Terrestrial Microwave Link Design

Terrestrial Microwave Link Design ‗Abdulrahman

1, Ong Sin Yee

2, Nurul Shafikah

3, Mohamud Mire mohamud

4

Radar Communication Laboratory, Faculty of Electrical Engineering

Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia [email protected]

[email protected]

[email protected]

[email protected]

Abstract—Microwave links provide the bulk of the

interconnectivity between sites in telecommunications networks

(especially mobile voice and data networks) because they are

rapidly deployable, relatively small and require less

infrastructure outlay than technologies such as fibre

transmission. Typical applications of microwave link includes

mobile backhaul links - between 2G/3G base stations and

WiMAX/LTE backhaul links. The basic components required for

operating a radio link are the transmitter, towers, antennas, and

receiver. To achieve point-to-point radio links, antennas are

placed on a tower or other tall structure at sufficient height to

provide a direct, unobstructed line-of-sight (LOS) path between

the transmitter and receiver sites. Before a microwave link can

be installed, an analysis and calculation of the microwave link

must be made first. The analysis should take place before the site

survey itself to get a clear idea about the dimensions of the

antennas. Our analysis consists in this paper consists of Free

space loss calculation and Link budget calculation.

Keywords— transmitter design, receiver design, point-to-point

microwave link, frequency of 9, 15 and 18 GHz, system level.

I. INTRODUCTION

A microwave link fundamentally consists of a transmitter

and a receiver. The transmitter and the receiver are each

connected to an antenna. This is typically a parabolic dish

antenna connected to the transmitter, and also typically a dish

antenna on the receiver. Based on operating 3G point-to-point

microwave link system which functioning frequency 9, 15 and

18 GHz only. The receiver always needs to be typically within

the range of kilometres of the transmitter, but the distance is

very much dependent on the path between the transmitter and

receiver, as in [1].

Before we discuss the different types of antennas, this is the

objectives as follows:

To understand the project and problem statement given.

To design a terrestrial microwave link system.

To analysis and discuss on the performance of the

designed system.

To determine the appropriate operating frequency to be

engaged in this microwave link system.

To do analysis on actual overall costing for the

microwave link design.

We should have a quick look at the subject of polarization,

as it is relevant to antennas used in terrestrial microwave

communications. Signals transmitted in any frequency band

have a property termed polarization, and this relates to the

geometric plane in which the electromagnetic waves are

transmitted or received. Hence polarization describes the

orientation of the electric field radiated from the antenna, as in

[2].

There is little fundamental difference between transmitting

antennas and receiving antennas, since the same antenna is

often used for both purposes. While some antennas can be as

simple as a wire thrown out of a window, for the best

performance the right type of antenna needs to be used. The

most important properties of an antenna are its radiation

pattern and its gain (the magnitude of the signal), whether it is

being used at the transmitter or receiver. In the case of a

transmitting antenna, the radiation pattern is a plot of the

power strength radiated by the antenna in different directions.

As a consequence of its radiation pattern, power radiated by

an antenna may be concentrated in a particular direction, and

this directivity is expressed in terms of power gain, as in [3].

In order to design terrestrial point-to-point link system,

there are several technical choices that we considered for

instance the microwave LOS link , the link budget , free space

path loss and its accuracy on the link analyses. The choice of

the transmission media is one the most important actions we

took, always at the first stages of the design of a

communication system. This section describes briefly the

different choices for establishing a link between two locations,

and the different advantages and drawbacks of each

alternative.

II. POINT TO POINT MICROWAVE LINKS

Point-to-Point (PTP) Microwave technology provides

dedicated, point-to-point connectivity using directional

antennas. 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 meters to several kilometres apart. PTP

links typically require clear Line of Sight (LOS) between the

transmitting antennas.

A. Microwave Line-of-Sight Systems

Microwave frequencies range from 300 MHz to 30 GHz,

corresponding to wavelengths of 1 meter to 1 cm. These

frequencies are useful for terrestrial and satellite

communication systems, both fixed and mobile.

