SOMEWHERE OUT THEREYou might not have noticed that QPSK and QAM are different. Okay, I guess you probably have noticed that, but it looks as though Our Bye-bye Commish (OBC) didn't, and that could be bad news for DTV broadcasters and viewers.
I don't know. Maybe I'm being too broad (and no cracks about my girlish figure, please!). As I'm sitting here writing this, four out of five of the FCC commissioners that were there before Jan. 19 are still there. Only Lord Chief High Hoo-Hah Kennard has left. But, just as President Bill Clinton left a legacy, so, too, did L.C. Triple-H Bill Kennard – and they both did one whole heck of a lot of it in their final week in office.
The bit of Kennard legacy that Nellie the Neuron is insisting that I rant about this lunar cycle is the DTV-cable must-carry order. To sum up the 91-page document, if you're a broadcaster with one channel (analog or digital), cable ops have to carry you. But, if you're transmitting both analog and digital, then you can choose must-carry only for the analog.
Oh, yeah – one more thing: Even though the other big DTV order of the last days of L.C. Triple-H Kennard's era said that over-the-air U.S. DTV is going to be 8-VSB, purely 8-VSB, and nothing but 8-VSB, the DTV-cable order said – oh, heck. Why don't I just let the thing speak for itself? Here's the first part of paragraph 76:
"Digital Modulation Techniques. We are mindful that digital television signals are transmitted in the 8-VSB digital broadcast modulation technique while operators will use either 64 or 256 QAM as the cable digital modulation technique. Both 64 and 256 QAM likely will provide cable operators with a greater degree of operating efficiency than does 8-VSB, and also permits the carriage of a higher data rate, with fewer bits devoted to error correction, when compared with the digital broadcast system. Therefore, we will permit cable operators to remodulate digital broadcast signals from 8-VSB to 64 or 256 QAM. We will not require cable operators to pass through 8 VSB."
The rest of the paragraph just says that if some cable op, by some strange quirk, actually wanted to ignore that spectrum efficiency and transmit 8-VSB, it could. Does the above sound hunky-dory to you? Alrighty, then, I guess I'd better hit you with the opening sentence of paragraph 79:
"We will not require a cable operator to provide subscribers with a set-top box capable of processing digital signals for display on analog sets."
Do you see a pattern beginning to emerge here? No? Please allow me to be of assistance.
There was another big FCC document issued in January, the 136-page 7th annual competition report. It says that, as of June of last year, 67,700,000 U.S. households were subscribed to cable TV. Give or take a few million, that's two-thirds of all the households in the country.
Now, then, I ain't one of those who believe that the 2006 date for mandatory retirement of NTSC at age 65 means a hill of beans, but at some point, unless everyone colossally screws everything up (which has been known to happen in the past), NTSC will be shut down. Maybe it'll be in 2025 – maybe later – but it probably is going to happen.
I suppose it's time for a brief recap:
1. Our Bedazzled Commish says the modulation standard for broadcast DTV is 8-VSB. Period. End of story.
2. Our Benevolent Commish says the modulation standard for cable doesn't have to be 8-VSB. As a matter of fact, OBC points out danged good reasons why a cable op would choose QAM over VSB.
3. Our Bemused Commish says cable ops do not have to provide QAM set-top boxes (STBs).
Hey – no problem! Consumers will just buy their own DTV STBs. As of this year, there's suddenly a whole mess of the little buggers on the market, from the DISH, Hughes, Mitsubishi, Panasonic, Philips, RCA, Samsung, Sony, Toshiba and Zenith brands. Ayup, that must be what home viewers can do.
"Mario, are you trying to say something here?"
Gee, I suppose I am. Every one of those there set-top boxes has an 8-VSB demod in it (the DISH one only if you get the over-the-air receiver card). And every one of them is also equipped for QPSK satellite reception.
'Twasn't ever thus. The first U.S. DTV STBs were equipped to demodulate 8-VSB (not even NTSC). Unity Motion and RCA later introed STBs that included satellite reception.
CAN'T ADD COFDM
Back around when the only U.S. STBs were 8-VSB, Sinclair asked to have COFDM added as a transmission option. They were shot down by folks saying (among other things) that it'd be too danged expensive to add COFDM demod capability to a DTV STB.
