2011-IONGNSS-CTTC的开源GNSS-SDR介绍论文_GNSS-SDR

GNSS-SDR

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GNSS-SDR: an Open Source Tool For

Researchers and Developers

Carles Fern

andez–Prades, Centre Tecnol

ogic de Telecomunicacions de Catalunya (CTTC), Spain.

Javier Arribas, Centre Tecnol

ogic de Telecomunicacions de Catalunya (CTTC), Spain.

Pau Closas, Centre Tecnol

ogic de Telecomunicacions de Catalunya (CTTC), Spain.

Carlos Avil

es, Carlos Avil

es Software (CAS), Germany.

Luis Esteve, Universitat Polit

ecnica de Catalunya (UPC), Spain.

BIOGRAPHY

Dr. Carles Fern

andez–Prades is a Research Associate at

the Centre Tecnol

ogic de Telecomunicacions de Catalunya

(CTTC), where he holds a position as a Coordinator of the

Communications Subsystems Area. He received the PhD

degree from Universitat Polit

ecnica de Catalunya (UPC) in

2006. His primary areas of interest include signal processing,

estimation theory, GNSS synchronization, and the design of

RF front-ends.

Mr. Javier Arribas is a PhD Candidate at the Centre

Tecnol

ogic de Telecomunicacions de Catalunya (CTTC). He

received the BSc and MSc degree in Telecommunication

Engineering in 2002 and 2004 respectively at La Salle

University in Barcelona, Spain. He is currently involved in

the SalleSat Cubesat picosatellite development project. His

primary areas of interest include statistical signal processing,

GNSS synchronization, estimation theory and the design of

RF front-ends.

Dr. Pau Closas received the MSc and PhD degrees in

Electrical Engineering from the Universitat Polit

ecnica de

Catalunya (UPC) in 2003 and 2009, respectively. Currently

he holds a position as a Research Associate at CTTC within

the Communications Subsystems Area. His primary areas of

interest include estimation theory, GNSS synchronization,

Bayesian ﬁltering and robustness analysis.

Mr. Carlos Avil

es is a Software Engineer and develops his

professional activities mainly in Berlin, Germany. He has

received a Computer Science Engineering degree from Uni-

versitat Oberta de Catalunya (UOC) in 2011. His Diploma

Thesis was developed as a collaboration with CTTC within

the GNSS-SDR project.

Mr. Luis Esteve is a Telecommunications Engineering stu-

dent at UPC. He is working on his MSc Thesis in collabora-

tion with CTTC within the GNSS-SDR project. He is teacher

and co-owner at Epsilon Formaci

on SL since 1999.

ABSTRACT

This paper introduces GNSS-SDR, an open source Global

Navigation Satellite System software-deﬁned receiver. The

lack of reconﬁgurability of current commercial-of-the-shelf

receivers and the advent of new radionavigation signals and

systems make software receivers an appealing approach to de-

sign new architectures and signal processing algorithms. With

the aim of exploring the full potential of this forthcoming sce-

nario with a plurality of new signal structures and frequency

bands available for positioning, this paper describes the soft-

ware architecture design and provides details about its im-

plementation, targeting a multiband, multisystem GNSS re-

ceiver. The result is a testbed for GNSS signal processing that

allows any kind of customization, including interchangeabil-

ity of signal sources, signal processing algorithms, interop-

erability with other systems, output formats, and the offering

of interfaces to all the intermediate signals, parameters and

variables. The source code release under the GNU General

Public License (GPL) secures practical usability, inspection,

and continuous improvement by the research community, al-

lowing the discussion based on tangible code and the analysis

of results obtained with real signals. The source code is com-

plemented by a development ecosystem, consisting of a web-

site (www.gnss-sdr.org), as well as a revision control

system, instructions for users and developers, and communi-

cation tools.

780

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24th International Technical Meeting of the Satellite Division of

The Institute of Navigation, Portland OR, September 19-23, 2011

Page Number:

