ECE105 - Microwave Link Design

bRepublic of the Philippines

A PROJECT DESIGN ON TRANSMISSION MEDIA AND ANTENNA SYSTEM

MICROWAVE LINK

DESIGN

JELORD KLINN D. CABRESOS

October 2014 Republic of the Philippines

Mindanao State University - Iligan Institute of Technology

College of Engineering

Direct line (063) 2351E-mail:[email protected] Homepage:http://www.msuiit.edu.ph/coe

MICROW VE LINK

DESIGN

INTRODUCTION

Every one of us, everywhere, is connected – exchanging data, news and opinions. Telecommunication has been part of our daily routine, and helps make life more convenient. Also it gives us access to more information, entertainment and ways to communicate that most of us never thought could be possible.

The microwave region of the electromagnetic spectrum is generally considered to overlap with the highest frequency radio waves. Its sources include artificial devices such as circuits, transmission towers, radars, masers, and microwaves oven, as well as natural sources such as the Sun and the Cosmic Microwave Background.

Microwave communication technology was developed in the 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. 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.

We have already arrived in the new era of ever-evolving technology. Oneof the best opportunities offered by modern technology is the development of microwave communications system. CALLULAR TELECOM, INC. proposed to expand its system to rural areas and to develop a high-speed and reliable point-to-point wireless bridge for data transmission under the latest requirements of modern wireless transmission equipment.

OBJECTIVES

This proposed project aimed to expand the communications system of the company to the designated rural areas, and to develop a high-speed wireless bridge for data transmission.

Specifically, this study aimed to:

 To design a reliable point-to-point Microwave Cellular Communications System.

 To design a Microwave Link System having the ideal reliability of 99.9999%

 To know the general principles of Microwave Communications.

SIGNIFICANCE OF THE STUDY

This project will be a significant endeavor in promoting good work environment and to provide reliable communication system in the particular rural areas.

Prior to the advent of commercial wireless communications in this day and age, most microwave designs were destined for profitable applications. This study will also be beneficial to the students to practice they have learned theoretically, and to cope up with the technological advancements.

Moreover, this design intends to introduce the basics of microwave link system and will serve as a reference for students who will take up this subject in the future.

SCOPES AND LIMITATIONS

This categorizes the reach and restrictions of the microwave communications system which might be useful to the readers of the paper.

The scope of the proposal project focused on:

 The system is comprised of one transmitter, and one receiver.

 The designed microwave link system is to operate at a frequency of 14 GHz.

 A circuit called Coupling Loop Interference Canceller is used to avoid co-channel interference for transmit-receive process.

The limitations of the project are as follows:

 The distance between sites is limited to 20 kilometers.

 The system is comprised of only one short hop.

 The designed system is only for cellular communication purposes only.

REVIEW OF RELATED LITERATURE

Microwaves are generally describes as electromagnetic waves with the range from approximately 500 Mhz to 300 Ghz or more. Therefore, microwaves signals, because of their inherently high frequencies, have relatively short wavelengths, hence the name “micro” waves. Microwaves are a form of electromagnetic radiation with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often restricting the range between 1 and 100 GHz (300 and 3 mm).

These are widely used in 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. Mobile phones, phone mast antennas (base stations), Digital Enhanced Cordless Telecommunications (DECT) cordless phones, Wi-Fi, WLAN, WiMAX and Bluetooth have carrier wave frequencies within the microwave band of the electromagnetic spectrum, and are pulse modulated. Most Wi-Fi computers in schools use 2.45 GHz (carrier wave). For full duplex (two-way) operation as is generally required of microwave communications systems, each frequency band is divided in half with the lower half identified as the low band and the upper half as the high band. At any given radio station, transmitter are normally operating on either the low or the high band, while receivers are operating on the other hand.

Feeder service microwave systems are generally categorized as short haul because they are used to carry information for relatively short distances, such as between cities within the same state. Long haul microwaves systems are those used to carry information for relatively long distances, such as interstate

and backbone route applications. Microwave radio systems capacities range from less than 12 voice-band channels to more than 22,000 channels. Early microwaves systems carried frequency-division-multiplexed voice-band and used conventional, no coherent frequency modulation techniques. More recently developed microwave systems carry pulse-code-modulated time-division-multiplexed voice-band circuits and used more modern digital modulation techniques, such Phase Shift Keying (PSK) or Quadrature Amplitude Modulation (QAM).

Microwave transmission refers to the technology of transmitting information or energy by the use of electromagnetic waves. It is known as a form of “line-of-sight” communication, because there must be nothing obstructing the transmission of data between microwave towers for signals to be properly sent and received. Microwave systems have many applications in the telephone industry because high quality circuits can be derived for inter-toll trunks, toll connecting trunks, extended area service trunks, subscriber service and special services. Microwave is also suitable for transmission of black and white or color television, data, and data under voice, with negligible impairment from impulse noise, delay distortion, frequency error, frequency response, or steady state noise.

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

Large Bandwidth. The bandwidth of microwave is larger than the common low frequency radio

waves. Thus, more information can be transmitted. Because of this, microwaves are used for point-to-point communications.

Portability and Reconfiguration Flexibility. Unlike with cables, you can pick up microwaves and

carry it to a new building. It also has multiple channels available.

Small Antenna Size. Microwaves allows to decrease the size of antenna. The antenna size can be

smaller as the size of antenna in inversely proportional to the transmitted frequency. Thus, we have of much higher.

Better Directivity. At microwave frequencies, there are better directive properties. This is due to

the relation that as frequency increase, wavelength decreases and as wavelength decreases, directivity increases and beam width decreases. So it is easier to design and fabricate high gain antenna in microwaves.

