US20040116132A1 - Rapid acquisition and system selection of mobile wireless devices using a system map - Google Patents

Abstract

The present invention enhances service system selection by a mobile unit in a wireless communication system. The mobile unit determines its geographic position, and based on that position selects the proper service system. The geographic position may be determined using a global position system, deck reckoning, or estimated from a last known position. The distance of varying service systems from the mobile station can then be calculated and a service system selected based on this distance. The mobile station may also use the position information in combination with a database including position information of service systems to select the proper service system. The position information of the service systems can be included in the system selection database. The mobile station may also map service systems based on position information and service availability. The mobile station can then subsequently refer to these maps to estimate available service.

Description

TECHNICAL FIELD
• This invention relates to wireless communication systems, and more particularly to cellular carrier selection within wireless communication systems.[0001]
BACKGROUND
• The use of wireless communication systems is growing with users now numbering well into the millions. One of the popular wireless communications systems is the cellular telephone, having a mobile station (or handset) and a base station. Cellular telephones allow a user to talk over the telephone without having to remain in a fixed location. This allows users to, for example, move freely about the community while talking on the phone.[0002]
• Cellular telephones may operate under a variety of standards including the code division multiple access (CDMA) cellular telephone communication system as described in TIA/EIA, IS-95, Mobile station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, published July 1993. CDMA is a technique for spread-spectrum multiple-access digital communications that creates channels through the use of unique code sequences. In CDMA systems, signals can be and are received in the presence of high levels of interference. The practical limit of signal reception depends on the channel conditions, but CDMA reception in the system described in the aforementioned IS-95 Standard can take place in the presence of interference that is 18 dB larger than the signal for a static channel. Typically, the system operates with a lower level of interference and dynamic channel conditions.[0003]
• A cellular telephone communication system typically provides services to an area by dividing the area into many smaller geographic areas, known as cells, each of which is serviced by a transmitter-receiver station, known as a cell site. The cell sites are connected through landlines, or other communication links, to so-called mobile telephone switching offices (MTSO's) which are, in turn, connected to the public switched telephone network (PSTN). According to current FCC rules, any given area is serviced by up to two competing providers of cellular airtime communication services (i.e., cellular carriers). The two service providers in any given geographic area, commonly referred to as “A” and “B” carriers, are assigned different groups of frequencies, or frequency sets, through which services are provided along paging, control, access, and voice channels, as would be understood by those reasonably skilled in the industry and as dictated by technical standards of appropriate regulatory agencies.[0004]
• When a mobile station first activates in a particular area, the mobile station searches for available service systems. Based on the service subscription and other factors, the mobile station has a preference when selecting a service system. The mobile station generally looks for a system supported by the subscriber, and if none if available the mobile system searches for a compatible system. At present, the mobile station simply searches for systems-regardless of the geographic location of the mobile station. What is desired is a system where the mobile station can limit the number of systems required for searching based on the geographic position of the mobile station.[0005]
SUMMARY
• The present invention enhances service system selection by a mobile unit in a wireless communication system. The mobile unit determines its geographic position, and based on that position selects the proper service system. The geographic position may be determined using a global position system, deck reckoning, or estimated from a last known position. The distance of varying service systems from the mobile station can then be calculated and a service system selected based on this distance. The mobile station may also use the position information in combination with a database including position information of service systems to select the proper service system. The position information of the service systems can be included in the system selection database. The mobile station may also map service systems based on position information and service availability. The mobile station can then subsequently refer to these maps to estimate available service.[0006]
• One aspect of the invention is a method of prioritizing a plurality of service systems in a wireless communication system. The method comprises determining a reference location and calculating a distance from the reference location to each of the plurality of service systems. The method the prioritizes the plurality of service systems based on the distance from the reference location. The reference location may be determined using a global positioning system or dead reckoning, among other techniques. The calculating step further comprises determining a drift term and adjusting the reference location based on the drift term.[0007]
• Another aspect of the invention is a method of prioritizing a plurality of service systems in a wireless communication system. The method comprises determining a reference location and obtaining a prioritized list of service systems based on the reference location. The reference location may be determined using a global positioning system or dead reckoning. The prioritized list of service systems based on the reference location is obtained from stored data within a mobile station. The data may be stored in the system selection database. The system selection database includes a position reference for each of the plurality of service systems.[0008]