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1. INTRODUCTION

Location has become an embedded feature not only on

medium and high-end mobile phones, but also on other

portable devices such as digital cameras and portable gam-

ing consoles. This massive deployment of GNSS receivers

requires a high level of integration, a low cost, a small size

and a low power consumption, which has pushed the lead-

ing GPS integrated circuit (IC) manufacturers such as Qual-

comm Inc., Broadcom Corporation, Cambridge Silicon Radio

(CSR, merged with SiRF in 2009), Texas Instruments Inc.,

STMicroelectronics, u-Blox AG, Maxim or MediaTek to of-

fer single-chip solutions easy to integrate in multi-function

devices. Thus, the radio frequency (RF) front-end and the

baseband processing are jointly implemented in monolithic

ICs, tiny black boxes leaving the user no possibility to in-

teract or to modify the internal architecture or the algorith-

mics. This approach is very convenient for location based

services and applications, since users and developers are in-

terested in using the location information (eventually taking

advantage of complementary information coming from wire-

less network providers) but not in how the position has been

obtained. Good examples of this abstraction can be found in

the application programming interfaces (APIs) of two major

operating systems for mobile devices: Apple’s iOS provides a

core location framework with objects that incorporate the ge-

ographical coordinates and altitude of the device’s location

along with values indicating the accuracy of the measure-

ments, when those measurements were made, and informa-

tion about the speed and heading in which the device is mov-

ing. A similar situation is found in Android, which provides a

location package that contains classes with descriptive-named

methods such as getLatitude(), getLongitude(), getAltitude(),

getSpeed(), getAccuracy() and so on. This abstraction layer

simpliﬁes a lot the job of the application developer, but leaves

no way to observe or modify any internal aspect of the re-

ceiver.

As an opposite driving force, the advent of a number of

new GNSS (Galileo, COMPASS), the modernization of ex-

isting ones (GPS L2C and L5, GLONASS L3OC) and the

deployment of augmentation systems (both satellite-based,

such as WAAS in the USA, EGNOS in Europe, and MSAS

in Japan; and ground-based, such as WiFi positioning and

Assisted GNSS provided by cellular networks) depict an un-

precedented landscape for receiver designers [1]. In the forth-

coming years, many new signals, systems and frequency

bands will be available for civil use, and their full exploita-

tion will require a thoughtful redesign of the receiver’s archi-

tecture and inner algorithms. In addition to being black boxes

hidden by an abstraction layer, current mass-market GPS ICs

are clearly constrained in terms of conﬁgurability, ﬂexibility

and capacity to be upgraded. This fact has headed receivers’

designers to the software radio paradigm, in which an analog

front-end performs the RF to intermediate frequency (or di-

rectly to baseband) conversion prior to the analog-to-digital

converter (ADC). All remaining signal and data processing,

including the hybridization with other systems, are deﬁned in

the software domain. This approach provides the designers

with a high degree of ﬂexibility, allowing full access and pos-

sibility of modiﬁcation in the whole receiver chain.

The last decade has witnessed a rapid evolution of GNSS

software receivers. Since the ﬁrst GPS Standard Positioning

Service software receiver described in [2], where the concept

of bandpass sampling (or intentional aliasing) was introduced,

several works were devoted to architectural and implemen-

tation aspects [3, 4, 5, 6, 7, 8, 9, 10, 11]. Textbooks [12]

and [13] increased the awareness of the community about the

great beneﬁts provided by software receivers with respect to

the traditional hardware-oriented approach, providing Matlab

implementations of a complete GPS receiver, and [14, 15]

provide discussions about high-level architecture design. In

[16], authors presented an analysis of software design pat-

terns and their application to GNSS software receivers.

Today, there are solutions available at academic and com-

mercial levels, usually not only including programming solu-

tions but also the development of dedicated RF front-ends. As

examples, we can mention the GSNRx (GNSS Software Nav-

igation Receiver [14]) developed by the Position, Location

And Navigation (PLAN) Group of the University of Calgary;

the ipexSR, a multi-frequency (GPS C/A and L2C, EGNOS

and GIOVE-A E1-E5a) software receiver developed by the

Institute of Geodesy and Navigation at the University FAF

Munich [17, 18]; or N-Gene, a fully software receiver de-

veloped by the Istituto Superiore Mario Boella (ISMB) and

Politecnico di Torino that is able to process in real time the

GPS and Galileo signals broadcast on the L1/E1 bands, as

well as to demodulate the differential corrections broadcast

on the same frequency by the EGNOS system. This receiver

is able to process in real-time more than 12 channels, using

a sampling frequency of approximately 17.5 MHz with 8 bits

per sample [19].

In this paper, we focus on signal processing, understood

as the process between the ADC and the computation of

code and phase observables, including the demodulation of

the navigation message. We purposely omit data process-

ing, understood as the computation of the navigation solu-

tion from the observables and the navigation message, since

there are a number of well-established libraries and applica-

tions for that (also in the open source side, such as GPSTk

[20, 21]). New available signals pose the challenge of mul-

tisystem, multiband receivers’ design, including issues such

as interference countermeasures, high-precision positioning

for the mass-market, assisted GNSS and tight hybridization

781

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below)

24th International Technical Meeting of the Satellite Division of

The Institute of Navigation, Portland OR, September 19-23, 2011

Page Number:

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with other technologies. In this context, this paper introduces

an open-source GNSS software deﬁned receiver (so-named

GNSS-SDR) released under the GNU General Public License

(GPL), thus ensuring the freedom of modifying, sharing, and

using the code for any purpose. This secures practical usabil-

ity, inspection, and continuous improvement by the research

community, allowing the discussion based on tangible code

and the analysis of results obtained with real signals. Hence,

it is also intended to be a framework for algorithm testing and

an educational tool, since everybody is allowed to peruse the

source code, see how the receiver is actually implemented,

and contribute with improvements, bug ﬁxes, and addition of

new features.

