06/09/07 Veena G Dikshit, Sc 'E', ADE, Bangalore Development of Global navigation satellite system...

06/09/07

Veena G Dikshit, Sc 'E' , ADE, Bangalore

Development of Global navigation satellite system (GNSS) Receiver

Veena G Dikshit

Sc ‘E’

ADE, Bangalore

06/09/07


Introduction

• GNSS GPS (USA), GLONASS (Russia), Galileo(Europe), Augmentation

Systems (SBAS, GBAS), IRNS (India), QuasiZenth (Japan)

• Fuelling growth during the next decade will be next generation GNSS

that are currently being developed.

Global Navigation Satellite Systems (GNSS) involve satellites,

ground stations and user equipment to determine positions around

the world and are now used across many areas of society

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GNSS SYSTEM

GPS Modernization

• Improved code on the L2 frequency of GPS (called L2C) –

• ionospheric error,

• more immune to RF interference and

• multipath.

• The first Block IIR-M during October 2005.

• Under currently published plans, that is not expected to occur until 2013

or beyond.

• A third civil frequency at 1176.45MHz (called L5) on the Block IIF satellites. Full

operational capability is unlikely until 2015.

• GPS-III, (extra L2 and L5 signals of the Block IIR-M and Block IIF satellites), Thirty

GPS-III satellites are planned for launch from about 2013 until 2018.

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GLONASS from Russia

• GLONASS-M (L1 and L2 bands ) satellites with an improved 7-year design

lifetime.

• 2007 to 2008 planned to launch GLONASS-K satellites with improved

performance, also transmit a third civil signal (L3).

• Stated intention is to achieve a full 24-satellite constellation transmitting

two civil signals by 2010.

• Full constellation is planned to be broadcasting three sets of civil signals

by 2012.

• Indian Government announced at the end of 2004 that it would be

contributing funds to assist Russia to revitalize GLONASS.

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Galileo from the European Union

• Constellation of 30 satellites, increased altitude (approximately 3000km higher

than GPS) which will enable better signal availability at high latitudes.

• Exact signal structure is still liable to change,

• Galileo satellites broadcast signals compatible with the L1(E5a E5b) and L5 GPS

signals. Galileo will also broadcast in a third frequency band at E6; which is not at

the same frequency as L2/L2C of GPS.

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• Current plan is to offer 5 levels of service:

o Open Service uses the basic signals, free-to-air to the public with performance similar to

GPS and GLONASS.

o Safety of Life Service allows similar accuracy as the Open Service but with increased

guarantees of the service, including improved integrity monitoring to warn users of any

problems.

o Public Regulated Service is aimed at public authorities providing civil protection and

security (eg police), with encrypted access for users requiring a high level of performance

and protection against interference or jamming.

o Search and Rescue Service is designed to enhance current space-based services (such as

COSPAS/SARSAT) by improving the time taken to respond to alert messages from

distress beacons.

o Commercial Service allows for tailored solutions for specific applications based on

supplying better accuracy, improved service guarantees and higher data rates.

