Investigation and simulation of CVOR and DVOR navigation systems in multi-track channels

Master's Thesis

Electrical Engineering - Telecommunication System Orientation

Abstract

     VOR navigation system is a radio navigation system that has tactical and non-tactical applications and is made into two types CVOR and DVOR. This system is widely used in military and civilian air services in most countries of the world by determining the position (direction) of the flying vehicle in relation to the ground station transmitter. The VOR navigation system works in the VHF frequency range from 0.108 MHz to 117.95 MHz in the form of 200 channels. The difference between CVOR and DVOR is only in the antenna structure of the ground station, because the receiver and the relationship of the signal sent from the transmitter of both systems are the same. The transmitter antenna consists of two main parts, sideband and carrier, to send two 30 Hz signals. The function of the VOR system is that it extracts the direction information from the phase difference of two 30 Hz reference and variable phase signals. The phase difference is different for each plane position. In other words, the phase difference of two 30 Hz signals changes linearly depending on the position of the plane. Two 30 Hz signals are sent under analog modulation from the ground station. In flight, the aircraft receives these two signals with the reflected signal from the ground surface, mountains and nearby obstacles such as hangars and buildings. Multipath signals interfere with the phase difference detection of two 30 Hz signals at the VOR receiver. The aim of this thesis is to investigate the effects of multipath phenomenon on CVOR and DVOR system and compare them through system modeling and simulation. In this regard, the effects of the multipath phenomenon on radio systems, communication channel modeling, ground station performance, transmission signal extraction, and receiver simulation have been investigated. Then, the performance of the VOR system in multi-path conditions will be specifically investigated. In this thesis, CVOR and DVOR navigation systems are compared in multi-path conditions and their differences in the real scenario with obstacles.

Since the invention of the airplane, various devices and methods have been invented to help the pilot to determine the flight path. In the old days, the pilot used tools such as high mountains, fire smoke, and unevenness to find his way, and now devices such as [1] GPS, [2] TACAN, [3] VOR, [4] WAAS, [5] LAAS, [6] INS and navigation and satellite maps have replaced them. The navigator can determine the position of the aircraft with only one of the WAAS and GPS satellite systems, but the information of the systems is updated from the satellite and cannot be used in some situations. Therefore, the use of systems such as VOR to determine the current position and set the next route becomes inevitable, which is our main topic in this thesis.

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VOR is a radio navigation radio on the VHF band for omnidirectional vision [7] of the pilot, which helps the pilot and navigator to determine the flight path according to the available navigation maps. Unlike NDB[8] which transmits the signal without direction, VOR signal information is transmitted in a directional manner. The first type of VOR system was used by the International Civil Aviation Organization in 1960 as a short-range navigation equipment (short-range can be defined as more than 200 nautical miles). In addition to the advantages, this device also has errors that we will describe in this thesis and how to improve them. Although the maintenance of VOR requires a lot of maintenance people, it is inevitable to accept the cost of VOR networks for air routes. VOR is currently used in two ways: Conventional VOR and Doppler VOR. Our aim in this dissertation is to compare CVOR and DVOR in the multipath channel [10] and examine the advantages of using DVOR over CVOR.

Introduction of CVOR and DVOR navigation system

and description of their operation principles

Chapter One

Introduction of CVOR and DVOR navigation system and description of their principles of operation

Introduction

In this chapter, an attempt is made to present the necessary preparations for examining the topic of this thesis by introducing the VOR navigation system. In short, it can be said that the main task of VOR is to determine the direction angle information [11] for the aircraft. The VOR navigation system is made in two types, CVOR[12] and DVOR[13]. The VOR system consists of two parts: a transmitter (ground station) that sends its signal to all aircraft within the receiving range, and an aircraft receiver that receives the signal and extracts the direction angle information after processing. In this chapter, principles and theory of operation, mission, applications, signal specifications and other features and system parameters of CVOR and DVOR system are examined separately. It should be mentioned in this text that the word VOR is used for both CVOR and DVOR systems. 1-1- Definitions and introduction of words Radial distance[14]: The line that connects the plane to the station is called radial distance, which is also referred to as distance or distance[15] in this text. Figure (1-1) shows the radial distance.

Side angle: The angle created between the magnetic north vector and the line from the aircraft body to the ground station, in the clockwise direction, is called the side angle. Figure (1-1) shows this angle.

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Radial[16]: The angle created between the magnetic north vector and the line from the ground station to the aircraft body in the clockwise direction is called radial. Figure (1-1) shows this content.

Figure 1-1- bearing angle and radial distance

1-2- Mission and function of the VOR system

The VOR system provides the following information to the pilot and navigator:

A- Determining the direction of the aircraft with respect to the ground station and displaying the direction information

B- Displaying the information related to the deviation from the path in degree unit

P - Identification of the ground station to the aircraft by sending Morse code (Appendix 3)

T - Radio communication between the station and the aircraft

D - Determination of the direction of the aircraft in relation to the station (approaching or moving away) by the symbol TO or FROM

H - Landing the aircraft

1-3- Navigation applications of the VOR system

As mentioned before, The aircraft receiver extracts the necessary information by processing the signal sent by the ground transmitter. Now this question is raised, in what direction the pilot can use the obtained navigation information. It can be said briefly: A - navigation along the route [17]

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If the flight stages are divided into the stages of takeoff [18], flying around the airport [19], main route, approach and arrival, landing [20] and movement on the runway [21], the main application of navigation with the VOR system is during the movement phase on the main route where the VOR receiver detects the deviation from the desired side angle. It displays to the pilot in terms of degrees and provides the possibility of compensation. B - Inaccurate approaches [22] According to the VOR system's ability to determine the deviation from the desired side angle in terms of degrees, it is also used in the approach phase. That is, according to the direction information and also the deviation from the pilot's path, he can easily determine the next destination.

T - Positioning

VOR produces a number of rads or position lines, the source of which is the transmitter. These rods, which are numbered from 1 to 360, are called radials. A radial is a 360 degree radii that departs from the VOR station in the direction of magnetic north. The radial is 90 degrees in the east direction, the radial is 180 degrees in the south direction, and the radial is 270 degrees in the west direction, all of which are numbered according to magnetic north. Rejection is called position line navigation[24]. One of the useful applications of VOR is finding your position with the fixed position method [25]. Position is found by the intersection of two position lines. The position line is a trace that is drawn from the station to the aircraft. The position is obtained from the collision of two trace lines from two neighboring VOR stations whose From flag is lit for the pilot. This method can be seen in Figure (1-2). Figure 1-2- Position extraction from two VOR stations [2] 1-4- Explaining the principles of CVOR system operation 5

CVOR navigation system is widely used in air services with the mission of determining the direction of the aircraft from the ground station.