"Line-of-sight" is a term used in radio system design to

describe a condition in which radio device antennas can

actually see each other. High frequency radios, such as those

used in Spread Spectrum Radio require line-of-sight between

antennas, as shown in Fig. 1, as in [4].

In the case of point-to-point radio links, antennas are placed

on a tower or other tall structure at sufficient height to provide

a direct, unobstructed line-of-sight (LOS) path between the

transmitter and receiver sites, as in [5].

Fig. 1 Line of sight of point-to-point application

B. Standards

Each country has a varying requirement for the licensing of

microwave radio links. In most cases this license only

addresses the transmitter, but in the same instance, it offers

regulatory protection to any interference that may affect the

microwave receiver.

In the United States, radio channel assignments are

controlled by the Federal Communications Commission (FCC)

for commercial carriers and by the National

Telecommunications and Information Administration (NTIA)

for government systems.

The FCC's regulations for use of spectrum establish

eligibility rules, permissible use rules, and technical

specifications. FCC regulatory specifications are intended to

protect against interference and to promote spectral efficiency.

Equipment type acceptance regulations include transmitter

power limits, frequency stability, out-of-channel emission

limits, and antenna directivity.

The International Telecommunications Union Radio

Committee (ITU-R) issues recommendations on radio channel

assignments for use by national frequency allocation agencies.

Although the ITU-R itself has no regulatory power, it is

important to realize that ITU-R recommendations are usually

adopted on a worldwide basis.

So, in our case, which is specifies the minimum

performance parameters for terrestrial fixed service digital

radio communications equipment‘s operating in the 13 GHz,

15 GHz and 18 GHz frequency bands. Systems considered are

able to respect ITU-R national or international grade

performance objectives, i.e. ITU-R Recommendations F.1189

for national, F.1092 for international and ITU-R

Recommendation G.826. We also respect to the ITU-R P.530-

12 – Propagation data and prediction methods required for the

design of terrestrial line-of-sight systems.

ATPC power level definitions and limits are shown in

Table 1.

We also make use of the Automatic Transmit Power

Control (ATPC) range in our project. ATPC is defined as the

power interval from the maximum (including tolerances)

output power level to the lowest transmitter output power

level. If implemented, the ATPC range shall not be less than

10 dB.

ATPC set manually to a fixed value for system

performance. Other than that, ATPC also set at maximum

provide power for Transmit (TX) performance.

TABLE 2

VALUE OF LINK BUDGET

C. Microwave Link Structure

The basic components required for operating a radio link

are the transmitter, towers, antennas, and receiver. Transmitter

functions typically include multiplexing, encoding,

modulation, up-conversion from baseband or intermediate

frequency (IF) to radio frequency (RF), power amplification,

and filtering for spectrum control. Receiver functions include

RF filtering, down-conversion from RF to IF, amplification at

IF, equalization, demodulation, decoding, and demultiplexing.

To achieve point-to-point radio links, antennas are placed on a

tower or other tall structure at sufficient height to provide a

direct, unobstructed line-of-sight (LOS) path between the

transmitter and receiver sites, as shown in Fig. 2, as in [6].

Radio transmitters are described in terms of power output

expressed in watts. The power output may also be expressed

in terms of decibels of gain (dB). Radio receivers are rated in

terms of sensitivity (ability to receive a minimal signal). The

rating is listed in terms of milliwatts (mW), or decibels of gain

(dB). Antenna cable is rated in terms of signal loss per foot

and expressed as dB of loss per foot. The antenna is rated in

terms of gain (dB). There are a number of software programs

that will calculate path loss by frequency and use the

specifications of the system hardware to help determine the

overall system feasibility.

Fig. 2 Point-to-point microwave link structure

III. MICROWAVE LINK DESIGN

A block diagram of a transmitter base station is shown in

Fig. 3. The transmitter base station of digitalization and

encoding, WCDMA Generation (modulator), and transmitter.

A block diagram of a receiver base station is shown in Fig. 4.

The transmitter base station of receiver, demodulator, and

digitalization and encoding.

