System Consideration of Point-to-Point Microwave Link Audio Transmission

Reader Impact Factor Score
[Total: 12 Average: 4.9]

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

Ei Shwe Sin, Khaing Wai Pyone & 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.

Abstract
Audio Transmission of point to point link is based on microwave link. In this research work, audio transmission link between TU Loikaw to Taungkwe Pagoda.The main objective of the project is to do experiment with variables to see effect on fade margin, availability, and path loss. In addition, the project is aimed to implement the PTP microwave link for audio transmission through microwave frequency 500MHz by using ePMP force 180 integrated radio modules. The link implementation and performance summary of the proposed point-to-point microwave link are achieved by using a RF Link Planning Tool-LinkPlanner Cambium Networks (4.9.1). This software is able to easily and quickly designnetworks based on geography, distance, antenna height, transmit power and other factors. In addition, it supports a link calculation indicating line-of-sight performance of the designed PTP communication link in terms oflink availability andthroughput, receiver sensitivity and other parameters.
Keywords: point-to-point microwave link, audio transmission, planning, guard interval, line-of-sight, fade margin.

Keywords: Microwave, ePMP Force, path profile, Fresnel zone, link budget

1. INTRODUCTION
Audio transmission is the transmission of information by microwave radio waves. A microwave link is a communications system that uses a beam of radio waves in the microwave frequency range to transmit audio or data between two locations, which can be from just a few feet or meters to several miles or kilometers apart. Microwaves are widely used for point-to-point communications because their small wavelength allows conveniently-sized antennas to directthem innarrow beams, which can be pointed directly at the receiving antenna. This allows nearby microwave equipment to use the same. frequencies without interfering with each other, as lower frequency radio waves do. Another advantage is that the high frequency of microwaves gives the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30 times that of all the rest of the radio spectrum below it. A disadvantage is that microwaves are limited to line of sight propagation; they cannot pass around hills or mountains as lower frequency radio waves can.he host computers at either end take full responsibility for formatting the data transmitted between them. The connection between the computer and the communications medium was generally implemented through an RS-232 or similar interface. Computers in close proximity may be connected by wires directly between their interface cards.When connected at a distance; each endpoint would be fitted with a modem to convert analog telecommunications signals into a digital data stream. When the connection uses a telecommunications provider, the connection is called a dedicated, leased, or private line. The ARPANET used leased lines to provide point-to-point data links between its packet-switching nodes, which were called Interface Message Processors.
The high-quality microwave point to point link can be quite challenging, and if it is not properly designed and implemented. It can cause major quality issues such as lower throughputs, link instability, and longer than expected latency[1]. In this research work, some key factors that should be considered in a proper point to point microwave link design.Operating distances for microwave links are determined by antenna size (gain), frequency band and link capacity. The availability of clear line-of-sight is crucial for microwave links for which the earth’s curvature has to be allowed. To design and implementation of 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. There are now many computer applications that can accurately predict the line of sight and path loss however, a visual survey by, and experienced engineer are also necessary [3].
The UHF band below 1 GHz is the best band for Audio in this system due to the combination of antenna size, propagation, low body loss absorption andambient noise floor, especially for body worn equipment [4]. So, 500MHz is chosen for operating frequency of point to point audio transmission link.

2. POINT TO POINT MICROWAVE LINK
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 kilometers apart [4]. PTP links typically require clear Line of Sight (LOS) between the transmitting antennas. Certain sound system applications require sending audio from a central location to one or more remote locations without using cable. This is termed “point-to-point” wireless. Various combinations ofwirelessmicrophone and personal monitor systems can be configured to send audio via a radio link to meet this need. General requirements for point-to-point wireless include.
(i). High fidelity audio
(ii). Line level in and line level out
(iii). AC-power capability for both transmitter and receiver
(iv). “Sufficient” transmission distance
Most radio communication products such as wireless intercoms, two-way radios, and mobile phones are unsuitable due to lack of audio fidelity. However, two common high-fidelity radio products that can be used in a point-to-point application are the wireless microphone system and the wireless in-ear monitor system [6]. Each of these has slightly different concerns/advantages in performance and in setup. In this work, point-to-point microwave link are achieved by using a RF Link Planning Tool-LinkPlanner Cambium Networks (4.9.1). Firstly, planning of microwave link are considered to get cable free accept.

