U.S. patent application number 10/436033 was filed with the patent office on 2003-11-20 for method for positioning of an electronic device, a system, and an electronic device.
This patent application is currently assigned to Nokia Corporation. Invention is credited to Pietila, Samuli, Valio, Harri.
Application Number | 20030214433 10/436033 |
Document ID | / |
Family ID | 8563955 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030214433 |
Kind Code |
A1 |
Pietila, Samuli ; et
al. |
November 20, 2003 |
Method for positioning of an electronic device, a system, and an
electronic device
Abstract
The present invention relates to a method for determining the
position of an electronic device (1) by means of satellites in a
positioning system. In the method, satellite orbit data and a
default position for the electronic device (1) are determined. In
the method, at least the following steps are taken: a determination
step for determining a first time data estimate by using said
default position, a computing step for computing an estimate of the
code phase of the satellite signal on the basis of said time data
estimate, the default position and the satellite orbit data, and a
searching step, in which a code-modulated signal transmitted by
satellites of a positioning system is received for searching the
signal of at least one satellite and for acquiring the signal by
using said estimate of the code phase. The invention also relates
to a system, in which the method is applied, as well as to an
electronic device (1).
Inventors: |
Pietila, Samuli; (Tampere,
FI) ; Valio, Harri; (Kammenniemi, FI) |
Correspondence
Address: |
WARE FRESSOLA VAN DER SLUYS &
ADOLPHSON, LLP
BRADFORD GREEN BUILDING 5
755 MAIN STREET, P O BOX 224
MONROE
CT
06468
US
|
Assignee: |
Nokia Corporation
|
Family ID: |
8563955 |
Appl. No.: |
10/436033 |
Filed: |
May 12, 2003 |
Current U.S.
Class: |
342/357.25 ;
342/357.63; 342/357.65 |
Current CPC
Class: |
G01S 19/243 20130101;
G01S 19/252 20130101; G01S 19/28 20130101 |
Class at
Publication: |
342/357.15 |
International
Class: |
G01S 005/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 16, 2002 |
FI |
20020929 |
Claims
1. A method for determining the position of an electronic device by
means of satellites in a positioning system, where satellite orbit
data is determined and a default position is determined for the
electronic device, wherein the method comprises at least: a
determination step for determining a first time data estimate by
using said default position, a computing step for computing an
estimate of the code phase of the satellite signal on the basis of
said time data estimate, the default position and the satellite
orbit data, and a searching step, in which a code-modulated signal
transmitted by satellites of a positioning system is received for
searching the signal of at least one satellite and for acquiring
the signal by using said estimate of the code phase.
2. The method according to claim 1, comprising changing said time
data estimate, if acquisition of the signal from at least one other
satellite cannot be performed on the basis of said first time data
estimate, wherein said computing step and searching step are
iterated, and that during each iteration, an altered time data
estimate is used in said computing step.
3. The method according to claim 1, wherein the electronic device
is used to receive information from a communication network,
wherein the data about said default position is received from the
communication network.
4. The method according to claim 3, wherein said communication
network used is a mobile communication network with base stations
for communication between the communication network and the
electronic device, and that said default position used is the
position of the base station through which the communication
between the mobile communication network and the electronic device
is carried out.
5. The method according to claim 3, wherein said communication
network used is a mobile communication network, in which the
position of the electronic device is determined, and that said
default position used is the position of the electronic device
determined in the communication network.
6. The method according to claim 1, comprising receiving the signal
of one satellite for determining said first time data estimate, and
performing acquisition of this signal to be received.
7. The method according to claim 1, comprising transmitting said
first time data estimate from the communication network to the
electronic device.
8. A system with means for determining the position of an
electronic device by means of code-modulated signals transmitted by
satellites in a positioning system, in which positioning system
satellite orbit data are determined, and which system comprises
means for determining a default position for the electronic device,
the electronic device comprising means for receiving code-modulated
signals transmitted by satellites in the positioning system,
wherein the system comprises: means for determining a first time
data estimate by using said default position, means for computing
an estimate of the code phase of the satellite signal on the basis
of said time data estimate, the default position and the satellite
orbit data, and means for searching the signal of at least one
satellite and for acquiring the signal by using said estimate of
the code phase.
9. The system according to claim 8, comprising means for changing
said time data estimate, if acquisition of at least one other
satellite signal has not been possible on the basis of said first
time data estimate, means for computing an estimate of the code
phase of the satellite signal and for iterating the searching of
the satellite signal, and means for using a changed time data
estimate for each iteration.