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GNSS Signal Spectrum

G alileo E5/A

G PS L2

1151

MH

z

1300

MH

z

G alileo E5/B

1164

MH

z

1188

MH

z

1215

MH

z

1239

MH

zG lonassG 2

1237

MH

z

1261

MH

z12

60M

Hz

G alileo E6

1559

MH

z

1610

MH

z

G PS L1

1563

MH

z

1587

MH

z

G lonassG 2

5010

MH

z

5030

MH

z

1591

MH

z

1254

MH

z12

58M

Hz

1593

MH

z

A R N S

R N S S * R N S S *R N S S

960M

Hz

R N S S

A R N S A R N S

5250

MH

z

G alileo C 1

R N S SG

alile

o E3

G PS L5

R N S S * shared w ith o ther services

1214

MH

z

G a lileo E 5/A or E 5/B frequency band optionsG

alile

o E1

Gal

ileo

E2

Gal

ileo

E4

Upper L-BandLow er L-Band C-Band

G alileo E5/A

G PS L2

1151

MH

z

1300

MH

z

G alileo E5/B

1164

MH

z

1188

MH

z

1215

MH

z

1239

MH

zG lonassG 2

1237

MH

z

1261

MH

z12

60M

Hz

G alileo E6

1559

MH

z

1610

MH

z

G PS L1

1563

MH

z

1587

MH

z

G lonassG 2

5010

MH

z

5030

MH

z

1591

MH

z

1254

MH

z12

58M

Hz

1593

MH

z

A R N S

R N S S * R N S S *R N S S

960M

Hz

R N S S

A R N S A R N S

5250

MH

z

G alileo C 1

R N S SG

alile

o E3

G PS L5

R N S S * shared w ith o ther services

1214

MH

z

G a lileo E 5/A or E 5/B frequency band optionsG

alile

o E1

Gal

ileo

E2

Gal

ileo

E4

Upper L-BandLow er L-Band C-Band

06/09/07


BENEFITS OF GNSS

• Availability of Signals • Extra satellites improve continuity

• Extra satellites and signals can improve accuracy

• Extra satellites and signals can improve efficiency

• Extra satellites and signals can improve availability (of satellites at a particular location)

• Extra satellites and signals can improve reliability

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GNSS RECEIVERS DESIGN APPROACHES

A typical GNSS Receiver

06/09/07


Software Receiver (SDR) Architecture

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Comparison of ASIC and SDR

Features ASIC SDRUpgradability • A fixed platform.

• Dictate the potential capabilities of the receiver

• Re-programmable• Re-configurable

Separation of Hardware

• Multi system upgrades changes in base band processing Hardware

• Simple software change

Acquisition • Serial search Acquisition• Convolution in the time domain• Using correlation technique

• Parallel Search Acquisition

• FFT, Multiplication in the frequency domain

• Buffering memory

Tracking • More efficient• Cost effective

• Depends on the processor MIPS availability

Power Consumtion

• Less power consumtion More power consumption

Cost effectiveness

• More Hardware, More cost Less Hardware less cost

06/09/07


Development of GNSS Receiver

• GPS L1 (Current)

• GPS L1 & L2

• GPS + GLONASS + SBAS

• GPS + L5 + GLONASS + GALILEO

• GPS + L5 + GLONASS + GALILEO + SBAS + GBAS

• GPS + L5 + GLONASS + GALILEO + SBAS + GBAS + IRNS

BY 2015 position every where with decimeter and even centimeter accuracy will be widely available and affordable

ISSUSES

• Lack of uniform compatibility

• Differing Timing of Operational availability

Hybrid receiver Architecture required

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architecture.

Software receiver approach is nearly ideal in terms of cost and system integration, as only a single front end is needed to process all of the signals

06/09/07


Challenges in the next generation receivers

• Antenna Unit

• Two Narrow band separated by 402 MHz

• Broad band antenna covering multiple band signals

• Challenge low cost satellite navigation receiver antenna requires – circular polarization with adequate axial ratio and the medium gain.

• RF Front end

• Challenge proper on/OFF chip filter design and component selection will improve the system performance.

06/09/07


Digital Signal processing (A Big Challenge !?)

• Multi-system receivers - Increased number of correlator channels

• Dual band 2 correlator

• Demand on the processing power depend on implementation

• Implementation depend on the dynamics of the application

• Approach either software correlator or trditional hardware correlator on

FPGA

• To process a single C/A code channel with one chip correlator spacing

reqire a processing capacity of 4 MIPS

• Increase in band width 2 t0 20 MHz wide band signals MIPS requirement

increases by factor of 10

• To reduce the noise level 2 bit signal sampling further MIPS requirement

increases by factor 3

• Finally for 48 channel 5760 MIPS are required

Demands are on the edge of currently available DSP

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Conclusion

Modernization trend, complexity, multitude of users and application,

Availability of different systems, differing time scale of availability are

Considered the development of the GNSS receiver for the defense

application offers a great challenge which need to be tackled right

from now

06/09/07 Veena G Dikshit, Sc 'E', ADE, Bangalore Development of Global navigation satellite system...

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