Low Power Consumption. The power required to transmit a high frequency signal is lesser than

the power required in transmission of low frequency signals. Microwaves have high frequency, thus requires less power.

Effect of Fading. The effect of fading is minimized by using line-of-sight propagation technique at

microwave frequencies. While at low frequency signals, the layers around the earth causes fading of the signal.

DISADVANTAGES

Line-of-Sight Propagation. Signal cannot bounce off any objects. You need to ensure that there

are no obstacles between towers.

Atmospheric Attenuation. Microwaves can suffer from attenuation due to atmospheric

conditions. Additionally, the higher the microwave frequency, the more susceptible to attenuation the communication will be.

Expensive Equipment. Microwave transmission and reception equipment is the most expensive

of all the types of wireless transmission.

Propagation Delay. This is primarily a disadvantage of satellite microwave. When sending

between two terrestrial stations using a satellite as a relay station, it can take anywhere from 0.5 to 5 seconds to send from the first terrestrial station through the satellite to the second station.

COMPONENTS OF MICROWAVE SYSTEM

Transmitter and Receiver. The basic building blocks of a microwave system are the radio

frequency (RF) transmitter and receivers. These units make it possible to send and receive information at microwave frequencies. Most microwave transmitters are capable of an output power of one watt or more. A transmitter used in terminal location has provisions for modulating the RF carrier with the baseband signals from the carrier multiplex equipment. Receivers are capable of providing a useable output with received microwave signal levels as low as -80 dBm. A terminal receiver includes a demodulator to provide the baseband output to the carrier multiplex.

Carrier Multiplex. The microwave RF equipment has a wide bandwidth which is capable of

a higher bit rate digital channel and demultiplexes them back into their individual channels at the other end of the loop.

Antennas. Parabolic or horn antennas are used to concentrate radiated energy into a narrow

beam for microwave transmission through free space. This results in the most efficient transmission of radiated power with a minimum of interference. An effective gain of 25 to 48 dB over an Omni-directional antenna is possible depending upon the size of the antenna and the microwave frequency used. 600 mm antenna used on a 23 GHz hop likely to provide similar performance to a 300 mm antenna used on a 26 GHz hop. Antennas are often used in conjunction with Randomes.

Randomes. Protective coverings used to prevent snow, ice, water or debris accumulating on a

microwave antenna. Heated randomes are available for use in areas where severe ice and snow conditions exist. Randomes can also reduce wind load across the tower. On the down side, using a randome results in lower antenna gain across the link.

Transmission Lines. A specialized cable or other structure designed to carry alternating

current of radio frequency, that is, currents with a frequency high enough that their wave nature must be taken into account. Transmission lines are used for purposes such as connecting radio transmitters and receivers with their antennas, distributing cable television signals, trunk lines routing calls between telephone switching centers, computer network connections, and high speed computer data buses.

Waveguide and Coaxial Cable. Transmission feeders exist to provide a means of coupling the

transmitter and receiver antenna. Waveguide is a circular, elliptical or rectangular metal tube or pipe through which electromagnetic waves are propagated in microwave and RF communications. The wave passing through the medium is forced to follow the path determined by the physical structure of the guide. This type of transmission line can be used for distances of a few feet up to several hundred feet. A typical of waveguide has a loss from about 1.7 dB per hundred feet at 6 Gigahertz (GHz) to about 3 dB per

hundred feet at 11 GHz. It is used at microwave frequencies above 2 GHz. The length of a waveguide run is more critical at higher frequencies since attenuation increases with frequency. Coaxial cable is a tyoe of wire that consists of a center wire surrounded by insulation and then a grounded shield of braided wire. The shield minimizes electrical and radio frequency interference. At low microwave frequencies, 2 GHz or less, coaxial cable can be used as the connecting facility between the transmitter, receiver and antenna instead of waveguide. The loss of coaxial cable depends on the type of conductor, the cable diameter, the type of dielectric, and the operating frequency. The cost of coaxial cable is less than waveguide and should be used when possible. Extreme attenuation of radio signals above 2 GHz in the coaxial cable generally prohibits its use at the higher microwave frequency bands.

Reflectors. Used in systems operating near a power substation to avoid the electromagnetic

interference (EMI) potential in place of using long runs of waveguide connected to a parabolic antenna at the top of the tower. A reflector may be mounted at a 45-degree angle at the top of the tower, while antenna is mounted horizontally at the base of the tower, aimed at the reflector. The microwave signal is radiated from the antenna, reflected off the reflector, and sent in a direction of propagation to the other end of the radio path, just as though the antenna was radiating directly from the top of the tower. However, this type “periscope” or “fly swatter” antenna system will not be authorized by the Federal Communications Commission (FCC) under ordinary circumstances because of its interference potential with communication satellites.

Repeaters. Microwave RF repeaters are commonly used by telecommunications system operators

to reliably and cost-effectively relay radio signals at remote locations, typically mountaintops and when bypassing obstructed paths. Active repeaters are used at one or more intermediate points to regenerate the signal when the distance between the transmitting and receiving equipment is too great to allow an acceptable receive level, when it is necessary to get around an obstacle, and when it is necessary to drop and insert channels at points in between the radio link. Passive repeaters are used when there is an

obstacle, e.g. mountain, within the line-of-sight (LoS) and the economics of installing an active repeater are prohibitive or there is no need to regenerate the signal. Two types exist: Reflective Passive Repeater, which act as a mirror reflecting the signal to bypass the obstacle; and Back-to-Back Passive Repeaters, which receive the signal from the launch antenna and feels it, via a waveguide, to another launch antenna, again bypassing the obstacle.

