Method and system for synchronizing base station and establishing location
With the increasing usage of mobile devices for communication, the need for wireless base-stations deployed in strategic locations is becoming increasingly important. The increased bandwidths being transmitted between the base-station and the mobile device has mandated that enhanced transmission formats and techniques be deployed, and, in order to operate correctly, these techniques require a tight synchronization in both time/phase, and in frequency, between the various base-stations serving a general area. Due to the need to establish the geographic location of the mobile device with a high degree of accuracy, it is also necessary to establish the location of the serving base-stations with a high degree of accuracy. The invention disclosed herein provides robust and practical methods for synchronizing base-stations, as well as providing for accurate location, by leveraging the usage of global navigation satellite systems receivers in conjunction with network based schemes for packet-based (time/phase/frequency) synchronization.
1. A method of establishing time and/or location of a first receiver, comprising:
estimating a plurality of pseudoranges based on satellite signal time delays, wherein the pseudoranges include at least one of (a) pseudoranges between the first receiver and one or more satellites estimated by the first receiver at distinct times, or (b) pseudoranges between one or more second receivers and one or more satellites estimated by the one or more second receivers, the one or more second receivers being syntonized with each other and with the first receiver;
determining at least one of a time offset of a clock of the first receiver or an estimated location of the first receiver by solving a set of equations formulated based on the estimated pseudoranges; and
setting at least one of a time of the clock of the first receiver or a stored location of the first receiver based on a signal reflective of the determined time offset or the estimated location, respectively.
2. The method of claim 1 , wherein each of the equations in the set of equations has form
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with c representing speed of light, δ 1 representing time offset of the clock of the first receiver or a clock in one of the second receivers, PR 1j1 (T n ) representing a pseudorange between the first receiver or the one of the second receivers and satellite j1, and ε 1j1 (T n ) representing error(s).
3. The method of claim 1 , further comprising:
determining a difference between an estimated pseudorange between the first receiver and one of the satellites and an estimated pseudorange between one of the second receivers and the one of the satellites; and
determining multipath has occurred or the first receiver or the one of the second receivers has moved, when the difference is greater than a predefined threshold value,
wherein each of the equations in the set of equations is formulated using a respective pseudorange estimated when multipath does not occur.
4. The method of claim 3 , wherein the first receiver or the one of the second receivers is determined to have moved if the difference between the estimated pseudorange between the first receiver and the one of the satellites and the estimated pseudorange between the one of the second receivers and the one of the satellites is greater than the predefined threshold value for an entire day.
5. The method of claim 1 , wherein the one or more second receivers and the first receiver are syntonized using Precision Timing Protocol (PTP) streams.
6. The method of claim 1 , further comprising:
receiving an estimated location of a master receiver, wherein the estimated location of the master receiver is used as an initial estimate of the location of the first receiver; and
iteratively performing the step of estimating the plurality of pseudoranges and solving sets of equations formulated based on the estimated pseudoranges to improve the estimate of the location of the first receiver.
7. The method of claim 5 , wherein the master receiver is a macro-cell receiver.
8. The method of claim 1 , wherein a plurality of the pseudoranges are estimated based on time delays of signals from a single satellite.
9. The method of claim 1 , further comprising:
selecting a set of four equations, formulated based on the estimated pseudoranges, so as to minimize measurement error,
wherein the selected set of equations is solved to determine the at least one of the time offset or the estimated location of the first receiver.
10. A global navigation satellite systems (GNSS) receiver device, comprising:
a memory; and
a processing unit programmed to establish time and/or location of the GNSS receiver by performing operations comprising:
estimating a plurality of pseudoranges based on satellite signal time delays, wherein the pseudoranges include at least one of (a) pseudoranges between the GNSS receiver and one or more satellites estimated by the GNSS receiver at distinct times, or (b) pseudoranges between one or more other receivers and one or more satellites estimated by the one or more other receivers, the one or more other receivers being syntonized with each other and with the GNSS receiver,
determining at least one of a time offset of a clock of the first receiver or an estimated location of the first receiver by solving a set of equations formulated based on the estimated pseudoranges, and
setting at least one of a time of the clock of the GNSS receiver or a stored location of the GNSS receiver based on a signal reflective of the determined time offset or the estimated location, respectively.