10. The system according to claim 8, in which the electronic device
is used to receive information from a communication network,
wherein the electronic device comprises means for receiving data
about said default position from the communication network.
11. The system according to claim 10, wherein said communication
network is a mobile communication network with base stations for
communication between the mobile communication network and the
electronic device, and that said default position used is arranged
to be the position of the base station through which the
communication between the mobile communication network and the
electronic device is arranged to be carried out.
12. The system according to claim 10, wherein said communication
network is a mobile communication network with means for
determining the position of the electronic device, and that said
default position used is arranged to be the position of the
electronic device determined in the mobile communication
network.
13. The system according to claim 8, wherein the means for
determining said first time data estimate comprise means for
receiving the signal of one satellite and means for acquisition of
the received signal.
14. The system according to claim 8, comprising means for
transmitting said first time data estimate from the communication
network to the electronic device.
15. An electronic device comprising means for determining the
position by means of code-modulated signals transmitted by
satellites in a positioning system, in which positioning system
satellite orbit data are determined, and which electronic device
comprises means for determining a default position for the
electronic device, and means for receiving code-modulated signals
transmitted by satellites in the positioning system, wherein the
electronic device comprises: means for determining a first time
data estimate by using said default position, means for computing
an estimate of the code phase of the satellite signal on the basis
of said time data estimate, the default position and the satellite
orbit data, and means for searching the signal of at least one
satellite and for acquiring the signal by using said estimate of
the code phase.
16. The electronic device according to claim 15, comprising means
for changing said time data estimate, if acquisition of at least
one other satellite signal has not been possible on the basis of
said first time data estimate, means for computing an estimate of
the code phase of the satellite signal and for iterating the
searching of the satellite signal, and means for using a changed
time data estimate for each iteration.
17. The electronic device according to claim 15, comprising means
for storing orbit data of said satellites.
18. The electronic device according to claim 15, comprising means
for performing mobile station functions.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 USC .sctn.119 to
Finnish Patent Application No. 20020929 filed on Dec. 27, 2001.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for determining
the position of an electronic device by means of satellites in a
positioning system in which satellite orbit data is determined, and
a default position is determined for the electronic device. The
invention also relates to a system with means for determining the
position of an electronic device by means of code-modulated signals
transmitted by satellites in a positioning system, in which
positioning system satellite orbit data is determined, and which
system comprises means for determining a default position for the
electronic device, the electronic device comprising means for
receiving code-modulated signals transmitted by satellites of the
positioning system. The invention further relates to an electronic
device comprising means for positioning by means of code-modulated
signals transmitted by satellites in a positioning system, in which
positioning system satellite orbit data is determined, and which
electronic device comprises means for determining a default
position for the electronic device, and means for receiving
code-modulated signals transmitted by satellites in the positioning
system.
BACKGROUND OF THE INVENTION
[0003] Typically, positioning receivers utilizing the GPS system
attempt to receive the signal of at least four different
satellites, on the basis of which the position (x, y and z
coordinates) of the positioning receiver as well as the time data
of the GPS system are computed in the positioning receiver. The
positioning is performed, for example, at the stage when the
positioning receiver is turned on. It takes a long time to receive
four different satellite signals, because the positioning receiver
must perform acquisition of each of the signal to be received. For
the acquisition and for receiving the signal from the satellites, a
positioning receiver of prior art must find out the number, Doppler
frequency and code phase of each signal to be received, before the
signal can be received. The number of operations required for this
step can be estimated by means of the number of satellites in the
system, variations in the Doppler frequency, and the number of
different code phases. For example, assuming that the satellite
positioning system comprises 32 satellites, Doppler frequencies are
searched from 21 different frequency ranges and there are 1023
different code phases, and the resolution of 1/2 chip is applied,
the product of these numerical values will give an idea about the
extent of the problem. With the above-presented figures, the number
of different combinations for the acquisition of the signal from a
single satellite will be in the order of 1,300,000
(=32.times.21.times.2046). The above-presented numerical values
correspond well to the situation in the GPS system presently in
use.
[0004] In some cases, the above-presented situation is made easier
by the fact that the positioning receiver has previously received
the signal of the satellites and has some kind of estimation of its
own position as well as satellite orbit data. It is thus possible
to use a previously determined position as a default position. When
the positioning receiver has some kind of time data, position data
and satellite orbit data, it is possible, by calculation, to
estimate the azimuth angles of the satellites to the positioning
receiver and to use this data to restrict the acquisition of the
signals of such satellites only, which are, on the basis of the
computation, above the horizon in relation to the position of the
positioning receiver at the time. Furthermore, assuming that the
positioning receiver stays still or moves slowly in relation to the
movement of the satellites, it is possible to further restrict the
searching range of the Doppler frequency of the signal propagated
along the line of sight.
