Nghiên cứu và phát triển kỹ thuật chỗng nhiễu giao thoa trong bộ thu GNSS (research and development of advanced interference mitigation techniques in GNSS receivers)

New design of notch filters on GNSS narrowband interference mitigation.. 28 2.3 Using Notch Filter on GNSS Narrowband Interference Mitigation .... 31 Chapter 3 New Design of Notch Filter

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

- NGUYEN THI THANH TU

RESEARCH AND DEVELOPMENT OF ADVANCED INTERFERENCE MITIGATION TECHNIQUES

BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƯỜNG ĐẠI HỌC BÁCH KHOA HÀ NỘI

- NGUYỄN THỊ THANH TÚ

NGHIÊN CỨU VÀ PHÁT TRIỂN

KỸ THUẬT CHỐNG NHIỄU GIAO THOA

TRONG BỘ THU GNSS

LUẬN VĂN THẠC SĨ KHOA HỌC

KỸ THUẬT MÁY TÍNH VÀ TRUYỀN THÔNG

NGƯỜI HƯỚNG DẪN KHOA HỌC :

1 TS Tạ Hải Tùng

2 TS Beatrice Motella

Hà Nội – 2015

In addition, I deeply acknowledgeProf Gustavo Belforte for his enthusiastic supports

I would like to thank the supports from all the NAVIS members I am thankful to Tran Trung Hieu, Nguyen Dinh Thuan, Truong Minh Duc, who gave me a lot of helpful advice I also appreciate Ms Nguyen Thi Ha Phuong, who has always encouraged me since the very beginning of my study

The list could not be complete without the Growing NAVIS project, funded by the European Commission under the FP7 Call Galileo.2011.4.3-1 – International Activities (Grant Agreement No 287203), for supporting my internship at ISMB from May to July, 2013

Last, and most importantly, I would like to thank my parents, my sister and her family for their love that definitely is my limitless support

COMMITMENT

I commit myself to be the person who was responsible for conducting this study All reference figures were extracted with clear derivation The presented results are truthful and have not published in any other person‟s work

NGUYEN Thi Thanh Tu

TÓM TẮT LUẬN VĂN

Ngày nay, các hệ thống định vị toàn cầu sử dụng vệ tinh (GNSS – Global Navigation Satelite System) đóng vai trò rất quan trong trong rất nhiều lĩnh vực khác nhau Một số ứng dụng GNSS dân sự quan trọng có thể kể đến như: giám sát các phương tiện giao thông, đồng bộ trong truyền thông và bản đồ Do đó, yêu cầu về tính chính xác và liên tục đối với các bộ thu GNSS ngày càng trở nên cấp thiết

Việc sử dụng kỹ thuật trải phổ trực tiếp, mang lại nhiều ưu điểm trong chống nhiễu cho các hệ thống GNSS như GPS, Galileo Tuy nhiên, các tín hiệu GNSS nhận được tại antenna thường có năng lượng thấp, dẫn đến việc chúng dễ bị tác động bởi các nguồn nhiễu khác nhau Tất cả các tín hiệu được truyền trong phạm vi tần số gần với băng tần tín hiệu GNSS đều có thể trở thành nguồn gây nhiễu cho bộ thu GNSS

Có nhiều loại nhiễu khác nhau tác động lên bộ thu GNSS, trong đó, nhiễu băng hẹp (narrow-band interference – NBI) là nhiễu có ảnh hưởng lớn nhất tới hiệu năng bộ thu GNSS Các nghiên cứu gần đây sử dụng Notch filter trong lọc nhiễu băng hẹp cho bộ thu GNSS cho thấy đây là phương pháp khả thi và hiệu quả Các bộ lọc notch filter đáp ứng xung vô hạn có độ phức tạp không cao và có thể dễ dàng triển khai một cách và hiệu quả

Trong khuôn khổ luận văn, tác giả đề xuất một thiết kế mới cho khối chống nhiễu băng hẹp trong bộ thu GNSS Khối này có khả năng phân loại nhiễu băng hẹp và tự động điều chỉnh cấu hình notch filter, sao cho chất lượng tín hiệu đầu ra đạt tốt nhất

Luận văn được xây dựng gồm 5 chương như sau:

 Chương 1 Fundamentals Mô tả sơ lược về một hệ thống GNSS nói chung, và

nguyên tắc hoạt động của hệ thống Trình bày các khái niệm liên quan đến nhiễu (interference), ảnh hưởng của nhiễu lên hiệu năng bộ thu và tổng quan về các phương pháp phòng chống

 Chương 2 Notch filter for GNSS narrowband interference mitigation Giới

thiệu Notch filter, bộ lọc có khả năng loại bỏ nhiễu băng hẹp trong bộ thu GNSS, các tham số quan trọng của Notch filter, và một cải tiến của Notch filter giúp bộ lọc có khả năng tự phát hiện tần số của nhiễu băng hẹp

 Chương 3 New design of notch filters on GNSS narrowband interference

mitigation Đề xuất một thiết kế mới của khối chống nhiễu băng hẹp trong bộ

thu GNSS

 Chương 4 Performance analysis Trình bày các kết quả đánh giá đề xuất đã

nêu trong chương 3

 Chương 5 Conclusion Tóm tắt nội dung luận văn, các kết quả đã đạt được

TABLE OF CONTENTS

Acknowledgments 3

Commitment 4

Tóm tắt Luận văn 5

List of Figures 9

List of Tables 11

List of Abrreviations 12

Introduction 13

Chapter 1 Fundamentals 16

1.1 GNSS Overview 16

1.1.1 Fundamentals of satellite navigation 17

1.1.2 GNSS receiver structure 19

1.2 Interference Threat 20

1.3 Interference Mitigation Techniques 23

Chapter 2 Notch Filter for GNSS Narrowband Interference Mitigation 26

2.1 Notch Filter 26

2.2 Adaptive Frequency Notch Filter 28

2.3 Using Notch Filter on GNSS Narrowband Interference Mitigation 31

Chapter 3 New Design of Notch Filter on GNSS Narrowband Interference Mitigation 33 3.1 Impact of Notch Filter on GNSS Signal 33

3.2 New Design of Narrowband Interference Mitigation Module for GNSS

Receiver 36

3.2.1 Interference Characterization Block 37

3.2.2 Notch Filter Configuration 53

Chapter 4 Performance Analysis 55

4.1 Bandwidth Estimation Algorithm 55

4.2 Quality of Filtered Signal 57

Chapter 5 Conclusion 61

References 62

LIST OF FIGURES

Figure 1.1 Fundamental of a satellite navigation system 17

Figure 1.2 Clock misalignments in a GNSS system 18

Figure 1.3 High-level architecture of a GNSS receiver 19

Figure 2.1 Frequency response of notch filter for two difference pole factors 26

Figure 2.2 Spectrum at the front-end output at different time instants (from [4]) 28

Figure 2.3 Power of filter output when notch frequency varies 29

Figure 2.4 Spectrum of an interfered signal before and after filtering 30

Figure 2.5 Adapted notch frequency of an ANF 31

Figure 2.6 High-level block diagram of the GNSS receiver chain 32

Figure 3.1 Proposed Interference Detection/ Estimation Unit 37

Figure 3.2 Notch frequency varies 38

Figure 3.3 Spectrum of the input signal 40

Figure 3.4 The signal power at the output of a NF and its derivative Bandwidth of NF is fixed at 30 kHz and whose frequency sweeps over the spectrum range 42

Figure 3.5 Bandwidth estimation algorithm 43

Figure 3.6 Interference bandwidth estimation for different NFs bandwidth 45

Figure 3.7 Proposed method for characterizing the incoming NBI 46

Figure 3.8 The accuracy of the interference bandwidth estimation algorithm versus 47

Figure 3.9 Notch frequency varies in the presence of a CWI 48

Figure 3.10 versus 52

Figure 3.11 Zoom of Figure 3.10 52

Figure 4.1 Simulation results: estimation of the interference bandwidth ( ) 55

Figure 4.2 Simulation results: estimation of the interference bandwidth ( ) 56Figure 4.3 Estimated interference bandwidth over time, in case of variable band 57Figure 4.4 Theoretical and practical C/N0 when bandwidth of interference

(ACARS Harmonics) and 58Figure 4.5 Theoretical and simulated C/N0 in case of CWI ( ) 59