Towers. The towers used in a microwave system must be strong enough to support the necessary

equipment to be installed on it, and rigid to prevent antenna deflection during windy conditions or ice loading. Two types of towers exist: Self-supporting Towers are either monopole or legged towers; and Guyed Towers cost about a third of price of a self-supporting tower but are often restricted in use because of the difficulty of acquiring enough land for guying. The height of the tower is determined by the terrain, the microwave frequency band used, the propagation characteristics, the distance between the transmitting and receiving ends of a path, and the required reliability. The tower must be high enough to provide a line-of-sight path above any obstructions. If reflection interference is a problem, the antenna mounting heights are critical and the optimum height may be less than the maximum height available on the tower.

Building. Microwave equipment should be located in the central office equipment building when

possible. There some situations, however, when RF equipment must be located remotely from a central office building, as in the case of an active RF repeater. In these situations, some type of building is sufficient. Where temperature and humanity variations exceed to operating limits of the microwave equipment, a heater or air conditioner is required to keep the equipment within its operating temperature range.

Primary and Secondary Power Equipment. Primary power sources for RF equipment may be DC

used. In some cases, thermoelectric generators or fuel cells can be used when the power requirements of the microwave equipment are low. Standby power equipment should be provided at microwave terminals or active repeater locations to maintain system operation in the event of a commercial power failure. Communication circuits are very important during times of emergency such as storms, floods and other disasters which may cause commercial power outages. Therefore, it is imperative that some type of standby power source be available for circuits derived by microwave. When microwave equipment is located in a central office building, standby power is usually available from central office equipment batteries or and engine-generator. However, at remoter sites standby power must be provided specifically for the microwave equipment. The standby power source may be batteries, and engine-generator or in some cases, a thermoelectric generator, fuel cell or solar energy.

Alarm System. When a microwave system has remote unattended stations, it is desirable to have

an alarm system or security system, which will report faults from the remote location to an attended office via microwave signal. The alarms will expedite the maintenance of the microwave systems and reduce the circuit outrage time. When alarms from a large number of unattended stations are reported to a central maintenance control center, consideration is often given to a computer-based alarm reporting system which prints out all changes in status at each station with time and date information. Alarm system is a system designed to detect intrusion – unauthorized entry – into a building or area. Security alarms are used in residential, commercial, industrial, and military properties for protection against burglary (theft) or property damage, as well as personal protection against intruders. Intrusion alarm systems may also be combined with closed-circuit television surveillance systems to automatically record the activities of intruders, and may interface to access control systems for electrically locked doors. Systems range from small, self-contained noisemakers, to complicated, multi-area systems with computer monitoring and control.

TERMS AND DEFINITIONS

Absorption. The reduction in power density due to non-free propagation.

Antenna. A metallic conductor system capable of radiating and capturing electromagnetic energy. Antenna-channel Interference Fade Margin (AIFM) (in decibels). Accounts for receiver threshold

degradation due to interference from adjacent channel transmitters.

Antenna Gain. A measure of directivity properties and electrical efficiency of the antenna. As a

transmitting antenna, the figure describes how well the antenna converts input power into radio waves headed in a specified direction. As a receiving antenna, the figure describes how well the antenna converts radio waves arriving from a specified direction into electrical power. When no direction is specified, "gain" is understood to refer to the peak value of the gain. A plot of the gain as a function of direction is called the radiation pattern. Antenna gain is usually defined as the ratio of the power produced by the antenna from a far-field source on the antenna's beam axis to the power produced by a hypothetical lossless isotropic antenna, which is equally sensitive to signals from all directions. Usually this ratio is expressed in decibels, and these units are referred to as "decibels-isotropic" (dBi). An alternative definition compares the antenna to the power received by a lossless half-wave dipole antenna, in which case the units are written as dBd. Since a lossless dipole antenna has a gain of 2.15 dBi, the relation between these units is: gain in dBd = gain in dBi - 2.15 dB. For a given frequency, the antenna's effective area is proportional to the power gain. An antenna's effective length is proportional to the square root of the antenna's gain for a particular frequency and radiation resistance. Due to reciprocity, the gain of any antenna when receiving is equal to its gain when transmitting.

Attenuation. The reciprocal of gain. The ration of the input quantity to the output quantity. Specifically,

a term that refers to a reduction in signal strength commonly occurring while transmitting analog or digital over long distance. Historically, attenuation is measured in dB but it can also be measured in terms of voltage.

Azimuth. The horizontal angular distance from a reference direction, either the southern or northern most

point of the horizontal.

Azimuth Angle. The horizontal pointing angle of an earth station antenna. Bandwidth. A range within a band of frequencies or wavelengths.

Baseband. The original band of frequencies of a signal before it is modulated for transmission of a higher

frequency.

Bluetooth. A wireless technology standard for exchanging data over short distances (using

short-wavelength UHF radio waves in the ISM band from 2.4 to 2.485 GHz) from fixed and mobile devices, and building personal area networks. Standardized as IEEE 802.15.1, but the standard is no longer maintained.

Branching Losses. Comes from the hardware used to deliver the transmitter/receiver output to/from the

antenna.

CMB. Cosmic Microwave Background. The thermal radiation assumed to be left over from the “Big Bang”

of cosmology.

Characteristic Impedance of Free Space. Equal to the square root of the radio of its magnetic permeability

to its electric permittivity.

Clutter Loss. Attenuation due to tress and buildings in the front of the antenna be propagated and back

Critical Angle. A maximum vertical angle frequency at which it can be propagated and still be refracted

back by the ionosphere.

Critical Frequency. The highest frequency that can be propagated directly upward and still be returned to

earth by the ionosphere.

dBm. Used to reference the power level at a given point to one milliwatt.

Decibel (dB). A logarithmic unit used to express the ratio between two values of a physical quantity, often

power or intensity. In other words, the basic yardstick used for making power measurements in communications.

