GNSS SYSTEM AND METHOD USING UNBIASED CODE PHASE TRACKING WITH INTERLEAVED PSEUDO-RANDOM CODE
Global Navigation Satellite System (GNSS) signals are first received and then down converted to an intermediate frequency (IF) and digitally sampled. The sampled signals are multiplied by a local replica of the incoming IF carrier (I ref generator and Q ref generator). The purpose is to remove the Doppler and move the results to baseband for later accumulation processing. Two parallel correlation kernel modules, one kernel assuming the navigation data D is 1 while the other assuming navigation data D=0 or (−1), are provided. The correlation kernel takes the code numerically-controlled oscillator (nco) phase of the prompt signal as input, and generates four output signals that are multiplied by the Doppler-removed incoming sample signal. An implementation of the pulsed signals accommodates navigation data D=1 and D=0 or (−1).
1 . A Global Navigation Satellite System (GNSS) receiver system adapted for receiving GNSS ranging signals and including a tracking algorithm, which receiver system includes:
a GNSS signal receiver;
a down converter adapted for downconverting a GNSS signal to an intermediate frequency (IF);
a digital sampler adapted for receiving and sampling said down-converted GNSS signal;
a multiplier adapted for multiplying said sampled signals by a local replica of the incoming IF carrier (I reference generator and Q reference generator) for removing Doppler;
first and second parallel correlation kernel modules;
said first parallel correlation kernel assuming the navigation data D=1; and
the second parallel correlation kernel assuming the navigation data D=0 or (−1).
2 . The receiver system according to claim 1 , which includes:
multiple signal paths corresponding to multiple signal bands respectively.
3 . The receiver system according to claim 2 wherein said signal bands include the civilian signal broadcast on the L2 frequency (1227.6 MHz) (L2C).
4 . The receiver system according to claim 2 wherein said signal bands include interleaved pseudo-random code.
5 . The receiver system according to claim 3 , which includes:
L2C being a composite code with civilian moderate length code (CM) modulated with navigation data and dataless civilian long length code (CL).
6 . The receiver system according to claim 5 , which includes:
CM XOR CNAV data with CL multiplexing.
7 . The receiver system according to claim 5 , which includes:
CM XOR legacy navigation data with CL multiplexing.
8 . The receiver system according to claim 1 wherein the D=1 and the D=−1 alternative waveforms are equally likely and are unpredictable in a real-time receiver.
9 . The receiver system according to claim 2 wherein said sampled signals are multiplied by a local replica of the incoming intermediate frequency (IF) carrier provided by an I reference generator and a Q reference generator.
10 . The receiver system according to claim 2 , which includes:
said signal paths including: a) a civilian moderate (CM) length code generator; b) a civilian long (CL) length code generator; and c) a coarse acquisition (C/A) code generator respectively.
11 . The receiver system according to claim 1 wherein said signals are represented by the equations:
I
prompt
=
[
R
(
τ
)
P
2
D
tx
cos
α
+
n
I
CM
]
×
D
rx
+
R
(
τ
)
P
2
cos
α
+
n
I
_
CL
(
1
)
Where:
R(τ) is the normalized correlation function of the CM/CL code, and τ is the delay between the local CM/CL code and that of the incoming. P is the received carrier power at the receiver front end, the ratio of ½ is because the carrier power is equally split between the CM and CL. D tx is the navigation data (1 or −1) as transmitted by the satellite, D rx is the navigation data as assumed by one of the two correlation kernels. D rx takes the value of 1 or −1. n I — cm is the noise resulting from the correlation of the local CM code against the incoming signal. n I — CL is the noise resulting from the correlation of the local CL code against the incoming signal, a is the phase error between the incoming carrier and the local replica carrier.
Q
prompt
=
[
R
(
τ
)
P
2
D
tx
sin
α
+
n
Q
CM
]
×
D
rx
+
R
(
τ
)
P
2
sin
α
+
n
Q
_
CL
I
prompt
=
[
R
(
τ
)
P
2
D
tx
cos
α
+
n
I
CM
]
×
D
rx
+
R
(
τ
)
P
2
cos
α
+
n
I
CL
=
R
(
τ
)
P
2
(
D
tx
×
D
rx
+
1
)
+
n
I
CM
×
D
rx
+
n
I
CL
For one of the correlation kernels, D rx =D tx , while for the other, D rx =−D tx , so the outputs from the two correlation kernels are:
H
0
:
D
rx
=
-
D
tx
I
prompt
=
R
(
τ
)
P
2
(
D
tx
×
D
rx
+
1
)
+
n
I
CM
×
D
rx
+
n
I
CL
=
R
(
τ
)
P
2
(
-
1
+
1
)
+
n
I
CM
×
D
rx
+
n
I
CL
=
n
I
CM
×
D
rx
+
n
I
CL
(
2
)
H
1
:
D
rx
=
D
tx
,
then
I
prompt
=
R
(
τ
)
P
2
(
D
tx
×
D
rx
+
1
)
+
n
I
CM
×
D
rx
+
n
I
CL
=
R
(
τ
)
P
2
(
1
+
1
)
+
n
I
CM
×
D
rx
+
n
I
CL
=
R
(
τ
)
2
P
+
n
I
CM
×
D
rx
+
n
I
CL
(
3
)
12 . A method of code phase tracking Global Navigation Satellite System (GNSS) composite signals, with one signal assuming D=1 and another signal assuming D=−1, which method comprises the steps of:
providing a receiver system including: a GNSS signal receiver; a down converter connected to the receiver and adapted for down converting a GNSS signal to an intermediate frequency (IF); a digital sampler adapted for receiving and sampling said down-converted GNSS signal; a multiplier adapted for multiplying said sampled signals by a local replica of the incoming IF carrier for removing Doppler;
providing first and second parallel correlation kernel modules;
said first parallel correlation kernel assuming the navigation data D=1; and
the second parallel correlation kernel assuming the navigation data D=0 or (−1).
13 . The method according to claim 12 , which includes additional steps of:
providing multiple signal paths corresponding to multiple GNSS signal bands respectively.
14 . The method according to claim 13 wherein said signal bands include the civilian signal broadcast on the L2 frequency (1227.6 MHz) (L2 C).
15 . The method according to claim 12 wherein said signal bands include interleaved pseudo-random code.
16 . The method according to claim 12 , which includes L2 C being a composite code with civilian moderate length code (CM) modulated with navigation data and dataless civilian long length code (CL).
17 . The method according to claim 12 , which includes additional step of:
providing CM XOR CNAV data with CL multiplexing.
18 . The method according to claim 12 , which includes additional step of:
providing CM XOR legacy navigation data with CL multiplexing.
19 . The method according to claim 12 wherein the D=1 and the D=−1 alternative waveforms are equally likely and are unpredictable in a real-time receiver.
20 . The method according to claim 12 wherein said sampled signals are multiplied by a local replica of the incoming intermediate frequency (IF) carrier provided by an I reference generator and a Q reference generator.
21 . The method according to claim 12 , which includes:
said signal paths including: a) a civilian moderate (CM) length code generator; b) a civilian long (CL) length code generator; and c) a coarse acquisition (C/A) code generator respectively.
22 . The method according to claim 12 , which includes:
said signal paths including: a) a civilian moderate (CM) length code generator; b) a civilian long (CL) length code generator; and c) a coarse acquisition (C/A) code generator respectively.