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6 differential aiding, 1 differential gps (dgps), 7 navigation modes – Navman LA000508 User Manual

Page 8: 8 core processor performance, 9 sensitivity, Table 3‑2: software processing performance, Table 3‑3: gps receiver performance

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LA000507G © 2006 Navman New Zealand. All rights reserved. Proprietary information and specifications subject to change without notice.

3.6 Differential aiding

3.6.1 Differential GPS (DGPS)
DGPS specification improves the Jupiter 20 horizontal position accuracy to <4 m 2 dRMS.

3.6.2 Satellite Based Augmentation Systems (SBAS) including WAAS and EGNOS
SBAS improves horizontal position accuracy by correcting GPS signal errors caused by

ionospheric disturbances, timing and satellite orbit errors. The Jupiter 20 is capable of

receiving WAAS and EGNOS differential corrections. Both SBAS and DGPS should improve

position accuracy. However, other factors can affect accuracy, such as GDOP (Geometric

Dilution of Precision), multipath, distance from DGPS reference station and latency of

corrections. Note also that XTrac does not support differential aiding.

3.7 Navigation modes

The Jupiter 20 GPS receiver supports 3D (three‑dimensional) and 2D (two‑dimensional) modes

of navigation.

3D navigation:

The receiver defaults to 3D navigation when at least four GPS satellites are being

tracked. In 3D navigation, the receiver computes latitude, longitude, altitude, and time from

satellite measurements.

2D navigation:

When less than four GPS satellite signals are available, or when a fixed altitude

value can be used to produce an acceptable navigation solution, the receiver will enter 2D

navigation mode using a fixed value of altitude determined by the host. Forced operation in 2D

mode can be commanded by the host.
In 2D navigation, the navigational accuracy is primarily determined by the relationship of the

fixed altitude value to the true altitude of the antenna. If the fixed value is correct, the specified

horizontal accuracies apply. Otherwise, the horizontal accuracies will degrade as a function of

the error in the fixed altitude.

3.8 Core processor performance

The standard Jupiter 20 with GSW2 software runs at a CPU clock speed of 12.28 MHz. Using

XTrac software (Jupiter 20S), the clock speed increases to 24.5 MHz. An SDK (Software

Development Kit) is available from SiRF to customise the Jupiter 20 firmware. Using the SiRF

SDK the clock speed can be increased up to 49 MHz.
The processing power used by the navigation software is shown in Table 3‑2.

Parameter

J20/J20D

J20S

typical performance

2‑3 MIPS

4‑5 MIPS

peak performance

6‑7 MIPS

8‑9 MIPS

Table 3-2: Software processing performance

3.9 Sensitivity

The GPS receiver performance of the Jupiter 20 is shown in Table 3‑3.

Parameter

J20/J20D

J20S

acquisition sensitivity

–135 dBm

33 dBHz

–135 dBm

33 dBHz

navigation sensitivity

–141 dBm

28 dBHz

–152 dBm

17 dBHz

tracking sensitivity

–143 dBm

26 dBHz

–154 dBm

15 dBHz

Table 3-3: GPS receiver performance