Software Simulation and Performance Test of a Point-to-Point Microwave Link for 4G Internet Access

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Published on International Journal of Informatics, Technology & Computers
Publication Date: August, 2019

Nang Tee Shar, Khu Say Wah & Wai Phyo Aung
Department of Electronic Engineering, TU (Loikaw)
Loikaw, Kayah State, Myanmar

Journal Full Text PDF: System Consideration of Point-to-Point Microwave Link Audio Transmission.

To design a successful and reliable point-to-point microwave link requires good theoretical knowledge about RF design and antennas, as well as good deal of practical experience. In addition, this research paper is aimed to implement the PTP microwave link for 4G internet access through microwave frequency 5.8 GHz band by using ePMP force 180 integrated radio modules. The link implementation and performance summary of the proposed point-to-point microwave links are achieved by using a software called RF Link Planning Tool-Link Planner Cambium Networks (4.9.1). This software is able to easily and quickly design networks based on geography, distance, antenna height, transmit power and other factors. It supports a link calculation indicating line-of-sight performance of the designed PTP communication link in terms of link availability and throughput, receiver sensitivity and other parameters.

Keywords: Point-to-Point microwave link planning, Guard interval, Line-of-Sight, Path profile, link budget & Path Loss.

Microwave transmission uses electromagnetic waves with very small wavelengths to transmit information. A microwave link system uses a beam of microwave radio waves between locations, which range from just a few meters to several kilometres. As the microwave signals are propagated through the lower atmosphere, they are sensitive to terrain, atmospheric, and climate conditions. And there are now many computer applications that can accurately predict the line of sight and path loss however, a visual survey by, and experienced engineers are also necessary. This software (RF Link Planning Tool-Link Planner Cambium Network) is a planning tool to design and implementation software with study of all of the design parameters and may be used by civil engineers and in site acquisition departments in the mobile service provider.

Cable free Microwave links have to be planned considering the following parameters:
1) Required distance (km/miles) and capacity (Mbps).
2) Desired Availability target (%) for the link.
3) Availability of Clear Line of Sight (LOS) be-tween end nodes.
4) Towers or masts if required to achieve clear LOS.
5) Allowed frequency bands specific to region/ country.
6) Environmental constraints, including rain fade.
7) Cost of license for required frequency bands.
Microwave signals are often divided into three categories: UHF (0.3-3 GHz), SHF (3-30 GHz) and EHF (30-300 GHz). To implement our own point-to-point microwave link, we have considered the first three factors in terms of required distance and capacity, desired availability target for the link and availability of Clear Line-of-Sight (LOS) between end nodes. Firstly, we select the two target sites, the first one is at the Technological University (Loikaw), and the other end is at the Taung Kwe Pagoda. These two sites are located in Loikaw, the capital of Kayah State. Moreover, for the required frequency band, the ISM (Industrial Science & Medical) 5.8 GHz band with the channel bandwidth 40 MHz has been chosen. At each site, the ePMP Force 180 integrated radio module offering a higher gain, integrated 16-dBi patch antenna has been operated for hardware research.

3.1 Coordinates and Radio Configuration
In this part, the user has to add the coordinates and radio configuration parameters as follows:
Coordinates can be obtained using GPS:
Site A: Technological University (Loikaw)
• Latitude: 19.65450N
• Longitude: 97.20850E
Site B: Taung Kwe Pagoda
• Latitude: 19.66750N
• Longitude: 97.20800E
The operation frequency selected: 5.8GHz
The goal of PTP link planning is to ensure that each direction of the link will perform to an acceptable level, measured by the Throughput and Availability values in the Performance Summary section of the Link Page.

Fig 1 Geography of the specified site locations using Google Earth Pro

3.2 Link Set up
The line-of-sight link is established between the Technological University (Loikaw) and the Taung Kwe Pagoda, Loikaw. Fig.1 shows the geographical view of the specified two sites which is supported from Google earth Pro. The transmitter station is setup on the second floor of the campus building located at the 19.65450° N, 97.20850° E with the antenna height 10 meters and the receiver station on the top of the Taung Kwe Hill located at the 19.66750° N, 97.20800° E with the antenna height 10 meters from the tip of Taung Kwe hill. The range of the two ends is about 1.44 kilometers. The antenna can operate within the 4910-5970 MHz bands and provide a gain of 16 dBi and a 3 dB beam width-azimuth at 5 GHz. According to the specification sheet, we select modulation scheme number MCS15 (64QAM 0.83) for maximum modulation mode, 5.8 GHz band of 40MHz bandwidth, 75/25 DU/UL ratio and frame duration 5ms.

Fig 2. Network sites of two specified endpoints Fig 3. Equipment setting ePMP configuration

3.3 Map and Getting Path Profile
In this part, the software finds the location of two sites A and B and draw the direct path between them. The accuracy of the LINK Planner results depends upon obtaining accurate path data. This data is a combination of terrain height and the obstructions above ground (e.g, trees and building), known as “clutter”. Path Profiler imports the path profile automatically in LINK Planner. The antenna height at each access of the link can be determined by creating a path profile but this project defines the antennas’ heights for site A and B are shown in Fig 2. When evaluating a proposed path, the path profile should be developed first. This will identify path obstructions from terrain features.

