HK1079947B - Subscriber station with dynamic multi-mode service acquisition capability - Google Patents

Description

Subscriber station with dynamic multi-mode service acquisition capability

RELATED APPLICATIONS

This application claims priority to U.S. provisional application No.60/380,406 filed on day 13, 2002 and U.S. provisional application No.60/390,373 filed on day 20, 2002.

Technical Field

The present invention relates to the field of wireless communications, service acquisition, and multi-mode subscriber (subscriber) stations, and more particularly to dynamic multi-mode wireless communication service acquisition capabilities in subscriber stations.

Prior Art

As wireless communication services become more prevalent throughout the world, a wide variety of different multiple access modes or protocols have emerged to allow multiple subscribers within a particular geographic area to access the limited spectrum at the same time. Examples of such modes or protocols include, but are not limited to AMPS, CDMA, GSM, and UMTS.

Wireless communication systems capable of providing services in accordance with different ones of these modes are also emerging worldwide. Many of these systems have disjoint coverage areas, while many have overlapping coverage areas. The cost and quality of service provided by these systems can and often do not vary. Thus, a user who roams into an overlapping coverage area may benefit by accessing a system in the coverage area that is cost and quality optimal for the user, even though the system is operating in a mode that is different from the mode in which the subscriber station is currently deployed.

In general, a subscriber station, or a local (home) system pre-configured to the subscriber station, uses a mode and cannot be dynamically reconfigured to perform other modes of operation, or, if possible, can be dynamically switched to only a very limited number of other modes, such as CDMA to AMPS or WCDMA to GSM, and does not maintain state information that allows for a smooth return to the previous mode, i.e., a return without significant loss of service can be made if the attempted switch is not successful or if the previous mode is the preferred mode and service in accordance with the previous mode is later made available. Furthermore, the user's relevant activities may require switching to another mode. For example, subscriber stations with the capability to dynamically switch between CDMA and GSM or WCDMA and CDMA mode operation are not currently available. The result is that many users cannot access wireless communication services from a single user station that is optimal in cost and quality for that subscriber.

The fully integrated network provides the subscriber station with instructions on the neighbor systems and how to use them. For a partially integrated network, the network may transmit an indication of other types of systems that the existing subscriber stations have the ability to use, but need not indicate where they can be found and how to use them. Some systems are not integrated and do not provide an indication of other types of systems that the existing subscriber station has the ability to use. Due to weak, or missing, indications and the fact that some systems do not provide such indications, e.g., GSM or WCDMA do not indicate the presence of CDMA, the multi-mode subscriber station must sometimes leave the system in use to check for a more desirable service mode. This results in a loss of service during the time that the subscriber station is looking for a more desirable system, or systems. These losses result in lost calls, directly proportional to the probability of a call during a loss of service. When a more desirable system is not found, the subscriber station returns to the previous, less desirable, but available system. Service loss is typically minimized by checking infrequently, for example every 3 minutes.

Disclosure of Invention

The present invention provides a system for providing dynamic multi-mode service acquisition capabilities in a subscriber station. The subscriber station is capable of operating in two or more modes.

The system includes first logic for indicating a time to scan condition time (time to scan condition) when the subscriber station is operating in a current operating mode having active and inactive states. In the dynamic state, the receiver in the subscriber station is turned on to enable the subscriber station to listen to the communication system. In the inactive state, to save power, the receiver of the subscriber station is turned off and the subscriber station cannot listen to the communication system.

The system also includes second logic, responsive to the first logic indicating a time to scan for conditions, for maintaining state information for a current mode of operation and attempting at least partial acquisition of communication services according to another mode of operation, the at least partial acquisition being arranged to begin when the subscriber station is in an inactive state in the current mode of operation and to end before the subscriber station transitions back to an active state in the current mode of operation.

If at least a portion of the acquisition attempt is successful, the system may cause the subscriber station to terminate operation according to the current mode of operation and begin operation according to another mode. If at least some of the acquisition attempts are unsuccessful, the system uses the maintained state information to allow the subscriber station to resume operation in the current mode of operation.

Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.

Brief Description of Drawings

The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the drawings, like numerals designate corresponding parts throughout the different views.

Fig. 1 is a simplified block diagram of one embodiment of a system for providing dynamic multi-mode service acquisition capabilities to a subscriber station in accordance with the present invention.