So, you can't add COFDM on account of it'd be too expensive, but you can add QPSK (with decoding for a completely different datastream, which gets there only if viewers add dishes) and end up dropping the price of the receivers. Hey – I suppose it makes some kind of sense to someone. But I promise I ain't going to rant this lunar cycle about the COFDM issue.
Nosiree! You won't find me pointing out that NxtWave's COFDM demod chip is just $15 in quantity versus $20 for the 8-VSB, and I'm not going to mention something I just saw on the Web about Oren having a new chip, the UX51365, that demods both 8-VSB and COFDM and even has a ghost canceller for NTSC! I would have checked it out for you on Oren's Web site, but that was last updated in July of 2000.
No, my lips are sealed. You won't see the term COFDM appearing anywhere in this column. But I would like to explore a wee bit about that QAM stuff.
Suppose you live in Houston and have Time Warner Cable. Suppose you like the good old Sony KW-34HD1 DTV, with a built-in 8-VSB receiver. It doesn't really matter whether it's a good 8-VSB receiver or not. Every 8-VSB receiver ever made will deliver lovely pix and sound from any old cable op's 8-VSB signal distribution. But that ain't why it doesn't matter whether it's a good 8-VSB receiver or not.
It doesn't matter on account of Time Warner Cable of Houston carries DTV as QAM. The Sony receiver can't demodulate that. You have to use the box provided by the cable op, which Our Beloved Commish says they don't have to provide. Clear?
On the other hand (where – hint to my secret identity! – I have five fingers), suppose you live on the island of Manhattan, where the very same Time Warner Cable op offers WCBS-DT. Suppose you buy an HD display only, figuring you'll get it fed from the HD cable box (which the cable op, once again, doesn't have to provide).
What HD cable box? The east-coast version of Time Warner Cable is using 8-VSB at the moment (for what little broadcast DTV they carry), even though the gulf-coast version is using QAM. You've got to go out and buy one of those there 8-VSB receivers with the built-in QPSK demod, even though the chance of your getting direct satellite service in the canyons of Manhattan island are kind of slim.
Oh, and there's another problem. If you want to watch the digital cable channels, you do need a QAM receiver; it's only for the WCBS-DT broadcast stuff (and, I'm told, HDTV HBO) that you need 8-VSB. So one of your STBs is really an STBTB (a set-top-box-top box).
I ranted once before about the tower of boxes you might need for everything, but chipmakers are coming to the rescue. Conexant's CX24420 has a QAM demod, two channels of PVR (hard-drive recorder), and a cable modem all in one package. But it ain't got 8-VSB demod capability.
Heck – don't let that bother you! There are other chipmakers in the world. Aside from that 8-VSB-COFDM chip I refused to mention to you earlier, Oren makes the OR51220 and the OR51221. Both of them demodulate both 8-VSB and QAM. Ditto for Broadcom's BCM3510. Ditto for NxtWave's NXT2000 and NXT2002.
TO THE RESCUE
Ayup, the chipmakers have come to our rescue by providing both QAM and 8-VSB demod capability. But, near as I can figure, out of the 10 brands of DTV STBs I listed earlier, give or take a little, I'd say roughly zero will work with a digital cable system. Zip. Zilch. None of them.
They've all got QPSK for satellite reception, which is probably a good idea on account of broadcast 8-VSB reception tending to be kind of spotty and almost no cable ops carrying any broadcast DTV. With the QPSK, folks with line-of-sight to the right satellite can at least rely on some HDTV reception.
So, time for another recap?
1. Two-thirds of U.S. homes watch TV via cable.
2. Our Beloved Commish said that cable doesn't have to carry DTV channels at all during the transition period.
3. When we're down to just DTV transmissions, they do have to carry them, but they can change them into QAM, so integrated receiver-displays are useless for demodulating the signals. So are combo 8-VSB-QPSK set-top boxes.
4. All current DTV STBs are combo 8-VSB-QPSK.
5. Our Beloved Commish says cable ops do not have to provide QAM demods to customers.
Oh, heck – maybe I'm painting too bleak a picture. First of all, as I said before, almost no cable systems are carrying any DTV signals, so there's nothing to worry about. Second of all, Our Beloved Commish promises to take another look at this sometime after 2003.
See? All is well.
Future US's leading brands bring the most important, up-to-date information right to your inbox
Thank you for signing up to TV Technology. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.