Multipoint Distribution Service (LMDS)
Local Multipoint Distribution Service (LMDS), or Local Multipoint Communication
Systems (LMCS), as the technology is known in Canada, is a broadband wireless
point-to-multipoint communication system operating above 20 GHz that can be used
to provide digital two-way voice, data, Internet, and video services. The term
"Local" indicates that the signals range limit. "Multipoint"
indicates a broadcast signal from the subscribers; the term "distribution"
defines the wide range of data that can be transmitted, data ranging anywhere
from voice, or video to Internet and video traffic. It provides high capacity
point to multipoint data access that is less investment intensive. Services using
LMDS technology include high-speed Internet access, real-time multimedia file
transfer, remote access to corporate local area networks, interactive video, video-on-demand,
video conferencing, and telephony among other potential applications. In the United
States LMDS uses 1.3 GHz of RF spectrum to transmit voice, video and fast data
to and from homes and businesses. With current LMDS technology, this roughly translates
to a 1 Gbps digital data pipeline. Canada already has 3 GHz of spectrum set aside
for LMDS and is actively setting up systems around the country. Many other developing
countries see this technology as a way to bypass the expensive implementation
of cable or fiber optics into the twenty-first century.
fixed wireless network has been commonly deployed to offer high-speed dedicated
links between high-density nodes in a network. More recent advances in a point-to-multipoint
technology offer service providers a method of providing high capacity local access
that is less capital intensive than wireline solution, faster to deploy than wireline,
and able to offer a combination of applications. Moreover, as large part of a
wireless network's cost is not incurred until the Customer Premise Equipment (CPE)
is installed, the network service operator can time capital expenditures to coincide
with the signing of new customers. LMDS provides an effective last-mile solution
for the incumbent service provider and can be used by competitive service providers
to deliver services directly to end-users.
BENEFITS OF LMDS
The main benefits of LMDS are listed below:
1 Lower entry and deployment costs
2 Ease and speed of deployment (systems can be deployed rapidly with minimal disruption
to the community and environment)
3 Fast realization of revenue (as a result
of rapid deployment)
4 Demand based build out (scalable architecture employing
open industry standards ensuring services and coverage areas can be easily expanded
as customer demand warrants)
5 Cost, shift from fixed to variable components.
(For wireline systems most of the capital investment is in the infrastructure,
while with LMDS a greater percentage of investment is shifted to CPE)
stranded capital when customers churn.
7 Cost-effective network maintenance,
management, and operating costs.
Past communication technologies focused their attention lower in
the RF spectrum because low frequency signals with enough power could be sent
long distances and penetrate buildings. Such is the case with television and radio.
LMDS, however, uses low powered, high frequency (25 -31 GHz) signals over a short
distance. LMDS systems are cellular because they send these very high frequency
signals over short line-of-sight distances. These cells are typically spaced 4-5
kilometers (2.5 - 3.1 miles) apart. LMDS cell layout determines the cost of building
transmitters and the number of households covered. Direct line-of-sight between
the transmitter and receiver is a necessity. Reflectors and/or repeaters can spray
a strong signal into shadow areas to allow for more coverage. Various isolation
techniques can be used to prevent interference between signals.
size is also influenced by the amount of local rainfall. Because LMDS signals
are microwaves, they are attenuated by water and lose strength. To correct this,
LMDS operators can either increase the power of their transmissions when it rains
in an attempt to ensure a strong signal reaches its destination, or they can reduce
their cell size. Leaves, trees and branches can also cause signal loss, but overlapping
cells and roof-mounted antennas generally overcome the problem.
system operators offer different services and have different legacy systems, financial
partners, and business strategies. As a result, the system architecture used will
differ between all system operators. The most common architectural type uses co-sited,
base-station equipment. The indoor digital equipment connects to the network infrastructure,
and the outdoor microwave equipment mounted on the rooftop is housed at the same
location (see Figure 2). Typically, the radio frequency (RF) planning for these
networks uses multiple sector microwave systems, in which transmit- and receive-sector
antennas provide service over a 90-, 45-, 30-, 22.5-, or 15-degree beamwidth.
The idealized circular coverage area around the cell site is divided into 4, 8,
12, 16, or 24 sectors.
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