• Another aspect of the invention is a mobile station for use in a wireless communication system. The mobile station comprises a position determination device and a database of system providers based oh position information. The position determination device may be a global positioning system. The database is included in the system selection database, and the selects one of the system providers based on the database information.[0009]
• Another aspect of the invention is a mobile station for use in a wireless communication system. The mobile station comprises a position determination device and a service detector. The service detector determines if service is available at any given position. The mobile station includes memory locations for storing data regarding service availability for a plurality of locations. A grouping of the memory locations provides a map of a service area showing service availability. The grouping of memory locations containing position information can be converted to a formula defining a service area. Each memory location stores both a latitude and a longitude of a position along with information indicating whether service was available at the position.[0010]
• Another aspect of the invention is a method of mapping a service system for a wireless communication system. The method comprises establishing a reference location and determining service availability for the reference location. Information on service availability for the reference location is then stored. The method further comprises collecting data on service information for a plurality of reference locations and combining the data to provide a map of a service area showing service availability. The combined data may be converted into a formula defining a service area.[0011]
DESCRIPTION OF DRAWINGS
• These and other features and advantages of the invention will become more apparent upon reading the following detailed description and upon reference to the accompanying drawings.[0012]
• FIG. 1 illustrates the components of an exemplary wireless communication system used by the present invention.[0013]
• FIG. 2 illustrates the system selection map structure according to the present invention.[0014]
• FIG. 3 is a flowchart illustrating the system selection process according to the present invention.[0015]
• FIG. 4A illustrates a first system map according to the present invention.[0016]
• FIG. 4B illustrates a second system map according to the present invention.[0017]
• FIG. 5 illustrates an exemplary system map having an exclusion area according to the present invention.[0018]
• FIG. 6 illustrates an exemplary system map showing a coverage boundary which is mapped according to the present invention.[0019]
DETAILED DESCRIPTION
• FIG. 1 illustrates components of an exemplary wireless communication system. A[0020]mobile switching center102 communicates with base stations104a-104k(only one connection shown). The base stations104a-104k(generally104) broadcasts data to and receives data frommobile stations106 within cells108a-108k(generally108). The cell108 is a geographic region, roughly hexagonal, having a radius of up to 35 kilometers or possibly more.
• A[0021]mobile station106 is capable of receiving data from and transmitting data to a base station104. In one embodiment, themobile station106 receives and transmits data according to the Code Division Multiple Access (CDMA) standard. CDMA is a communication standard permitting mobile users of wireless communication devices to exchange data over a telephone system wherein radio signals carry data to and from the wireless devices.
• Under the CDMA standard,[0022]additional cells108a,108c,108d, and108eadjacent to thecell108bpermitmobile stations106 to cross cell boundaries without interrupting communications. This is so becausebase stations104a,104c,104d, and104ein adjacent cells assume the task of transmitting and receiving data for themobile stations106. Themobile switching center102 coordinates all communication to and frommobile stations106 in a multi-cell region. Thus, themobile switching center102 may communicate with many base stations104.
• [0023]Mobile stations106 may move about freely within the cell108 while communicating either voice or data.Mobile stations106 not in active communication with other telephone system users may, nevertheless, scan base station104 transmissions in the cell108 to detect any telephone calls or paging messages directed to themobile station106.
• One example of such a[0024]mobile station106 is a cellular telephone used by a pedestrian who, expecting a telephone call, powers on the cellular telephone while walking in the cell108. The cellular telephone scans certain frequencies (frequencies known to be used by CDMA) to synchronize communication with the base station104. The cellular telephone then registers with themobile switching center102 to make itself known as an active user within the CDMA network.
• When detecting a call, the cellular telephone scans data frames broadcast by the base station[0025]104 to detect any telephone calls or paging messages directed to the cellular telephone. In this call detection mode, the cellular telephone receives, stores and examines paging message data, and determines whether the data contains a mobile station identifier matching an identifier of the cellular telephone. If a match is detected, the cellular telephone establishes a call with themobile switching center102 via the base station104. If no match is detected, the cellular telephone enters an idle state for a predetermined period of time, then exits the idle state to receive another transmission of paging message data.
• When a[0026]mobile station106 activates, themobile station106 searches for an active and desirable wireless communication system. Different areas may be served by multiple wireless communication systems, and depending on the selected service provider and other factors, themobile station106 selects which system to operate within. The present invention provides a means to use location information to enhance proper system selection. The invention defines a system selection map and system selection algorithm that use the map to optimize the service acquisition process.
