Chapter 18: MMDS and LMDS

MMDS( Multichannel Multipoint Distribution Service)

Broadband Radio Service (BRS) formerly known as Multichannel Multipoint Distribution Service (MMDS), also known as Wireless Cable, is a wireless telecommunications technology, used for general-purpose broadband networking or, more commonly, as an alternative method of cable television programming reception.

MMDS allows two-way voice, data and video streaming. It operates at a lower frequency than LMDS (typically within specified bands in the 2-10GHz range) and therefore has a greater range and requires a less powerful signal than LMDS. MMDS is a less complicated, cheaper system to implement. As a consequence, the CPE is cheaper, thus it has a wider potential addressable market. It is also less vulnerable to rain fade - the interference caused by adverse weather conditions that can undermine the quality of the microwave signal. However, the bandwidth offered by LMDS makes this the more viable option.

Advantage of MMDS

• It has chunks of under-utilized spectrum that will, once completely digital, become increasingly valuable and flexible.
• System Implementation, which is little more than putting an installed transmitter on a high tower and a small receiving antenna on the customer’s balcony or roof, is quick and inexpensive.
• Moreover, since MMDS services have been around for 20 years, there is a wealth of experience--at least in respect to the one-way distribution technology.

Disadvantage of MMDS:

• Large upstream bandwidth in MMDS band requires careful planning, filtering etc.
• Limited capacity without sectorization, cellularization which adds complexity and cost
  
  
  
  

WHAT KIND OF COVERAGE AREA CAN BE EXPECTED FROM AN MMDS SYSTEM?

The term “coverage” should be defined as it relates to the service range of an MMDS system since wireless cable systems transmit at micro wave frequencies (2.0-2.9 GHz), all receive sites must have a clear “line-of-sight” path to the transmit antennas. Therefore, coverage area of an MMDS system is limited to the line-of-sight radius from the transmit site.

LMDS(Local Multipoint Distribution Service)

LMDS is a broadband wireless access technology originally designed for digital television transmission (DTV). It was conceived as a fixed wireless, point-to-multipoint technology for utilization in the last mile. LMDS commonly operates on microwave frequencies across the 26 GHz and 29 GHz bands. In the United States, frequencies from 31.0 through 31.3 GHz are also considered LMDS frequencies.

LMDS is a fixed broadband line-of-sight, point-to-multipoint, microwave system, which operates at a high frequency (typically within specified bands in the 24-40GHz range) and can deliver at a very high capacity, depending on the associated technologies. Given the complexity of the equipment required (and the power needed to deliver signals) both of these technologies are regarded as prohibitively expensive for the consumer market. Therefore, LMDS operators will initially be targeting enterprises and network operators, although the consumer market is likely to emerge over time as the cost of CPE comes down (partly driven by the take-up of IP). It should be noted that CPE costs $5,000 for LMDS in the 26GHz range.

Advantage of LMDS:

• Very large bandwidth available for data, IP telephony, video conferencing services
• Large Capacity
• Small Cell size, 2-8Km
• Network management and maintenance is vary cost effect
  
  
  
  

Disadvantage of LMDS:

• Does not cover entire metropolitan area of a large city without adding  many cells at high cost
• Signal strength is greatly reduced by the presence of heavy rainfall

Benefits using MMDS, LMDS and unlicensed band together:

• Complete coverage of a large city  right in the beginning
• Lower infrastructure and deployment costs
• More type of services can be offered ie. lower cost services with MMDS network and high bandwidth services with LMDS network
• Can grow subscribers and services by adding additional LMDS cells
• More options to address interference with other ITFS and MMDS licensees
• Lower back haul costs - LMDS and MMDS cells can be used for back haul

Example of combined combined MMDS / LMDS / Unlicensed band network:

• Overlay MMDS and LMDS network on top of each other
• MMDS network used for less dense rural areas and to increase overall coverage area
• LMDS network used in densely populated down town areas  and business parks
• Add additional LMDS cells as needed to increase capacity and to offer higher bandwidth services 
• Minor modification to Hub equipment

Difference between the LMDS AND MMDS

LMDS and MMDS use different areas of the spectrum. Their location in the spectrum offers specific characteristics which make them different. One example is that LMDS is typically used between 3 - 5 miles line of site distance from the main hub/office. However, MMDS can be used around 30 miles from the main hub/office and also requires line of site. The big difference between the two is bandwidth.

Sources:

http://en.wikipedia.org/wiki/Local_Multipoint_Distribution_Service

http://www.mobilecomms-technology.com/projects/mmds/

http://www.lmds.vt.edu/LMDS_about_fluid.html

http://www.rficsolutions.com/publishedpapers/Broadbandwireless.pdf