WO2012055026A1

WO2012055026A1 - Method and apparatus for determining a position of a gnss receiver

Info

Publication number: WO2012055026A1
Application number: PCT/CA2011/001194
Authority: WO
Inventors: Mohamed Youssef; Ashkan Izadpanah
Original assignee: Rx Networks Inc.
Priority date: 2010-10-26
Filing date: 2011-10-26
Publication date: 2012-05-03
Also published as: US10018730B2; US20150219769A1; US20120249368A1

Abstract

Methods and apparatus for determining a position of a GNSS receiver are provided. An initial position derived from a non-GNSS positioning application is used to help the GNSS receiver determine its location after the GNSS receiver has estimated all possible GNSS satellite pseudoranges. The initial position derived from a non-GNSS positioning application is further used to help the GNSS receiver acquire GNSS satellites in multipath and weak reception conditions where multiple correlation peaks are present in the signal from the GNSS satellites.

Description

METHOD AND APPARATUS FOR DETERMINING A POSITION OF A GNSS

RECEIVER

TECHNICAL FIELD

[0001] The present application relates methods and apparatus for acquiring satellites in a Global Navigation Satellite System (GNSS) and fixing a position of a GNSS receiver.

BACKGROUND DISCUSSION

[0002] A Global Navigation Satellite System (GNSS) receiver receives information from at least four GNSS satellites in order to determine its position in three dimensions. The approximate distance between a GNSS satellite and a receiver is generally referred to as a pseudorange. When less than four pseudoranges are acquired, a standalone GNSS receiver fails to fix its three-dimensional position. This is typically due to signal degradation in challenging environments such as indoors, in densely forested areas or in deep urban locations, for example, where attenuation and multipath effects make it difficult for the GNSS receiver to discriminate and acquire information from the required number of GNSS satellites.

[0003] Other non-GNSS positioning techniques use several technologies such as

WiFi and Cellular-based positioning, for example, which can provide a source of additional information to assist a GNSS receiver when it cannot acquire a sufficient number of GNSS satellites in stand-alone mode. This form of cooperation between a GNSS receiver and any other positioning technology is referred to as Assisted-GNSS (A- GNSS). The assistance information generally includes ephemeris data (real or synthetic), timing data and/or position estimation.

[0004] The most well known GNSS is the Global Positioning System (GPS). In conventional Assisted-GPS (A-GPS) where initial position assistance is available, the initial position assistance can help the receiver by allowing it to focus on signals from satellites passing overhead. More generally, however, this position estimate just provides a fallback position in case the GPS receiver still fails to acquire information from a sufficient number of satellites. Such techniques have been described as hybrid positioning and generally involve an either/or selection between the outputs of two or more positioning technologies including GPS, A-GPS, WiFi and Cellular-based positioning, for example.

SUMMARY

[0005] In one aspect, there is provided a method of determining a position of a

GNSS receiver including: receiving, at the GNSS receiver, information from at least two GNSS satellites; determining possible positions of the GNSS receiver using the information from the at least two GNSS satellites; receiving an estimated location area from a non-GNSS positioning application; superimposing the estimated location area over the possible positions and determining which one of the possible positions is closest to a centre of the estimated location area; and setting one of the possible positions that is closest to a centre of the estimated location area as the position of the GNSS receiver.

[0006] In another aspect there is provided a method of determining a position of a

GNSS receiver including: determining possible positions of the GNSS receiver using information from at least one GNSS satellite; receiving, at the GNSS receiver, a signal from another GNSS satellite, the signal comprising more than one correlation peak; calculating a candidate pseudorange for each correlation peak of the signal; receiving an estimated location area from a non-GNSS positioning application; for each candidate pseudorange, superimposing the estimated location area over the possible pseudorange and determining which one of the candidate pseudoranges is closest to a centre of the estimated location area; and setting the candidate pseudorange that is closest to one of the possible positions of the GNSS receiver and closest to a centre of the estimated location area as the pseudorange of the GNSS satellite.