• The area covered by a wireless communication system can generally be approximated with system circles or other shapes. Each system may be defined by one or more circles which, when combined, approximate the general service area of the system. Each of the system circles may be defined by a data set containing the system circle latitude (latitude[0027]_s), the system circle longitude (longitude_s), and the radius of the system circle (radius_s). As shown in FIG. 2, a system selection map may contain varying levels, and the varying levels may be diagramed in asystem tree200. Thesystem tree200 shows a system selection map having two levels (level N and level N+1). In level N, thesystem tree200 has asystem group M_i205. In level N+1, thesystem group M_i205 of FIG. 2 has a plurality of child system nodes including a child system {N+1.1}210, a child system {N+1.2}215, and other child systems until child system {N+1.n_N+1}220. Thesystem group M_i205 of FIG. 2 also has a plurality of child system group nodes including a child system group {N+1.1} 225, a child system group {N+1.2}230, and other child systems groups until child system group {N+1.M_N+1}220. Each of the child systems groups may have its own child systems or child system groups. Of course, thesystem group M_i205 may also have no child systems or no child system groups.
• The[0028]system group M_i205, each of thechild systems210,215,220, and each of thechild system groups225,230,235 are generally defined as a circle having a centerpoint and a radius. The centerpoint of each circle may be defined by a corresponding set of coordinate points {latitude_s, longitude_s}. As depicted in FIG. 2, the radius of each system and system group may vary. Thesystem group M_i205 encompasses, at a minimum, the centerpoint of each child node. Thesystem group M_i205 may also encompass the majority of the child nodes, or completely encompass the child nodes.
• The present invention uses a reference location {latitude[0029]_r, longitude_r} for themobile station106 to enhance the system selection process. Theprocess300 of using position information to enhance system selection is shown in FIG. 3. The process begins at astart state305. Proceeding tostate310, themobile station106 determines if the position information is available. The position information may be available to themobile station106 from a variety of sources, including a global positioning system (GPS), base station triangulation, dead reckoning, and any other positioning system that is well known in the art. If the position information is available, theprocess300 proceeds along the YES branch tostate315. Atstate315, themobile station106 obtains the position information. The position information is stored as the reference location {latitude_r, longitude_r}.
• Proceeding to[0030]state320, themobile station106 determines if the system selection database contains position information. The system selection database provides themobile station106 with information for the user zones to which themobile station106 is subscribed. The system selection database contains information on user zone priority, user zone identification, user zone system identification, user zone name, active flag, priority control field, notification flag, user zone revision, and overhead parameters. According to the present invention, an additional field is inserted into the system selection database containing position information. The position information can be listed with each entry in the system selection database, or may be included only for each group of listings. By including position information in the system selection database, themobile station106 can use the position information of themobile station106 combined with the position information in the system selection database to determine the most desirable system. If the system selection database does not contain any position information, theprocess300 proceeds along the NO branch tostate345, which will be described below. If the system selection database does contain position information, theprocess300 proceeds tostate325.
• In[0031]state325, themobile station106 retrieves the system listings from the system selection database. Based on the position information, themobile station106 can classify each of the systems with a priority level, with the system having the highest priority being the most desirable system and the first system with which themobile station106 attempts to connect.
• Returning to[0032]state310, if position information is not available, theprocess300 proceeds along the NO branch tostate335. Instate335, themobile station106 determines a reference location {latitude_r, longitude_r}. The reference location is an approximation of the position of themobile station106, and may be the last known position available, any nearby or recently communicated infrastructure location, the last known system circle centerpoint, or any other position information that may be available to themobile station106.
• Proceeding to[0033]state340, themobile station106 determines an estimated drift factor (radius_d). The drift factor is used when timing information is available and no system has been available for a significant amount of time. If timing information is not available, the drift factor (radius_d) is set to 0. The drift factor can be calculated using the formula:
• radius_d=(t−t_last-system)V_max
• where t is the current time, t[0034]_last-systemis the time that service was last available on the last known system, and V_maxis the maximum expected velocity that themobile station106 would travel during the period without service.
• Proceeding to[0035]state345, themobile station106 calculates the distance to each available system (d_sys(n)). As stated above, the location of each system is defined by a set of coordinate points {latitude_s, longitude_s}. Themobile station106 uses the reference location and the drift factor to determine the distance to each available system (d_sys(n)) according to the following formula:$d_{\mathrm{sys}\left(n\right)}=\frac{\sqrt{\left({\mathrm{latitude}}_s-{\mathrm{latitude}}_r\right)+\left({\mathrm{longitude}}_s-{\mathrm{longitude}}_r\right)}}{{\mathrm{radius}}_s+{\mathrm{radius}}_d}$

