Navcom SF-3050 A Computationally Efficient Ambiguity Reso User Manual download pdf

A COMPUTATIONALLY EFFICIENT AMBIGUITY

RESOLUTION TECHNIQUE

Ron Hatch, Tenny Sharpe, NavCom Technology, Inc.

BIOGRAPHY

Ron Hatch is the Director of Navigation Systems at

NavCom Technology, a company of which he was a co-

founder. He has developed a number of innovative

techniques for processing GPS measurements and has

obtained more than a dozen patents related to GPS. Ron is

currently the president of the Institute of Navigation, is a

Fellow of the ION and has received the Kepler and

Thurlow awards from the ION.

Mr. Tenny Sharpe is Director of Advanced Development

at NavCom Technology Inc. Mr. Sharpe received a B.S.

in Physics from Case Institute of Technology and a M.S.

in Computer Science from the University of California,

Los Angeles. Mr. Sharpe has over 30 years experience in

the development of aerospace and industrial electronics.

His specializations are software and systems design for

GPS navigation systems.

ABSTRACT

A new method of carrier-phase ambiguity resolution is

described. The new technique is a variation of the least-

squares residual search technique in the ambiguity

domain. It uses a very efficient algorithm to compute the

residuals associated with each potential combination of

ambiguities to be tested. Several other techniques are

employed to simplify the calculations and to enhance the

probability of identifying the correct ambiguity vector.

The intent is to minimize the number of data epochs

required to correctly identify the integer ambiguity values.

The capability of the technique to rapidly identify the

correct ambiguity vector is illustrated by plotting the

results of scoring runs which exercise the search

algorithms using recorded field data taken over different

rover-to-base separation distances. To maximize the

number of searches exercised in these runs, as soon as the

ambiguity vector is identified, the results are cleared and a

new search is initiated with all navigation parameters re-

initialized. Some navigation results are also shown which

are typical of RTK carrier-phase navigation results.

INTRODUCTION

The RTK ambiguity resolution technique implemented

within the NavCom dual-frequency receiver has several

unique features designed to minimize the computational

task while ensuring that a minimal data collection interval

is required. The fundamental approach is similar to

several least-squares residual search techniques which

have been employed by others. [1-4]

The first unique feature is that the base station transmits

corrections rather than the raw data, which most RTK

implementations transmit. This has several advantages:

1) it offloads part of the computation from the user

receiver to the base station receiver; 2) it allows code

smoothing of the base station data to occur even before

the user receiver is turned on, which ensures a more

accurate initial code solution; 3) it simplifies the

processing algorithms because no differencing across

receivers is required.

The second unique feature is a simplified computational

technique to generate the residuals resulting from

candidate ambiguity vectors. This technique is the main

subject of the paper and will be explored in some detail.

The search process is a two-stage process which depends

upon the availability of dual-frequency measurements at

both the base-station receiver and the user receiver. First a

wide-lane search is performed and up to 10 ambiguity

vectors, which meet specific requirements (e.g. residuals

less than a threshold value) are saved for further

processing. In the second stage, each of the ambiguity

vectors determined in the first stage are tested by

searching each satellite (except the first to avoid

redundant clock solutions) across the two narrow-lane

ambiguity values which result in a narrow-lane measured

range closest to the corresponding wide-lane measured

range. Those narrow-lane combinations, which meet a

number of specific criteria, are scored and if more than

one are acceptable their relative score is used to determine

whether or not one of them can be declared the correct

ambiguity vector.

1 2 3 4 5 6 7

Summary of Contents

Page 1 - RESOLUTION TECHNIQUE

A COMPUTATIONALLY EFFICIENT AMBIGUITY RESOLUTION TECHNIQUE Ron Hatch, Tenny Sharpe, NavCom Technology, Inc. BIOGRAPHY Ron Hatch is the Direct

Page 2

2 INITIAL CODE SOLUTION The primary motivation in the initial code solution is to obtain the most accurate code solution possible with as few measure

Page 3

3 )()(/)(2121rriiwriiwRRNφφφφλ−+−−−= (5) where the superscript, i, represents each satellite in turn and the superscript, r, represents the re

Page 4

4information content to the deviation one will obtain in attempting to step to any other narrow or wide-lane ambiguity value. While the deviation is

Page 5 - 10 Hours, 13,659 Searches

5Figure 1. Short Baseline Scoring Run Search Time vs. Run Time Figure 2. Short Baseline Scoring Run Histogram of Search Times NCT2000D RTK Search Ti

Page 6 - 1.25 Hours 1,772 Searches

6Figure 3. Five Kilometer Scoring Run Figure 4. Five Kilometer Scoring Run NCT2000D RTK Search Times-60-3003060900 0.25 0.5 0.75 1 1.25Time (hours)Se

Page 7 - Std. Dev. (cm.) 0.4 0.5 1.1

7 Figure 5. RTK Navigation Results – Horizontal Position Scatter Plot CONCLUSION A new approach to the ambiguity resolution process has been describe

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Navcom SF-3050 A Computationally Efficient Ambiguity Reso User Manual

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