chapter 18: MMDS and LMDS

MMDS and LMDS

Overview:

MMDS   

               

Multichannel Multipoint Distribution Service, also known as MMDS or 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 is used in Canada, Mexico, Dominican Republic, Iceland, Ireland, Russia, Slovenia, Brazil, Barbados, Australia, Nigeria, Pakistan, Sri Lanka, Thailand, Uruguay, India, Belarus and Cambodia. It is most commonly used in sparsely populated rural areas, where laying cables is not economically viable, although some companies may also offer MMDS services in urban areas. ), 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.

LMDS

is a wireless technology able to transmit a large amount of data and information at a very high rate of speed using microwave radios. One microwave radio is installed onto a building at the client site and another microwave radio installed at the LMDS base station. It can be constructed in a point to point or point to multipoint fashion.

 is a system for broadband microwave wireless transmission direct from a local antenna to homes and businesses within a line-of-sight radius, a solution to the so-called last-mile technology problem of economically bringing high-bandwidth services to users. LMDS is an alternative to installing optical fiber all the way to the user or to adapting cable TV for broadband Internet service. Depending on the implementation, LMDS offers a bandwidth of up to 1.5Gbps downstream to users and 200 Mbps up stream from the user. A more typical data rate is 38 Mbps downstream. Some services offer both downstream

WHAT IS MMDS?

A digital wireless transmission system that works in the 2.2-2.4 GHz range. Also known as "Advanced Wireless Services" (AWS) and "wireless cable, it requires line of sight between transmitter and receiver, which can be 30 or more miles apart.

MMDS was designed initially as a one-way service for bringing cable TV to subscribers in remote areas or in locations that are difficult to install cable. It supports approximately 33 analog channels and more than 100 digital channels of TV. In late 1998, the FCC opened up the technology for two-way transmission, enabling MMDS to provide data and Internet services to subscribers.

Frequency

–         Based on high frequency, low-powered signals over short distances

–         LMDS used the following ranges of frequencies

•          27.5 MHz and 28.35 MHz

•          29.1 MHz and 29.25 MHz

•          30 GHz, 31.075 GHz, and 31.225 GHz

Architecture

–         Cells (like a cellular telephone system)

–         LMDS is a fixed wireless technology for buildings

Layout

–        MMDS hub is typically located on a high point

•         Uses a point-to-multipoint architecture that multiplexes communications to multiple users

–        Tower has a backhaul connection to carrier’s network

•         Carrier network connects with the Internet

–        MMDS signals can travel longer distances

•         Provide service to an entire area with only a few radio transmitters

–       MMDS cell size can have a radius of up to 35 miles (56 kilometers)

Multichannel Multipoint Distribution Service (MMDS)

System Configuration

The wireless system consists of head−end equipment (satellite signal reception equipment, radio transmitter, other broadcast equipment, and transmission antenna) and reception equipment at each subscriber location (antenna, frequency conversion device, and set−top device).

Signals for MMDS broadcast at the transmitter site originate from a variety of sources, just like at cable head−ends. Satellite, terrestrial, and cable delivered programs, in addition to local baseband services, comprise the material to be delivered over MMDS. All satellite−delivered baseband formats are remodulated and subsequently up−converted to microwave frequencies.

Here's how a wireless cable system works:

    1.  The cable studio, along with the head−end, receives programming from a variety of sources (see the following section). Each source is assigned a channel number, processed to improve quality, encoded, and then sent to a transmitter. The signal is broadcast in the super−high−frequency (SHF) range. Using an omni−directional transmit pattern, the signal reaches subscribers located up to 50 KM from the antenna, depending on the terrain and transmit power.

    2.  Wireless cable signals are received by the subscriber's small rooftop antenna, decoded (pay TV), and down−converted to standard TV channels on the subscriber's TV set.

