MICROWAVE RADIO COMMUNICATIONS

> Microwave communication uses microwave as the carrier of signals, which is similar to optical fiber communication that uses light as the carrier of signals. Simply speaking, transmitting module and optoelectronic inspection module used for receiving in the optical fiber transmission system are similar to the transmitting and receiving antenna. Compared with the optical fiber communication with wire channels, microwave channel is wireless and microwave communication is much more complicated.

> It is also the transmission of signals via radio using a series of microwave towers. It is known as a form of "line of sight" communication, because there must be nothing obstructing the transmission of data between these towers for signals to be properly sent and received.

> Microwave is electromagnetic wave with frequency from 300MHz to 300GHzand it is a finite frequency band of the entire electromagnetic wave spectrum. According to the microwave transmission feature, microwave can be viewed as plane wave. Along the transmission direction, the plane wave has no longitudinal components of electric field and magnetic field. Both electric field and magnetic field are vertical to the transmission direction. Thus, the plane wave is called transverse electromagnetic wave and marked as TEM wave.

Microwave Communication Technology was Developed in the 1940's

> The technology used for microwave communication was developed in the early 1940's by Western Union. The first microwave message was sent in 1945 from towers located in New York and Philadelphia. Following this successful attempt, microwave communication became the most commonly used data transmission method for telecommunications service providers.

> With the development of satellite and cellular technologies, microwave has become less widely used in the telecommunications industry. Fiber-optic communication is now the dominant data transmission method. However, microwave communication equipment is still in use at many remote sites where fiber-optic cabling cannot be economically installed.

Advantages of Microwave Radio1. Do not require a right-of-way acquisition between stations.

2. Each station requires the purchase or lease of only small area of land.

3. Because of their high operating frequencies, microwave radio systems can carry large quantities of information.

4. High frequencies mean short wavelengths, which require relatively small antennas.

5. Radio signals are more easily propagated around physical obstacles such as water and high mountains.

6 .Fewer repeaters are necessary for amplification.7. Distances between switching centers are less.8. Underground facilities are minimized.9. Minimum delay times are introduced.

10. Minimal crosstalk exists between voice channels.

11. Increased reliability and less maintenance are important factors.

Disadvantages1. It is more difficult to analyze and design circuits at microwave frequencies.

2 .Measuring techniques are more difficult to perfect and implement at microwave frequencies.

3. It is difficult to implement conventional circuit components (resistors, capacitors, inductors, and so on) at microwave frequencies.

4. Transient time is more critical at microwave frequencies.

5 It is often necessary to use specialized components for microwave frequencies.

6. Microwave frequencies propagate in a straight line, which limits their use to line-of-sight applications.

Analog vs Digital Microwave

Modulation:

1. Analog

‡ FM

2. Digital

‡ PSK (satellite)‡ QAM

‡ PCM (satellite)

Microwave Communication Can Be Analog or Digital

Microwave communication takes place both analog and digital formats. While digital is the most advanced form of microwave communication, both analog and digital methods pose certain benefits for users.

In the year of 1947, Bell lab built the first analogue microwave trial circuit (TD-X) between New York and Boston. This circuit used vacuum tube to amplify signals and adopted the frequency modulation (FM) mode. Analog microwave communication may be most economical for use at your tower sites simply because it is already paid for and in service.

Digital microwave communication utilizes more advanced, more reliable technology. It is much easier to find equipment to support this transmission method because it is the newer form of microwave communication. Because it has a higher bandwidth, it also allows you to transmit more data using more verbose protocols. The increased speeds will also decrease the time it takes to poll your microwave site equipment. This more reliable format provides for more reliable reporting with advanced communication equipment, while also allowing you to bring in your LAN connection when it becomes available at the site.

Characteristics of Digital Radio Communication System Radio communication system, especially the digital radio communication system, has the following advantages:

> Can be rapidly installed

> Can use the existing network infrastructure repeatedly (digital radio uses the Infrastructure of the analogue radio)> Can cross complicated terrains (rivers, lakes and mountains)> Can use point-to-point radio transmission structure in the remote mountains> Can rapidly restore the communication after the natural disasters> Can protect hybrid multiple transmission media.

Why FM?FM signals are relatively insensitive to amplitude

nonlinearities can be transmitted through amplifiers that have compression or amplitude nonlinearity with little penalty are less sensitive to random noise can be propagated with lower transmit powers inter-modulation noise is a function of signal amplitude and the magnitude of the frequency deviation.

Why not AM?more sensitive to amplitude nonlinearities

inherent in wideband microwave amplifiers inter-modulation noise is a function of signal amplitude.

FM MICROWAVE RADIO SYSTEM

System characteristics provide flexible, reliable, and economical point-to-point communications using Earth’s atmosphere for the transmission medium.

FM microwave systems used with the appropriate multiplexing equipment are capable of simultaneously carrying from a few narrowband voice circuits up to thousands of voice and data circuits. It can be configured to carry high-speed data, facsimile, broadcast-quality audio and commercial television signals. more economical means for providing communications circuits where there are no existing metallic cables or optical fibers or where severe terrain or weather conditions exist. FM microwave systems are also easily expandable.

FM MICROWAVE RADIO SYSTEMThe baseband

composite signal that modulates the FM carrier�

1. FDM voice-band channels

2. TDM voice-band channels3. Broadcast-quality composite video or picturephone4.Wideband data