MMDS and LMDS: Into thin air |  Networking

The wireless industry has been buzzing with a couple new technologies for providing
wireless broadband access to the Internet in metropolitan areas: MMDS (Multi-channel
Multipoint Distribution Service) and LMDS (Local Multipoint Distribution Service). In
the near future, these technologies will surely revolutionize the "last mile" delivery
of information to businesses and homes.

With MMDS, a transmitting tower placed at a high elevation provides radio connectivity
to multiple sites within a 35-mile radius. Each of these sites has a receiving dish
located on top or along side their building. In some cases, repeaters may extend the
range into remote areas.

MMDS features include:

  • Operation in the 2.1 to 2.7 GHz radio frequencies
  • Data rates up to 10 Mbps
  • Up to 35-mile range
  • No line-of-sight requirements

MMDS is likely to prevail as the preferred choice for fixed wireless broadband
connectivity in North America. Network service providers, such as HREF= target=new>Sprint, are deploying MMDS
technology to reach local customers without negotiating access agreements with regional
Bell operating companies. You should begin seeing MMDS become available in larger
cities throughout 2001.

The advantage to the customer using MMDS service is the ability to quickly establish a
high-bandwidth connection to the Internet and pay less than the price of equivalent
wired connections. Initial capital outlay for MMDS is minimal, and the customer only
pays a monthly service fee. In addition, an MMDS connection is much more feasible in
difficult-to-wire areas where rivers and highways preclude the feasible installation of

An LMDS system consists of a series of cells defined by individual base stations
interconnected to a central control point. In addition, LMDS transmissions are
strictly line of sight. For this reason, carriers will probably only target business
districts where high rooftop mounting of subscriber dishes is possible. Companies will
probably subscribe to LMDS services for ATM telephony and streaming video applications.

LMDS offers the following features:

  • Operation at 24-GHz, 28-GHz, 31-GHz, 38-GHz, and 40-GHz radio frequencies
  • Data rates up to 155 Mbps with 2-mile ranges
  • Line-of-sight operation

Some companies (e.g., Adaptive
and Alcatel) offer LMDS
products; however, public services will probably not be available for another year or

Stay tuned. Next time we'll take a closer look at signal distortions you should be
aware of when installing wireless LANs.

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