IBTSS-05-OMM
EXISTING TRACKING ARCHITECTURES LITERATURE
REVIEW
INTRODUCTION
Human kind has forever seeked for means to find its way to get “there and back again”. Lack of vital resources has further drawn people to explore beyond their known territories, striving to improve their life conditions. In today’s demanding context, being at the right place, at the right time has never been so critical. To meet and overcome these common expectations, satellite-based synchronized communications have opened the way to time-based wireless and autonomous positioning, leading to the automation of many repetitive tasks… Until recently, navigation receivers based on open civil signals were limited to GPS L1 Coarse Acquisition (C/A). Initially, these signals were only intended for the acquisition of the more precise, but encrypted, P(Y) signals used by the U.S. military and their allies. Over the last decade, the use of GPS has spread into unforeseen applications. This increasingly popular trend has led to the integration of GPS receivers into everyday-life products in fields as varied as transportation, communications, tourism, emergency services and many more, as seen in Figure 0.1.
SURVEY OF GNSS SIGNALS
Current concerns regarding signals coexistence in an already crowded spectrum are defined in terms of interoperability and compatibility. “Compatibility” refers to the ability of two or more systems to perform their functions, while sharing the same environment (C/S2ESC – Software & Systems Engineering Standards Committee, 1990). Hence, the ability of multiple satellite navigation systems to co-exist and be used separately (or jointly), without interfering with one another, has lead to international regulation initiatives. On the other hand, “interoperability” refers to the ability of two or more systems to exchange information and use it (C/S2ESC – Software & Systems Engineering Standards Committee, 1990). Thus, in order to allow open services of multiple satellite navigation systems to be jointly used (providing improved user capabilities over those from single service), these systems should be derived from common design principles to simplify user equipment, such as GNSS receivers.
PROPAGATION MEDIUM AND SIGNAL PROCESSING IMPACTS ON NAVIGATION SIGNALS
Prior being broadcast by through their satellite antenna, signals defined in Chapter 2 are impaired by system integrity (such as the accuracy of ephemerides data modelling their orbit), by on-board clock and amplifier. Civil GPS positioning receivers have known a wide commercial interest, especially after 2000 when the GPS Selective Availability (SA) was deactivated.
The Standard Positioning Service (SPS) accuracy had then improved from roughly 30 to 5 m, thus making atmospheric delays and multipath the most important error sources to overcome.
When activated, SA intentionally induced jitter onto the publicly available L1 C/A signal in a pseudo-random way, making civil navigation less interesting without the required correction.
Signals out of the satellite antenna propagate through the underlying medium before reaching the receiver antenna and being further processed. This chapter aims at providing an overview of these different sources of perturbation, both external and within the receiver.
Propagation Medium Error Sources
As GNSS signals propagate from the satellite to the receiver through the atmosphere, they may be impeded by the medium itself as well as by interferences and multipath. This section shortly reviews the different error sources external to the receiver. Some numerical values may be found in Table 3.1.
Atmosphere Impacts
As signals transit through all the atmosphere layers, they are impacted by two of them. The ionosphere is part of the upper atmosphere, in altitudes ranging from 50 to 1000 (or more) km. Moreover, the troposphere induces an error due to its high level of humidity, which can be realistically be modelled through both its dry and wet components.
EXISTING TRACKING ARCHITECTURES LITERATURE REVIEW
With all the enthusiasm brought up by the Global Navigation Satellite Systems (GNSS) being deployed or modernized, lots of efforts have been invested into successfully mitigating the different navigation error sources. Furthermore, over the past years, satellite positioning has known an increasing popularity across a variety of application fields, most of which are now consumer-based hand-held products (Blackroc Technology, 2015). Indeed, GPS receivers are now being included in Personal Device Assistants (PDA), wearables and smart phones through limited-resources hardware (HW) chips for consumer mobile applications.
GENERAL CONCLUSION
The satellite navigation field continues along a constant evolution, leading receivers to break through initially incompatible markets, such as hostile environments and confined spaces; recent technological and algorithmic advances can now mitigate or solve the traditional limitations of GPS, namely availability, integrity, accuracy and resistance to interference. Amongst other, the flexibility of the universal tracking channel provides tools for robust receivers, enabling them to adapt to their environment or frequency conditions by harvesting the best available signals. By doing so, the current work meets objectives defined in the introduction, with foreseable positive impacts in both research and commercial domains. In order to appreciate the complexity of such work, this work has undergone vulgarizing the different aspects of navigation receivers.
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Table des matières
INTRODUCTION
CHAPTER 1 SIGNAL MODULATION AND AUTO-CORRELATION FUNCTION
BACKGROUND FOR TRACKING LOOPS
1.1 BPSK Correlation
1.2 BOC Correlation
1.3 Early-Late Processing
1.4 Code Phase Jitter
1.4.1 Coherent EML
1.4.2 Non-Coherent EMLP
1.4.3 Non-Coherent DP
1.5 Modulations and Auto-correlation Summary
CHAPTER 2 SURVEY OF GNSS SIGNALS
2.1 GPS Constellation
2.1.1 GPS L1 C/A
2.1.2 GPS L1C
2.1.3 GPS L2C
2.1.4 GPS L5
2.1.5 GPS summary
2.2 GLONASS Constellation
2.2.1 CDMA-compliant modernized GLONASS signals
2.2.2 GLONASS Summary
2.3 Galileo Constellation
2.4 BeiDou Constellation
2.5 GNSS Civil Signals Summary
CHAPTER 3 PROPAGATION MEDIUM AND SIGNAL PROCESSING
IMPACTS ON NAVIGATION SIGNALS
3.1 Propagation Medium Error Sources
3.1.1 Atmosphere Impacts
3.1.1.1 Ionosphere
3.1.1.2 Troposphere
3.1.2 Multipath
3.1.3 RF Interference
3.1.4 Propagation Model
3.2 Receiver Error Sources
3.2.1 Receiver Front-End
3.2.2 Receiver Tracking Channels
3.2.3 Signal and Noise Quantification
3.2.3.1 Calibration channel
3.2.3.2 Real Signal – Complex Noise
3.2.3.3 Beaulieu
3.2.3.4 Signal to Noise Variance
3.2.3.5 Moment Method
3.2.3.6 Narrowband-Wideband Power Radio
3.2.3.7 Variance Summing Method
3.2.3.8 Weighted Bandwidths Ratio
3.2.3.9 Methods Comparison
3.3 Signal Impairment Sources Summary
CHAPTER 4 EXISTING TRACKING ARCHITECTURES LITERATURE
REVIEW
4.1 BPSK-like
4.2 Multi-correlators
4.3 Code Correlation Reference Waveforms
4.4 Sub-Carrier Correlation Cancellation
4.5 Side Peak Cancellation
4.6 Multi-Loops
4.7 Frequency-Domain
4.8 BOC Tracking Architectures Summary
GENERAL CONCLUSION
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