[0007] In yet another aspect there is provided a mobile device including: an antenna; a GNSS receiver for receiving information from GNSS satellites; and a processor in communication with the GNSS receiver; the processor for receiving the information from the GNSS receiver and calculating pseudoranges for each acquired GNSS satellite, the processor receiving an estimated location area from a non-GNSS positioning application, superimposing the estimated location over possible positions determined based on overlap between the pseudoranges and setting the possible position that is closest to the centre of the estimated location area as the position of the GNSS receiver. [0008] In still another aspect there is provided a mobile device including: an antenna; a GNSS receiver for receiving signals from GNSS satellites; and a processor in communication with the GNSS receiver; the processor for receiving the signals and calculating possible pseudoranges for each correlation peak of a GNSS satellite, the processor receiving an estimated location area from a non-GNSS positioning application, superimposing the estimated location over the possible pseudoranges and setting the possible pseudorange that is closest to one of the possible positions of the GNSS receiver and closest to the centre of the estimated location area as the pseudorange of the GNSS satellite.

[0009] Collaboration methods between a GNSS receiver and non-GNSS positioning with respect to the use of initial position assistance are provided. In the methods and apparatus of the present embodiments, non-GNSS technologies collaborate with a GNSS receiver and provide positioning information to facilitate fixing of a position of a GNSS receiver when the GNSS receiver is unable to fix its position independently.

[0010] Other aspects and features of the present embodiments will become apparent to those ordinarily skilled in the art upon review of the following description of specific in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the present application will now be described, by way of example only, with reference to the attached Figures, wherein:

[0012] Figure 1 is a schematic diagram of a mobile device including a GPS receiver in communication with GPS satellites;

[0013] Figure 2 is a block diagram of components of the mobile device of Figure

1 ;

[0014] Figure 3 is a block diagram of a GPS receiver in communication with a satellite acquisition application and a position determining application;

[0015] Figure 4 is a block diagram depicting operation of a GPS receiver;

[0016] Figure 5 is a flow diagram depicting processing of correlation peaks;

[0017] Figure 6 is a flow diagram depicting operation of a satellite acquisition application;

[0018] Figure 7 is a schematic diagram showing possible positions of a GPS receiver as determined using the satellite acquisition application; [0019] Figure 8 is a flow diagram depicting a method of determining a position of a GPS receiver using assisted positioning information from a non-GNSS positioning application when less than four GPS satellites are available;

[0020] Figure 9 is a flow diagram depicting a method of determining a position of a GPS receiver when two GPS satellites are available;

[0021] Figure 10A is a schematic diagram showing two possible positions of a

GPS receiver when information from two GPS satellites is received;

[0022] Figure 10B is a schematic diagram showing possible positions of a GPS receiver determined using the limited satellite availability GPS receiver according to an embodiment;

[0023] Figure 10C is a schematic diagram showing possible positions of a GPS receiver as determined using a hybrid positioning system of the prior art;

[0024] Figure 1 1 is a schematic diagram depicting operating of a GPS receiver using satellite acquisition application and a position determining application according to an embodiment;

[0025] Figure 12 is a schematic diagram showing possible positions of a GPS receiver using satellite acquisition application and a position determining application according to an embodiment; and

[0026] Figure 13 is a flowchart depicting collaboration between the GPS receiver, satellite acquisition application, position determining application and position assisted- GPS application.

DETAILED DESCRIPTION

[0027] It will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well- known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Also, the description is not to be considered as limiting the scope of the embodiments described herein. [0028] It will be appreciated by a person skilled in the art GPS is referred to throughout the present application by way of example only. The methods and apparatus of the present application are applicable to any GNSS.

[0029] Referring to Figure 1 , a mobile device 10 receives information from GPS satellites in order to determine its position. The mobile device 10 may be a cell phone, a personal digital assistant, a Smartphone, an asset tracking device, a tablet or laptop computer, a navigation device or another device that is capable of determining its position with the help of a non-GNSS positioning application. In the embodiments described herein, assisted position information derived from a non-GNSS positioning application includes at least initial/coarse position assistance, which helps the GPS receiver 14 locate the GPS satellites passing overhead more quickly than a standalone GPS receiver, for example. The assisted position information derived from a non-GNSS positioning application may be available locally, on the mobile device 10, may be available through direct communication with a computer or may be available via wireless communication with a server or database.

