Development of Global navigation satellite system GNSS Receiver

1
Development of Global navigation satellite system
(GNSS) Receiver

• Veena G Dikshit
• Sc E
• ADE, Bangalore

2
Introduction
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

• 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.

3
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.

4
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.

5

• 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.

6

• Current plan is to offer 5 levels of service
• Open Service uses the basic signals, free-to-air
  to the public with performance similar to GPS and
  GLONASS.
• 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.
• 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.
• 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.
• Commercial Service allows for tailored solutions
  for specific applications based on supplying
  better accuracy, improved service guarantees and
  higher data rates.

7
GNSS Signal Spectrum
8
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

9
GNSS RECEIVERS DESIGN APPROACHESA typical GNSS
Receiver
10
Software Receiver (SDR) Architecture
11
Comparison of ASIC and SDR
12
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

13
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
14
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.

15

• 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

16
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