LIST OF TABLES

Table 1.1 Interference threshold versus interference bandwidth for GPS receivers in track mode [16] 21Table 1.2 Potential interference sources [6] 22Table 1.3 Possible interference mitigation techniques to a standard GPS receiver [17] 24Table 4.1 Performance of the proposed architecture in case of CWI 60Table 4.2 Performance of the proposed architecture in case of band-limited interference 60

LIST OF ABRREVIATIONS

ACARS Aircraft Communication Addressing and Reporting System AGC Automatic Gain Control

ANF Adaptive Notch Filter

C/N0 Carrier to Noise density ratio

CWI Continuous Wave Interference

DS-SS Direct Sequence-Spread Spectrum

EGNOS European Geostationary Navigation Overlay Service

FFT Fast Fourier Transform

FIR Finite Impulse Response

GNSS Global Navigation Satellite System

ICB Interference Classification Block

IF Intermediate Frequency

IIR Infinite Impulse Response

IRNSS Indian Regional Navigation Satellite System

LMS Least Mean Square

MSAS Multi-functional Satellite Augmentation System

NBI Narrow-band Interference

NCB Notch Filter Configuration Block

QZSS Quasi-Zenith Satellite System

RFI Radio Frequency Interference

SNR Signal to Noise Ratio

WAAS Wide Area Augmentation System

WBI Wide-band Interference

INTRODUCTION

Nowadays the Global Navigation Satellite Systems (GNSSes) play a fundamental role

in several fields, belonging to very different areas Tracking of vehicles fleets (trains, trucks, or vessels), synchronization of communications and energy distribution networks, logistics, and mappings are examples of important civil applications Within this scenario, the requirements that GNSS receivers have to fulfill, both in terms of accuracy and continuity, are becoming more and more stringent

GNSS systems like GPS and Galileo are based on the Direct Sequence-Spread Spectrum (DS-SS) technique, which intrinsically gives them a high level of robustness

At the same time, it has to be considered that the satellite signals arrive at the receiver antenna with an extremely low level of power This makes them vulnerable to different disturbances All the system transmitting at carrier frequencies close to the band of interest are potential sources of interference for a GNSS receiver Even small leakages out of their allocated bandwidth can become threats for the receiver

Among many types of disturbances, narrow band interference (NBI) might cause serious receiver performance degradation Recently, notch filters, which pass all frequencies except those in a narrow stop or rejection band centered on a central frequency, have been considered as an effective technique for mitigating NBI There are several ways to implement a notch filter, among which the infinite impulse response notch filter (IIR NF) has a low complexity and efficient implementation In this thesis, through the assessment of the carrier to noise density ratio of the filtered signal, a new design of the interference mitigation module based on the IIR NF is proposed This module has an ability to classify the incoming interference into CWI or band-limited interference Then, it configures the notch filter appropriately so that the interference suppression is optimized

The thesis includes 5 chapters as follows:

Chapter 1 Fundamentals This chapter gives an overview of Global Navigation

Satellite Systems, interferences and their effects of interference on performance of GNSS receivers And a summary of interference mitigation techniques is presented

Chapter 2 Notch filter for GNSS narrowband interference mitigation: In this

chapter, Notch filter, one of the interference mitigation techniques, is introduced It is modified into Adaptive notch filter in order to detect automatically the interference frequency The application of notch filter in GNSS interference mitigation is also introduced through block diagram of receiver

Chapter 3 New design of notch filters on GNSS narrowband interference mitigation This chapter presents the impact of notch filters on the quality of GNSS

signal via carrier to noise density ratio Then, a new design of the narrowband interference mitigation module using notch filter, which optimizes the carrier to noise density ratio of the filtered signal, is proposed

Chapter 4 Performance analysis In this chapter, the performance analysis of the

proposed design in chapter 3 is proved

2 Tu Thi-Thanh Nguyen, Tung Hai Ta, Beatrice Motella "An Adaptive Bandwidth Notch Filter for GNSS Narrow Band Interference Mitigation", The First NAFOSTED Conference on Information and Computer Science (NICS 2014), 13-14 March 2014, Hanoi

3 Tu Thi-Thanh Nguyen, Beatrice Motella, Tung Hai Ta, “A New Design of GNSS Narrowband Interference Mitigation Using Notch Filter”, ION‟s Pacific PNT Conference 2015 (accepted)

CHAPTER 1 FUNDAMENTALS 1.1 GNSS Overview

A satellite navigation system is a system of satellites allowing electronic receivers to determine their location (longitude, latitude, and altitude) by means of the signal transmission time from satellites [15] Depending on the scale and purpose of use, it can be classified as:

