When using digital sidebands, in-band on-channel (IBOC) is a hybrid way of broadcasting digital radio and analogue radio broadcast signals simultaneously on the same frequency.
The addition of the digital sidebands is more effective in the United States, since FM broadcast band channels are spaced at 200 kHz rather than the standard 100 kHz elsewhere. Because of the 200 kHz spacing, stations with contemporaneous or contiguous coverage regions will not be spaced at less than 400 kHz in practise.
Outside of the United States, spacing can be as high as 300 kHz, causing issues with the IBOC digital sidebands.
Multiple programme channels are possible with IBOC, albeit this may need the removal of some existing subcarriers to make more bandwidth available in the modulation baseband. This could eventually lead to the demise of stereo on FM.
IBOC is incompatible with analogue stereo on AM, therefore any extra channels are limited to extremely compressed voice, such traffic and weather. By eliminating the baseband monophonic audio in FM, stations can eventually transition from hybrid mode (both analogue and digital) to all-digital. There are three ways of IBOC broadcasting currently in use.
IBOC’S ARCHITECTURE
The proprietary HD Radio system developed by iBiquity Digital Corporation, which transmits energy beyond the allotted 100 kHz FM channel, was the first and currently only digital technology approved for use on AM and FM broadcast frequencies by the Federal Communications Commission in the United States.
Interference concerns with neighbouring channels may arise as a result of this. With over 1,556 stations transmitting HD radio in the United States, plus over 800 new multicast channels, this is the most widely used technology (as of Jan 2010).
There is a one-time licence fee to iBiquity Digital for the use of its intellectual property, as well as new equipment expenditures that range from $50,000 to $100,000 per station in the United States (2010).
FMeXtra
The other option is Digital Radio Express’s FMeXtra, which employs subcarriers within the existing broadcast instead.
This system was only recently implemented. The system is compatible with RBDS and HD Radio in hybrid mode, but not in all-digital mode. The stereo subcarrier can be eliminated to allow more room in the modulation baseband for FMeXtra.
The system, however, is incompatible with other 67–92 kHz subcarriers that have generally fallen out of use. The system is significantly less expensive and hard to set up, requiring simply that it be connected to an existing exciter and no licencing requirements.
FMeXtra provides all of the user features of HD Radio, including multicast capabilities, which allows you to broadcast multiple audio programmes at the same time.
The aacPlus (HE-AAC) codec is used. With conditional access and encryption, FMeXtra can manage listening.
DRM
Digital Radio Mondiale permits several data streams to be transmitted at the same time as an audio signal. The VHF DRM mode supports bandwidths ranging from 35 to 185 kilobits per second and up to four simultaneous data streams, allowing 5.1 surround DVD grade audio to be transmitted alongside other multimedia material such as photos, video, and HTML.
While broadcasts digitally encoded using HE-AAC or xHE-AAC are not backwardly compatible with existing FM receiver equipment, DRM’s ability to operate within the internationally agreed FM spectrum of 88-108 MHz makes it a viable candidate for future adoption as countries begin to phase out analogue broadcasts.
Radio Broadcasting in High Definition
iBiquity also developed a mediumwave HD Radio system for AM broadcasting, which is the first digital AM broadcasting system approved by the Federal Communications Commission in the United States.
Injecting digital sidebands above and below the audible portion of the analogue audio on the principal carrier is used in the HD Radio system. This technique additionally injects further digital information on the phase-modulated component of the carrier, which is phase modulated in quadrature.
It is based on the AM stereo paradigm, where a digital signal is placed where the analogue stereo decoding information would be placed by the C-QUAM system.
Cam-d
Another option is CAM-D, which is more of an extension of the current system. Leonard R. Kahn, the father of AM stereo, invented it. It blends the treble with the analogue baseband after encoding it on very small digital sidebands that don’t interfere with neighbouring channels.
It is not designed to be multichannel capable, unlike the other two, preferring quality over quantity. Unlike the HD system, which iBiquity refers to as “hybrid digital,” the CAM-D system is a true analog-to-digital hybrid. Some engineers believe that with the correct engineering, CAM-D might be compatible with analogue AM stereo.
CAM-detractors D’s point to a number of flaws:
1. Because the system is primarily analogue, it will be subject to artificial interference and noise just like the current AM system.
2. There are virtually no receivers available for the system, and no major manufacturer has announced any plans to start producing them at this time.
3. The cost of retrofitting with CAM-D is higher than the cost of purchasing a new solid-state transmitter that is HD-ready.
MODES OF OPERATION AT THE IBOC
There are three modes of operation for the IBOC. IBOC enables for a Hybrid and Extended Hybrid mode of operation before switching to an All-Digital mode of operation, allowing for a smooth transition from analogue to digital.
Using orthogonal frequency division multiplexing (OFDM), the digital signal is modulated onto a large number of subcarriers that are sent concurrently.
Mode Hybrid
The digital signal is inserted within a bandwidth of 69.041 kHz, with 129.361 kHz on either side of the analogue FM signal in this mode. The IBOC Hybrid mode digital signal is broadcast in sidebands on either side of the analogue FM signal, with each sideband being approximately 23 dB lower in power than the FM signal’s overall output.
