An ultra-low-cost antenna array frontend for GNSS application

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International Collaboration Centre for Research and Development on Satellite Navigation Technology in South East Asia An ultra-low-cost antenna array frontend for GNSS application Thuan D.

1 International Collaboration Centre for Research and Development on Satellite Navigation Technology in South East Asia An ultra-low-cost antenna array frontend for GNSS application Thuan D. Nguyen, Vinh T. Tran Tung H. Ta, Letizia Lo Presti NAVIS Centre, Hanoi University of Science and Technology, Vietnam Australian Centre for Space Engineering Research, School of Electrical Engineering and Telecommunication, UNSW Politecnico di Torino, Italy IGNSS 2016

2 Outline Motivation of design a low-cost antenna array frontend Proposed design for a low-cost antenna array frontend Problems and Solution in designing the low-cost frontend Synchronizing the received data Mitigating clock drift Verification of the antenna array frontend Phase offset among antenna elements Carrier to noise ratio improvement Conclusion and further works

3 Motivation of design a low-cost antenna array frontend Threats to GNSS signals: Jamming (prevent GNSS receivers track GNSS signals) Spoofing (provide the false position to GNSS receivers) Detect and locate the source of interference Receiver/ Spoofer Counterfeit signal is much stronger than authentic signal

Motivation of design a low-cost antenna array frontend Antenna array based technique is the most effective technique to detect and mitigate interference because it is able to: Control the reception

4 Motivation of design a low-cost antenna array frontend Antenna array based technique is the most effective technique to detect and mitigate interference because it is able to: Control the reception pattern of the array Increase signal-to-noise ratio Suppress interference Determine the DOA of GNSS satellites and interference s m t = s 1 t τ m = s 1 t Δρm c Δρ m = p m a s θ, φ = X m sin θ cos φ + Y m sin θ sin φ + Z m cos θ

5 Overview of antenna array frontend for GNSS Limitations of the existing antenna array frontend for GNSS: Cumbersome Costly Difficult for expansion (synchronization is performed in hardware part) Difficult to deployment BPF ADC BPF ADC Interleaving samples BPF ADC ~ ~

6 Proposed antenna array frontend In our design, the synchronization block is carried out by our specialized algorithm BPF ADC BPF ADC BPF ADC USB/Ethernet USB/Ethernet USB/Ethernet Synchronization ~ ~ USB Hub Master Element (Equipped TCXO) Slave (Shared TCXO) Elements Master

7 Problems and Solution in designing the low-cost frontend Synchronization Problem: Element signals are collected separately, they must be synchronized prior to use Solution: Due to the use of a common clock for ADC Time difference among elements is a product of a multiple of samples and the sampling period. The number of samples can be evaluated based on GNSS SDR Subframe X τ 1 τ 2 Subframe X τ 3 Subframe X Subframe X Element 1 Element 2 Element 3 Element 4

8 Problems and Solution in designing the low-cost frontend Clock phase shift Problem: Regardless of the use of a common clock for all elements, the tuned frequency of Local Oscillator (LO) is slightly different in each element corrupt the phase offset completely. 8 x 104 the tracking output of SV Inphase Prompt Quadrature Prompt the tracking output of SV 9 Amplitude Time (ms) Quadrature Prompt Inphase Prompt

9 Problems and Solution in designing the low-cost frontend Clock phase shift Solution: Δf = IQ m(k) IQ m k 1 2πT d Shift Frequency Hz seconds

10 Problems and Solution in designing the low-cost frontend Clock phase shift Solution (continue): GPS Simulator RTL2832 dongle Tracking loop Represent the delay between this element and the first element RTL2832 dongle Clock phase shift mitigation carrier phase 1 Scatter plot of SV RTL2832 dongle ~ TCXO Code & Carrier replica Clock phase shift mitigation Normalized quadrature prompt Carrier phase Normalized inphase prompt

Clock phase shift mitigation Clock phase shift mitigation Carrier phase offset

11 Antenna Array Frontend Verification Experiment setup schematic GPS Simulator RTL2832 dongle RTL2832 dongle RTL2832 dongle ~ TCXO Tracking loop Code & Carrier replica Clock phase shift mitigation Clock phase shift mitigation Carrier phase offset Carrier phase offset The phase difference among the elements should be the same for all satellites

12 Antenna Array Frontend Verification Achieved results: Normalized Q-channel amplitude Phase offset between element 2 and element 1 Phase offset between element 3 and element Tracking Output of Element 2 PRN 17 PRN 5 PRN 13 PRN 9 Normalized Q-channel amplitude Tracking Output of Element 3 PRN 17 PRN 5 PRN 13 PRN Normalized I-channel amplitude Normalized I-channel amplitude

13 Antenna Array Frontend Verification Achieved result: The C/N0 increase when using antenna array: dbhz Element 1 Element 2 Element 3 Beamed signal ms

14 Conclusion The preliminary results are very promising for not only GNSS application but also the other field. In the future, such antenna array frontend will be used to suppress interference, point to the source of the interference and spoofing to benchmark the performance of the frontend.

15 THANK YOU FOR YOUR ATTENTION!!!

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