[0005] However, the positioning receiver does not necessarily have
precise time data of the GPS system, wherein the positioning
receiver will not be capable of estimating the position of the
satellites at a very high precision.
[0006] However, to restrict the searching range of the code phases,
the positioning receiver should have very precise time data,
because the length of one chip is very short. For example, in the
GPS system, one chip is about 0.98 .mu.s and the code iteration
interval (epoch) is about 1 ms. Such precision cannot be achieved
with conventional real time clocks (RTC) used in positioning
receivers. Therefore, in conventional positioning receivers, the
estimation of code phases of such satellite signals which have not
been acquired, is not possible until the acquisition of signals
from at least four different satellites has been completed and the
position of the positioning receiver and the time data of the
system have been determined on the basis of these signals. In
conventional positioning receivers of prior art, the acquisition of
four signals is performed and the position and the time data are
determined without knowledge about the code phase. First after
these four different signals have been found and received and used
for determining the time data of the system and the position of the
positioning receiver at some precision, the signals of other
satellites are searched and acquired by using the code phase data.
The information to be determined on the basis of these satellites
can be used to improve the positioning precision. This acquisition
of four different satellite signals will take a long time,
particularly if the signals are weak. In practice, the time taken
for the acquisition may thus be several tens of minutes, even
several hours, which, in most applications in practice, means that
the positioning receiver cannot be used. Particularly indoors, the
signal strength may be so weak that acquisition will not be
possible and the positioning will not be successful.
[0007] The GPS satellite system applies two kinds of satellite
orbit data, Ephemeris and Almanac, of which Ephemeris is the more
accurate one. The accuracy of the Ephemeris orbit data is less than
one metre, whereas the Almanac orbit data will indicate the
satellite position at an accuracy of about 0 to 3 km. Each
satellite only transmits the Ephemeris orbit data of its own, but
the Almanac orbit data is transmitted to all the satellites.
SUMMARY OF THE INVENTION
[0008] It is an aim of the present invention to provide a method
for accelerating the positioning of a positioning receiver, a
positioning system, as well as an electronic device. The invention
is based on the idea that the acquisition of the signal of one
satellite is performed in the positioning receiver of an electronic
device by using a known position, which is relatively close to the
position of the electronic device at the time, as a default
position for the electronic device. In an advantageous embodiment
of the invention, this default position is the known location of a
base station in a mobile communication network. On the basis of
this default position and one satellite signal, it is possible to
form a relatively precise estimate of the time data of the system,
wherein this time data is used to estimate the code phase in
signals of one or more other satellites. When the code phase is
known within an accuracy of a few chips, it will be easier to
search the satellite signals than by searching from all the
different code phases possible. To put it more precisely, the
present invention is primarily characterized in that the method
comprises at least:
[0009] a determination step for determining a first time data
estimate by using said default position,
[0010] a computing step for computing an estimate of the code phase
of the satellite signal on the basis of said time data estimate,
the default position and the satellite orbit data, and
[0011] a searching step, in which a code-modulated signal
transmitted from a satellite in a positioning system is received
for searching the signal of at least one satellite and for
acquiring the signal by using said estimate of the code phase.
[0012] The system according to the present invention is primarily
characterized in, that the system comprises:
[0013] means for determining a first time data estimate by using
said default position,
[0014] means for computing an estimate of the code phase of the
satellite signal on the basis of said time data estimate, the
default position and the satellite orbit data, and
[0015] means for searching the signal of at least one satellite and
for acquiring the signal by using said estimate of the code
phase.
[0016] Furthermore, the electronic device according to the present
invention is primarily characterized in that the electronic device
comprises:
[0017] means for determining a first time data estimate by using
said default position,
[0018] means for computing an estimate of the code phase of the
satellite signal on the basis of said time data estimate, the
default position and the satellite orbit data, and
[0019] means for searching the signal of at least one satellite and
for acquiring the signal by using said estimate of the code
phase.
