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The HD Multiplex: What Will Be Possible?

Philipp Schmid discusses his paper on the HD Mulitiplex, which he will present at the NAB Show Broadcast Engineering Conference

In anticipation of this year�s Broadcast Engineering Conference at the NAB Show, we got in touch with Nautel’s�Philipp Schmid, who will discuss his paper on the HD Mulitiplex. His presentation will be held Saturday, April 16, at 3:25 p.m., in conference room S219.

Radio:�Your presentation is titled, �Digitizing Terrestrial Radio.� Briefly, can you summarize the subject matter of your overall presentation for those who may not be able to see it?

Schmid: At the Ennes workshop, I will be speaking on Nautel�s revolutionary HD Multiplex technology concept that allows broadcasters to combine multiple HD Radio transmissions to create a single all-digital multiplex of audio services. The hybrid FM+HD Radio adoption is well underway with key markets, such as New York, now approaching 20% (18.6% Dec 2015) of cars on the road being equipped with HD Radio receivers. Now is the time to plan for the future and look towards all-digital broadcasting and leave behind the shackles of a hybrid simulcast consisting of both the analog and digital signals. The presentation will provide an overview of the technology but mostly cast a vision of what will be possible with HD Multiplex.

Radio:�Let�s talk about the potential impact the HD Multiplex could have on the consumer, what is the HD Multiplex?

Schmid:The HD Multiplex takes three or more independently modulated In-Band-On Channel (IBOC) signals used in HD Radio and shifts them in frequency to land on adjacent radio dials and adds them together. Nautel�s innovation is in the way we control the signal to be efficiently broadcast in our transmitters. I can demonstrate up to 15 audio services emitted from a single transmitter receivable on common HD Radio receivers deployed today. The demonstration will be shown on Nautel’s booth (N2522) and can also be viewed online at Nautel�s website.

What makes this technology attractive is that it solves the chicken-and-the-egg problem of who will broadcast the signal if there are no receivers and who will buy receivers when there are no signals to be received? Being backward compatible with existing receivers means that this technology already has over 30 million receivers to draw on, paving the way for a quick adoption of the concept. Even if only 20% of my listener base is able to tune into HD Multiplex today, turning my single FM audio service into 9-15 exclusively digital audio services can already be as profitable for the station, provided the content is compelling. Increasing HD Radio adoption and penetration now presents a huge growth opportunity for my station.

Radio:��Describe the HD Multiplex�s impact on AM and FM bands.

Schmid:It is no secret: the FM band is full in urban markets all over the world; FM has reached its capacity and over packing the FM band can have negative interference effects. HD Multiplex solves this problem through improved spectral efficiency in two ways.

Firstly, HD Radio can deliver four to five times more audio streams per Hz of bandwidth compared to FM.�

Secondly, the HD Radio signal is more robust compared to FM allowing unrelated transmissions to be short spaced with less dead zone in the middle. Only HD Multiplex can leverage those two benefits together. What this means is that we can take todays offering of about 30 stations or audio services on a typical radio dial to 300 audio services along with broadcast data services such as weather and traffic. The added channel capacity will allow AM broadcasters to move into the FM band and enjoy better sound quality and lower transmission costs. In the U.S., AM broadcasters are presently given the opportunity to apply for a translator in the FM band that can be located up to 250 miles from the main AM transmitter. Perhaps, these broadcasters should work together to collectively operate networks of digital HD Multiplex transmitters (one for each AM transmitter) to reduce transmission costs and gain the opportunity to be heard on multiple translators via side channels.

Unlike other digital audio broadcast solutions that make use of additional frequency bands, HD Multiplex will maintain the FM band for sound broadcasting as initially intended leaving the additional bands for other purposes like digital TV or cellular. Since HD Multiplex uses the same receiver base for FM, hybrid FM+HD and HD Multiplex, a gradual conversion of the band can be anticipated and a hard switch off is not required. Existing FM broadcasters may opt to convert to HD Radio by simulcasting on HD Multiplex on a different channel while maintaining the original FM broadcast. That way a family of stations may share the installation and operating costs of the HD Multiplex and go digital at the same time.

This Q&A will be continued in a second installment later this week. ��

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