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NAVIGATION
INS-GPS-GLONASS navigation
fusion scheme for high
dynamics guided projectiles
This paper presents a comprehensive study on the combining of GPS and GLONASS
for receivers and the advantages of either system in case of restricted visibility of
satellites and degraded performance of geometric Dilution of Precision
G Satheesh Reddy
Outstanding Scientist,
Research Center Imarat,
Defence Research
and Development
Organisation (DRDO),
Hyderabad, India
Manjit Kumar
Scientist, Research Center
Imarat, Defence Research
and Development
Organisation (DRDO),
Hyderabad, India
The Satellite Navigation solution
is the most preferable, effective
and economic aid to various Low and
Medium Grade Inertial Sensors in
order to get better Navigation accuracy
for medium and long duration of
navigation solutions. The navigation
data from INS and Sat. Receiver at
different intervals is synchronized
and fused together by using Kalman
Filter algorithm so as to obtain precise
Navigation solution as long as Sat.
Receiver tracks healthy and suffi cient
number of Satellites constellation. The
major limiting factor with the mostly
used/popular GPS system performance
is the availability of Satellites and the
geometry of Satellites in view at any
particular point in space and time. In
order to alleviate this restriction for
single constellation (i.e. GPS), it stands
to reason that more observations to be
introduced to provide increased levels
of positioning continuity and higher
levels of data redundancy. The recent
enhancement of GLONASS satellite
system suggests combined use with
GPS, in order to increase the satellites
availability as well as Navigation
Solution continuity and accuracy.
Taking the advantage of combined GPS-
GLONASS systems, the new Hybrid
Navigation scheme has been developed
to fuse the data from INS, GPS and
GLONASS systems by using the raw
measurements ( Pseudo ranges and Delta
Pseudo-ranges) of GG Receiver and
which are Synchronized to INS clock
(Real-Time algorithms are adopted). The
INS system is implemented in the strap
down confi guration and the Extended
Kalman fi lter is used to fuse the Inertial
and GPS-GLONASS Raw measurements
data in tightly coupled architecture.
Integration of GPS-
GLONASS systems
The GPS and GLONASS satellites
transmit ranging signal and the ephemeris
data at two different frequencies in the
L-band. To our interest, L1 transmitting
frequencies for both the systems are
shown below. We can also state the
transmitted C/A code signal on L1
frequencies from GPS and GLONASS
satellites by following equations:
where:
A = amplitude of transmitted signal
N = frequency channels of GLONASS (-7
to +6)
C gps (t)= 10 bit C/A code of a GPS
C glo (t)= 9 bit ML code of GLONASS
D gps (t)= 50 Hz Ephemeris data of GPS
D glo (t)=50 Hz Ephemeris data of
GLONASS
M(t)=100 Hz Meander sequence of
GLONASS
f L1,gps = L1 frequency of GPS
Coordinates August 2012 | 35