[0020] The present invention shows remarkable advantages over
solutions of prior art. When applying the method according to the
invention, it is possible to significantly accelerate the
acquisition of signals from satellites used for positioning,
because the inaccuracy in the estimate of the code phase can, by
the method, be limited to a few chips after the time data has been
determined relatively accurately by means of the default position
and the signal of one satellite. Thus, by the method, even a
quadruple rate can be easily achieved in positioning, compared with
receivers of prior art. On the other hand, to improve the accuracy,
the time of acquisition of a signal from a satellite can be even
quadrupled, and the positioning can still be performed as fast as
by positioning receivers of prior art. Fast positioning has, for
example, the advantage of reducing the time of keeping the
positioning receiver in the active state and thereby cutting down
the power consumption of the positioning receiver, which is
advantageous particularly in portable devices.
DESCRIPTION OF THE DRAWINGS
[0021] In the following, the invention will be described in more
detail with reference to the appended drawings, in which
[0022] FIG. 1 shows the operation of the method according to a
preferred embodiment of the invention in a reduced flow chart,
[0023] FIG. 2 shows the error in the distance between the satellite
and the receiver as a function of the azimuth and the elevation
angle of the satellite, when the horizontal distance between the
default position and the real position of the receiver is about 5
km,
[0024] FIG. 3 shows a situation in which the method is applied,
and
[0025] FIG. 4 shows a positioning receiver according to a preferred
embodiment of the invention in a reduced block chart.
DETAILED DESCRIPTION OF THE INVENTION
[0026] In the following description, the method according to an
advantageous embodiment of the invention will be exemplified with
the GPS satellite positioning system, but it will be obvious that
the invention is not limited to be used in this system only. FIG. 3
shows an example situation of applying the invention, and FIG. 4
shows an electronic device 1 according to an advantageous
embodiment of the invention in a reduced block chart. The
electronic device 1 comprises, for example, a positioning receiver
2 as well as communication means 3, such as mobile communication
means. By these communication means 3, the electronic device 1 may,
if necessary, communicate with a communication network 4, such as a
mobile communication network. Furthermore, the electronic device
comprises a control block 5 which preferably comprises a processor
MCU and/or a digital signal processor DSP. For the use, the
electronic device 1 is provided with at least one user interface 6,
preferably comprising a display 7, a keypad 8 and audio means 9a,
9b, 9c. For storing data and application software, the electronic
device is provided with memory means 10.
[0027] When the electronic device 1 is turned on, it is preferably
determined if the electronic device 1 contains satellite orbit
parameters (Ephemeris orbit data and/or Almanac orbit data),
previously determined position data and/or time data stored in it.
If there is no sufficiently up-to-date orbit data, position data or
time data, this is downloaded, for example, via the communication
network 4. From the communication network 4, it is possible to
download the orbit parameters, rough time data of the system, as
well as position data of a reference point. The reference point
used is preferably the position of a known point in the
communication network 4, such as the position of the base station
11 which is used as the so-called serving base station for the
electronic device 1 at the time, that is, as the base station via
which the electronic device 1 and the communication network 4 are
communicating. Typically, the distance between the electronic
device 1 and the serving base station is not longer than some tens
of kilometres, preferably not more than about 30 km. However, it
will be obvious that within the invention, said maximum distance
may also be longer or shorter than 30 km.
[0028] FIG. 1 shows, in a block chart, different steps in the
method according to a preferred embodiment of the invention. The
electronic device 1 selects a satellite transmitting a signal to
receive, for example a first satellite SV1 in the situation of FIG.
3. In this selection of the satellite, it is possible to use
methods of prior art. After this, the searching of the selected
satellite signal, and its acquisition, if possible, is started in
the positioning receiver 2. In the flow chart, step 101 shows the
above-described determination of data and selection of the
satellite.
[0029] For example, on the basis of the signal-to-noise ratio, it
is examined in the positioning receiver if such a satellite signal
can be received whose strength will be sufficient for the
demodulation of navigation data transmitted in the signal (step
102). In a situation in which such a satellite signal, whose
strength will be sufficient for the demodulation of navigation data
transmitted in the signal, can be received in the positioning
receiver 2, said time data can be determined directly from the
satellite signal (step 103).
[0030] However, it is not always possible to find any satellite
signal which would be sufficiently strong for the demodulation of
navigation data. It is thus possible to use, for example,
correlation methods, known as such, using known reference data
which is correlated (preferably cross-correlated) with the
satellite signal to be received (step 104). By means of the
cross-correlation, an attempt is made to find such a point where
the known reference data is present in the signal, and on the basis
of this, the acquisition of the satellite signal is performed in
the positioning receiver 2, to find the time of week data. The
cross-correlation result will be the better, the longer the
reference data that can be used in the cross-correlation.