 Global Navigation Satellite System: A satellite navigation system with global coverage such as: GPS (United States), Galileo (EU), GLONASS (Russian), and COMPASS (China) Among them, GPS and GLONASS were the full orbital constellations, Galileo are in the process of being developed, and Compass, the satellite navigation system is covering China, has been expanded into a global system

 Regional Navigation Satellite System: Some countries such as Indian, Japan have developed their own satellite navigation system Indian Regional Navigation Satellite System (IRNSS) was approved in 2006 with the intention

of the system to be completed by middle of 2015 The Quasi-Zenith Satellite System (QZSS) was authorized by the Japanese government in 2002 and expected to be fully operational status by the end of 2017

 Augmentation System: In order to improve the accuracy, integrity and availability of GNSSes, especially GPS, augmentation systems have been developed There are two types: local area augmentation systems with the limited coverage; and wide area augmentation systems The latter uses satellites

to broadcast augmentation information to users Examples are WAAS (USA), EGNOS (EU), MSAS (Japan) [18]

1.1.1 Fundamentals of satellite navigation

The position of a GNSS receiver in space can be found from the intersection of 3 spheres as described in Figure 1.1 The center and the radius of each sphere are the position of a satellites and the distance measured from the receiver to the satellite, respectively

Figure 1.1 Fundamental of a satellite navigation system

Let us denote is the receiver position, which is also the unknown variables; and is the position of satellite, which can be calculated using the message transmitted by the corresponding satellite In order to determine , it is necessary to know positions and distances to the receiver

of at least 3 satellites

The distance from the receiver to a satellite is measured based on the transmission time

of the signal between them:

[ ] (1.1) where is the speed of light, is the transmission time, and is the bias between the receiver clock and the satellite clock, as shown on Figure 1.2 This bias exists because the atomic clocks on all the satellites are designed with a very high accuracy, while the low cost clock on the receiver does not meet this requirement

Figure 1.2 Clock misalignments in a GNSS system

The bias is a new variable For this reason, it is necessary to know the positions of at least 4 satellites The receiver‟s position is found by solving the system of equations:

{

√

√

√

√

(1.2)

1.1.2 GNSS receiver structure

In general, a conventional GNSS receiver includes 3 main functioning blocks: RF front-end, Digital signal processing, and Navigation processing as seen in Figure 1.3

Figure 1.3 High-level architecture of a GNSS receiver

These blocks are described as follows [9, 15]

 Radio frequency front-end: After arriving at the receiver‟s antenna, the GNSS signal (with the noise and the interference components) is filtered, down-converted to the Intermediate Frequency (IF), and sampled by the front-end

 The digital signal processing is divided into 2 stages: acquisition, tracking and data demodulation

o The function of signal acquisition is to provide GNSS satellites in view, their code delay and Doppler shift frequency To do these tasks, the acquisition stage performs a search in three dimensions, namely PRN identification, code delay and Doppler shift Each set of three parameters forms a local replica signal The correlation between this local signal and the incoming one is used to decide the best-match set The estimated set

is then transferred to the tracking stage for finer estimation

o The estimates of Doppler shift and code delay in the acquisition process are initial values with a low accuracy Thus, they are fed for tracking

process to be estimated continuously and more accurately This process tries to generate a local replica signal with the least bias with respect to the code and carrier in received signal Once the signal of a satellite is tracked, the navigation data bits can be readily recovered and then the navigation message is obtained

 Navigation processing: The obtained navigation message contains the satellite‟s position When at least 4 satellites are tracked, the positioning process can be performed by solving a system of equations (1.2) as introduced in section 1.1.1

1.2 Interference Threat

It has to be considered that the satellite signals arrive at the receiver antenna with an extremely low level of power (approximately 20 dB below the noise floor) This makes them vulnerable to different disturbances, among which the Radio Frequency Interference (RFI) from external sources is one of the main threats As defined in [16]:

Interference noise is noise that comes in at the same frequency (ies) as the wanted signal and can mask (or overwhelm) parts of the desired signal All the systems

transmitting at carrier frequencies close to the band of interest are potential sources of interference for GNSS receivers Even small leakages out of their allocated bandwidth can become threats for the receivers Moreover, the growing number of wireless communication infrastructures increases the probability that some out of band energy affects the performance of GNSS receivers

