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LMDS Tutorial
LMDS Defined
A past tutorial on fixed
wireless technology defined local multipoint distribution service
(LMDS) as spectrum in the 27.5GHz to 28.35 GHz, 29.1GHz to 29.25 GHz,
and 31GHz to 31.3 GHz bands, which is used for high-bandwidth, point-to-multipoint
applications.
LMDS Auctions
A total of 986 licenses are available for spectrum
within each of the 493 geographic basic trading areas (BTAs). The
Federal Communications Commission (FCC) has held two spectrum auctions
for the sale of this spectrum. The first, held in 1998, was not as
successful as the FCC had predicted. Therefore a second auction was
held in 1999. Between the two auctions, all of the LMDS licenses were
sold.
Technology
The technology uses
a cellular-like network architecture of microwave radios placed at the
client's location and at the company's base station to deliver fixed
services, mainly telephony, video and Internet access. The use of time-division
multiple access (TDMA) and FDMA (frequency DMA) technology allows multiple
customers within a 3-5 mile coverage radius to share the same radio
channel. Customers can receive data rates between 64kbps to 155Mbps.
An LMDS system consists of four parts:
- The network operations center (NOC) houses
the network management system (NMS) equipment that manages large
regions of the customer network.
- A fiber-based infrastructure connects separate
NOCs.
- The base station, usually located on a cellular
tower, is where the conversion from fibered infrastructure to wireless
infrastructure occurs.
- The customer premises equipment (CPE) typically
includes microwave equipment mounted on the outside of a consumer's
home or business as well as equipment located within the building,
providing modulation, demodulation, control, and interface functionality.
LMDS systems offer several advantages
for providers:
- Low entry and deployment
costs - Due to the fact that a large part of a wireless network's
cost is not incurred until the CPE is installed, the operator is
able to stage capital expenditures gradually with new customer acquisition.
- Speed of deployment - A
fiberless network requires no trenches, backhoes or construction,
only a radio at the customer's location and another one on a tower
in a central location. This enables a quicker deployment schedule
than most broadband services.
- Demand-based buildout -
LMDS uses a scalable architecture combined with industry standards
to ensure service can be expanded as customer demand increases.
- Variable component cost
- Most wireline systems require a large capital investment for the
infrastructure component. LMDS systems shift the cost to the CPE,
which means the operator only spends money when a revenue-paying
customer signs on.
Limitations:
- The system requires line-of-site (LOS) between
the CPE and base station hub. This could require the use of repeaters
to forward signals over obstacles.
- LMDS signals are affected by moisture, which
could result in "rain fade," or the disruption of signals
as a result of heavy rain. Increasing the power used to transmit
the signals can usually alleviate problems associated with rain
fade.
Terms
TDMA - Time
Division Multiple Access - A digital transmission technology that allows
multiple users to access a single radio-frequency (RF) channel without
interference by allocating time slots to each user within each channel.
FDMA - Frequency Division Multiple
Access - A transmission technology in which each subscriber is assigned
a specific frequency channel, that can then be used by no one but them.
FDMA reduces interference, but severely limits the number of users.
Additional sources of information*
*The WAVE Report is not responsible for content on
additional sites
12/12/01 |
