# US 7,609,204 B2 · System and method for dynamically estimating output variances for carrier-smoothing filters

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- Number: US 7,609,204 B2
- Document ID: US7609204B2
- Status: Granted
- Kind: B2
- Application number: 11/215,169
- Filed: 2005-08-30
- Published: 2007-03-01
- Granted: 2009-10-27
- Earliest claimed: 2005-08-30
- Assignees: Honeywell International Inc.
- Inventors: Reed R. May; Kenneth S. Morgan
- Web page: https://patentgrep.com/patent/US7609204B2

## CPC

- G01S 19/15: Aircraft landing systems
- G01S 19/32: Multimode operation in a single same satellite system, e.g. GPS L1/L2
- G01S 19/43: using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

An improved system and method is disclosed for dynamically estimating the output variances of carrier-smoothing filters used, for example, in GPS receivers. By accurately estimating the output variances of the carrier-smoothing filters as they transition from initialization to steady-state operation, it is possible to calculate any required protection levels without having to wait for the filters to fully stabilize. As one example, a system for estimating output variances of a carrier-smoothing filter for use in a satellite navigation system receiver is disclosed, which includes a plurality of smoothing filters associated with a navigation processing unit in a satellite navigation receiver. One or more processors associated with the navigation processing unit executes an algorithm for each smoothing filter, which provides a method for dynamically calculating an output variance for a respective smoothing filter as it transitions in response to new input variance values. The method also predicts the settling point of the output variance for that smoothing filter given a set of pseudorange and carrier-phase values to be applied. Therefore, using this novel output variance prediction method, precision navigation applications such as, for example, airborne GPS-based precision landing system applications can begin operations with suitable calculated protection level values without having to wait for the smoothing filters to stabilize. Thus, such precision landing systems are available for use as soon as the required protection level values are reached.

## Claims

### Claim 1

A method for dynamically estimating output variances for a smoothing filter, comprising the steps of:
receiving a signal at a receiver;
defining a current output term for the smoothing filter;
determining a total variance of the smoothing filter;
determining a variance of said current output term of the smoothing filter;
incrementally calculating said variance of said current output term of the smoothing filter;
deriving a steady-state variance for an output of the smoothing filter;
defining said steady-state variance as a function of a variance of an input pseudorange value (ρ) and a variance of an input accumulated carrier phase value (∅ACC) of the smoothing filter; and
filtering the received signal based upon at least the defined steady-state variance.

### Claim 2 (depends on 1)

The method of claim 1, further comprising the steps of: redefining said steady-state variance as a function of at least one of a plurality of input variances and a gain coefficient.

### Claim 3 (depends on 1)

The method of claim 1, further comprising the step of:
redefining said current output term with a plurality of previous output terms; and
generalizing said redefined current output term, by defining said current output term for a sample interval of n=0 to N.

### Claim 4 (depends on 1)

The method of claim 1, whereby said steady-state variance for said output of said smoothing filter is defined as a function of a plurality of input variances and a filter gain coefficient, wherein α is a filter gain of the smoothing filter, wherein β is (1−α), and wherein the steady-state variance is expressed as
σ
S
∞
2
⁡
[
α
(
2
-
α
)
]
⁢
σ
ρ
2
+
[
2
⁢
β
(
2
-
α
)
]
⁢
σ
ϕ
2
.

### Claim 5 (depends on 1)

The method of claim 1, wherein said smoothing filter comprises a Hatch filter.

### Claim 6 (depends on 1)

The method of claim 1, wherein said smoothing filter comprises a pseudorange smoothing filter for use with a satellite navigation receiver system.

