Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-04-20
2003-10-21
Trost, William (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S067110, C455S067160, C701S213000, C701S214000, C342S357490, C342S357490
Reexamination Certificate
active
06636744
ABSTRACT:
RELATED APPLICATION
Related subject matter is disclosed in the following application filed concurrently herewith and assigned to the same assignee hereof: U.S. patent application entitled “Obtaining Round Trip Time Delay Parameter For A Wireless Terminal Of An Integrated Wireless-Global Positioning System”, Ser. No. 09/552,897.
FIELD OF THE INVENTION
The present invention relates generally to an integrated wireless-global positioning system and, more particularly, to obtaining and selectively using the pilot phase offset time delay parameter for a wireless terminal of an integrated wireless-global positioning system.
DESCRIPTION OF THE RELATED ART
Global positioning systems, which are satellite based, provide accurate, three dimension position information to worldwide users.
FIG. 1
depicts a global positioning system (GPS)
10
. The GPS
10
comprises a plurality of satellites
12
-j and at least one GPS receiver
14
, where j=
1
,
2
, . . . , n. Each satellite
12
-j orbits the earth at a known speed v
j
and is separated by a known distance from the other satellites
12
-j. Each satellite
12
-j transmits a global position signal
11
-j which includes a carrier signal with a known frequency f modulated with a unique pseudo-random noise (PN-j) code and navigational data (ND-j) associated with the particular satellite
12
-j. The PN-j code includes a unique sequence of PN chips and navigation data ND-j which includes a satellite identifier, timing information and orbital data, such as elevation angle &agr;j and azimuth angle &phgr;j.
FIG. 2
depicts a typical 20 ms frame of the GPS signal
11
-j which comprises twenty full sequences of a PN-j code in addition to a sequence of navigation data ND-j.
GPS receiver
14
comprises an antenna
15
for receiving GPS signals
11
-j, a plurality of correlators
16
-k for detecting GPS signals
11
-j and a processor
17
having software for determining a position using the navigation data ND-j, where k=
1
,
2
, . . . , m. GPS receiver
14
detects GPS signals
11
-j via PN-j codes. Detecting GPS signals
11
-j involves a correlation process wherein correlators
16
-k are used to search for PN-j codes in a carrier frequency dimension and a code phase dimension. Such correlation process is implemented as a real-time multiplication of phase shifted replicated PN-j codes modulated onto a replicated carrier signal with the received GPS signals
11
-j, followed by an integration and dump process.
In the carrier frequency dimension, GPS receiver
14
replicates carrier signals to match the frequencies of the GPS signals
11
-j as they arrive at GPS receiver
14
. However, due to the Doppler effect, the frequency f at which GPS signals
11
-j are transmitted changes an unknown amount &Dgr;f
j
before the signal
11
-j arrives at the GPS receiver
14
. Thus, each GPS signal
11
-j will have a frequency f+&Dgr;f
j
when it arrives at the GPS receiver
14
. To compensate for the Doppler effect, GPS receiver
14
replicates the carrier signals across a frequency spectrum f
spec
ranging from f+&Dgr;f
min
to f+&Dgr;f
max
until the frequency of the replicated carrier signal matches the frequency of the received GPS signal
11
-j, wherein &Dgr;f
min
and &Dgr;f
max
are a minimum and maximum change in the frequency the GPS signals
11
-j will undergo due to the Doppler effect as they travel from satellites
12
-j to GPS receiver
14
, i.e., &Dgr;f
min
≦&Dgr;f
j
≦&Dgr;f
max
.
In the code phase dimension, GPS receiver
14
replicates the unique PN-j codes associated with each satellite
12
-j. The phases of the replicated PN-j codes are shifted across code phase spectrums R
j
(spec) until the replicated carrier signals modulated with the replicated PN-j codes correlate, if at all, with the GPS signals
11
-j being received by the GPS receiver
14
, where each code phase spectrum R
j
(spec) includes every possible phase shift for the associated PN-j code. When the GPS signals
11
-j are detected by the correlators
16
-k, GPS receiver
14
extracts the navigation data ND-j from the detected GPS signals
11
-j and uses the navigation data ND-j to determine a location for the GPS receiver
14
.
A GPS enables a ground based receiver to determine its position by measuring the time difference required for GPS signals initiated from two or more satellites to be received by a wireless terminal. The pseudorange is defined as this time difference times the speed of light. The pseudorange is not the real range because it contains errors caused by the receiver clock offset. To determine a two-dimensional position (latitude and longitude) usually requires receiving signals from three satellites. To determine a three-dimensional position (latitude, longitude, and altitude) requires receiving pseudoranges from four or more satellites. This precondition, however, may not always be satisfied, especially when the direct satellite signals are obstructed, such as when a wireless terminal is inside a building.
GPS receivers are now being incorporated into wireless telephones or other types of mobile communication devices which do not always have a clear view of the sky. In this situation, the signal-to-noise ratios of GPS signals
11
-j received by GPS receiver
14
are typically much lower than when GPS receiver
14
does have a clear view of the sky, thus making it more difficult for GPS receiver
14
to detect the GPS signals
11
-j.
Integrated wireless-global positioning (WGP) systems were developed to facilitate the detection of GPS signals
11
-j by GPS receivers. The WGP system facilitates detection of GPS signals
11
-j by reducing the number of integrations to be performed by correlators searching for GPS signals
11
-j. The number of integrations is reduced by narrowing the frequency range and code phase ranges to be searched. Specifically, the WGP system limits the search for GPS signals
11
-j to a specific frequency or frequencies and to a range of code phases less than the code phase spectrum R
j
(spec).
The position of a wireless terminal may also be determined from information obtained from a wireless network. The information typically includes pilot phase offset (PPO) signals. The PPO measurement contains the information of the distance between the wireless terminal and the BS. Pilot phase offset is the measurement of the code phase in a pilot signal. It consists of information of the distance between the wireless terminal and the BS plus a bias that is the same for all pilot phase offset (PPO) measurements from any one base station. If pilot phase offset measurements from two BSs are available, two pilot phase offset measurements can be used to construct one pilot phase offset measurement by subtracting one pilot phase offset measurement from the other. The subtraction cancels out the unknown constant, and so the PPO measurement is the distance from the wireless terminal to one BS minus the distance from the wireless terminal to the other BS. If three of more PPO measurements are available, the 2D position of a wireless terminal may also be determined from triangulation schemes. One problem with using wireless network based signals to determine the location of a wireless terminal is that the measurement errors of the PPO is usually much larger than the satellite based navigational system measurement errors. Another problem is that three or more measurements may not always be available for the purpose of position determination.
An integrated wireless-global positioning (WGP) system relies on both the satellite navigation system and the wireless communication system to determine the location of a wireless terminal. The integrated wireless-global positioning system combines the data from both the wireless network and the satellites navigation system to obtain an integrated position solution. By combining information from both the global positioning system and the wireless network, it is possible to increase the positioning accuracy and, at the same time, overcome the requirement of having at least three measurements.
FI
Ewart James D.
Lucent Technologies - Inc.
Trost William
LandOfFree
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