Bob, I found some more reading re:LMDS,MMDS
in general higher frequency more bandwidth
for example NexLink in US paid about 1 billion $ for lincense
techweb.com
"
Is all this having much of an impact on LMDS rollout plans?
Not much, according to Carlton O'Neal, vice president of
marketing at LMDS startup Ensemble Communications Inc.
(San Diego). As a licensed service having to deal with the
hassles of line-of-sight antenna placement such as roof access
to public buildings, LMDS technology was always anticipated
to take longer to deploy than MMDS, O'Neal said. But its
ability to scale to speeds common in the DSL and
cable-modem worlds makes the service much more attractive
than those in lower frequency bands, according to Ensemble"
------------------------
Data Communication article about Broadband Wireless:
data.com
"Also, because the unlicensed bands are available to anybody,
performance can be lower if different providers choose to offer
competing services in the same area. Two ISPs (Internet service
providers) operating in the same coverage area could limit throughputs
to half of what might normally be possible, for instance. And since
there are no governing bodies overseeing unlicensed spectrum, the
carriers have to figure out a solution. Still, in spite of these limitations,
such services could be very attractive to smaller and medium-sized
businesses because they?re very competitively priced. As for
low-frequency bands that offer more bandwidth, there?s MMDS
(multichannel multipoint distribution service), at 2.5 GHz. It has 200
MHz of bandwidth, and since it is a licensed band, interference from
other providers is not an issue. A number of ISPs are using the
MMDS band to target small and medium-sized businesses, in some
cases relying on a hybrid approach?wireless for the downlink and
PSTN (public switched telephone network) for the uplink. In general,
lower frequencies translate into much larger coverage radii, as large as
35 miles. Both Sprint Corp. (Kansas City, Mo.) and MCI Worldcom
Inc. (Jackson, Miss.) have acquired companies with MMDS spectrum
so they can use wireless for the local loop.
Higher frequencies (24 GHz or above) are sometimes called the
millimeter wave band, because of the millimeter size of their
wavelengths. These licensed bands are much larger, and at 28 GHz, the
LMDS band, carriers have more than 1 GHz to work with. With
modulations offering an effective throughput of 1 bit per second (4
QAM, or quadrature amplitude modulation) to about 4 bit/s (64 QAM)
for every Hz of frequency, 1 GHz represents up to 4 Gbit/s of
aggregated throughput (after coding overhead). However, this rate gets
divvied up among customers and between neighboring cells or
portions of cells called sectors. At these higher frequencies, connection
distances shrink to about two miles. Since the bands are licensed, users
should experience no interference. |
