MMDS and LMDS: Into thin air


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 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 cabling.

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 Broadband and Alcatel) offer LMDS products; however, public services will probably not be available for another year or two.

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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