Thinking of broadband access for the last-mile–now being
recognized as the first-mile–everyone talks about optical fibre or ADSLs.
However, frustrated by the complexities, cost and time involved in digging and
laying optical fibre–or implementing DSL, with only 1.5 Mbps to offer, on
incumbent's copper infrastructure–one would certainly like to look for an easy
way out. And that is offered by the air. Air space represents higher freedom and
the ability to move fast. That has made wireless the fastest transmission medium
to deploy, and generally inexpensive too. Microwave technology has truly come to
the rescue there.
George Gilder, in his latest book "Telecosm", says,
"Above 14 GHz–at wavelengths running from millimeters of microwaves down
to the nanometers of visible light–is the new frontier of the millenium,
empires of air and fibre that command some fifty thousand times more
communications potential than all the lower frequencies we now use put together.
A purely human invention, they provide the key arena of economic activity for
the new century." Rightly, to be able to exploit the freedom associated
with air, one looks to microwave technologies.
The First-Mile: Missing Gigabit Link
Advances in fibre technology have extended the capacity of
WANs to terabits per second–i.e. trillions of bits per second. With gigabit
computers and gigabit Ethernets, LANs have also evolved to Gbps. However, to
connect the two is still the biggest challenge: to help solve the customer's
nightmare of crawling at kilobits speed, which a typical Internet user faces,
between these gigabit worlds.
The LMDS Way
Local Multipoint Distribution Service (LMDS) is an ideal
solution for bringing high-bandwidth services to homes and offices within the
last-mile–an area where cable or optical fibre may not be convenient or
economical. Having architectural similarities with cellular networks, LMDS is a
fixed (non-mobile) point-to-multipoint wireless access technology that typically
operates in the 28 GHz band and offers Line-of-Sight (LoS) coverage up to 3-5
km. Depending on the local licensing regulations in a country, such broadband
wireless systems may operate anywhere from 2 to 42 GHz.
Though data transfer rates for LMDS can reach 1.5 to 2 Gbps,
in reality it is designed to deliver data at speeds between 64 Kbps to 155 Mbps
(as against 9.6 Kbps offered by 2G cellular networks like GSM), a more realistic
downstream average being around 38 Mbps.
Vendors are taking steps to meet the fast increasing demand
for capacity. For instance, Giganet has expanded its 115 Mbps products to handle
higher data rates and has introduced upgrades to its FibreAir product to deliver
311 and 622 Mbps data rates using the same amount of spectrum. In the US,
operators could offer as much as 622 Mbps using the typical 50 MHz wide channel.
Giganet also offers ability to interface with various transport protocols,
including IP, ATM and Sonet, the solutions being available in a range of
frequencies.
At such speeds, LMDS may be the key to bringing multimedia
data–supporting voice connections, the Internet, videoconferencing,
interactive gaming, video streaming and other high-speed data applications–to
millions of customers worldwide over the air.
As with other wireless networks, LMDS technology offers the
advantage that it can be deployed quickly and relatively inexpensively. New
market entrants who do not have an existing network–like incumbent's copper
wires or fibres–can rapidly build an advanced wireless network and start
competing. LMDS is also attractive to incumbent operators who need to complement
or expand existing networks. For example, operators who are setting up a service
primarily based on DSLs, but who want their service to be universally available,
could use it to fill in the gaps in their coverage. And while cable modems are
making inroads into the residential (and home-office markets), the business
market is the niche for LMDS.
LMDS operates in a large–previously unallocated–expanse
of the radio spectrum, thus offering a huge bandwidth opportunity, hitherto
unexploited. In the US, the Federal Communications Commission (FCC) auctioned to
LMDS operators a total bandwidth of about 1.3 GHz in the 'millimeter' waveband
at frequencies of about 28 GHz. Canada has 3 GHz of spectrum set aside for local
multipoint communications systems (digital cellular phone systems operate at
about 800 or 900 MHz with a typical bandwidth allocation of 30 MHz or less).