### Claim 7

A receiver system, comprising:
a preamplifier unit;
a down-converter unit, an input of said down-converter unit coupled to an output of said preamplifier unit;
an analog-to-digital conversion unit, an input of said analog-to-digital conversion unit coupled to an output of said down-converter unit;
a processing unit, said processing unit coupled to an output of said analog-to-digital conversion unit; and at least one smoothing filter, a plurality of inputs of said at least one smoothing filter coupled to said processing unit, said processing unit operable to:
define a current output term of said at least one smoothing filter;
determine a total variance of said at least one smoothing filter;
determine a variance of said current output term of said at least one smoothing filter;
incrementally calculate said variance of said current output term of said at least one smoothing filter;
derive a steady-state variance for an output of said at least one smoothing filter; and
redefine said steady-state variance as a function of a variance of an input pseudorange value (ρ) and a variance of an input accumulated carrier phase value (∅ACC) of said at least one smoothing filter.

### Claim 8 (depends on 7)

The receiver system of claim 7, wherein said at least one smoothing filter comprises a carrier-phase smoothing filter for pseudoranges.

### Claim 9 (depends on 7)

The receiver system of claim 7, further comprising a global positioning system receiver.

### Claim 10 (depends on 7)

The receiver system of claim 7, wherein said processing unit is further operable to:
redefine said steady-state variance as a function of at least one of a plurality of input variances and a gain coefficient.

### Claim 11

A navigation receiver, comprising:
means for preamplifying a received signal;
means for converting a preamplified signal from a radio frequency to an intermediate frequency, said means for converting coupled to an output of said means for preamplifying;
means for converting an analog signal received from said means for converting to a digital form;
smoothing means; and
processing means coupled to said smoothing means, for defining a current output term for said smoothing means, determining a total variance term for said smoothing means, determining a variance of said current output term, of said smoothing means, incrementally calculating said variance of said current output term of said smoothing means, deriving a steady-state variance for an output of the smoothing mean, and redefining said steady-state variance as a function of a variance of an input pseudorange value(ρ) and a variance of an input accumulated carrier phase value (∅ACC) of the smoothing means.

### Claim 12 (depends on 11)

The navigation receiver of claim 11, wherein said processing means is further for redefining said steady-state variance as a function of at least one of a plurality of input variances and a gain coefficient.

### Claim 13 (depends on 11)

The navigation receiver of claim 11, wherein said smoothing means comprises a carrier-phase smoothing filter for pseudoranges.

### Claim 14 (depends on 11)

The navigation receiver of claim 11, further comprising a global positioning system receiver.

### Claim 15

A computer program product, comprising:
a computer-usable medium having computer-readable code embodied therein for configuring a computer processor, the computer program product comprising:
a first executable computer-readable code configured to cause a computer processor to define a current output term for a smoothing filter;
a second executable computer-readable code configured to cause a computer processor to determine a total variance of said smoothing filter;
a third executable computer-readable code configured to cause a computer processor to determine a variance of said current output term of said smoothing filter;
a fourth executable computer-readable code configured to cause a computer processor to incrementally calculate said variance of said current output term of said smoothing filter;
a fifth executable computer-readable code configured to cause a computer processor To derive a steady-state variance for an output of the smoothing filter; and
a sixth executable computer-readable code configured to cause a computer processor to redefine said steady-state variance as a function of a variance of an input pseudorange value (ρ) and a variance of an input accumulated carrier phase value (∅ACC) of the smoothing filter.

### Claim 16 (depends on 15)

The computer program product of claim 15, further comprising:
a seventh executable computer-readable code configured to cause a computer processor to redefine said steady-state variance as a function of at least one of a plurality of input variance and a gain coefficient.

### Claim 17 (depends on 15)

The computer program product of claim 15, wherein said smoothing filter comprises a carrier-phase smoothing filter for a plurality of pseudoranges.

### Claim 18 (depends on 15)

The computer program product of claim 15, wherein said smoothing filter comprises a smoothing filter for a global positioning system receiver.

### Claim 19 (depends on 15)

The computer program product of claim 15, wherein said smoothing filter comprises a Hatch filter.

### Claim 20 (depends on 15)

The computer program product of claim 15, wherein said smoothing filter comprises a carrier-phase smoothing filter for a plurality of pseudorange measurements.