[0030] As shown in Figure 2, the mobile device 10 includes an antenna 12 for receiving wireless signals, a GPS receiver 14 in communication with the antenna 12, a processor 16 in communication with the antenna 12 and the receiver 14. The mobile device 10 further includes a memory 18 that communicates with the processor 16. The mobile device 10 may communicate with a computer to receive an estimated location area from a non-GNSS positioning application via a cellular data network, such as GPRS, EDGE, 3G, 4G, WLAN, 802.11g, or 802.11 η, for example. The mobile device 10 may further be capable of short range communication using Bluetooth™, for example. In one embodiment, the mobile device 10 includes an antenna 12 and some GPS receiver components. For example, the GPS receiver 14 may include a front end and a digitizer only. In this embodiment, other GPS receiver components, the processor 16 and the memory 18 may be hosted remotely on a server, for example.

[0031] As shown in Figure 3, the GPS receiver 14 is capable of receiving signals from GPS satellites and communicating with a non-GNSS positioning software application 20. The non-GNSS positioning software application 20 may be stored as computer readable code in memory 18 of the mobile device 10 or, alternatively, stored on a server remote from the mobile device 10. The non-GNSS positioning application 20 may be any positioning application capable of providing a coarse position estimate. Example of non- GNSS positioning applications include: WiFi-based positioning, cellular-based positioning (including but not limited to mobile standards such as GSM, CDMA, UMTS, LTE), land- mobile radio systems (including but not limited to VHF systems used in private or public safety applications), radio-broadcast positioning (including, but not limited position based on radio broadcast transmission towers such as FM or TV stations), or other data network infrastructure based positioning (including but not limited to IP routers, data modems or Internet protocols such as GeolP).

[0032] Referring also to Figure 4, the GPS receiver 14 includes a signal processing unit 22, which acquires satellites, and a navigation unit 24, which fixes the position of the GPS receiver 14. As shown, the GPS receiver 14 communicates with a satellite acquisition application 26 and a position determining application 28. The satellite acquisition application 26 and the position determining application 28 are software applications that are stored as computer readable code in memory 18 and executable by the processor 16. In general, the satellite acquisition application 26 identifies "true" pseudoranges when multiple candidate pseudoranges are determined to acquire more GPS satellites and the position determining application 28 reduces positioning uncertainty when satellite availability is limited.

[0033] Referring still to Figure 4, the signal processing unit of the GPS receiver 14 receives satellite signals from available GPS satellites and sends pre-processed digitized satellite signals (l,Q) to the satellite acquisition application 26. The signal processing unit 22 determines and sends pseudoranges of acquired satellites to the navigation unit 24, which in turn sends the pseudoranges of acquired satellites to the position determining application 28. The estimated location area from the non-GNSS positioning application 20 is received by both the satellite acquisition application 26 and the position determining application 28 in order to fix a position of the GPS receiver 14. In one embodiment, the satellite signals and the estimated location area are received at generally the same time.

[0034] The satellite acquisition application 26 uses the estimated location area from the non-GNSS positioning application 20 to discriminate between multiple candidate peaks to determine which is the "true" correlation peak. When the GPS receiver correlates the pre-processed satellite signal with its replicas locally generated, the GPS receiver: i) may not find any candidate correlation peaks in the signal, ii) may find multiple candidate correlation peaks due to signal attenuation or multipath, or iii) may find one distinct candidate correlation peak. When one distinct candidate correlation peak is identified, a pseudorange associated with that candidate correlation peak is determined by the GPS receiver 14 to be an acquired satellite.

[0035] Referring to Figure 5, correlation peaks are output from a correlator 30, or matched filter, of the GPS receiver 14. The inputs of the correlator 30 are the GPS pre- processed signals and its replicas locally generated in the GPS receiver 14. The correlator 30 may be referred to a grid of correlators because the correlator 30 includes a predefined search space. In prior art (assisted) GPS receivers, no satellite may be acquired unless a distinct correlation peak is found.

[0036] In general, correlators 30 use the estimated location area from the non-GNSS positioning application 20 to define a correlator search space, accelerate a search and reduce an area of uncertainty in order to extract a distinct correlation peak. When a distinct correlation peak is not found, multiple candidate correlation peaks are considered by the satellite acquisition application 26. When multiple candidate correlation peaks are identified for a particular GPS satellite, candidate pseudoranges that correspond to the multiple candidate correlation peaks are calculated. The estimated location area from the non-GNSS positioning application 20 is used in combination with pseudoranges of GPS satellites that have been acquired (i.e. satellites for which a distinct correlation peak was found) to select the "true" pseudorange out of the candidate pseudoranges when a "true" pseudorange exists.