The remainder of the paper is as follows: Section 2

sketches the main characteristics and goals of the proposed

software receiver, identifying possible signal sources, brieﬂy

describing the overall receiver architecture and design pat-

terns, and analyzing which are the most useful formats for

data output. Then, Section 3 provides architectural and mech-

anistic details about the different abstraction layers, from

sample ﬂow management to the actual implementation of sig-

nal processing algorithms. The Section also describes im-

portant features beyond the receiver’s source code, such as

the development ecosystem, quality assurance, or how we ad-

dressed portability. Finally, Section 4 concludes the paper.

2. RECEIVER’S OVERVIEW

The proposed receiver provides an interface to different suit-

able RF front-ends and implements all the receiver chain up

to the navigation solution. Its design allows any kind of

customization, including interchangeability of signal sources,

signal processing algorithms, interoperability with other sys-

tems, output formats, and offers interfaces to all the interme-

diate signals, parameters and variables. The goal is to write

efﬁcient and truly reusable code, easy to read and maintain,

with fewer bugs, and producing highly optimized executables

in a variety of hardware platforms and operating systems. In

that sense, the challenge consists of deﬁning a gentle bal-

ance within level of abstraction and performance. The pro-

posed software receiver runs in a commodity personal com-

puter and provides interfaces through USB and Ethernet buses

to a variety of either commercially available or custom-made

RF front-ends, adapting the processing algorithms to differ-

ent sampling frequencies, intermediate frequencies and sam-

ple resolutions. This makes possible rapid prototyping of spe-

ciﬁc receivers intended, for instance, to geodetic applications,

observation of the ionospheric impact on navigation signals,

GNSS reﬂectometry, signal quality monitoring, or carrier-

phase based navigation techniques. Testing is conducted both

by the systematic functional validation of every single soft-

ware block (following a test-driven developing approach and

using unit testing as a veriﬁcation and validation methodol-

ogy), and by experimental validation of the complete receiver

using both real and synthetic signals.

2.1. Signal sources

An appealing feature for a software receiver is the possibil-

ity of working in real-time with real signals, when the pro-

cessor is fast enough, or in an ofﬂine mode (post-processing)

working with raw signal samples stored in a ﬁle, when the

complexity of the implementation prevents from a real-time

processing. Signals might also need to be created by syn-

thetic signal generators in order to conduct experiments with

controlled parameters.

Ideally, an all-software receiver should perform digitiza-

tion right after the antenna. Due to technological constraints,

there is still the need for ampliﬁcation and down-conversion

before the ADC, the so-called RF front-end. We also need

an interface between the ADC output and the PC (or other

general-purpose processor) in which the software receiver is

running. This “hardware portion” of the receiver can be im-

plemented with commercial off-the-shelf components or tak-

ing advantage of existing RF application-speciﬁc ICs. Mod-

ern ones feature single-conversion GNSS receivers, including

the low noise ampliﬁer (LNA) and mixer, followed by the

image-rejected ﬁlter, programmable gain ampliﬁer (PGA),

voltage-controlled oscillator (VCO), frequency synthesizer,

crystal oscillator, and a multibit (usually up to 3 bits) ADC

equipped with an automatic gain control (AGC) system.

There are several signal grabbers commercially avail-

able. For instance, the Universal Software Radio Peripheral

(USRP) [22] is a general-purpose family of computer-hosted

hardware for software radios that, equipped with a DBSRX

daughterboard [23] that can be used as a customizable RF

front-end for GNSS receivers. Other more-speciﬁc, lower

cost solutions are usually composed of an antenna, a RF IC

front-end, a complex programmable logic device (CPLD) that

arranges sample bits in bytes, and a USB 2.0 microcontroller.

This is the case of the SiGe GN3S Sampler v2, based on the

SiGe 4120 GPS IC [24], that provides a data stream with a

sampling frequency of 16.3676 MHz and a bandwidth up to

4.4 MHz; the NSL’s Primo (based on the Maxim’s MAX2769

RF IC front-end [25], that allows to conﬁgure a bandwidth of

2.5, 4.2, 8,or18 MHz and has a sampling frequency of up

to 40 MHz) and Primo II (same characteristics but dual band,

using a couple of MAX2769); and the IFEN’s NavPort-III,

a RF front-end able to work simultaneously in 4 frequency

bands, with a bandwidth of 13 MHz each [26].

The state-of-the-art RF IC developments for GNSS re-

ceivers in 2011 focus on offering small size (25 mm

is a typi-

cal footprint), low power consumption (around 20 mA at 3 V),

broader bandwidths than the commonly encountered 2 MHz

782

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24th International Technical Meeting of the Satellite Division of

The Institute of Navigation, Portland OR, September 19-23, 2011

Page Number:

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剩余14页未读，继续阅读

陈熙昊

2023-07-24

这篇论文对开源GNSS-SDR进行了详尽的介绍，内容丰富、相当实用。

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