18-07-2014, 12:10 PM
IBOC TECHNOLOGY
IBOC TECHNOLOGY.pptx (Size: 360.71 KB / Downloads: 13)
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.
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
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.
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 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
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