Ionosphere delay measurement using carrier phase
One or more atmospheric propagation effects are estimated by using a phase comparison between and upper sideband and a lower sideband of a modulated signal. In one embodiment, one or more propagation effects are estimated by using a phase comparison between an upper sideband and a lower sideband of a satellite navigation signal. In one embodiment, one or more ionospheric propagation effects are estimated by using a phase comparison between an upper sideband and a lower sideband of a GPS M-code signal.
1. A method of compensating for ionospheric delay, the method comprising:
receiving a first modulated radio frequency signal from a satellite source;
receiving a second modulated radio frequency signal from the satellite source;
determining a first phase difference between an upper sideband and a lower sideband of the first modulated radio frequency signal;
determining a second phase difference between an upper sideband and a lower sideband of the second modulated radio frequency signal;
resolving integer phase ambiguity by using the first phase difference and the second phase difference; and
determining a correction for a range measurement to the satellite source based at least in part on the determined first phase difference and the determined second phase difference.
2. The method of claim 1 , wherein the satellite source is a Global Positioning System (GPS) satellite, and wherein the first modulated radio frequency signal corresponds to L1 and the second modulated radio frequency signal corresponds to L2.
3. The method of claim 2 , wherein resolving integer phase ambiguity comprises determining integer values for n and m such that the following are in agreement:
TECu
(
θ
relL
1
)
=
θ
relL
1
3.9903075
+
n
·
90.218611
;
and
TECu
(
θ
relL
2
)
=
θ
relL
1
6.575211
+
m
·
54.750686
;
wherein θ relL1 corresponds to the first phase difference, and wherein θ relL2 corresponds to the second phase difference.
4. The method of claim 1 ,
wherein determining the first phase difference comprises:
tracking a first carrier phase corresponding to the upper sideband of the first modulated radio frequency carrier signal;
tracking a second carrier phase corresponding to the lower sideband of the first modulated radio frequency signal; and
extracting a difference between said first carrier phase and said second carrier phase to determine the first phase difference;
and wherein determining the second phase difference comprises:
tracking a third carrier phase corresponding to the upper sideband of the second modulated radio frequency signal;
tracking a fourth carrier phase corresponding to the lower sideband of the second modulated radio frequency signal; and
extracting a difference between said third carrier phase and said fourth carrier phase to determine the second phase difference.
5. An apparatus for compensating for ionospheric delay, the apparatus comprising:
a first receiver front end configured to receive a first modulated radio frequency signal from a satellite source;
a second receiver front end configured to receive a second modulated radio frequency signal from the satellite source;
a first phase discriminator configured to determine a first phase difference between an upper sideband and a lower sideband of the first modulated radio frequency signal;
a second phase discriminator configured to determine a second phase difference between an upper sideband and a lower sideband of the second modulated radio frequency signal;
a resolver configured to resolve integer phase ambiguity by analysis of the first phase difference and the second phase difference; and
an estimator configured to determine a correction for a range measurement to the satellite source based at least in part on the determined first phase difference and the determined second phase difference.
6. The apparatus of claim 5 , wherein the satellite source is a Global Positioning System (GPS) satellite, and wherein the first modulated radio frequency signal corresponds to L1 and the second modulated radio frequency signal corresponds to L2.
7. The apparatus of claim 5 , wherein the resolver is further configured to determine integer values for n and m such that the following are in agreement:
TECu
(
θ
relL
1
)
=
θ
relL
1
3.9903075
+
n
·
90.218611
;
and
TECu
(
θ
relL
2
)
=
θ
relL
1
6.575211
+
m
·
54.750686
;
wherein θ relL1 corresponds to the first phase difference, and wherein θ relL2 corresponds to the second phase difference.
8. The apparatus of claim 5 ,
wherein the first phase discriminator comprises:
a first tracker configured to track a first carrier phase corresponding to the upper sideband of the first modulated radio frequency signal;
a second tracker configured to track a second carrier phase corresponding to the lower sideband of the first modulated radio frequency signal; and
a first phase comparator configured to extract a difference between said first carrier phase and said second carrier phase to determine the first phase difference;
and wherein the second phase discriminator comprises:
a third tracker configured to track a third carrier phase corresponding to the upper sideband of the second modulated radio frequency signal;
a fourth tracker configured to track a fourth carrier phase corresponding to the lower sideband of the second modulated radio frequency signal; and
a second phase comparator configured to extract a difference between said third carrier phase and said fourth carrier phase to determine the second phase difference.