Chapter 17: Microwave and Radio-Based System

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 centimeters; 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 centimeters down to 1.0 cm.

Microwaves are widely used for point-to-point communications because their small wavelength allows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna. This allows nearby microwave equipment to use the same frequencies without interfering with each other, as lower frequency radio waves do. Another advantage is that the high frequency of microwaves gives the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30 times that of all the rest of the radio spectrum below it. A disadvantage is that microwaves are limited to line of sight propagation; they cannot pass around hills or mountains as lower frequency radio waves can.

Properties:

• Suitable over line-of-sight transmission links without obstacles

• Provides large useful bandwidth when compared to lower frequencies (HF, VHF, UHF)

•     Affected by the refractive index (temperature, pressure and humidity) of the atmosphere, rain (see rain fade), snow and hail, sand storms, clouds, mist and fog, strongly depending on the frequency.

Uses:

Wireless transmission of information

• One-way (e.g. television broadcasting) and two-way telecommunication using communications satellite
• Terrestrial microwave radio broadcasting relay links in telecommunications networks including e.g. backbone or backhaul carriers in cellular networks linking BTS-BSC and BSC-MSC.

Wireless transmission of power

• Proposed systems e.g. for connecting solar power collecting satellites to terrestrial power grids

Advantage:

• No cables needed
• Multiple Channels available
• Wide Bandwidth
• Able to transmit Large quantities of data
• Relatively low costs

Disadvantage:

• Line of sight will be disrupted if any obstacle, such as new building are in the way
• Signal absorption by atmosphere. Microwaves are suffer from attenuation due to atmospheric condition
• Towers are expensive to build
• Subject to electromagnetic and other interference

A microwave link is a communications system that uses a beam of radio waves in the microwave frequency range to transmit video, audio, or data between two locations, which can be from just a few feet or meters to several miles or kilometers apart. Microwave links are commonly used by television broadcasters to transmit programmes across a country, for instance, or from an outside broadcast back to a studio.

Uses of microwave links:

• In communications between satellites and base stations

• As backbone carriers for cellular system
• In-short range indoor communications
• Telecommunications, in linking remote and regional telephone exchanges to larger(main) 
• Exchanges without the need for copper/optical fiber lines

Bandwidth:

Bandwidth is always a touchy subject. It can become a "never satisfied drain" on the corporate

bottom line if due diligence is not practiced. There is a direct relationship to cost and total

bandwidth. The more bandwidth needed, the greater the cost.

It's wiser to buy bandwidth as you need it and not before (there will be a small amount of

incremental add−on, but limited). In the future, there will be the following:

• More choices
• Increase providers
• Greater availability
• Lower Cost

The risks associated with buying bandwidth fall into the two categories pointed out earlier:

• buying too little bandwidth will increase incremental growth costs that can add up to more than buying a larger quantity at the onset would.
• buying more bandwidth  than immediately needed means paying for bandwidth that may not be required for some time, or that will be less expensive in the future.

Having too much bandwidth is possible. Having too much reliability is just the opposite.

Organizations lose significant amounts of money when the network connection is too slow, but far

more when the link is down completely.

Microwave radio is a flexible and cost-effective alternative for transmission of voice, data, and video services in all parts of a fixed or wireless mobile network, including applications for the backhaul or direct access services. With the scale and flexibility of today’s new radio technology, implementing a microwave network is more economical and easier than ever.Microwave Networks Incorporated provides fixed wireless products for next generation “converged” networks.

Sources:

http://www.sqa.org.uk/e-learning/NetTechDC01CCD/page_44.htm

http://www.ehow.com/list_6137210_microwave-radio-communications-advantages-disadvantages.html

http://www.microwavenetworks.com/solutions/white-papers/ethernet-applications-and-how-microwave-radios-can-play-a-part/

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

Broadband Telecommunications Handbook, Second Edition