3. IMPLEMENTATION OF A POINT-TO-POINT MICROWAVE LINK IN LINKPLANNER
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. To allow LINKPlanner to predict Throughput and Availability, the planner must enter the variables that affect link performance, such as: band, region, equipment, antenna height, terrain, obstructions, and reflection.

Fig .1 Geography of the specified site locations used Google Earth

3.1 Get path profile
The accuracy of the LINKPlanner results depend upon obtaining accurate path data. This data is a combination of terrain height and the obstructions above ground (e.g, trees and building), which is generally known as “clutter”. Path Profiler imports the path profile data automatically in LINKPlanner. The antenna height at each access point of the link can be determined by creating a path profile. When evaluating a proposed path, the path profile should be developed first. This will identify path obstructions from terrain features. Fig.1 shows the original path profile getting from the PTP microwave link between the proposed endpoints.

Fig 2. Profile updated with obstructions

In operation, the receiving and transmitting antennas should be pointed toward each other and oriented vertically. Elevation for best line of sightwill further improve range. Under ideal conditions, this system should becapable of stereo transmission upto 2500 ft and mono operation up to 3500 ft.
Wireless audio links are built by using the transmitter, receiverand RF equipment. Both transmitter and receiver products can be rack mounted, and they both can be AC powered. This is especially useful for permanent or semi-permanent installations, where AC power is available. It also eliminates the need to replace batteries. The transmitter and receiver are both tunable in 25 kHz steps throughout their operating frequency ranges, providing excellent flexibility in frequency selection.
Identify available frequency spectrum in the area where the system will be used. Any line level audio signal input to the Transmitter should now be present at the outputs of the receiver.A directional antenna, like the PA805SWB, is recommended for the transmitter and for the receiver. Use of directional antennas may extend the operating distance to 500 feet (150 meters) and beyond, given optimum conditions and a clear line-of-sight between antennas. In this work, the audio transmission point to point link is performed between TU Loikaw to Taungkwe Pagoda.

Table 1 Performance summary for long guard interval

3.2 System Consideration of Audio Transmission
Certain sound system applications require sending audio from a central location to one or more remote locations without using cable. This is termed “point-to-point” wireless. Various combinations of wireless microphone and personal monitor systems can be configured to send audio via a radio link to meet this need. General requirements for point-to-point wireless include.
a. High fidelity audio
b. Line level in and line level out
c. AC-power capability for both transmitter and receiver
d. “Sufficient” transmission distance
Most radio communication products such as wireless intercoms, two-way radios, and mobile phones are unsuitable due to lack of audio fidelity. However, two common high-fidelity radio products that can be used in a point-to-point application are the wireless microphone system and the wireless in-ear monitor system. Each of these has slightly different concerns/advantages in performance and in setup.
It is necessary at the receiver is adapting the stereo (TRS) mini-phone jack output to connect to the destination audio system. This is effectively an unbalanced, -10dBV signal, suitable for most line level input devices. Note that most PSM receivers are equipped with switchable limiters. It is recommended that the limiter be switched off for point-to-point applications in order to obtain the maximum drive level.
Once audio connections are made, the PSM receiver should be secured to an elevated location to allow best line of sight to the PSM transmitter. Again, weather protection for the receiver can be provided by a ziplock bag or similar covering.
A significant difference between PSM and wireless microphones for this application is that the PSM can transmit two audio channels (multiplexed) per radio frequency while the wireless microphone system can transmit only one audio channel per radio frequency. If stereo transmission is required PSM is more costand spectrum- efficient.

Fig 3. Audio Transmission with Point-to-Point Microwave Link

The implementation steps to be considered are:
Step1.Frequency Selection
Step 2. Modify the Receiver to Defeat the Tone Key Squelch Circuit
Step 3. Program the Receiver
Step 4. Program the Transmitter
Step 5. Verify Point-to-Point Operation

4. CONCLUSIONS
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. In this work, the transmission of voice using point to point link is tested. Point-to-point microwave link are achieved by using a RF Link Planning Tool-Link Planner Cambium Networks (4.9.1).Also, the effectiveness of the interleaving techniques is inefficient with audio file that has higher bit rate than 64 kbps. Our main objective was to understand and design point to point microwave link system and also to analyze the performances of design system whether, Link budge, Free Space Loss and line of sight.