Fig. 3 Transmitter base station block diagram

Fig. 4 Receiver base station block diagram

D. Description of the Purpose and Operation of All the Major

Components of Base Stations

1) Digitalization and Encoding: using ADC at transmitter

to convert the information from analogue to digital and it

using DAC at receiver to convert the information from digital

to analogue. Encoding using orthogonal coding, spreading,

and correlation that W-CDMA uses a variable length code.

The length of spreading code is also known as the spreading

factor. Base station that receives a transmitted data sequence

and attempts to demodulate it using the ―wrong‖ orthogonal

code, would interpret the information as noise.

2) Transmitter: The transmitter produces a microwave

signal that carries the information to be communicated. The

transmitter has two fundamental functions: generating

microwave energy at the required frequency and power level,

and modulating it with the input signal so that it conveys

meaningful information. Modulation is accomplished by

varying some characteristic of the energy in response to the

transmitter‘s input.

3) Transmission Line: The transmission line carries the

signal from the transmitter to the antenna and, at the receiving

end of the link, from the antenna to the receiver. At

microwave frequencies, coaxial cables and, especially, hollow

pipes called waveguides are used as transmission lines.

4) W-CDMA Generation (Modulator): The access

technology, W-CDMA (Wideband Code Division Multiple

Access), is termed UTRA (UMTS Terrestrial Radio Access).

The information that was modulated onto the carrier from the

carrier itself. It could be audio and/or video information, or

other data. The modulator accomplished by puts the

information or intelligence onto a carrier wave at the

transmitter input.

5) Receiver: The receiver extracts information from the

microwave signal and makes it available in its original form.

To accomplish this, the receiver must demodulate the signal to

separate the information from the microwave energy that

carries it. The receiver must be capable of detecting very

small amounts of microwave energy, because the signal loses

much of its strength on its journey.

6) Demodulator: Demodulator is a circuit used in AM

(amplitude modulation) and FM (frequency modulation)

receivers to separate the information that was modulated onto

the carrier from the carrier itself. It could be audio and/or

video information, or other data. A demodulator is the

analogue of the modulator. The demodulator pulls it off so it

can be processed and used on the other end.

E. Brief Description of the Basic Operation of Transmitter

and Receiver

A block diagram of a transmitter is shown in Fig. 5. The

transmitter of mixer with local oscillator, band pass filter, RF

amplifier, cable and antenna. A block diagram of a receiver is

shown in Fig. 6. The transmitter of antenna, cable, receiver,

lower noise amplifier, band pass filter and mixer with local

oscillator.

Fig. 5 Transmitter block diagram

Fig. 6 Receiver block diagram

1) Lower Noise Amplifire (LNA): LNA is an electronic

amplifier used to amplify possibly very weak signals (for

example, captured by an antenna). It is usually located very

close to the detection device to reduce losses in the feedline.

An LNA is a key component which is placed at the frontend

of a radio receiver circuit. Per Friss‘ formula, the overall noise

figure (NF) of the receiver‘s front-end is dominated by the

first few stages. A good LNA has a low NF (e.g. 1 dB), a very

large enough gain (e.g. 20 dB) and should have large enough

intermodulation and compression point. The gain of the LNA

is 22 dB and the NF is 2.5 dB.

2) RF Amplifier: RF Amplifier (power amplifier) is a type

of electronic amplifier used to convert a low-power radio-

frequency signal into a larger signal of significant power,

typically for driving the antenna of a transmitter. It is usually

optimized to have a high efficiency, high output power

compression, good return loss on the input and output, good

gain and optimum heat dissipation.

3) Band Pass Filter (BPS): Band Pass Filter is a device

that passes frequencies within a certain range and rejects

frequencies outside that range. An ideal band pass filter would

have a completely flat passband (e.g. with no gain/attenuation

throughout) and would completely attenuate all frequencies

outside the passband. Additionally, the transition out of the

passband would be instantaneous in frequency. In practice, no

bandpass filter is ideal. The filter does not attenuate all

frequencies outside the desired frequency range completely; in

particular, there is a region just outside the intended passband

where frequencies are attenuated, but not rejected. This is

known as the filter roll-off, and it is usually expressed in dB

of attenuation per octave or decade of frequency.