11. The GNSS receiver of claim 10 , wherein each of the equations in the set of equations has form
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1
c
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1
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1
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2
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with c representing speed of light, δ 1 representing time offset of the clock of the GNSS receiver or a clock in one of the other receivers, PR 1j1 (T n ) representing a pseudorange between the GNSS receiver or the one of the other receivers and satellite j1, and ε 1j1 (T n ) representing error(s).
12. The GNSS receiver of claim 10 , the operations further comprising:
determining a difference between an estimated pseudorange between the GNSS receiver and one of the satellites and an estimated pseudorange between one of the other receivers and the one of the satellites; and
determining multipath has occurred, or the GNSS receiver or the one of the other receivers has moved, when the difference is greater than a predefined threshold value,
wherein each of the equations in the set of equations is formulated using a respective pseudorange estimated when multipath does not occur.
13. The GNSS receiver of claim 12 , wherein the GNSS receiver or the one of the other receivers is determined to have moved if the difference between the estimated pseudorange between the GNSS receiver and the one of the satellites and the estimated pseudorange between the one of the other receivers and the one of the satellites is greater than the predefined threshold value for an entire day.
14. The GNSS receiver of claim 10 , wherein the one or more other receivers and the GNSS receiver are syntonized using Precision Timing Protocol (PTP) streams.
15. The GNSS receiver of claim 10 , the operations further comprising:
receiving an estimated location of a master receiver, wherein the estimated location of the master receiver is used as an initial estimate of the location of the GNSS receiver; and
iteratively performing the step of estimating the plurality of pseudoranges and solving sets of equations formulated based on the estimated pseudoranges to improve the estimate of the location of the GNSS receiver.
16. The GNSS receiver of claim 15 , wherein the master receiver is a macro-cell receiver.
17. The GNSS receiver of claim 10 , wherein a plurality of the pseudoranges are estimated based on time delays of signals from a single satellite.
18. The GNSS receiver of claim 10 , the operations further comprising:
selecting a set of four equations, formulated based on the estimated pseudoranges, so as to minimize measurement error,
wherein the selected set of equations is solved to determine the at least one of the time offset or the estimated location of the GNSS receiver.
19. A method of establishing time and/or location of a first receiver, comprising:
estimating a plurality of pseudoranges based on satellite signal time delays, wherein the pseudoranges include at least one of (a) pseudoranges between the first receiver and one or more satellites estimated by the first receiver at distinct times, or (b) pseudoranges between one or more second receivers and one or more satellites estimated by the one or more second receivers, the one or more second receivers being syntonized with each other and with the first receiver;
determining at least one of a time offset of a clock of the first receiver or an estimated location of the first receiver by solving a set of equations formulated based on a plurality of the estimated pseudoranges; and
setting at least one of a time of the clock of the first receiver or a stored location of the first receiver based on a signal reflective of the determined time offset or the estimated location, respectively, wherein:
the pseudoranges include a first pseudorange between the first receiver and a satellite estimated based on a time delay of a first satellite signal received by the first receiver and a second estimate of a pseudorange between one of the second receivers and the satellite,
the first satellite signal received by the first receiver is determined to be a multipath signal if a difference between the first and second pseudorange estimates is greater than a predefined threshold value, and
the estimated first pseudorange is used in the determining of the at least one of the time offset or the estimated location of the first receiver if the first satellite signal is not determined to be a multipath signal.
20. The method of claim 19 , wherein the first receiver and the one of the second receivers are syntonized using a Precision Timing Protocol (PTP) stream which delivers timing references from the first receiver to the one of the second receivers.