DECT. Digital Enhanced Cordless Telecommunications (Digital European Cordless Telecommunications), is

a standard primarily used for creating cordless phone systems. It is originated in Europe, but is now being adopted increasingly worldwide. The younger brother of GSM - Global System for Mobile - it is by contrast a radio access technology, rather than a comprehensive system architecture; DECT has been designed and specified to interwork with many other types of network, such as the PSTN (conventional telephone networks), ISDN (new digital and data phone networks), GSM (mobile phone networks) and more.

Diffraction. The bending of a wave around objects or the spreading after passing through a gap. It is the

phenomenon that allows light or radio waves to propagate (peek) around corners.

Digital Modulation. The transmitted of digitally modulated analog signals (carriers) between two or

points in a communications system.

Direct Waves. (See Free Space Path).

Dispersive Fade Margin. Gains in the equipment which are factored in because of technical improvements

DSL. Digital Subscriber Line (originally, Digital Subscriber Loop). A family of technologies that provide

internet access by transmitting digital data using a local telephone network which uses the public switched telephone network.

Duplexing. A duplex communications system is a point-to-point system composed of two connected

parties or devices that can communicate with one another in both directions. There are two types of duplex communication systems: full-duplex and half-duplex. In a full-duplex system, both parties can communicate to the other simultaneously. An example of a full-duplex device is a telephone; the parties at both ends of a call can speak and be heard by the other party simultaneously. In a half-duplex system, in contrast, each party can communicate to the other but not simultaneously; the communication is one direction at a time. An example of a half-duplex device is a walkie-talkie two-way radio that has a “push-to-talk” button when the local user wants to speak to the remote person, they push this button, which turns on the transmitter but turns off the receiver, so they cannot hear the remote person.

E-lines. European digital carrier system.

ETSI. European Telecommunications Standards Institute.

Fading. The variations in the field strength of radio signal, usually gradual, that are caused by the changes

in the transmission medium.

Fading Margin. A design allowance that provides for sufficient system gain or sensitivity to accommodate

expected fading, for the purpose of ensuring that the required quality of service is maintained.

FCC. Federal Communications Commission. An independent agency created to regulate interstate

communications by radio, television, wire, satellite and cable.

Field Intensity. The intensity of the electric and magnetic fields of an electromagnetic wave propagating

First Fresnel Zone. Circular portion of a wavefront transverse to the line between an emitter and a more

distant point, where the resultant disturbance is being observed, whose center is the intersection of the front with the direct ray, and whose radius is such that the shortest path from the emitter through the periphery to the receiving point is one-half wavelength longer than the direct ray.

Flanges. Interconnect part of a microwave antenna system together.

Flat Fade Margin. In an analog microwave radio system, it is equal to the system total gain minus the

system total losses. In digital microwave radio system, the “flat” or thermal fade margin (TFM) is calculated from the system total gain minus the system total losses.

Free Space Path. The line of signal path directly between transmit and receive antennas. Also called, the

direct waves.

Free Space Path Loss. The loss in signal strength of an electromagnetic wave that would result from a

line-of-sight path through free space, usually air, with no obstacles nearby or to cause reflection or diffraction.

Frequency. The number of occurrences of a repeating event per unit time. Specifically, the number of

cycle computed per second by an alternating quantity, the term usually in describing frequency is cycle per second, on Hertz.

Fresnel Zone. The area around the visual line-of-sight that radio waves spread out into after they leave

the antenna. This area must be clear or else signal strength will weaken. It also describes the amount of the front lobe power to the back lobe power of an antenna.

Full Duplex. (See Duplexing).

Gas Absorption. Primarily due to the water vapor and oxygen in the atmosphere in radio relay region. The

absorption peaks are located around 23 GHz for water molecules and 50 to 70 GHz for oxygen molecules. The specific attenuation (dB/km) is strongly dependent frequency, temperature and the absolute or relative humidity of the atmosphere.

Great Circle Distance. The shortest distance between any two points a sphere.

Ground Wave. An electromagnetic wave that travels along the surface of earth, sometimes called,

“surface waves”.

Guard Band. A narrow frequency band provided between adjacent channels in certain portions of the

radio spectrum to prevent interference between stations.

Half Duplex. (See Duplexing).

Interference Fade Margin (IFM). The depth of fade to the point at which RF interference degrades to the

BER to 1x10-3. The actual IFM value used in a path calculation depends on the method of frequency coordination to receiver.

K-Factor. The ratio of a hypothetical effective earth radius over 6370 km, which is the true mean earth

radius.

Line of Sight. An unobstructed view from transmitter to receiver.

Link Budget. The accounting of all the gains and losses from the transmitter, through the medium (free

space, cable, waveguide, etc.) to the receiver in a telecommunication system. It accounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains, feed line and miscellaneous losses.

Long Haul. Long-haul microwave radio networks are implemented in a variety of different topologies and

almost always consist of a series of interconnected radio hops.

Maximum Usable Frequency (MUF). The highest frequency that can be used for sky-wave propagation

between two specific points on earth’s surface.

Microwave. These are ultra-high, super high and extremely high frequencies.

Microwave Communication. A high radio frequency link specifically designed to provide signal connection

between two points.

Microwave Link Design. A methodical, systematic and sometimes lengthy process that includes:

Loss/Attenuation Calculations, Fading and Fade Margins Calculations, Frequency Planning and Interference Calculations, and Quality and Availability Calculations.

Miscellaneous Losses. Unpredictable and sporadic in character like fog, moving objects crossing the path,

poor equipment installation, less than perfect antenna alignment, etc.

MLS. Microwave Landing System, an all-weather, precision landing system, includes a wide selection of

channels to avoid interference.