4) Local Oscillator: To generate a signal normally for the

purpose of converting a signal of interest to a different

frequency using a mixer. This process of frequency

conversion, also referred to as heterodyning, produces the sum

and difference frequencies of the frequency of the local

oscillator and frequency of the input signal of interest. These

are the beat frequencies. Normally, the beat frequency is

associated with the lower sideband, the difference between the

two.

5) Cable: The cable is to provide power from a power

source to some piece of equipment or tool. The basic and sole

purpose of a power cable is to transport electrical energy from

the source of the electricity to the device.

6) Antenna: The last part of the microwave system is the

antennas. On the transmitting end, the antenna emits the

microwave signal from the transmission line into free space.

At the receiver site, an antenna pointed toward the

transmitting station collects the signal energy and feeds it into

the transmission line for processing by the receiver. Antennas

used in microwave links are highly directional, which means

they tightly focus the transmitted energy, and receive energy

mainly from one specific direction. By concentrating the

received signal, this characteristic of microwave antennas

allows communication over long distances using small

amounts of power.

7) Microwave tower: A microwave tower is a structure

built to enhance wireless communication. For them to work,

they have to cover large areas using an interconnecting pattern

and they can be located anywhere. Most of them are located

close to where people habit and to power supply areas.

F. Signal spreading in W-CDMA transmitter and receiver

The process start with IF input 350 MHz then convert to 9

GHz or 15 GHz or 18 GHz. The data is then "spread‖ using a

code which is running at either 9 GHz or 15 GHz or 18 GHz

code rate. The resulting spread bits are called chips and the

resulting transmitted spread rate is expressed as either 9 GHz

or 15 GHz or 18 GHz. The distance is fixed to 10km. The

receiver of base station will see this spread signal together

with noise, interference, and messages on other code channels

in the same RF frequency slot. The interference can come

from other signal. The base station‘s demodulator then

reapplies the code and recovers the original data signal. The

signal spreading as shown in Fig. 7.

Fig. 7 Signal spreading in W-CDMA transmitter and receiver

G. Signal spreading in W-CDMA transmitter and receiver

The typical technical characteristics of microwave point to

point transmission links as follows:

Range: microwave point to point links use 10 km.

Microwave radio communication requires clear line-of-

sight (LOS) between the respective endpoints. Increase

in range typically requires higher antenna heights to

account for the ―earth bulge‖.

Data Rate: Microwave PTP systems can support up to

Gigabit speeds.

Frequency Bands: Microwave PTP links operate in

Licensed and Unlicensed frequency bands

Licensed frequency bands require expensive license.

However there are multiple benefits associated with

using licensed frequencies including

High system availability

Secure as compared to unlicensed band

Optimum system performance due to lack of

interference

Lower long term operational cost

Considerations with licensed band

H. Applications

Microwave PTP can be used for a very wide range of

applications. Currently mostly PTP Microwave systems are

used for cellular backhaul application, for example Mobile

backhaul links between 2G/3G base stations. Cellular

companies utilize PTP microwave links for their equipment

connectivity.

Enterprise networks utilize microwave PTP system for

Internet/Intranet access, corporate voice, File transfers, Video-

conferencing. PTP systems are commonly used for last mile

access to the PSTN and other voice and data networks.

PTP microwave system are widely used for increasing rural

telephony and network extensions.

IV. LINK ANALYSIS AND BUDGET

A. Free space loss path calculation

The Free Space Path Loss (FSPL) measures the power loss

in free space without any obstacles. So for end-users, it is

important to know the approximate frequency between the

transmitter and receiver while maintaining a certain link

quality at different data transfer rates.

FSPL depends on two parameters:

Frequency of radio signals

Wireless transmission distance

In our task, we choose to fix the parameter distance and

varied the frequency. The following formula can reflect the

relationship between them as follows:

( ) ( ) ( ) (1)

d = distance (10 km)

f = frequency (9 GHz, 15 GHz, 18 GHz)

K= constant that depends on the units used for d and f

If d is measured in kilometres, f in MHz, the formula is:

( ) ( ) ( ) (2)

1) FSPL (dB) of 9 GHz

( ) ( ) ( )

( )

2) FSPL (dB) of 15GHz

( ) ( ) ( )

( )

3) FSPL (dB) of 18 GHz

( ) ( ) ( )

( )

B. Link Budget Calculation

A wireless link budget for a point-to-point radio link

accounts for all the gains and losses from the transmitter,

through cables, antennas and free space to the receiver.