Normally, the RF interference is classified as wide-band (WB) or narrow-band (NB), depending on the ratio between the interference and the desired GNSS signal bandwidths [5] In this sense, an interference might be classified differently, depending

on the specific GNSS signal that is considered (e.g., the same interference can be classified as wide for the GPS L1 C/A code and narrow for the GPS P(Y) code) The

limit for a narrow-band interference is a single tone [5], usually refer to as continuous wave (CW)

Table 1.1 Interference threshold versus interference bandwidth

for GPS receivers in track mode [16]

Bandwidth Receiver Interference Threshold

Linearly increasing from -120 dBm to -113.5 dBm Linearly increasing from -113.5 dBm to -110.5 dBm -110.5 dBm

Linearly increasing from -110.5 dBm to -97.5 dBm Linearly increasing from -97.5 dBm to -91.5 dBm Linearly increasing from -91.5 dBm to -89.5 dBm

Interferences affect the performance of GNSS receivers, especially in the synchronization processes For acquisition process, they increase the noise floor; therefore, reduce the ability of signal detection [1] This might make the receiver unable to find its position, because it can not see enough satellites For tracking process, interferences increase the code tracking error, and then might lead to the loss

of track in the receiver [6] In [16], the author showed the susceptibility of GPS receivers versus the interference bandwidth (Table 1.1) It can be seen that signals with bandwidth up to 700 Hz is the most severe threat with the lowest thresholds of -126.5 dBm

The potential sources of non-intentional interference might come from the harmonics

of some telecommunication signals such as: VHFCOM, SATCOM Communications, Aircraft Communication Addressing and Reporting System (ACARS), TV channels,

FM channels, as illustrated in Table 1.2 [6]

Table 1.2 Potential interference sources [6]

In Vietnam, the Circular No 29, dated 27 December 2013, issued by The Ministry of Information And Communications stated that three organizations of broadcasting the digital terrestrial television services in Vietnam have the right to use the channel 27 [518 – 526 MHz], at the center frequency 522 MHz It can be seen in the Table 1.2, the

3rd harmonic of this channel is inside L1 band; thus, it is one of the potential interference sources for L1 band of GNSS signals

1.3 Interference Mitigation Techniques

As mentioned above, the presence of interference might cause a serious decrease in receiver performance Therefore, it is necessary to research and develop interference monitoring techniques, including: detection, characterization, localization and mitigation [9] Among them, the mitigation techniques play an important role to ensure that the receiver still works in the interfered environment Interference mitigation techniques can be classified into 3 categories, depending on its position on the receiver diagram [17]: A/D converter, Post-correlation techniques, and Pre-correlation techniques They are shown in ascending order of complexity in Table 1.3 Obviously, the more complex these techniques are, the more effective they achieve

 A/D Converter: GNSS receivers often use a single bit A/D converter to reduce the cost and the power consumption However, in the presence of CWI, the loss

of lock threshold of these receivers might decrease up to 5-7 dB Adaptive A/Ds use more than one bit for quantization and adaptively adjust their signal thresholds according to the received power

 Post-correlation techniques: are implemented by modifying the tracking loops of receiver in order to improve the tracking thresholds

 Pre-correlation techniques: are applied prior to the tracking loop Considering the frequency domain, a narrowband interference can be removed by a filter,

removing interference is the notch filter For spatial domain, an antenna array can be used to reduce (or remove) the interference according to its direction The combination between filters and beamforming techniques give a high performance in interference suppression

Table 1.3 Possible interference mitigation techniques to a standard GPS receiver [17] Interference Mitigation Techniques Performance Implementation

Data Wiping Open Loop Carrier Tracking Vector Loops

Integration with INS

Can be implemented either internally

or external to GPS receiver

Temporal/FFT domain Filters

Dual Polarisation Antenna 20 – 40 dB against

narrow band + broadband interferences

Spatial Filters Space-Time Filters

Among many types of interference, NBI might cause a serious receiver performance degradation For this kind of disturbing signal, the NF has proved to be an efficient mitigation technique, since it can be considered as a good compromise between

efficiency and complexity Thus, this thesis focuses on the class of narrow-band interferers, where the term „narrow‟ has to be considered with respect to the GPS L1 C/A code and the Galileo E1 signals (i.e., the interference bandwidth is within tens of kilohertz)

