RAIMMODE

Configures RAIM mode

Platform:

OEM719, OEM729, OEM7500, OEM7600, OEM7700, OEM7720, PwrPak7, CPT7, CPT7700, SMART7, SMART2

This command is used to configure Receiver Autonomous Integrity Monitoring (RAIM) operation. This command uses RTCA MOPS characteristics which defines the positioning accuracy requirements for airborne lateral navigation (LNAV) and vertical navigation (VNAV) at 3 stages of flight:

  1. En route travel

  2. Terminal (within range of air terminal)

  3. Non-precision approach

In order to ensure that the required level of accuracy is available in these phases of flight, MOPS requires the computation of protection levels (HPL and VPL). MOPS has the following definitions that apply to NovAtel’s RAIM feature:

Horizontal Protection Level (HPL) is a radius of the circle in the horizontal plane. Its center is at the true position, that describes the region, assured to contain the indicated horizontal position. It is the horizontal region where the missed alert and false alert requirements are met using autonomous fault detection.

Vertical Protection Level (VPL) is half the length of the segment on the vertical axis. Its center is at the true position, that describes the region, assured to contain the indicated vertical position when autonomous fault detection is used.

Horizontal Alert Limit (HAL) is a radius of the circle in the horizontal plane. Its center is at the true position, that describes the region, required to contain the indicated horizontal position with the required probability.

Vertical Alert Limit (VAL) is half the length of the segment on the vertical axis. Its center is at the true position, that describes the region, required to contain the indicated vertical position with certain probability.

Probability of False Alert (Pfa) is a false alert defined as the indication of a positioning failure, when a positioning failure has not occurred (as a result of false detection). A false alert would cause a navigation alert.

Detection strategy

NovAtel’s RAIM detection strategy uses the weighted Least-Squares Detection (LSA) method. This method computes a solution using a LSA and is based on the sum of squares of weighted residuals. It is a comparison between a root sum of squares of residuals and a decision threshold to determine a pass/fail decision.

Isolation strategy

NovAtel RAIM uses the maximum residual method. Logically it is implemented as a second part of Fault Detection and Exclusion (FDE) algorithm for LSA detection method. Weighted LSA residuals are standardized individually and the largest residual is compared to a decision threshold. If it is more than the threshold, the observation corresponding to this residual is declared faulty.

The Detection strategy and Isolation strategy are used for all RAIM modes (USER, DEFAULT, APPROACH, TERMINAL and ENROUTE.

Message ID: 1285

Abbreviated ASCII Syntax:

RAIMMODE mode [hal [val [pfa]]]

Factory Default:

RAIMMODE default

Input Example:

RAIMMODE user 100 100 0.01

RAIMMODE terminal

Field

Field Type

ASCII Value

Binary Value

Description

Format

Binary Bytes

Binary Offset

1

Command header

-

-

RAIMMODE header

This field contains the command name for abbreviated ASCII or the message header for ASCII (see page 1) or Binary (see page 1).

-

H

0

2

MODE

See Table: RAIM Mode Types

When the MODE is set to DEFAULT, protection levels are not calculated and the values for HAL, VAL and PFA are set to 0.0.
When the MODE is set to USER, APPROACH, TERMINAL or ENROUTE, protection levels are calculated.

Enum

4

H

3

HAL

5 ≤ HAL ≤ 9999.99

Horizontal alert limit (m) (Default = 0.0)

Double

8

H+4

4

VAL

5 ≤ VAL ≤ 9999.99

Vertical alert limit (m) (Default = 0.0)

Double

8

H+12

5

PFA

(Pfa) = 1e-7Pfa ≤ 0.25

Probability of false alert (Default = 0.0)

Double

8

H+20

RAIM Mode Types

Binary

ASCII

Description

0

DISABLE

Do not do integrity monitoring of least squares solution

1

USER

User will specify alert limits and probability of false alert

2

DEFAULT

Use NovAtel RAIM (default)

3

APPROACH

Default numbers for non-precision approach navigation modes are used - HAL = 556 m (0.3 nm), VAL = 50 m for LNAV/VNAV

4

TERMINAL

Default numbers for terminal navigation mode are used - HAL = 1 nm, no VAL requirement

5

ENROUTE

Default numbers for enroute navigation mode are used - HAL = 2 nm, no VAL requirement