[0037] Referring also to Figure 6, the satellite acquisition application 26 identifies candidate correlation peaks in the signal at 32. When no candidate correlation peaks are found, no GPS satellite may be acquired at 34. When one distinct correlation peak is found, then the GPS satellite is acquired at 36. When more than one candidate correlation peak is found, candidate correlation peaks are identified at 38 and possible positions (i.e. candidate pseudoranges) are determined at 40 for each candidate correlation peak. The estimated location area from the non-GNSS positioning application 20 is then used to determine at 42 which candidate correlation peak is the "true" correlation peak. At 44, the position of the GPS receiver may be fixed using the navigation unit 24 or the position determining application 28.

[0038] Referring to Figure 7, in one example, four candidate correlation peaks of a satellite vehicle (SV) are found and four candidate pseudoranges (cp cp₂,cp₃, a.nd c ₄) are calculated based on the candidate correlation peaks. The candidate pseudoranges are then combined with two already acquired GPS pseudoranges, which are identified by reference numerals 46 and 48, to estimate possible two-dimensional positions of the multiple correlation peak determination GPS receiver 14. The possible two-dimensional position estimates are: (cp₁, cp₂,cp_5rand c ₄) and {PW* _< P∑V ₂.> ^CP4)^→ Pi}- The estimated location area from the non-GNSS positioning application 20 is then used to discriminate between the possible position estimates. As shown in Figure 1 1 , the possible position a which was derived from the candidate pseudorange cp₃ is the best possible position due to overlaps found between the three pseudoranges

^and ^tne estimated location area from the non-GNSS positioning application. Thus, a third GPS satellite is considered to be acquired with a true pseudorange value, Psv^, equal to cp₃.

As shown, the final two-dimensional position fix is estimated from the acquired GPS satellites and the position uncertainty of the estimated location area from the non-GNSS positioning application.

[0039] In general, the satellite acquisition application 26 increases the number of acquired GPS satellites and hence, improves overall satellite availability and satellite geometry. The satellite acquisition application 26 has the ability to accept multiple candidate correlation peaks, perform calculations therewith, and then use the estimated location area from the non-GNSS positioning application 20 to recommend the "true" correlation peak.

[0040] Referring back to Figure 4, the positioning determining application 28 uses different methods to fix the position of the GPS receiver 14 depending on the number of GPS satellites that are available. Referring also to Figure 8, when information from three GPS satellites is received, the position of the GPS receiver 14 is solved using the estimated location area from the non-GNSS positioning application 20 to constrain a mathematical model, such as constrained least squares estimation, for example, to force the mathematical model of a GPS receiver to converge within a visible region determined by the estimated location area from the non-GNSS positioning application.

[0041] Referring to Figure 8, at 50, pseudoranges are computed either by the signal processing unit 22 or by the satellite acquisition application 26. At 52, the receiver clock bias ( t„) is estimated from the GPS receiver previous position fix. The position determining application 28 then computes all possible GPS receiver positions using pseudoranges and the receiver clock bias ( tj at 54. When at least one of the computed GPS receiver positions is within a vicinity of the position provided by the estimated location area from the non-GNSS positioning application, then this position is accepted, at 56. Otherwise, at 58, the position determining application 28 computes the corrected geometrical range (e.g. Euclidean distance) between the GPS receiver and the satellite passing overhead. At 60, the position determining application 28 computes all possible candidates GPS receiver clock offsets using pseudoranges and corrected geometrical ranges. At 62, the position determining application 28 uses different constrained optimization models utilizing information regarding pseudoranges and receiver clock offsets in order to fix the GPS receiver position.

[0042] When information from at least two GPS satellites is received, the GPS receiver 14 executes the method of determining a location of a GPS receiver 14 of Figure 9. At 64, the GPS receiver 14 receives information from two GPS satellites; at 66, the GPS receiver 14 determines two possible positions of the GPS receiver 14 based on the information, as shown in Figure 10A; at 68, the GPS receiver 14 receives an estimated location area from the non-GNSS positioning application; at 70, the estimated location area is superimposed over the possible positions, as shown in Figure 10B; and at 72, the one of the possible positions that is closest to a center of the estimate location area is set as the position of the GPS receiver 14.

