advantages of IBOC a system design that can inherently simulcast both analog and digital services, using the current frequency assignment (ie does not require additional spectrum). a system design that enables broadcasters to maximise the use of existing infrastructure; thereby minimising upgrade costs. a receiver design that avoids abrupt reception failures, common in some digital systems at the edge of the coverage area.

Continue………. IBOC-FM may provide auxiliary audio services, such as surround sound, or Multiple audio channels. at the end of the simulcast period, the robustness of the signal is significantly increased, providing options to reduce transmitter power for the same coverage area; 

Disadvantages The final system design is not yet complete, cc USA. A 9 kHz design for Australian conditions has not yet been developed or tested. A 9 kHz design would also result in a reduced data capacity and consequently audio quality compared to the 10 kHz version;

Conclsion: Stations that have stayed to digital broadcasting straightforward and affordable.Facilities that have not,shouldbconsider a plan of staged hardware upgrades schedule with IBOC implementation.

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