Not Just for Backhaul Anymore: Cable Expands Wireless Links2/13/2000 7:00 PM Eastern
A new generation of wireless-broadband systems now entering
the production stream may finally mean that the tools are at hand to make over-the-air
connectivity a viable alternative to wireline systems for a growing list of potential
users, including cable operators.
Cisco Systems Inc., for example, named the first customer
for its new point-to-multipoint VOFDM (vector-orthogonal frequency-division modulation)
system, and it is working with several cable operators to test the technology for various
They include point-to-point backhaul between headends and
remote hubs and point-to-multipoint connectivity to the business community, Cisco director
of marketing for broadband wireless Steve Smith said.
"We have a large customer in the cable space
who's doing backhaul to cable headends using our point-to-point system," Smith
said. "They're using it over a 15-mile link where the costs of using fiber would
be much higher."
The unnamed operator and others testing the gear for such
applications are operating over unlicensed spectrum at the 5.7-gigahertz tier, which is
one of the many frequency categories targeted by Cisco and other providers of the latest
crop of point-to-multipoint systems.
Initially, Cisco had been uncertain about whether to make
the technology available at the very high-frequency "millimeter" tiers such as
LMDS (local multipoint distribution service), but the company has decided that the market
need in that category merits development of product, Smith said.
Along with providing a robust substitute for fiber in
backhaul applications -- a mainstay of microwave applications in cable for decades -- the
new technology supports two-way point-to-multipoint services including DOCSIS-based (Data
Over Cable Service Interface Specification) data and voice.
This has strong appeal for operators that want to extend
their new data-service platforms into the business community, Smith noted.
"Cable doesn't pass a lot of the strip malls and
industrial parks where there's an opportunity to generate significant new revenues
from the data-networking platform operators already have in place," he added.
Cable-industry interest in wireless broadband is indeed
intensifying, given the availability of ever more unlicensed and licensed spectrum, as
well as improved technology that makes serving the business community a viable option for
cable operators, Cable Television Laboratories Inc. president Richard Green said.
"We'll continue to monitor the technical
developments closely, building on the foundation we laid in wireless when we started
looking at PCS [personal-communications services] several years ago," Green added.
CableLabs board members did not add a formal initiative in
this area to the organization's already-crowded agenda at its latest board meeting,
Green said. But the combination of ongoing CableLabs research in the technology and
individual MSO test initiatives may be all that operators need to determine whether the
wireless route is worth taking, he added.
The first publicly announced user of Cisco's
point-to-multipoint system -- ASICs (application-specific integrated circuits) for which
are being developed by Broadcom Corp. -- is MMDS (multichannel multipoint distribution
service) operator Nucentrix Broadband Networks Inc., which controls licenses in 87
Midwestern and Texas markets.
Nucentrix -- which is now operating high-speed two-way data
services commercially in Austin and Sherman, Texas, under development licenses -- plans to
switch to the Cisco platform as quickly as possible following a round of testing
that's slated to begin in April, CEO Carroll McHenry said.
"Our plan is to be able to deploy on a wide scale by
the fourth quarter, but that's highly dependent on the outcome of the trials and the
timing of the licensing process," McHenry said, noting that some 40 of 57 currently
operating markets should be operational with two-way data services by the end of 2001.
"In the short to medium term, we're targeting the
SOHO [small office/home office] and small-business markets, but we expect to expand into
the residential market with these services, including voice, as equipment volume goes up
and prices come down," he added.
The Cisco system offers a more viable approach to offering
interactive services over MMDS than current-generation platforms, McHenry said.
He cited the new orthogonal-modulation system and the
multipath signal-integration technique of the VODFM platform as key differentiators, along
with the fact that the system can be implemented on DOCSIS-based circuit cards inserted
into Cisco routers.