[0043] As shown in Figure 10B, the position derived from the non-GNSS positioning application 20 using, for example, Access Points (APs), is used to solve the position ambiguity. An AP is a wireless router or device that is used to access data networks. An AP may be WLAN router, 802.11g, 802.11 b or a cellular base station (i.e. GPRS, EDGE, 3G, 4G). As shown, the final position estimates for the limited satellite availability GPS receiver 14 are based on acquired GPS satellite information as well as the estimated location area from the non-GNSS positioning application, (i.e. two-dimensional position variance).

[0044] Figure 10C schematically depicts how a hybrid positioning system of the prior art determines a position of a GPS receiver. In this scenario, the hybrid positioning engine simply fallbacks to the estimated location area from the non-GNSS positioning application. Hence, the final position fix based solely on the estimated location area from the non-GNSS positioning application. The final position fix is represented by (*. y) , while the shaded area around the fixed position represents the positioning uncertainty retrieved from the estimated location area from the non-GNSS positioning application. [0045] An advantage to the method of determining a location of a GPS receiver 14 is that the final position, as well as the position uncertainty, is based solely on information from the acquired GPS satellites. As such, the final position fix, and its uncertainty, is more accurate than prior art hybrid and non-GNSS positioning applications.

[0046] The GPS receiver 14 may operate using the satellite acquisition application 26, the position determining application 28 or both the satellite acquisition application 26 and the position determining application 28. Referring to Figure 1 1 , the GPS receiver 14 uses both the satellite acquisition application 26 and the position determining application 28 to acquire satellites and fix a position of the GPS receiver 14. Using the satellite acquisition application 26, two different sets of pseudoranges are determined. The first set of pseudoranges, [1.— are derived from acquired GPS satellites each with a distinct correlation peak. The second set of pseudoranges, Ι¹· ·"* -^] , are candidate pseudoranges derived from multiple candidate correlation peaks for each GPS satellite pseudorange. The satellite acquisition application 26 determines "true" pseudorange for the respective GPS satellites based on prior art hybrid and non-GNSS positioning applications and the candidate pseudoranges. When the "true" pseudoranges have been determined, the satellite pseudoranges are considered to be acquired and are then used in the position determining application 28 of FIG. 4.

[0047] Referring to Figure 12, an example of a GPS receiver 14 that uses both the satellite acquisition application 26 and the position determining application 28 to acquire satellites and fix a position of the GPS receiver 14 is shown. In this example, one GPS satellite has been acquired by a standalone GPS receiver and the standalone GPS receiver fails to fix its position. In order to acquire a second GPS satellite, two candidate correlation peaks, which were found by the correlator 32, are used to calculate two candidate pseudoranges. This generates four possible two-dimensional positions, as shown in Figure 12. The position determining application 28 is used to 1 ) recommend the best possible position and thus, acquire the second GPS satellite with the correct correlation peak; and 2) assist the GPS receiver 14 to reduce position uncertainty and hence, be able to fix the position of the GPS receiver 14.

[0048] Figure 13 depicts an example of collaboration between the GPS receiver, the satellite acquisition application 26, the position determining application 28 and the non- GNSS positioning application. In Figure 13, the satellite acquisition application 26 and the position determining application 28 of the mobile device 10 may collaborate with other related satellite acquisition applications 26 and positioning determining applications 28, operating on the same or different mobile devices. In Figure 13, the satellite acquisition applications 26 and the position determining application 28 on the mobile device may collaborate with other GPS receivers 14, operating on the same or different mobile devices. In general, GPS receivers in different devices may collaborate when the GPS receivers are within an acceptable range of one another based on non-GNSS positioning.

[0049] In one embodiment, a GPS receiver 14 is capable of switching between operating as: i) a standalone GPS receiver, which receives signals from four GPS satellites, ii) an assisted-GPS receiver, which uses GNSS orbital data or estimated location areas from a non-GNSS positioning application to allow the GPS receiver to locate GPS satellites in range more quickly, iii) a GPS receiver operable when satellite availability is limited and iv) a GPS receiver 14 operable when more than one correlation peak is determined.

[0050] The methods and apparatus of the present embodiments facilitate fixing of a three-dimensional position of a GNSS receiver, such as a GPS receiver, when the number of acquired satellites is less than four. By integrating GNSS and non-GNSS positioning systems, rather than using a non-GNSS positioning system as a fallback, greater accuracy in position determination may be achieved. The methods and apparatus described herein provide 1) improved discrimination between possible pseudoranges so that more GPS satellites may be acquired as compared to stand-alone modes and 2) a reduction in the area of positioning uncertainty.