CHAPTER 2 NOTCH FILTER FOR GNSS NARROWBAND

INTERFERENCE MITIGATION

Since most of the GNNS signals are a spread signal, a narrow-band interference can be depressed in the frequency domain by a notch filter This chapter introduces notch filters and an architecture of GNSS receivers, where notch filter is a part of the interference mitigation module

2.1 Notch Filter

A notch filter (NF) is a filter that passes all frequencies except those in a stop or

rejection band centered on a central frequency Therefore, a notch filter can be defined

by two parameters: the notch bandwidth B N, and notch frequency Notch frequency

is the center frequency to be removed, and notch bandwidth is the width of frequency region in which the signal power is reduced by 3 dB

Figure 2.1 Frequency response of notch filter for two difference pole factors

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 -15

-10 -5 0 5

Normalized Frequency (  rad/sample)

There are several ways to implement a notch filter, normally categorized into three main classes: the Fast Fourier Transform (FFT)-based, the Finite Impulse Response (FIR), and the Infinite Impulse Response (IIR) notch filter [4] FFT – based NF used FFT algorithm to evaluate the signal spectrum If any frequency component passes a predefined threshold, it will be considered as a CWI and removed by setting at zero This algorithm brings the capability of working with multiple CWI to FFT-based NF The second type is FIR filter, which removes the interference by combining several weighted input samples This type of filter is often designed with linear phase response

in order to ensure that there is no distortion in the output of filter Both FFT-based and FIR NF have their own advantages However, these types of notch filter require high computation cost In recent years, IIR notch filters are considered for GNSS interference mitigation because of their low computational requirements, efficient implementation and low number of parameters to be adapted [2]

The IIR two-pole NF has the following transfer function [2]:

Figure 2.1 reports the frequency responses of a notch filter with two different pole factors It is clear that the pole factor decides the width of the notch: the closer is

to unity, the narrower the notch is In other words, the notch bandwidth is characterized

by the pole factor , as it decides which frequency components will be removed

2.2 Adaptive Frequency Notch Filter

When using NF to remove interference, it is necessary to know the notch frequency (or interference frequency) However, in reality, this parameter is unknown and might vary over time as shown on Figure 2.2 Thus, an adaptive notch filter (ANF) is designed to

estimate and track it automatically To do this, it is important to note that if the notch

frequency matches the interference carrier ( ), the power of signal after filtering will be a minimum It is because the interference power is often much higher

than the usual received signal (includes useful signal and noise) This statement is proved on Figure 2.3, where the power of output filter is investigated with varying notch frequency

Figure 2.2 Spectrum at the front-end output at different time instants (from [4])

Thus, the ANF can be implemented by using Least Mean Square (LMS) algorithm to minimize the power of filter output, as follows [2] The zero of transfer function

(2.1) is updated iteratively If the interference is present, the angle of will converge

to the interference frequency

The iterative rule to update is:

where denotes the stochastic gradient, is the algorithm step and [ ] is the output

of the notch filter [2]

Figure 2.3 Power of filter output when notch frequency varies

The power spectrums of signal before and after filtering are shown on Figure 2.4 An interference source produces a very high peak in the spectrum in Figure 2.4.(a), and it

is removed by ANF and disappears in Figure 2.4.(b)

Figure 2.5 shows the evolution of adapted frequency during the adaptation process It converges to the interference frequency after about one thousand samples (equivalent

to about 1ms for this data set)

0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4

a Original spectrum

b Spectrum after filtering

Figure 2.4 Spectrum of an interfered signal before and after filtering

Figure 2.5 Adapted notch frequency of an ANF

2.3 Using Notch Filter on GNSS Narrowband Interference Mitigation

Notch filter has been proved to be an efficient interference mitigation technique Thus, several interference mitigation modules using the notch filter were proposed Figure 2.6 shows a high-level block diagram of the GNSS receiver chain, where the Interference mitigation module is present After arriving at the receiver‟s antenna, the GNSS signal (with the noise and the interference components) is filtered, down-converted to the Intermediate Frequency, and sampled by the front-end Then, the

‘Interference Mitigation module’ is in charge of:

 Sampled signal goes through an ANF

 A detection control system detects the presence of interference depending on the convergence of notch filter

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 4.09