Multipath Fading. The dominant fading mechanism for frequencies lower than 10 GHz. A reflected wave

causes a multipath, in other words, a reflected wave reaches the receiver as the direct wave that travels in a straight line from the transmitter.

Multipath Interference. When signals arrive at a remote antenna after being reflected off the ground, or

refracted back to earth from the sky (sometimes called ducting), they will subtract (or add) to the main signal and cause the received signal to be weaker (or stronger).

Parabolic Antenna. The medium that bridges information from the transmitting to the receiving end using

the microwave communications system, with both single and dual polarized feeds available. Frequencies from 1.7 to 23.6 GHz can be accommodated just by changing out the feed assembly. Various mounting hardware and accessories availably. Dual frequency and specialty feed are also available.

Polarization. The orientation of the electric field vector in respect to the surface of the earth. Power Density. The rate at which energy passes through a given surface area.

Propagation Losses. Losses due to Earth’s atmosphere and terrain.

Radio Frequency (RF) Propagation. Free-space propagation of electromagnetic waves. Radio Horizon. The curvature of earth presents a horizon to space-wave propagation.

Rain Attenuation. Attenuation of radio waves when passing through moisture-bearing cloud formations

or areas in which rain is falling, increase with the density of the moisture in the transmission path.

Received Signal Level. The actual received signal level (usually measured in negative dBm) presented to

the antenna port of a radio receiver from a remote transmitter.

Receiver Sensitivity. The weakest RF signal level, measured in negative dBm, that a radio needs receive in

order to demodulate and decode a packet of data without errors.

Receiver Sensitivity Threshold. The signal level at which the radio runs continuous errors at a specified bit

rate.

Reflection. The ability of electromagnetic transmission to bounce off a relatively smooth surface.

Refraction. Occurs when a wave crosses a boundary from one medium to another. A wave entering a

Refraction – Diffraction Fading. Also known as k-type fading. For low k values, the Earth’s surface

becomes curved and terrain irregularities, man-made structures and other objects may intercept the Fresnel Zone. For high k values, the Earth’s surface gets close to a plane surface and better lower antenna height is obtained. The probability of refraction-diffraction fading is therefore indirectly connected to obstruction attenuation for a given value of Earth-radius factor.

Short Haul. Short-haul microwave networks are licensed and unlicensed microwave radio systems that

are historically less than 250 miles in length with the same availability objective of 99.98% as a long-haul system 400 miles in length. Although short-haul microwave radio was strictly defined in the past, modern deployments have seen short-haul microwave radio systems applied to a broad range applications. These systems are often high capacity radio links and in many cases are designed to achieve high availabilities.

Surface Wave. (See Ground Wave).

System Operating Margin. The difference, measured in dB, between the nominal signal level received at

one end of a radio link and the signal level required by that radio to assure that a packet of data is decoded without error.

Thermal Fade Margin (TFM). The difference between the normal received signal RSL at the input of

microwave receiver expressed in dBm, and the receiver’s threshold (given by the manufacturer) expressed in dBm (TFM = RSL – TH).

Transmit Power. The RF power coming out of the antenna port of a transmitter.

Waveguide. A special type of transmission line that consist of a conducting metallic tube through which

high frequency electromagnetic energy is propagated.

Wi-Fi. Wireless Fidelity, a local area wireless technology that allows an electronic device to exchange data

FACTOR CONSIDERATION IN CHOOSING THE SITE

Microwave is becoming a popular choice over wire line transport over many wireless carriers. It is an attractive option for several reasons, especially as radio equipment costs decrease. Low monthly operating costs can undercut those of typical expenses, proving it more economical in the long run. But before moving forward, make sure to understand all the considerations which will affect the deployment of the design.

It is essential to comprehend the relationship between capacity, frequency band, path distance, tower heights, radio equipment and antennas.

Frequency Options

A wavelength is the distance in between the repeating units of a wave, as measured from one point on a wave to the corresponding point in the next unit. For example, the distance from the top – called the crest – of one wave unit to the crest of the next is one wavelength. In physics notation, wavelength is often designated by the Greek letter lambda. Wavelength is inversely proportional to the frequency of a wave. In other words, the shorter the wavelength is, the more wave units will pass in a given amount of time.

Wavelengths in lower frequencies are longer, which is important because wavelength determines how the atmospheric affects transmission. The atmosphere may refracts longer waves. Refraction can reduce the length of the path, or microwave hop.

The microwave link bands can be roughly grouped together: Less Than 3 GHz. Many UHF analog microwave links still are deployed in the 400-MHz band with the 1.4-GHz band now being used for

low-capacity, digital links. The 2.4 GHz is used for unlicensed links. In these lower frequency bands, long hops, even greater than 100 km, can be accommodated. This is due to the more robust modulation schemes and the less stringent line-of-sight requirements. Due to the larger wavelength, the antenna surface accuracy on solid parabolic dishes is not critical and simple horn feed can be used; therefore, the antennas are much cheaper, even though they are often physically large. Low-cost grid antennas, yagis, and flat panel antennas can be also used.

3-11 GHz. This group of frequencies is typically where the main medium-to-high capacity long haul

band links are deployed; 4 GHz, 6 GHz, 7/8 GHz, and 11 GHz are typical. The 5.8 GHz is used for unlicensed links. These links require full line-of-sight and are affected mainly by multipath fading. Thirty miles (50 km) is considered the ideal hop length that balances the requirement to maximize hop length with costs, ease of design, and deployment complication. Short hops should not be put in these bands, as they are a waste of valuable spectrum.

13-38 GHz. This group of frequencies is used for short hops, and there is an abundance of

spectrum. The main fading effect is from rain attenuation. Links below 30 km can typically be deployed in the 13-GHz or 15-GHz band, whereas for every short hops (less than 5 km), the 38-GHz band should be used. Other link frequencies in this category are 18 GHz, 23 GHz, 26 GHz (ETSI), 32 GHz (new band) and 38 GHz. The 24 GHz is used for unlicensed links.

