MMDS and LMDS

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. It is also 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.

Technology

The BRS band uses microwave frequencies at 2.1 GHz and from 2.5 GHz to 2.7 GHz. Reception of BRS-delivered television and data signals are done with a rooftop microwave antenna. The antenna is attached to a down-converter or transceiver to receive and transmit the microwave signal and convert them to frequencies compatible with standard TV tuners (much like on satellite dishes where the signals are converted down to frequencies more compatible with standard TV coaxial cabling), some antennas use an integrated down-converter or transceiver. Digital TV channels can then be decoded with a standard cable set-top box or directly for TVs with integrated digital tuners. Internet data can be received with a standard DOCSIS Cable Modem connected to the same antenna and transceiver.

            Local Multipoint Distribution Service (LMDS) is a digital wireless transmission system that works in the 28 GHz range in the U.S. and 24-40 GHz overseas. It requires line of sight between transmitter and receiving antenna, which can be from one to four miles apart depending on weather conditions. LMDS provides bandwidth in the OC-1 to OC-12 range, which is considerably greater than other wireless broadband services.

LMDS is a new type of stationary (fixed) broadband wireless access technology designed for a mass subscriber marketplace. Based on millimeter microwave frequencies - 24GHz and above - LMDS now offers a potential for cheaper in-building bandwidth than newly installed fiber or copper. In fact, it's the microwave technology that could make wireless data for the enterprise both cheap and ubiquitous.  While several vendors are offering products today, this technology is still in early development stages.

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.

Throughput capacity and reliable distance of the link depends on common radio link constraints and the modulation method used - either phase-shift keying or amplitude modulation. Distance is typically limited to about 1.5 miles (2.4 km) due to rain fade attenuation constraints. Deployment links of up to 5 miles (8 km) from the base station are possible in some circumstances such as in point-to-point systems that can reach slightly farther distances due to increased antenna gain.

sources:

http://mobileinfo.com/Hot_Topics/LMDS&MMDS.htm

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

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

http://www.answers.com/topic/local-multipoint-distribution-service

Microwave - and Radio - Based System

A Microwave System is a system of equipment used for microwave data transmission. The typical microwave system includes radios located high atop microwave towers, which are used for the transmission of microwave communications using line of sight microwave radio technology. This system is composed of at least two microwave towers. At the top of these towers are microwave antennas. These antennas are what allow the transmitter hardware of the microwave system to transmit data from site to site. The area between the microwave system components must be clear of any major structures, such as tall buildings, mountains, or other objects that could potentially obstruct microwave transmission. Only when this has been achieved can data travel through the microwave system. This is why microwave communication is categorized as a “line of sight” technology. 

           Microwave transmission refers to the technology of transmitting information or energy by the use of radio waves whose wavelengths are conveniently measured in small numbers of centimetres; these are called microwaves. This part of the radio spectrum ranges across frequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengths from 30 centimetres down to 1.0 cm.

            Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies significantly below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. Information is carried by systematically changing (modulating) some property of the radiated waves, such as amplitude, frequency, phase, or pulse width. When radio waves pass through an electrical conductor, the oscillating fields induce an alternating current in the conductor. This can be detected and transformed into sound or other signals that carry information.

            For the propagation and interception of radio waves, a transmitter and receiver are employed. A radio wave acts as a carrier of information-bearing signals; the information may be encoded directly on the wave by periodically interrupting its transmission (as in dot-and-dash telegraphy) or impressed on it by a process called modulation. The actual information in a modulated signal is contained in its sidebands, or frequencies added to the carrier wave, rather than in the carrier wave itself. The two most common types of modulation used in radio are amplitude modulation (AM) and frequency modulation (FM). Frequency modulation minimizes noise and provides greater fidelity than amplitude modulation, which is the older method of broadcasting.

Microwave vs. Radio

Microwave and radio waves are light waves of different lengths on the same end of the electromagnetic spectrum. The other types of waves are infrared, visible light, ultraviolet, x-rays and gamma rays. Microwave and radio waves are not visible to the naked eye and are used for everyday and scientific purposes. The attributes and uses of each wavelength are quite different—microwaves for cooking food and providing radar and radio waves being used for common information transmission.

Different Wavelengths

·         Radio waves are the longest in the light spectrum. Some radio waves are as short as a few inches while others are miles long and all can be used to transmit information. Microwaves are behind radio waves in length on the electromagnetic scale, although they are much shorter, from a few centimeters to about a foot in length. The most well-known type of microwave is the longer wave, which is used in microwave ovens.

Uses

·         Radio waves can carry sound for devices such as radio and cell phones, and they carry images and information for televisions, telescopes and satellites. Microwaves are most commonly known for microwave ovens in most homes, where the short light waves actually cook food. Microwaves are also used for information transmission, typically in scientific and military operations, such as phone calls and transferring data from one computer to another. Microwaves also power radar transmissions.

Transmission

·         Microwaves travel better through varying weather conditions, such as rain, clouds and haze and have broader uses than radio waves. One of these uses was the development and further use of radar. Radar uses "short bursts of microwaves" that create "echoes" from the objects they hit, according to NASA. Radio is harder to filter because the wavelengths are large and need to be “caught” in satellites or groups of satellites. Radio waves do not travel as well as microwaves through clouds and haze, which is why the radio in your home can break up during poor weather.

  sources:

http://www.ehow.com/about_6710602_microwave-vs_-radio.html

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

http://www.answers.com/topic/microwave-transmission

http://www.dpstele.com/dpsnews/techinfo/microwave_knowledge_base/microwave_system.php

http://www.infoplease.com/ce6/sci/A0860618.html

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