[0031] In some situations, it is possible to use the orbit
parameters stored in the memory means 10 of the electronic device 1
as the orbit parameters, the time data of the real time clock (RTC)
12 of the electronic device 1 as the time data, and a predetermined
position stored in the memory means 10 of the electronic device 1
as the reference point position data. Thus, the receiver will not
need any information from the communication network. However, the
time data should be correct at a precision of a few seconds;
preferably, the maximum error in the time data should be in the
order of 3 s. The orbit parameters should be the valid ones, and
the reference point position data should not be substantially less
correct than the corresponding position data obtained from the
communication network.
[0032] After the time of week data has been determined, the chip
step is set to its initial value, preferably zero (step 105). In
the method according to an advantageous embodiment of the
invention, this chip step will be used in the fine adjustment of
the code phase, as will be presented below in this description.
[0033] Normally, the acquisition of at least four different
satellite signals by the positioning receiver is needed to
determine the three coordinates x, y, z of the position as well as
the time data. In the present invention, the position of a known
reference point, such as the position of said serving base station
11 in the mobile communication network, is set as the default
position. Thus, the acquisition information determined above in
step 103 or 104 on the basis of one satellite signal, as well as
the selected position of the reference point, are used in the
positioning receiver 2 to compute the time data (step 106). If the
real positions of the reference point and the electronic device 1
are substantially the same, the time data determined at this stage
will correspond to the real time data. In practical situations,
however, the reference point does not normally fully correspond to
the real position of the electronic device 1, but it may even have
a deviation in the order of kilometres. In spite of this, the time
data computed in step 106 will be very close to the real one,
because in any case, the differences in the signal propagation
times will be relatively small, the differences in the propagation
distances being in the order of a few kilometres or some tens of
kilometres. Utilizing this information, it is assumed that the
determined time data can be used for determining the code phase in
such a way that the error is in the order of a few chips at a
maximum. This is a considerable improvement to the situation of
prior art, in which the correct code phase must be determined from
even all the possible different code phases. For example, in the
GPS system, this would mean scanning through 1023 different code
phases even several times, if the searching is to be performed at
several different frequencies to find out the correct Doppler
frequency.
[0034] After the estimated time data has been determined on the
basis of said reference point, orbit data and one satellite signal,
the code phase estimate can be computed for all the signals of the
satellites to be searched, at an accuracy of a few chips (step
107). The satellites to be searched are, for example, the second
SV2, third SV3 and fourth SV4 satellites in the situation of FIG.
3. For each satellite signal to be searched, a default code phase
is set, which is obtained by summing up the determined code phase
and the value of the chip step (step 108). After this, said default
code phase value is used in the positioning receiver 2 for signal
acquisition (step 109). If the acquisition of a satellite signal to
be searched is possible, the default code phase value is correct
for this satellite. Advantageously, the positioning receiver 2
comprises several receiving channels CH1, CH2, CHn, preferably at
least three receiving channels, wherein acquisition of one
satellite signal to be searched can be attempted at each receiving
channel substantially simultaneously. If there are fewer receiving
channels than satellite signals to be tracked, the acquisition of
the satellite signals to be tracked is performed at least partly
consecutively.
[0035] In the next step 110, it is examined if a sufficient number
of signals transmitted by satellites has been found, that is, if
acquisition of all the satellite signals to be tracked has been
completed. If the desired number of signals has been found, these
signals can be used to further define the positioning and the time
data by using position computation and time determination
algorithms known as such (step 112). However, if a sufficient
number of satellite signals was not found, the value of the chip
step is changed in step 111, for example on the basis of a
predetermined permutation algorithm. One such permutation algorithm
is -0.5, +0.5, -1.0, +1.0, -1.5, +1.5, . . . ; that is, during the
first permutation, the chip step is given the value -0.5, during
the second permutation the value +0.5, during the third permutation
the value -1.0, etc. Consequently, the value of the variable is
changed on both sides of the zero point to find out the correct
code phase value. However, it will be obvious that the present
invention is not limited to this permutation algorithm only, but
also another kind of permutation algorithm can be applied. After
the value of the chip step has been changed, the operation will
continue from step 106, where the three position coordinates x, y,
z as well as the time data are recalculated to correspond to the
situation at the time. Also the steps 107 to 110 are taken. If a
sufficient number of satellite signals was still not found with
this new code phase value either, the step 111 is taken again to
change the value of the chip step, and the steps 106 to 110 are
iterated. Said steps 106 to 111 are iterated until a sufficient
number of satellite signals has been found, or until another
criterion has been met, for example a maximum number possibly set
for the iterations has been exceeded.