  
• The distance (d[0036]_sys(n)) is calculated for each available system.
• Proceeding to[0037]state350, themobile station106 disregards any systems located beyond a threshold distance (d_sys(n)>d_threshold). The threshold distance (d_threshold) may be predetermined or themobile station106 may calculate the threshold distance (d_threshold) based on prior performance. Of course, if it is desired for themobile station106 to consider all available systems, the threshold distance may be ignored. After any systems beyond the threshold distance are removed, themobile station106 prioritizes the remaining systems. Prioritization of the systems is well known in the art and will not be described herein.
• Proceeding to[0038]state330, the mobile station selects the highest priority system and attempts to connect to that system. The system is chosen from either the list generated from the system selection database information or the list calculated by themobile station106.
• Proceeding to[0039]state355, themobile station106 determines if service is available on the selected system. If service is available, the mobile-unit106 connects with the service and theprocess300 proceeds along the YES branch to anend state360. Returning tostate355, if service is not available, theprocess300 proceeds along the NO branch back tostate330, where the next highest priority system is selected and connection attempted. This process is repeated until themobile station106 connects to a system, at which point theprocess300 terminates in theend state360.
• The present invention may also use the position information to create a map of serving systems within the[0040]mobile station106. The map may be used to determine the likelihood of service being available from any particular system at any geographic location. When amobile station106 obtains service, it can begin to map the service area. The current position information (which may be stored as a {latitude, longitude}), along with the service information is recorded within themobile station106. The more amobile station106 travels within a service area, the more detailed the map.
• FIG. 4A illustrates a[0041]map400 according to one embodiment of the present invention. Themap400 illustrates aservice area402 defined by a series ofpoints405,410,415,420,425,430,435, and440. Each of the series ofpoints405,410,415,420,425,430,435, and440 is recorded by themobile station106 by recording the {latitude, longitude} of each point along with the information that service is available at that point. In general, it is not necessary to map points inside the service area, as those points would be assumed to have service. However, if an area inside a service area does not have service, that information may also be mapped as will be discussed below. After a service area is mapped, it may be possible to condense themap400 down from a number of points to an equation defining themap400. For example, if the service area generally defined a circular area, themap400 may be condensed to a centerpoint and a radius. By condensing themap400 to an equation, the amount of memory required to store themap400 within themobile station106 is reduced.
• As shown in FIG. 4, there may be areas within a[0042]service map400 such as apoint450 that are within the service area, but themap400 may not completely define. For example, in FIG. 4, thepoint450 is within theservice area402, but because only thepoints420 and425 define the outer perimeter of the service area, themobile station106 cannot accurately predict whether service is available at thepoint450. One technique that may be used to enhance the accuracy of themobile station106 is to include a confidence factor. The confidence factor is a measure of how definite themobile station106 is that the current location has service, and may range for example from 0 (not confident) to 1 (extremely confident). If amobile station106 is in an area that has not been mapped, the confidence factor for that area would be 0. If themobile station106 looks for service in at an exact location it had service before, the confidence factor would be 1.
• In FIG. 4A, the series of[0043]points405,410,415,420,425,430,435, and440 define theservice area402. However, because no points have been recorded at the top of the arc, that shape can only be approximated. Therefore, if service is desired at thepoint450, themobile station106 would assign a relatively low confidence factor that service is available at that point. However, if themobile station106 records data at anadditional point445 as shown in FIG. 4B, theservice area402 becomes better defined. Therefore, themobile station106 can now assign a higher confidence factor to thepoint450.
• Some areas located within a service area may not have coverage available or may have poor coverage. This may happen for a variety of reasons, including entering a tunnel, encountering natural obstacles such as hills, or entering the basement of a building. FIG. 5 illustrates a[0044]service map500 having aservice area505. Theservice area505 generally defines the geographic area where service may be expected to be available. In general, any points within theservice area505 would have a high confidence factor. However, theservice area505 may include anexclusion area510. Theexclusion area510 defines an area within theservice area505 where themobile station106 has determined that either no service is available, or the service is weak. Theexclusion area510 may also define that service is only available for a certain operating mode. For example, digital service may not be available in theexclusion area510 but service may be available on an analog network.
• The use of mapping and the confidence factor may be used to predict the availability of service when the[0045]mobile station106 moves a long distance between measured points. FIG. 6 illustrates aservice map600 having apoint605 where service is available. The service boundary is indicated by aline610. If themobile station106 is turned off at thepoint605, no further mapping occurs. As themobile station106 travels east from thepoint605, themobile station106 will pass the service boundary. If themobile station106 is turned on again at apoint615 where no service is available, themobile station106 will not know at what point service is lost. However, themobile station106 does know that service is available at thepoint605, so as the mobile station travels west, the confidence factor is increased. Of course, themobile station106 is continually mapping new points to enhance the mapping area stored in memory.
• Numerous variations and modifications of the invention will become readily apparent to those skilled in the art. Accordingly, the invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The detailed embodiment is to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.[0046]