[0051] The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope of the present application, which is defined solely by the claims appended hereto.

Claims

What is claimed is:

1. A method of determining a position of a GNSS receiver comprising: receiving, at the GNSS receiver, information from at least two GNSS satellites; determining possible positions of the GNSS receiver using the information from the at least two GNSS satellites; receiving an estimated location area from a non-GNSS positioning application; superimposing the estimated location area over the possible positions and determining which one of the possible positions is closest to a centre of the estimated location area; and setting one of the possible positions that is closest to a centre of the estimated location area as the position of the GNSS receiver.

2. A computer readable medium comprising instructions executable on a processor for implementing the method of claim 1.

3. A method as claimed in claim 1 , wherein the information from at least two GNSS satellites and the estimated location area from the non-GNSS positioning application are received at generally the same time.

4. A method as claimed in claim 1 , wherein the non-GNSS positioning application is an application capable of providing an initial position.

5. A method as claimed in claim 4, wherein the non-GNSS positioning application is based on one of: WiFi, Cellular, land-mobile radio, radio broadcast and GeolP.

6. A method as claimed in claim 1 , comprising receiving GNSS satellite information from a GNSS receiver of another mobile device.

7. A method of determining a position of a GNSS receiver comprising: determining possible positions of the GNSS receiver using information from at least one GNSS satellite; receiving, at the GNSS receiver, a signal from another GNSS satellite, the signal comprising more than one correlation peak; calculating a candidate pseudorange for each correlation peak of the signal; receiving an estimated location area from a non-GNSS positioning application; for each candidate pseudorange, superimposing the estimated location area over the possible pseudorange and determining which one of the candidate pseudoranges is closest to a centre of the estimated location area; and setting the candidate pseudorange that is closest to one of the possible positions of the GNSS receiver and closest to a centre of the estimated location area as the pseudorange of the GNSS satellite.

8. A computer readable medium comprising instructions executable on a processor for implementing the method of claim 7.

9. A method as claimed in claim 7, wherein the information from at least two GNSS satellites and the estimated location area from the non-GNSS positioning application are received at the same time.

10. A method as claimed in claim 7, wherein the non-GNSS positioning application is an application capable of providing an initial position.

11. A method as claimed in claim 10, wherein the non-GNSS positioning application is based on one of: WiFi, Cellular, land-mobile radio, radio broadcast and GeolP.

12. A method as claimed in claim 7, comprising receiving GNSS satellite information from a GNSS receiver of another mobile device.

13. A mobile device comprising: an antenna; a GNSS receiver for receiving information from GNSS satellites; and a processor in communication with the GNSS receiver; the processor for receiving the information from the GNSS receiver and calculating pseudoranges for each acquired GNSS satellite, the processor receiving an estimated location area from a non-GNSS positioning application, superimposing the estimated location over possible positions determined based on overlap between the pseudoranges and setting the possible position that is closest to the centre of the estimated location area as the position of the GNSS receiver.

14. A mobile device as claimed in claim 13, comprising two or more GNSS receivers wherein the processor receives the information from the two or more GNSS receivers.

15. A mobile device as claimed in claim 13, wherein the processor receives GNSS satellite information from a GNSS receiver of another mobile device.

16. A mobile device comprising: an antenna; a GNSS receiver for receiving signals from GNSS satellites; and a processor in communication with the GNSS receiver; the processor for receiving the signals and calculating possible pseudoranges for each correlation peak of a GNSS satellite, the processor receiving an estimated location area from a non-GNSS positioning application, superimposing the estimated location over the possible pseudoranges and setting the possible pseudorange that is closest to one of the possible positions of the GNSS receiver and closest to the centre of the estimated location area as the pseudorange of the GNSS satellite.

17. A mobile device as claimed in claim 16, comprising two or more GNSS receivers wherein the processor receives the information from the two or more GNSS receivers and calculates the possible pseudoranges for each correlation peak of the satellite signals received by the GNSS receivers.

18. A mobile device as claimed in claim 16, wherein the processor receives GNSS satellite information from a GNSS receiver of another mobile device.