60-90 GHz (Millimeter Bands). More recently, massive amounts of spectrum (over 5 GHz) have

been made available in the E-band. The three key band are 79 GHz (71 to 76), 80 GHz (81 to 86) and 90 GHz (92 to 95). Path loss is not excessive (around 0.5 dB per km), despite the high frequency, and so they are practical for hops up to a few kilometers. It must be remembered that 23 GHz is on a resonant peak, so there is no linear scaling of losses between 23 GHz and 90 GHz; 60 GHz for unlicensed links. This

additional spectrum in these millimeter bands will become very necessary as lots of next generation base stations are rolled out, all requiring backhaul connections to the network.

Terrain and Weather

Terrain such as mountains, hills, trees and building can block a microwave signal and limit the distance of a microwave path.

Capacity is another important consideration. Radios can be configured to carry a certain amount of traffic in a specific frequency. Based on capacity and radio equipment, antenna size, tower heights and terrain elevation will play a major role on how the system will be planned and constructed. These four factors also will dictate system’s reliability, multi-path, fading, fade margin calculations, Fresnel zone clearance, interference analysis, system diversity and distance specifications.

A large antenna will be used for longer path. It requires large towers with higher wind factors as well. As a result, existing tower loads must also be considered to ensure that the design can be implemented on existing structures. Also, the attenuation must be taken into account. The reduction as a signal travels through equipment, transmission lines or air. The term often refers to the impact of rain, or fog, as well as normal signal loss in the wave guide and microwave system.

Path reliability normally has to meet the same standards as the rest of the microwave system. Reliability objectives are often stated on a per hop basis or end-to-end.

Due to multi-path phenomena, obstruction, and rain attenuation, fading mechanisms is also considered. Equipment and power-source reliability demands are dealt with through a combination of highly reliable components plus designs that incorporate redundancy and protection.

Equipment Selection

When selecting equipment, determine the amount of power the system uses to transmit and receive signals. More power usage equates to higher operating costs. System planners should perform path calculations to establish fade margins and system gain, considering an estimate of system downtime for the locale of the planned radio. Fade margin is the allowance made to accommodate estimated propagation fading without exceeding a specific signal-to-noise ratio.

With careful attenuation to link gain power, antenna height, receiver sensitivity, free space loss, attenuation and availability requirements, microwave radio can be integrated radio effectively into virtually any wireless system.

Population

Sites A and B are located at the municipality of Manticao, Misamis Oriental where the population is not that large, to avoid so much external interference.

SITE DESCRIPTION

Municipality of Manticao, Misamis Oriental

Founded in February 7, 1949. Manticao is located in the province of Misamis Oriental in Region X Northern Mindanao which is a part of the Mindanao group of islands. It is seated 41 km west-south-west of province capital Cagayan de Oro City. Administratively, the Municipality of Manticao is subdivided into 13 barangays. One forms the center of the town, whereas the other 12 are in the outlying areas. Some of them are even several kilometers away from the poblacion.

Manticao has a total land area of 123.02 km2 _{with approximately 30,000 inhabitants. According}

to the Phillippine income classification for provinces, cities and municipalites, it is a 4th _{class municipality.}

The urbanization of Manticao is classified as partly urban.

SITE A: Poblacion, Manticao,

Misamis Oriental

SITE B: Tuod, Manticao,

Misamis Oriental

Population

Approx. 8,000

Approx. 3,000

Location

Latitude: 8°24’15” N

Longitude: 124°17’12” E

Latitude: 8°20’36” N

Longitude: 124°21’15” E

Elevation Above the

Sea Level

5 meters

95 meters

Temperature

28.55° C

Maximum

Temperature

33.17° C

Wind Speed

5 mph WNW

Humidity

72.75%

Cloudiness

24%

Pressure

1010 mb

Precipitation Amount

9.72 mm

MICROWAVE LINK PLANNING

Transmitter and Receiver Equipment Specifications

CFQ series 13 GHz digital microwave radio unit

Frequency range: 13.75 – 14.25 GHz

Waveguide: WR75

Frequency = 10 – 15 GHz

Internal dimension = 0.750 x 0.375 in

Gain = 20 dB

Connector: RF Connector/SMA Female/50 Ohms

Flange: UBR 120

Antenna: VP4A-142

Path Length: 20 km Center Frequency: 14 GHz

Type of Map: Topographical Map, Scale = 1:50,000 Reliability Requirement: 99.9999%

Configuration: Non-Protected (1+0)

Traffic Capacity: 1 x E3 with a rate of 34.368 Mbps and a capacity of 480 channels

Locations: Site A Site B

LINK BUDGET COMPUTATIONS

I. Azimuth Angle Computation

C = Longitude B – Longitude A = LOB – LOA = 124°21’15” – 124°17’12” = 0°4’3” ½C = 0°2’1.5” (LB + LA) = 8°20’36” + 8°24’15” = 16°44’51” ½(LB + LA) = 8°22’25.5” (LB – LA) = 8°20’36” – 8°24’15” = -0°3’39” ½(LB – LA) = -0°1’49.5”

Log tan ½(Y + X) = log cot ½C + log cos ½(LB – LA) – log sin ½(LB + LA)

tan ½(Y + X) = log-1 _{[log cot ½C + log cos ½(L}

B – LA) – log sin ½(LB + LA)]

½(Y + X) = tan-1 _{log-1 _{[log cot (0°2’1.5”) + log cos (-0°1’49.5”) – log sin (8°22’25.5”)]}}

½(Y + X) = 89°59’42.31”