[0036] In the above-described method according to an advantageous
embodiment of the invention, the accuracy of the time data to be
computed in the first step is substantially directly proportional
to the difference of the distances between the satellite used in
the first step and the reference point, and between the satellite
and the electronic device. This difference depends, for example, on
the azimuth and the elevation angles of the satellite, and on the
difference between the reference point and the real position.
[0037] FIG. 2 illustrates the error in the distance between the
satellite and the electronic device 1 as a function of the azimuth
and the elevation angle of the satellite, when the distance between
the reference point and the electronic device 1 is about 5 km.
Here, it is assumed that both the electronic device 1 and the
reference point are located on a plane, and that the satellite
orbit is at the height of 20,000 km in relation to the reference
point. From FIG. 2, it can be seen, for example, that when the
elevation angle is large, preferably in the order of 80 to
90.degree., or when the azimuth is close to .+-.90.degree., the
distance error is, in practice, insignificant. In such situations,
the time data solved by the method of the invention is very close
to the real time data, wherein the code phase data computed for the
other satellites to be searched on the basis of it are very
accurate. Correspondingly, when the satellite is close to the
horizon, wherein the elevation angle is small, and the azimuth is
preferably in the order of 0 or .+-.180.degree., the distance error
is in the order of .+-.5 km. In such a situation, the distance
between the reference point and the electronic device causes a
distance error which is substantially of the corresponding
magnitude. This distance error of 5 km corresponds to an error of
approximately 16.7 ns in the time data, wherein the error in the
computed code phase will be about 17 chips. However, this error is
reduced when the value of said chip step is changed by permutation
and by iteration of said steps 106 to 111.
[0038] Consequently, the function of the chip step is to compensate
for the error in the estimated time data, which is due to the use
of the reference point as the default position. If the permutation
limits used for the value of the chip step are, for example, .+-.20
chips, it is possible, by the method according to the invention, to
eliminate an error in the order of 5.8 km (=290 m/chip.times.20
chips) in the estimated distance between the satellite and the
electronic device. In practice, for example in network-based
positioning, wherein a mobile communication network is used for
positioning of an electronic device 1, the error in the positioning
will be less than 5 km. Thus, by the method according to the
invention, the accuracy can be improved, without a need to change
the value of the chip step more than .+-.20 chips. Thus, the number
of iterations of the steps 106 to 111 can be kept within reasonable
limits. In connection with network-based positioning, the reference
point used is not necessarily the position of the serving base
station 11 but position data obtained in network-based
positioning.
[0039] In a method according to another advantageous embodiment of
the invention, sufficiently accurate time data is transmitted to
the electronic device 1 via a communication network 4, such as a
mobile communication network. Thus, the positioning device 2 does
not need to find the signal of the first satellite and to perform
acquisition of this signal, but it is possible in the method to
move on from the step 101 directly to the step 105, in which the
chip step is set to its initial value. In other respects, the steps
of the method correspond to the above-presented steps 106 to
111.
[0040] The invention can also be applied in such a way that the
position of the reference point is changed instead of adjusting the
time data. At the stage when the position of the reference point is
sufficiently close to the real position of the electronic device 1,
it is possible to search the desired satellite signals, if they are
accessible in the location of the positioning device 1 at all.
However, it is more efficient to change the time data, because the
change in the time data will have no effect on the geometry between
the satellites and the positioning receiver. Instead, the change of
the reference point will alter, for example, the azimuths and/or
the elevation angle in relation to the reference point.
[0041] The method according to the invention can be primarily
implemented by software in the control block of the electronic
device 1. As the positioning receiver 2 of the electronic device 1
according to the invention, it is possible to use receiver
structures known as such.
[0042] The invention can also be applied in situations in which the
positioning receiver 2 has, for a moment, lost such a satellite
signal which the positioning receiver 2 has acquired. Also in such
a situation, the above-described method is used, that is, for the
positioning, the signal of one satellite is tracked or the time
data is received from the communication network and the acquisition
of the signals of the other satellites is performed. In solutions
of prior art, however, so-called re-acquisition is performed,
utilizing the previously obtained code phase information and
possibly the latest determined position data.
[0043] It is obvious that the present invention is not limited
solely to the above-presented embodiments but it can be modified
within the scope of the appended claims.
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