     3. One of the two systems are normally used for multiple−dwellings (condo, apartment, and so on) to receive and distribute wireless TV.

     a. The building management pays for all units to receive the programming from a single communal antenna. This agreed fee is usually based on the number of potential viewers.

      b. In other buildings, a single community antenna is installed with each tenant subscribing separately and billed separately by the cable company.

     4. In all cases, deposits are paid by subscribers that cover receiver system costs, much like cable subscribers.

LMDS and similar systems are used to span the last mile to the user's facilities. LMDS transmits at an extremely high data rate, but is limited to from two to four miles. MMDS, which operates at lower frequencies, can span 30 or more miles.

Local multipoint distribution service (LMDS)

–         Fixed broadband technology that can provide a wide variety of wireless services

•          High-speed Internet access

•          Real-time multimedia file transfer

•          Remote access to local area networks

•          Interactive video, video-on-demand, video conferencing

•          Telephone service

–         Can transmit from 51 to 155 Mbps downstream and 1.54 Mbps upstream

•          Over a distance of up to about 5 miles (8 kilometers)

Local Multipoint Distribution Service (LMDS)

Frequency

–         Based on high frequency, low-powered signals over short distances

–         LMDS used the following ranges of frequencies

•          27.5 MHz and 28.35 MHz

•          29.1 MHz and 29.25 MHz

•          30 GHz, 31.075 GHz, and 31.225 GHz

Architecture

–         Cells (like a cellular telephone system)

–         LMDS is a fixed wireless technology for buildings

Internet Access

The hottest application for MMDS is Internet access; this differs from MMDS' original application of one−way "wireless cable" service to deliver television programming. This application never proved popular, and most license holders are now concentrating on data service. An MMDS .

connection is just like any other ISP connection: normally a router port with a connection for the external ISP network.

The Transmit Antenna

The bandwidth allocated to MMDS operators can vary from 200 to over 300 MHz, depending on the number of channels and their spacing. Wide bandwidth is a requirement of MMDS antennas

together with downward tilt and horizontal radiation patterns to concentrate on the signal in the

service area.

The Transmission Line

This is another critical component that can have a substantial effect on system losses. Major

head−end sites typically use 50 or 100 watt transmitters, yet often only 50 percent of this power

reaches the antenna after passing through channel combiners and transmission feeders.

Waveguides from the antenna to the radio equipment vary to reduce loss and add gain.

Channel Combiners

MMDS sites normally transmit a number of channels. Special filters (channel combiners) are used to combine the outputs of the transmitters to the transmission feeder and antenna. The design of these combiners is critical to ensure they are stable with temperature, have low return loss, and provide low pass band loss.

Local Multipoint Distribution Service (LMDS)

Whenever the concept of the competitive environment enters a discussion, two other discussions ensue: the WLL and the use of LMDS. This chapter will look at some of the movement in this area to understand how and why the last mile has become so critical in meeting the demands for higher−speed broadband communications. Moreover, when looking at the incumbent local exchange carriers' (ILEC) copper−based plant, one can only marvel at the lack of foresight in fending off the competition.

A graphic representation of the local loop and some trouble spots is shown:

Multiple areas of competition at the local loop:

Competitor	Concept	Technology
CATV companies	Cable TV for voice and Internet access	Cable modem technology
CATV companies	Fiber to the Curb (FTTC), Coax to the door for data and voice plus entertainment	Hybrid Fiber Coaxial (HFC), (FTTC)
Cellular and PCS suppliers	Broadband PCS as a single number for all wireless voice, paging, and data access	PCS on TDMA and CDMA or GSM
Local competitors	Broadband voice and data services on wireless local loop	LMDS and MMDS
CLECs	Fiber or copper to the door	SONET and local drops on copper
SONET and local drops on copper	Wireless access through various methods	Wireless Local Loop (WLL)

Resources:

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

Broadband Telecommunications Handbook - VPNS,3GW,GPRS,MPLS,VoIP,SIP – 2