Log tan ½(Y – X) = log cot ½C + log sin ½(LB – LA) – log cos ½(LB + LA)

tan ½(Y – X) = log-1 _{[log cot ½C + log sin ½(L}

B – LA) – log cos ½(LB + LA)]

½(Y – X) = tan-1 _{log-1 _{[log cot (0°2’1.5”) + log sin (0°1’49.5”) – log cos (8°22’25.5”)]}}

Azimuth Angle

X = ½(Y + X) – ½(Y – X) Y = ½(Y + X) + ½(Y – X)

X = 89°59’42.31” – 42°19’54.57” Y = 89°59’42.31” + 42°19’54.57” X = 47°39’47.61” (Site A) Y = 132°19’36.88” (Site B)

II. Minimum and Maximum Elevation of Site A and Site B hmin = d2/(flower*k)

hmin = 102/[(13.75)(4/3)] = 5.45 m

Where: d = (path length, in kilometers)/2

hmin = minimum site elevation, in meters

flower = low band transmit frequency, in GHz

k = 4/3

III. Minimum Reliable Tower Height

Lk = (d1*d2)/(flower*k) = [(10)(10)]/[(13.75)(4/3) = 5.45 m Lf = 17.3*F%*√ 𝑑1𝑑2 𝑓𝑙𝑜𝑤𝑒𝑟𝐷 = 17.3*0.60*√ (10)(10) (13.75)(20) = 6.25 m L = Lk + Lf + LFH = 5.45 m + 6.25 + 100 m = 111.70 m

Where: L = clearance criteria in meters

Lk = curvature factor, in meters

Lf = Fresnel factor, in meters

LFH = arbitrary fixed height, in meters (clearance criteria at fixed height of 100 m)

d1 = distance from site A to point, in kilometers

d2 = distance from site B to point, in kilometers

D = path distance in kilometers

F% = Fresnel zone percentage factor, 60% flower = low band transmit, in GHz

d1 d2 LFH Lf Lk L 0 20 100 0.00 0.00 0.00 1 19 100 2.73 1.04 103.77 2 18 100 3.76 1.96 105.72 3 17 100 4.47 2.78 107.25 4 16 100 5.01 3.49 108.50 5 15 100 5.42 4.09 109.51 6 14 100 5.74 4.58 110.32 7 13 100 5.97 4.96 110.93 8 12 100 6.13 5.24 111.37 9 11 100 6.23 5.40 111.63 10 10 100 6.25 5.45 111.70 11 9 100 6.23 5.40 111.63 12 8 100 6.13 5.24 111.37 13 7 100 5.97 4.96 110.93 14 6 100 5.74 4.58 110.32 15 5 100 5.42 4.09 109.51 16 4 100 5.01 3.49 108.50 17 3 100 4.47 2.78 107.25 18 2 100 3.76 1.96 105.72 19 1 100 2.73 1.04 103.77 20 0 100 0.00 0.00 0.00

IV. Free Space Loss FSL = 92.45 + 20 log (fGHz*D) LBF: FSL = 92.45 + 20 log (13.75*20) = 141.24 dB HBF: FSL = 92.45 + 20 log (14.25*20) = 141.55 Db Where: fGHz = frequency

D = path distance in kilometers

V. Received Signal Level

RSL = PO + AGTX + AGRX – CLTX – CLRX – WLTX – WLRX – FSL

LBF: RSL = 32 + 42.70 + 42.70 – 0.5 – 0.5 – 12.51 – 12.51 – 141.24 = -49.86 dB

HBF: RSL = 32 + 42.70 + 42.70 – 0.5 – 0.5 – 12.51 – 12.51 – 141.55 = -50.17 dB

VI. Thermal Fade Margin TFM = RSL – MRT

LBF: TFM = -49.86 – (-83) = 33.14 dB HBF: TFM = -50.17 – (-83)

Computation for Low Band Frequency (13.75 GHz)

Parameters Value Unit

Microwave Radio Output Power 32.00 dBm

Connector Loss (Tx) 0.50 dB

Waveguide Loss (Tx) 12.51 dB

Antenna Gain (Tx) 42.70 dB

Free Space Loss 141.24 dB

Antenna Gain (Rx) 42.70 dB

Waveguide Loss (Rx) 12.51 dB

Connector Loss (Rx) 0.50 dB

Power Input to Receiver (RSL) -49.86 dB

Minimum Receiver Threshold -83 dB

Computation for High Band Frequency (14.25 GHz)

Parameters Value Unit

Microwave Radio Output Power 32.00 dBm

Connector Loss (Tx) 0.50 dB

Waveguide Loss (Tx) 12.51 dB

Antenna Gain (Tx) 42.70 dB

Free Space Loss 141.24 dB

Antenna Gain (Rx) 42.70 dB

Waveguide Loss (Rx) 12.51 dB

Connector Loss (Rx) 0.50 dB

Power Input to Receiver (RSL) -50.17 dB

VII. Net Path Loss NPL = Power Output – RSL LBF: NPL = 32 – (-49.86) = 81.86 dB HBF: NPL = 32 – (-50.17) = 82.17 dB

VIII. Rain Loss

CCIR/ITU-R Recommendation 530 rain attenuation

For Low Band Frequency (LBF): 13.75 GHz M = (log f1 – log fX)/(log f1 – f2) note: f1<fX<f2

k = log-1 _{[log k}

1 – M (log k1 – log k2)]

k = log-1 _{[log 0.0335 – 0.61 (log 0.0335 – log 0.0168)]}

k = 0.02198903

α = α1 – M (α1 – α2)

α = 1.099 – 0.61 (1.099 – 1.154) α = 1.13255

For High Band Frequency (HBF): 14.25 GHz M = (log f1 – log fX)/(log f1 – f2) note: f1<fX<f2