A Primary Main (PM) sideband refers to the hybrid sidebands. The host analogue stream could be mono or stereo, and it could also have additional communication channels.
The digital sidebands’ total power is 20 dB lower than the FM analogue carrier’s nominal power, with a power relative to total analogue FM power of 41.39 dB/kHz.
Hybrid Mode (Extended)
In this mode, extra digital signals are injected closer to the analogue signal, using a bandwidth of 27.617 kHz and 101.744 kHz on either side of the original FM signal.
To boost digital capacity, the IBOC Stretched Hybrid mode digital sidebands are extended towards the analogue FM signal.
The Primary Extended (PX) sidebands are the extended hybrid sidebands. The digital sidebands’ total power is 20 dB lower than the FM analogue carrier’s nominal power, with a power relative to total analogue FM power of 41.39 dB/kHz.
Different modulation methods are used by different radio systems:
AM (amplitude modulation) – in an AM transmitter, the modulation signal changes the amplitude (strength) of the radio carrier wave.
FM (frequency modulation) – in an FM transmitter, the modulation signal changes the frequency of the radio carrier wave.
There are many additional types of modulation that can be employed. In some cases, only one or both modulation sidebands are sent instead of a carrier wave. In the transmitter, the modulated carrier is amplified and applied to a transmitting antenna, which transmits the energy as radio waves. The information is transmitted to the receiver location through radio waves.
The radio wave produces a little oscillating voltage in the receiving antenna, which is a weaker version of the current in the sending antenna, at the receiver.
This voltage is applied to the radio receiver, which amplifies the weak radio signal before demodulating it to extract the original modulation signal from the modulated carrier wave. A transducer converts the modulation signal back to a form that can be used by humans: an audio signal is converted to sound waves by a loudspeaker or earphones, a video signal is converted to images by a display, and a digital signal is applied to a computer or microprocessor that interacts with humans.
DAB uses spectrum more efficiently than analogue FM radio, allowing it to provide more radio services for the same amount of bandwidth. However, if the bit-rate allotted to each audio programme is insufficient, the sound quality will suffer substantially.
Although DAB reception quality drops swiftly when the signal intensity falls below a crucial threshold, FM reception quality degrades slowly with the falling signal, enabling effective coverage over a greater region, DAB is more resistant in terms of noise and multipath fading for mobile listening. The MP2 audio codec was used in the first iteration of DAB.
IBOC Capabilities:
IBOC allows the broadcaster to set the desired audio quality and data transfer rate, but there is a trade-off between audio quality and data transmission rate, as one might assume. The audio quality is close to CD quality at 96 kbps, however data is limited to 1 kbps in Hybrid mode.
The bit rate can be modified in 8 kb/s steps with IBOC. Additional data capacity, exceeding that of today’s mobile phones (9–19kb/s), is accessible by delivering audio at the satellite DARS3 bit rate of 64 kb/s.
When audio quality isn’t as crucial, the audio bit rate can be as low as 48 kbps, but the audio quality will be similar to that of a telephone.
The analogue and digital audio channels in IBOC are separated by a 4.5 second delay. The receiver first collects the analogue signal before beginning to decode the audio on the digital sidebands, which takes a few seconds.
The IBOC receiver reverts to the analogue signal if 10% of the digital data blocks sent during transmission are damaged. IBOC’s “blend-to-analog” feature is what it’s called.
The audio quality of the blend process is believed to be the same as that of analogue audio, and the procedure does not lower the audio quality below that of analogue.
Field experiments show that Hybrid FM IBOC digital coverage is comparable to analogue coverage, although IBOC reception is possible in regions where analogue service quality is already poor due to interference such as co-channel interference, impulse noise, and multi-path fading.
The following are some of the alleged advantages over standard analogue FM broadcasting:
• Near-total immunity to common FM multipath reception
problems;
• Full stereo coverage has been considerably increased;
• the ability to cast data in a variety of ways: and
• a cost-effective way for FM broadcasters to begin the digital transition
• IBOC’s use of OFDM enables for on-channel digital repeaters.
Conclusion:
Within the emission requirements, the three modes of operation in the IBOC emission spectrum fell in love with Australian FM sound broadcasting services. The introduction of hybrid IBOC digital transmission for the presence of signal and noise reduced the potential for a considerable loss in home stereo receiver and portable radio receiver host analogue audio quality, according to objective test results.
It should be evident that this is not a car radio receiver (highly selective reception). Subjective evaluation of the ABC environment without quality analogue audio from the host to introduce any substantial difference in the IBOC.
The introduction of hybrid IBOC digital transmission has a reduction potential of a first adjacent analogue audio quality, the automobile radio receiver, the audio signal by – lowering noise, according to objective test results. In the objective and subjective evaluation of test outcomes in the United States, worse audio quality is recorded.
In Australia, this effect is unlikely to be significant because a higher rate of protection is being planned for protection against initial adjacent channel interference.
The effect of an extension of hybrid IBOC digital transmission and digital analogue hosts, as well as neighbouring channel audio quality, has not yet been assessed in the United States.