Recognizing LMDS as a means of beaming data and voice over
short distances to a switching office, McCaw's Nextlink, in mid-1999, paid
nearly $700 million to purchase LMDS licences and the spectrum with aim to
provide fixed wireless coverage for 95 percent of the US population.
How LMDS Works
Sending digital signals of the required complexity at 28 GHz
is made possible by recent advances in technologies such as Digital Signal
Processors (DSPs), advanced modulation systems and Gallium Arsenide (GaAs)
integrated circuits, which are cheaper and function much better than silicon
ones at these high frequencies.
Unlike a cellular mobile phone network, in which a user can
move one cell to another, the transceiver of an LMDS customer has a fixed
location and remains within the same cell. Normally the customers' antennas are
located on rooftops, to get a good LoS to the hub transceiver.
It Has Limitations Too
Like in other microwave applications, LMDS cell size too is
limited by "rain fade", i.e. distortions of the signal caused by
raindrops scattering and absorption of the waves. Also, walls, hills and even
leafy trees block, reflect and distort the signal, creating significant shadow
areas for a single transmitter. Some operators may serve a cell with several
transmitters to increase coverage; most prefer one transmitter per cell, sited
to target as many users as possible.
Positioning: The Marketing Advantage
The fast deployment helps to capture a customer fast.
However, another advantage–faced with a high churn of customers–of the
technology is the ability to move around the hub equipment to different customer
locations. It is a distinct advantage against the networks of wires, cables, and
fibres. Also, LMDS systems send data using asynchronous transfer mode, which
allows a mixture of data types to be interleaved. Thus, a high-quality voice
service can run concurrently over the same data stream as Internet, data and
video applications. LMDS can be positioned as a versatile, cost-effective option
for both providers and users of broadband services, using the rapid and
inexpensive deployment.
Initially, LMDS operators target SMEs in densely populated,
urban areas because of the technological requirement of LoS between the hub base
station and the buildings served and the signal propagation range of one to
three kilometers.
There are 11 significant LMDS operators in US–the biggest
ones being Advanced Radio Telecom (ART), NextLink Communications, Teligent, and
Winstar. NextLink, founded by Craig McCaw in 1994, holds the largest number of
28 GHz LMDS licences there. The company has launched commercial services in five
of its markets and expects to be operational in 25 markets by the end of this
year. Earlier this year, NextLink also bought national ISP Concentric Networks,
which enables NextLink to expand its DSL, virtual private network and
Web-hosting services.
According to the Strategis Group, by year 2003 LMDS network
coverage will be close to 20 percent of businesses as against 5 percent
presently. According to IGI Consulting, at the end of 2000 there will be 26,000
LMDS business users, growing to 5,10,000 by 2003.
Action in Asia Pacific
Hong Kong was one of the firsts to issue LMDS licences. The
Infocomm Development Authority (IDA) of Singapore approved three organizations
to conduct LMDS trials in early 2000. For example, one of them, Pacific
Internet's trial will include Broadband Internet (i.e. over 2 Mbps),
Video-on-Demand, Voice-over-IP, high-speed digital data transmission, as well as
conventional voice calls. It will thus explore opportunities in providing
broadband data access to selected corporate and residential customers. It will
use ultra high frequency microwave in the 25-31 GHz frequency range to send and
receive two-way broadband signals through the base station installations atop
buildings. Pacific Internet considers the advantages of LMDS as greater
bandwidth than radio, TV and cellular combined, and a low start-up cost relative
to costs incurred in installing broadband wireline networks. In Singapore, the
heavy rain interference with signals may limit the distance between cells to 1.5
km.
Now in India
In India too, operators like Gateway Systems are offering
LMDS solution. Initial focus is on business customers mainly in large cities
like Mumbai, Pune, Delhi, Bangalore, etc., which have concentration of offices
or apartments located in high-rise buildings.
The day is not far when the thin air will help deliver to us the broadband
applications running all the way on the fat fibre-optic pipes, putting George
Gilder's empires of air and fibre at mankind's service.
Niraj K Gupta
www.telecombyNirajGupta.com