Fig 4. Map

3.4 Fresnel Zone
A path profile is a graphical representation of the path traveled by the radio waves. The size of each Fresnel zone varies based on the frequency of the radio signal and the length of the path. For a fixed path, the first Fresnel zone becomes narrower with increasing frequency and larger antennas. Path proofile shows the clearence of a microwave beam and its Fresnel zone above the ground with the effective Earth radius factor as the parameter. The required clearence creates a cigar shape between the endpoints and it described by 0.6 of the first Fresnel zone.

Fig 5. Frenel Zone
The general equation for calculating the Fresnel zone radius at any point P in between the endpoints of the link is shown in equation(1).

F=17.32 (1)
where F= radius of Fresnel zone in meters, d1=the distance to P from one end in km, d2= the distance to P from one end in km, f= the operation frequency in GHz, d= the total distance between two end points.

Fig 6. Original Path Profile

Fig.6 provides the datas along the path that should be taken into account in the design process. After specifying the range along the path, the terrain height at that point, and the obstruction height into the original path, the updated path profile with obstructions can be generated as in Fig.8. In Fig.8, the line of sight is blocked because there is obstructions within the specified Fesnel Zone. The Fresenel Zone is shown in Fig.6. the blue line and the straight line path is shown in grey line above it.

The tool calculates the EIRP ( Effective Isotropic Radiated Power) for the required system.Maximum EIRP is the output power at a signal when it is concentrated into a smaller area by the antenna.
EIRP = PT -LC+Ga (2)
where,PT = output power at the transmitter(dBm),LC = Cable losses(dB) and Ga = Antenna gain(dBi).
In this part, we assume the cable losess (LC) has no losses and it equals to zero. So, the EIRP results 45.5 dBm.

4.1 Free Space Path Loss
Free space loss is the extended attenuation of a signal as it travels away from the transmitting device. When a signal radiates from the antenna, it spreads out over an increasingly larger distance. As the area covered

Fig 7. Add obstruction datas to Path between end points

Fig 8. link budget configuration at each end

LFSL = 92.45+20log (d) + 20log (f) (3)

where f = frequency (GHz) and d= distance between link endpoints (km)
In general calculation, the result of free space path loss is 110.64dB but the simulation result shows 110.88dB and it includes excess path loss with 0.22dB.
The Predicted received power can be calculated as
where PRX = predicted received power (dBm), PTX = transmitter output power (dBm), GTX= transmitter gain (dBi), LTX = transmitter losses (cable losses), LFSL = free space path loss (dB),
LM = miscellaneous losses (fading margin, polarization mismatch, losses, dB), LRX = receiver losses (dB), GRX = receiver antenna gain (dBi).

4.2 Link Availability
This parameter is expressed in percentage and determines for what percentage of time the link has been established over a certain period. A reliable microwave link should have link availability as good as 99.999%.

Fig 9. Performance Summary for Short guard interval

Fig 10. Performance Summary for Long guard interval

4.3 Performance Details
This section contains more detail about the predicted performance of the link. The data can either be displayed in chart or tabular form as shown in Fig 11. Table-1 describes the comparison of the link performance in terms of aggregate throughput, path loss, system gain margin and fade margin.

Fig 11. Performance detail showing the data with modulation coding scheme number and modulation mode

Table 1. Comparison of the link performance
Bandwidth 20MHz 40MHz
Guard Interval Guard Interval
Performance to TU(loikaw) Short Long Short Long
Mean IP Predicted (Mbps) 30.97 27.83 64.95 59.39
Mean IP Required (Mbps) 5 5 5 5
% of Required IP 619% 557% 1299% 1168%
Min IP Required (Mbps) 1 1 1 1
Min IP Availability Required 99.99% 99.99% 99.99% 99.99%
Min IP Availability Predicted 100% 100% 100% 100%
Performance to TG Pagoda Short Long Short Long
Mean IP Predicted (Mbps) 101.28 91.06 210.97 189.81
Mean IP Required (Mbps) 5 5 5 5
% of Required IP 2026% 1821% 4219% 3796%
Min IP Required (Mbps) 1 1 1 1
Min IP Availability Required 99.99% 99.99% 99.99% 99.99%
Min IP Availability Predicted 100% 100% 100% 100%
Aggregate IP Throughput (Mbps) 132.25 118.89 275.92 248.20
Free Space Path Loss (dB) 110.88 110.88 110.88 110.88
System Gain Margin (dB) 35.10 35.10 30.10 30.10
Fade Margin (dB) 8.10 6.10
Predicted Received Power -50 dBm ±7 dB
IEEE 802.1p Frame Size 1518 bytes
Frequency Band 5.8GHz

For point-to-point microwave links, the antenna on the two sides should be in line of sight of each other. The line of sight can be limited by natural or man-made obstacles and also by the earth’s curvature which limits the practical distance of microwave links to 50-60km. A visualization software tool LINK Planner, is used to help predict where and how equipment will work. The program can calculate the path length of the link between two points, free space loss, fade margin, link availability, and maximum throughputs for the system. But, the effected of the different parameters such as atmospheric conditions, multipath fading and losses condition without going into detailed mathematical equations.

The authors would like to express their thanks to all the members of Board of Study of TU (Loikaw).