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Now, what’s tomorrow’s challenge?

APN-001 Rev 1 November 12, 1997

TECHNICAL BULLETIN

NOVATEL’S NARROW CORRELATOR TRACKING TECHNOLOGY

The NovAtel GPS single frequency product is a high performance 12 channel receiver capable of

independently tracking the C/A code and carrier phase of all GPS satellites in view. It employs a

patented Narrow Correlator tracking technology that drastically improves the pseudo-range

accuracy and significantly rejects multipath signals.

Using high performance microprocessors, most GPS receivers adopt digital correlation

techniques to de-modulate the incoming satellite signal. The correlation process is used to

measure the phase offset between the incoming GPS signal and the locally generated signal. The

pseudo-range is derived from this phase offset. The degree of C/A code correlation directly

affects the signal power output from the correlator. Figure 1 illustrates the relationship between

the signal strength and the C/A code correlation. It can be seen that as the C/A code approaches

the “perfect” match condition, the signal strength becomes the greatest.

Figure 1 - Common Correlator Technology - Susceptible to Noise

The ability of a GPS receiver to accurately measure pseudo-ranges is a function of how well the

correlation peak can be measured. High accuracy receivers usually have multiple correlators, as

shown in the diagrams. The GPS receiver assigns one correlator to remain on the correlation

peak (correlator 1 in figure 1). Another two correlators are positioned the width of one C/A code

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chip on both sides of the correlation slope (correlators 2 and 3 in figure 1). The problem with

this type of receiver is that since correlators 2 and 3 are placed 1 chip away from the peak, they

are located just above the natural noise floor. As a result, the receiver will be more susceptible to

noise and multipath, limiting the pseudo-range accuracy of the receiver to about 1 meter.

Figure 2 - NovAtel Narrow Correlator Tracking Technology - The Difference

NovAtel’s patented Narrow Correlator tracking technology is capable of locating the other

correlators as close as 1/20

of a C/A code chip spacing from the correlation peak (figure 2).

The advantage of this approach is that it allows the receiver to predict more accurately where the

correlation peak is. The pseudo-range measurement accuracy is improved ten-fold to about 10

centimeters and is less susceptible to multipath signals.

If you require a more in depth information about the Narrow Correlator tracking technology or

other NovAtel GPS products, please contact:

NovAtel, Inc.

1120 – 68

Avenue N.E.

Calgary, Alberta

Canada, T2E 8S5

Phone: toll free at 1-800-NOVATEL (Canada and the US only) or at (403) 295-4900

Fax: (403) 295-4901

Email: support@novatel.ca