These efficiencies make it possible to offer a robust
symmetric service at multiple data rates with coverage to non-line-of-sight locations from
a single transmitter, McHenry noted. "Very likely, we will sectorize our transmitters
first, then move to multiple-transmitter deployments as our customer base grows to
accommodate demand," he added.
Cisco isn't alone in using a wireless adaptation of
the cable industry's DOCSIS platform as a means of providing highly integrated
multitiered classes of service in the wireless domain.
A longtime player in the field, the former Phasecom Inc.,
now renamed Vyyo Inc., introduced a point-to-multipoint system based on "DOCSIS
Plus" that will operate at any spectrum tier, from the UHF band all the way to 30
GHz, vice president of systems management Eric Wilson said.
"Our architecture takes advantage of the data-side
access and QoS [quality-of-service] management capabilities of DOCSIS, while adding
enhancements to optimize the system for wireless," Wilson said, noting that the
system operates in native packet formats downstream, while using time-division
multiplexing for return transport.
The core of the system is a base-station chassis with
plug-in space for six modules supporting multiple configurations of downstream and
upstream transmission capacity, which will soon include provision for 16 and 64 QAM
(quadrature amplitude modulation), as well as QPSK (quadrature phase shift key), he noted.
The company is also working on adding new levels of
flexibility to the system by providing for dynamic allocation of bandwidth across the
various subchannels of a 6-megahertz channel, Wilson said.
By using the sectorization capabilities of Vyyo's
transmitter system, operators can allocate multiple shared-usage channels, effectively
doubling capacity, he added.
"If you reuse the frequency over five channels
pointing in opposite directions in the north and south sectors and five channels in the
east and west sectors, you are supporting the equivalent of 20 channels of capacity from a
single transmitter," Wilson said.
Vyyo also took steps to combine and equalize multipath
reflections to bring the microreflection time gaps to within the tolerance levels of the
DOCSIS wireline environment -- on the order of 1 to 2 microseconds, versus the typical 8
to 10 microseconds encountered in the wireless domain, he added.
"Being DOCSIS-compatible allows us to take advantage
of the inherent data and voice-over-IP [Internet protocol] capabilities," Wilson
noted, adding that the firm would be DOCSIS 1.1-compliant with gear that it plans to ship
three to four months from now.
Another vendor pegging its fortunes to a more IP-friendly
transmission environment is Ensemble Communications Inc., which is now in field trials
with two of the top five wireless carriers, according to vice president of marketing
While the company originally expected its product release
in the second quarter of this year to put it in a catch-up position with providers of
previous-generation equipment, the failure of that equipment to take off and the resulting
slow pace of wireless-broadband rollouts has greatly improved Ensemble's prospects,
"The air links available up until now have not been
sufficiently flexible to support the pricing and usage models that you need to compete in
the real world," he added.
Along with providing the mechanisms for dynamically
assigning bandwidth at preset pricing levels, the system provides support for bursting
large quantities of data on top of the guaranteed service a given customer has signed up
for, O'Neal said.
Because such bursts can be accommodated via unused portions
of a given channel stream at any given moment, this means operators can assure customers
that they'll have added bandwidth available when they need it, while maximizing the
number of customers served by any one channel.
O'Neal said other features of the Ensemble
"Adaptix" air-link protocol include the use of adaptive time-division duplexing,
which allows variable rates of data to flow in both directions over a single channel;
adaptive TDMA (time-division multiple access), which supports variable packet lengths to
maximize burst-rate bandwidth efficiency; and adaptive modulation, which provides for
delivery of signals over the highest level of modulation that's feasible at a given
moment in the fluctuating atmospheric environment of the transmission path.
While Ensemble's system will register at about a 6 on
a scale of 1 to 10 in the pricing of wireless-broadband systems, the overall cost of
infrastructure based on its technology versus other systems will be much lower, due to the
flexibilities the company has built into the technology, O'Neal said.
The system -- which includes 64 QAM as one of the
dynamically assignable modulation options -- operates over any frequency tiers between 10
GHz and 43 GHz.