M = (log 12 – log 14.25)/(log 12 – log 15) M = 0.77

k = log-1 _{[log k}

1 – M (log k1 – log k2)]

k = log-1 _{[log 0.0335 – 0.77 (log 0.0335 – log 0.0168)]}

k = 0.01969012

α = α1 – M (α1 – α2)

α = 1.099 – 0.77 (1.099 – 1.154) α = 1.14135

IX. Effective Rain Path Length DO = 35 x e-0.015*R0.001 DO = 35 x e-0.015*180 DO = 2.3522 DE = D/[1 + (D/DO)] DE = 20/[1 + (20/2.3522)] DE = 2.1047 km

Where: DE = effective rain path length

R0.001 = rainfall rate at 0.001% outage

X. Unit Rain Attenuation

For Low Band Frequency (LBF): 13.75 GHz k = 0.02198903

α = 1.13255 y = k*(R0.001) α

y = 0.02198903*(180) 1.13255

y = 7.87798

For High Band Frequency (HBF): 14.25 GHz k = 0.01969012

α = 1.14135 y = k*(R0.001) α

y = 0.01969012*(180) 1.14135

Rain Attenuation Arain = DE*y LBF: Arain = (2.1047)(7.87798) = 16.581 dB HBF: Arain = (2.1047)(7.38420) = 15.542 dB

XI. Atmospheric Losses

o Oxygen Absorption Loss

AO = [7.19*10-3 + (6.09/(f2 + 0.227)) + (4.81/((f – 57)2 + 1.5))](f2*10-3) LBF: AO = [7.19*10-3 + (6.09/(13.752 + 0.227)) + (4.81/((13.75 – 57)2 + 1.5))](13.752*10-3) = 0.03985 dB/km AO for 20 km = 0.797 dB HBF: AO = [7.19*10-3 + (6.09/(14.252 + 0.227)) + (4.81/((14.25 – 57)2 + 1.5))](14.252*10-3) = 0.03768 dB/km AO for 20 km = 0.754 dB

o Wave Vapor Loss

AH2O = [0.067 + (3/((f-22.3)2 + 7.3)) + (9/((f-183.3)2 + 6)) + (4.3/((f-323.8)2 + 10))](f2*α*10-4)

LBF: AH2O = [0.067 + (3/((13.75 – 22.3)2 + 7.3)) + (9/((13.75 – 183.3)2 + 6)) + (4.3/((13.75 –

323.8)2 _{+ 10))](13.75}2_*1.13255*10-4₎

= 2.24122 x 10-3 _dB/km

HBF: AH2O = [0.067 + (3/((14.25 – 22.3)2 + 7.3)) + (9/((14.25 – 183.3)2 + 6)) + (4.3/((14.25 –

323.8)2 _{+ 10))](14.25}2_*1.14135*10-4₎

= 2.52548 x 10-3 _db/km

AH2O for 20 km = 0.051 dB

XII. Reliability Calculation o Flat Fade Margin

FMFlat = -10 log [10(-FMthermal/10) + 10(-FMdiff/10)]

LBF: FMFlat = -10 log [10(-33.14/10) + 10(-33.14/10)]

= 30.13 dB

HBF: FMFlat = -10 log [10(-32.83/10) + 10(-32.83/10)]

= 29.82 dB

o Composite or Effective Fade Margin

FMComposite = -10 log [10(-FMthermal/10) + RD*10(-FMdispersive/10)]

LBF: FMComposite = -10 log [10(-33.14l/10) + 3*10(-70/10)]

= 33.137 dB

HBF: FMComposite = -10 log [10(-32.83/10) + 3*10(-70/10)]

o K – Q Reliability Calculation U = K-Q*fb_*Dc_*10(-FMeff/10) LBF: U = (1x10-9_)(13.751.2₎₍₂₀3.5₎₍₁₀(-33.14/10)₎ = 4.032 x 10-7 R = (1 – U) x 100% = (1 – 4.032x10-7_{) x 100%} = 99.9999% HBF: U = (1x10-9_)(14.251.2₎₍₂₀3.5₎₍₁₀(-32.83/10)₎ = 4.520 x 10-7 R = (1 – U) x 100% = (1 – 4.520x10-7_{) x 100%} = 99.9999%

CONCLUSION

Microwave link design is a specific sort of engineering in the broader field of communications. The clear line of sight, choosing an appropriate frequencies which may be used for a specific distance, and path terrain condition, are just few out of several factors that should be considered in designing.

To have some certainty as to whether the wireless link will be reliable, an RF path analysis needs to be performed. The size of each Fresnel Zone varies based on the frequency of the radio signal and the length of the path. As frequency decreases, the size of the Fresnel Zone also increases. The midpoint of this requires the most clearance of any point in the path.

Upon the completion of this design, the needed outcomes and conditions regarding the design were able to meet, and a point-to-point Cellular Link System were made having a 99.9999% reliability.

REFERENCES

Books:

Ayers, Mark. Telecommunications System Reliability Engineering, Theory, and Practice. 1st _ed.

Hoboken, New Jersey: John Wiley & Sons, Inc., 2012.

Manning, Trevor. Microwave Radio Transmission Design Guide. 2nd _{ed. 685 Canton Street,}

Norwood: Artech House Publishers, 2009.

Tomasi, Wayne. Electronic Communications Systems: Fundamental Through Advanced. 5th _ed.

Upper Saddle River, New Jersey: Pearson Education, Inc., 2004.

Internet Sources: www.google.com.ph/maps www.mapanet.eu www.microwave-planning.com www.philippine-islands.ph www.softwright.com www.webopedia.com www.wikipedia.org www.worldweatheronline.com