[BC] Another Method for Digital Radio Broadcasting

[David L. Hershberger]

Hi Mark,

My understanding is that ISDB-T is similar to DVB-T, which means it is
basically COFDM. However, I believe that ISDB-T includes better interleaving
than the DVB-T standard for better rejection of impulse noise. So, the
Japanese system is much closer to the European system than the American ATSC
system. Receiver improvements have benefitted the ATSC system much more than
the COFDM systems in the last few years, so I think that A-VSB holds better
promise. The single carrier systems (such as 8VSB and A-VSB) give better
noise threshold performance and better weak signal multipath performance,
using the best receiver techniques available today.

The bit rate available for A-VSB packets is adjustable, but I would say that
up to 1.25 megabits of actual payload capacity could be allocated for A-VSB
before hitting the "threshold of pain" on the video payload. (But that will
depend on how many video streams are being broadcast and whether any are
HDTV.) A-VSB uses a 1/4 rate code to get its most robust performance
(necessary for mobile reception). So that means that if you steal 5 megabits
away from video, you get the 1.25 megabits of usable A-VSB payload. The
reduced bit rate for the A-VSB packets is the price that is paid to get the
outstanding mobile and noise performance from A-VSB. The payload of an 8VSB
signal is 19.39 megabits. So if 14 megabits is allocated to TV, and we can
take up to 5 megabits for A-VSB packets and the A-VSB training sequences,
then we can have a lot of radio programs on one TV transmitter. As video
encoders continue to improve, that will free up more A-VSB packet capacity
for a given video quality level.

But for radio use, 1.25 megabits is plenty. You can put a Whole Bunch of
radio signals in that - around 19 good quality stereo programs at 64
kbits/sec, and more than that if some of the radio signals are mono, using
the best coding techniques available today. If you only wanted to put one or
two radio programs on a TV transmitter, the effect would be negligible.

There have been other schemes to transmit internet packets, pay TV, etc.
over "excess capacity" on DTV signals, but using some of that capacity for
radio makes a lot more sense to me, especially for AM broadcasters.

Dave


----- Original Message ----- 
From: Mark Humphrey
To: Broadcasters' Mailing List
Sent: Thursday, December 14, 2006 10:23 AM
Subject: Re: [BC] Another Method for Digital Radio Broadcasting


On 12/13/06, David L. Hershberger <dave at w9gr.com> wrote:

> There is another way to do digital radio broadcasting - use DTV
> transmitters.  Comments are welcome.

Dave,

Isn't this similar to the approach taken in Japan?  I believe the
Japanese use the same means of transmission (ISDB-T) for both TV and
digital "radio" services.  Like A-VSB, it supports mobile reception as
well as on-frequency repeaters, but the ISDB modulation scheme is
different.

Do you know how many bits/sec an A-VSB channel would provide?

It sounds like a workable technical solution for "truly portable"
digital radio, but I'm afraid the "defenders of the status quo" here
in the US will take legal steps to block that use.

Mark