Hi Chaz:
Although DOCSIS compliant modems will have reasonable
margins early on, I expect that over time they will become
a commodity. So price will matter a lot. Within this context,
the Universal cable modem that Terayon is contemplating
will probably be very expensive since in addition
to the basic DOCSIS 1.0 mode of operation, it will be
backward compatible with Terayon's current cable
modems (S-CDMA both ways), and forward compatible
with what Terayon hopes to be the DOCSIS 2.0 standard
(QAM downstream, S-CDMA upstream). IMHO, Terayon should
just try to focus on the QAM downstream, S-CDMA upstream
solution, since it offers the most promising technical choice.
Terayon's current S-CDMA modem offers only about 15Mb/sec
transmission per 5MHz channel in both the downstream and
upstream directions. The 256 QAM downstream format allows
at least 40Mb/sec per channel, so it is a better
downstream solution. For upstream modulation, the current
15 Mb/sec offered by S-CDMA is quite good, particularly
for pure coax networks.
Regarding to Geof's comment about Terayon's CTO making
claims which are hard to believe, I suspect this refers
to the claim that the new S-CDMA upstream modulation
scheme will allow 30Mb/sec per 5MHz upstream channel,
or 6 bits per Hertz. This is an unbelievable level
of spectral efficiency for CDMA. This claim certainly
deserves close scrutiny. As a benchmark, IS-95 carries
about 1 bit/Hz (it uses QPSK, but the same data sequence
and two different chipping sequences are used for the
in-phase and quadrature components of the signal).
admittedly, IS-95 is unsynchronized, while for S-CDMA,
all stations are synchronized, but the level of
spectral efficient advertised by Terayon stretches
credulity.
Concerning the superiority of DMT for noise robustness,
I agree that Ultracom would be expected to make this claim,
but based on general communications principles, the
multicarrier approach represents the best way of
allocating transmitted bits to frequency bands with
a higher signal to noise ratio. The problem of DMT
is its high hardware complexity.
Finally, I forgot to mention in my earlier posts that
Terayon has strong support in Japan. Like IS-95,
it looks like Asia might come to the rescue of S-CDMA.
Best regards,
Bernard Levy |