The link budget values are shown in Table 2.

Estimating the value of the "power" in the different parts of

the radio link is necessary to be able to make the best design

and the most adequate choice of equipment. The equation of

link budget as follow:

Link Budget = Tx power (dBm) + Tx Antenna Gain (dBi) +

Rx Antenna Gain (dBi) – Tx Cable losses (dB)

– Rx Cable Losses (dB) –FSPL (3)

TABLE 2

VALUE OF LINK BUDGET

Frequency Tx

Power

(dBm)

Tx/Rx

Antenna

Gain

(dBi)

Tx/ Rx

Cable

Losses

(dB)

FSPL

(dB)

9 GHz 18 34.0 22.1 131.52

15 GHz 18 32.1 23.1 135.96

18 GHz 18 38.6 27.3 137.55

*For Tx Power is assumed to be equal to 18dBm for all the

frequency. For others, the value is taken from the data sheet.

1) Link Budget (dB) of 9 GHz

( ) ( )


( ) ( )


( ) ( ) *For Rx sensitivity (minimum received signal) to be assumed = 110 dB

The performance of any communication link depends on

the quality of the equipment being use. The receive power or

the link budget is determined by transmit power, transmitting

antenna gain, receiving antenna gain and some losses. With

that value, we have to minus with Free Space Path Loss of the

link path and make a comparison with the receiver sensitivity.

The difference between the minimum received signal level

and the actual received power is called the link margin. The

link margin must be positive, and should be maximized.

Based on the calculation on the Free Space Path Loss and

Link Budget Calculation the frequency of 9 GHz is the most

appropriate frequency compare to 15 GHz and 18 GHz

because of the lowest value of losses (131.52 dB) and it

receive the highest power (based on link budget). Moreover,

the link margin for 9 GHz is 20.28 dB which the link margin

should be maximized for reliable link.

