Ambiguity Resolution Technique

yakzephyrAI and Robotics

Nov 24, 2013 (3 years and 11 months ago)

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Ground
-
Based Altimetry Using a Single
-
Receiver Single
-
Frequency GNSS Phase
Ambiguity Resolution Technique

G.
Stienne
*

S.
Reboul

J.
-
B.
Choquel

M. Benjelloun

SPACE REFLECTO 2013


System
geometry


Software
receiver

-
Signal
processing

architecture

-
Phase
processing

in open
loops


Altimetry

measurement


Ambiguity

resolution


Experiments


Conclusion, prospectives

2

Overview

System
geometry
:
ground
-
based

applications

3


is

the
path

difference

between

the direct and the
reflected

signal

4

Receiver architecture

Code generator

Carrier replica
(frequency)

Phase processing

(POL)

Code generator

Carrier replica
(frequency, phase)

Code and phase
processing (DLL
-
POL)

Direct

signal

RHCP

Reflected

signal

LHCP

Same

oscillator

for the
digitizing

Pseudorange

variations

In open
loops
, phase
measurements

are
angular

Additional

code
delay
(s)

Filter

defined

as the
Kalman

filter

but
with

the
Circular

Normal
von

Mises distribution


Prediction

step
:








Update
step
:


Phase tracking: circular filter (linear evolution case)

with

11

with

and

6

Phase tracking: circular change estimator

When

a cycle slip
occurs

(
high

dynamics
,
low

Signal to Noise Ratios),
it

can

be

detected

and
its

amplitude
estimated

via a GLR change
estimator

defined

following

the
von

Mises
distribution.

The estimations of (cycle slip position)

and (cycle slip amplitude) are
based

on the inversion of (
filter

innovation)


7

Ranging
: code vs phase

Both

the code and the phase of a GNSS signal are
periodic

C/A code
period
:



Phase
period
:

Range
periods
:



GNSS codes are square
signals
. The
observed

code
delays

are
piecewise

constant. The
sampling

frequency

defines

the
measurements

resolution
.
Ranging

precision
:
several

meters
.




The carrier
is

continuous
,
and
so

the phase
delays
.
Ranging

precision
:
centimeter
.

Phase
ambiguity

8

Phase
pseudoranging

Pseudorange

variations

Received

signal
frequency

Replicated

signal
frequency

Phase
delay

between

the
received

signal and
its

replica

Pseudorange

at

t=0


ambiguity

Local
oscillator

noises

9

Phase altimetry

Direct signal:

Reflected

signal:

Choosen

common

Common for a GNSS
-
R
receiver

Same

receiver

clock

errors
,
atmospheric

errors
,
orbit

errors

on
both

signals

10

Pseudorange

at

t=0

The
pseudorange

at

t=0
is

obtained

by
dating

the code
using

the data message

1 ms

Known

emission

date (TLM)

Received

code

Known

reception

date

The
telemetry

word

emission

is

dated
,
so

the
emission

of
each

code
period

can

be

dated

with

the
precision

of the satellite
atomic

clock
.


The first code
delay
, , has to
be

precisely

estimated

in
order

to
get

a
precise

datation
at

t=0.


11

Precise

estimation of

Code
delays

Phase variations
applied

to
each

code
delay

Principle

:
averaging

the code
delays

obtained

over the
whole

acquired

signal

Method

:
Bring

each

delay

back to the
origin

using

the
estimated

phase variations

12

Experiments

:
principle

Graduations for
accurately

known

height

modifications

13

Experiments

:
principle

Constant
height

for the

reflecting

water

Several

acquisitions (7 seconds)

Precisely

known

variations on
the
antenna

height

between

two

acquisitions

The variations of
should

be

observed

Observation of
several

satellite
footprints

=>
same

measured

heights

First test
:

Second test

:

Experiments

:
observed

footprints

14

Experiments

:
results

15

The
height

is

constant over time:
good estimation of the phase

The
results

on satellites 21 and 25
differ

by up
to 2
meters
:
wrong

estimation of or
with

the signal of the satellite 21 or occurrence of a
parasitic

multipath

On satellite 25, the water
level

variations
differ

by up to 20
centimeter

from

what

was

expected

16

Conclusion & prospectives



Development

of a mobile GNSS
reflectometer



Short signal
durations
, no double
difference



Robust

and
precise

height

variations estimations
with

1
millisecond

of
coherent

integration



Still

imprecisions

on
altimetry

measurements

linked

to
the phase
ambiguity

resolution





Need

for more
experiments

in
order

to
find

the
limits

of the
proposed

ambiguity

resolution

technique



Airborne

experiments

Thank

you

for
your

attention

17

GPS L1 signal structure

Emitted signal :

Received signal:

Code
delay

Phase
delay

L1 carrier

C/A code

Data message

Modulation

Multiplexing

Emitted

signal