Claims (27)

What is claimed is:

1. A method of prioritizing a plurality of service systems in a wireless communication system comprising:

determining a reference location;

calculating a distance from the reference location to each of the plurality of service systems; and

prioritizing the plurality of service systems based on the distance from the reference location.

2. The method ofclaim 1, wherein the reference location is determined using a global positioning system.

3. The method ofclaim 1, wherein the reference location is determined using dead reckoning.

4. The method ofclaim 1, wherein the reference location is a last known location of a mobile station.

5. The method ofclaim 1, wherein the calculating step further comprises:

determining a drift term; and

adjusting the reference location based on the drift term.

6. The method ofclaim 5, wherein the drift term is determined using the equation:

radius_d=(t−t_last-system)V_max

where t is a current time, t_last-systemis a time that service was last available on a last known system, and V_maxis a maximum expected velocity that a mobile station would travel during the period without service.

7. The method ofclaim 6, wherein the distance is calculated using the equation:

$d_{\mathrm{sys}\left(n\right)}=\frac{\sqrt{\left({\mathrm{latitude}}_s-{\mathrm{latitude}}_r\right)+\left({\mathrm{longitude}}_s-{\mathrm{longitude}}_r\right)}}{{\mathrm{radius}}_s+{\mathrm{radius}}_d}.$

8. A method of prioritizing a plurality of service systems in a wireless communication system comprising:

determining a reference location; and

obtaining a prioritized list of service systems based on the reference location.

9. The method ofclaim 8, wherein the reference location is determined using a global positioning system.

10. The method ofclaim 8, wherein the reference location is determined using dead reckoning.

11. The method ofclaim 1, wherein the prioritized list of service systems based on the reference location is obtained from stored data within a mobile station.

12. The method ofclaim 11, wherein the data is stored in the system selection database.

13. The method ofclaim 12, wherein the system selection database includes a position reference for each of the plurality of service systems.

14. A mobile station for use in a wireless communication system comprising:

a position determination device; and

a database of system providers based on position information.

15. The mobile station ofclaim 14, wherein the position determination device is a global positioning system.

16. The mobile station ofclaim 14, wherein the database is included in the system selection database.

17. The mobile station ofclaim 14, wherein the mobile station selects one of the system providers based on the database information.

18. A mobile station for use in a wireless communication system comprising:

a position determination device;

a service detector which determines if service is available at any given position; and

memory locations for storing data regarding service availability for a plurality of locations, wherein the grouping of the memory locations provides a map of a service area showing service availability.

19. The mobile station ofclaim 18, wherein the position determination device is a global positioning system.

20. The mobile station ofclaim 18, wherein a grouping of memory locations containing position information can be converted to a formula defining a service area.

21. The mobile station ofclaim 18, wherein each memory location stores both a latitude and a longitude of a position along with information indicating whether service was available at the position.

22. A method of mapping a service system for a wireless communication system comprising:

establishing a reference location;

determining service availability for the reference location; and

storing the information on service availability for the reference location.

23. The method ofclaim 22, wherein the reference location is established using a global positioning system.

24. The method ofclaim 22, wherein the reference location is determined using dead reckoning.

25. The method ofclaim 22, further comprising:

collecting data on service information for a plurality of reference locations; and

combining the data to provide a map of a service area showing service availability.

26. The method ofclaim 25, further comprising converting the combined data into a formula defining a service area.

27. The method ofclaim 22, wherein the stored information includes both a latitude and a longitude of the reference location along with information indicating whether service was available at the reference location.

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