V. COST BUDGET

A. Cost Budget for Transmitter and Receiver using 9 GHz

No Component Name and Picture Gain NF Quantity Total Price

1 Mixer with

Local

Oscillator

HMC144

GaAs MMic Triple-Balanced

5-20 GHz

10 10 2 RM143.49

2 Bandpass

Filter

K&L S/N 1 9SB10-

7000/T4000-O/O

5-9 GHz

1 1 2 RM1,240.00

3 RF Amplifier

P35-4150-000-200

2-18 GHz

6 7.5 1 RM274.95

4 Low Noise

Amplifier

AMMP-6220

6-20 GHz

22 2.5 1 RM141.60

5 Antenna

HPD2-10

High-Performance Dual Polarized

9-10 GHz

34 2 RM2,298.00

6 Cable RG405 U Cable

Coax 0.5-20 GHz

4 m RM218.04

7 Cable

EW85, HELIAX® Standard Elliptical

Waveguide

8.5–9.8 GHz

1.17 984ft RM91,069.20

8 Microwave

tower

Microwave

Communication

tower 295m

2 RM6,379.00

Total RM101,764.28

B. Cost Budget for Transmitter and Receiver using 15 GHz


1 Mixer with

Local

Oscillator

HMC144

GaAs MMic

Triple-Balanced 5-20 GHz

10 10 2 RM143.49

2 Bandpass

Filter AFL05158 12-18 GHz

3.1 3.1 2 RM1,654.90

3 RF

Amplifier

P35-4150-000-200

2-18 GHz

6 7.5 1 RM274.95

4 Low Noise

Amplifier

AMMP-6220

6-20 GHz

22 2.5 1 RM141.60

5 Antenna

HSX6-144-B4A/A

HSX High Performance, Super

High XPD

Parabolic Shielded Antenna, dual

32.1 2 RM2,862.00

polarized

14.4 – 15.35 GHz


Coax 0.5-20 GHz

4 m RM218.04

7 Cable

EW132-144,

HELIAX® Standard Elliptical

Waveguide

14.4–15.35 GHZ

1.15 984ft RM135,467.28

8 Microwave tower

Microwave Communication

tower 295m

2 RM6,379.00

Total RM147,141.26

C. Cost Budget for Transmitter and Receiver using 18 GHz


1 Mixer with Local

Oscillator

HMC144

GaAs MMic

Triple-Balanced 5-20 GHz

10 10 2 RM143.49

2 Bandpass

Filter

K-Band Filter

18-20 GHz

1 1 2 RM1,877.68

3 RF Amplifier

P35-4150-000-200

2-18 GHz

6 7.5 1 RM274.95

4 Low Noise Amplifier

AMMP-6220

6-20 GHz

22 2.5 1 RM141.60

5 Antenna

HPLPD1-18

High-Performance

Dual Polarized 17.7-19.7 GHz

38.6 2 RM3,426.00


Coax 0.5-20 GHz

4 m RM218.04

7 Cable

EWP180-180,

HELIAX®

Premium Elliptical

Waveguide

1.09 984ft RM135,467.28

8 Microwave tower

Microwave Communication

tower 295m

2 RM90,311.52

Total RM104,992.28

Based on the cost budget of 9 GHz is the most appropriate

compare to 18 GHz and 15 GHz because of the lowest cost

budget (RM101,764.28).

VI. CONCLUSION

Microwave link design is a specific sort of engineering in

the broader field of communications. Most installers know

that clear line of sight is required between two antennas, but

there is a lot more to it than that. To have some certainty as to

whether your wireless link will be reliable, an RF path

analysis needs to be performed. Our main objective was to

understand and design terrestrial microwave link system and

also to analyse the performances of design system whether,

Link budge, Free Space Loss and line of sight. Furthermore

our designing link system to be operating these frequencies 9,

15 and 18GHz after analysis we were able to meet the needed

appropriate operating frequency, lastly therefore we were

able to make a terrestrial microwave link system. To get the

good performance should use the 9 GHz because based on the

calculation on the Free Space Path Loss and Link Budget

Calculation the frequency of 9 GHz is lowest value of losses

(131.52 dB) and lowest Cost Budget that is RM101,764.28.

ACKNOWLEDGMENT

We would like to express our deepest gratitude and

appreciation to our laboratory instructor‘s Prof .Madya

Dr .Mohamad Ngasri Bin Dimon and Dr. Kamaludin bin

Mohd Yusof for their excellent guidance, caring, patience,

suggestions and encouragement who helped usto coordinate

our project especially to design the link. We would also like to

acknowledge with much appreciation to all those who gave us

the possibility to complete this project. A special thanks goes

to the crucial role of the staff of the Radar communication

Laboratory. Last but not least, again we would like to say

many thanks go to our laboratory instructors, Prof .Madya

Dr .Mohamad Ngasri Bin Dimon and Dr. Kamaludin bin

Mohd Yusof, who are given as full effort guiding in our team

to make the goal as well as the panels especially in our project

presentation that has improved our presentation skills by their

comment and tips.

REFERENCES

[1] (2010) Safari Books Online homepage. [Online] Available:

http://my.safaribooksonline.com [2] (2012) Diginet Terrestrial Link. [Online] Available:

http://www.diginet.be/products/telecom/terrestrial-links/

[3] (2011) Radio Waves, Inc. - The Leader in Microwave Antenna Innovation® [Online] Available: www.radiowavessinc.com

[4] (2013) Eogogics Inc Microwave Line-of-Sight Systems [Online]

Available: http://www.eogogics.com/talkgogics/infocenter/microwave-line-of-sight-systems

[5] (2012) FM Video System Link Analysis [Online] Available:

http://www.cobham.com/static/GMS%20Calc%20Files/calc_fm.asp [6] (2011) IEEE Global History Network -Microwave Link Networks

[Online] Available:

http://www.ieeeghn.org/wiki/index.php/Microwave_Link_Networks

Terrestrial Microwave Link Design

Design

Transcript of Terrestrial Microwave Link Design