The proliferation of different GNSS systems (GPS L2 & L5, Galileo, etc) opens new possibilities in the design of new receivers which could take advantage of the different options available. The use of extra GNSS systems can improve end user accuracy and service availability. A very interesting option is to produce an all digital receiver which has the advantage of not increasing the hardware elements while providing the flexibility needed in order to cope with different signals. In this letter a special digital signal processing is used in order to employ a single front-end for different frequency bands: GPS L1 and Galileo E5 bands. We gauge the competence of a hardware implementation on a FPGA of such a front-end aided with a code tracking loop and show empirical results of the effects of a jammering signal on the system.

1. Performance Evaluation of
a Direct Sampling GNSS
Receiver
Ignacio (Iñaki) Olabarrieta, A. Alonso, I. Arizaga, J‐M. Perre
Tecnalia Research & Innovation + Thales Avionics
Ignacio.olabarrieta@tecnalia.com

2. Índice
1. Introducción
2. Estrategia de Adquisición Directa
3. Lazo de “Tracking”
4. Detalles de nuestra Implementación
5. Resultados

3. Introducción

4. 11
64
11
76
.4
5
E5a/L5
11
8?
12
E5b
07
.1
12 4
12 14
15
Introducción
12
27
.6
L2
E5a/E5b Galileo
12
37
12
60
12
78
.7
E6
5
13
00
15
4
15 4
SAR
45
15
59
15
E2
63
15
75
L1
.4
2
15
87
15
E1
Fr 91
e
(M que
Standard GPS
H nc
z) y

5. Estrategia de Adquisición Directa

6. Estrategia de Adquisición Directa
• “Undersampling”:

7. Estrategia de Adquisición Directa
153.7 MHz
Fs GPS L1 Galileo E5a Galileo E5b
(MHz) (MHz) (MHz) (MHz)
1383.3 191.7500 207.2500 176.2500
691.6 191.7500 207.2500 176.2500
461.1 191.7500 207.2500 176.2500
307.4 38.0556 53.5556 22.5556
251.5 66.0000 81.5000 50.5000
153.7 38.0556 53.5556 22.5556
110.7 25.7600 41.2600 10.2600

8. Lazo de “Tracking”

9. Lazo de “Tracking”

10. Detalles de nuestra Implementación

11. Detalles de nuestra Implementación
Virtex 4
ADC 1500 MHz (PROGRAMABLE)
Input Bw =1.7 GHz
Resolución de 8 bits
Digital Front‐End
IF1= 38 Filter
Filter X IF2=1.5MHz Decimator
Band L1 22->18 bits 48->8 bits Decimation
R=5
14 bits coef (17-0) (27-20) L1 R=2
14 bits coef 22->8 bits
L.O: 39.5 MHz
(18-11)
Filter
ADC 8bits Filter IF1= 53.6 X IF2=15MHz Decimation Mx Out
Fs=153.7 MHz Band E5a 23->18 bits 48->8 bits E5 R=2 8 bit
22->8 bits
14 bits coef (17-0) (27-20) 14 bits coef (18-11)
L.O: 38.6 MHz 22->8 bits
(18-11)
Filter
Filter IF1= 22.6 X IF2= 15MHz Decimation
Band E5b 23 ->18 bits 48->8 bits E5 R=2
14 bits coef (17-0) (27-20) 14 bits coef
L.O: 37.6 MHz
“SDR Direct‐Sampling Device for multistandar GNSS Signals”, A.Alonso, J‐M. Perré and I.Arizaga CSNDSP 2008

12. Resultados

13. Resultados
GNSS Signal/ Carrier +Noise Signal Receiver
Generator1 Platform
(1175 MHz) (40 dB.Hz)
= 39 dB.Hz
= 1.7 m

14. Resultados
Signal
GNSS Signal/ Carrier + Noise Generator1
(1175 MHz) Receiver
+ Platform
Signal
Jammer Signal
10 kHz Bw Generator 2
(x MHz)
Receptor Analógico Receptor Digital