Fig. 2A is a timing diagram illustrating an example of transitions between active and inactive states in a subscriber station operating in a GSM mode of operation.

Fig. 2B is a timing diagram illustrating an example of transitions between active and inactive states in a subscriber station operating in a CDMA mode of operation.

Fig. 3 illustrates an example of a correlation function derived from a pilot signal of a CDMA system.

Fig. 4 is a simplified block diagram of one implementation of a system for providing dynamic multi-mode service acquisition capabilities to a subscriber station in accordance with the present invention.

Fig. 5A illustrates an example of a format of a system record in a preferred roaming list.

Fig. 5B illustrates an example format of an acquisition record for a CDMA system in a preferred roaming list.

Fig. 5C-5D illustrate examples of formats for acquisition records for PCS CDMA systems in the preferred roaming list.

Fig. 6 is a simplified flow diagram illustrating a method of dynamically acquiring service in a subscriber station in accordance with one embodiment of the present invention.

Detailed Description

As used herein, terms such as "about" and "substantially" are intended to allow some leeway in mathematical accuracy to account for tolerances acceptable in the industry, for example, for values modified by "about" or "substantially" to deviate upwardly or downwardly from the range of 1% -20% of the value.

Furthermore, as used herein, the term "logic" refers to an implementation as hardware, software, or a combination of hardware and software. Additionally, the term "memory" refers to any processor-readable medium, including but not limited to RAM, ROM, EPROM, PROM, EEPROM, disk, floppy disk, hard disk, CD-ROM, DVD, etc., on which a series of instructions are stored for execution by the processor.

The term "processor" refers to any device capable of performing a function in response to executing a sequence of instructions, including, but not limited to, a general or special purpose microprocessor, a finite state machine, a controller, or a computer.

Referring to fig. 1, a first embodiment of a system 110 for providing dynamic multi-mode service acquisition capabilities to a subscriber station 106 is illustrated. The subscriber station 106 is capable of operating in two or more modes.

The system 110 includes first logic for indicating a scan condition time when the subscriber station 106 is operating in a current mode having active and inactive states. In the active state, the receiver in the subscriber station 106 is turned on to enable the subscriber station to listen to the communication system. In the inactive mode, to conserve power, the receiver in the subscriber station 106 is turned off and the subscriber station cannot listen to the communication system.

The system 110 also includes a second logic 104 that maintains state information for the current operating mode in response to the scan condition time indicated by the first logic 102. Generally, the state information should be sufficient to allow return to the current mode of operation without significant loss of service, and may also include a time or time reference for the current mode, air interface protocol variables for the current mode, and/or hardware states required to be able to restore the current mode after other modes are accessed. The second logic 104 also attempts at least partial acquisition of communication services in accordance with the other mode of operation, the attempt to at least partially acquire being scheduled to begin when the subscriber station 106 is in an inactive state of the current mode of operation and to end before the subscriber station 106 transitions back to an active state of the current mode of operation.

The system 110 also includes a third logic 108. If at least a portion of the acquisition attempt is successful, the third logic 108 causes the subscriber station 106 to cease operation according to the current mode of operation and to begin operation according to the other mode of operation. If at least some of the acquisition attempts are not successful, the third logic 108 uses the maintained state information to allow the subscriber station 106 to resume operation in the current mode of operation.

In one implementation, the one or more modes include a first mode and a second mode, where the first mode is a GSM mode and the second mode is a CDMA mode. It is well known that when in GSM mode, a subscriber station periodically transitions back and forth between active and inactive states. For example, an idle subscriber station is typically assigned to a paging group, and pages to stations in the group are typically broadcast in predetermined time slots at 235.4 millisecond time periods, which is the duration of a GSM control multiframe. In this time slot, the subscriber station needs to turn on its receiver when a page is directed to it. However. For the remaining duration of the control multiframe, the subscriber station may turn off the receiver and enter an inactive state. This situation is illustrated in fig. 2A, where the time slots in which the subscriber station is active are indicated by numerals 202A, 202b, 202 c. As shown, these slots are spaced apart from each other to control the time period of the multiple frames, 235.4 milliseconds.

In this implementation, the first logic 102 detects the scan condition time when the subscriber station is operating in the GSM mode of operation. The indication of the time to scan condition may be triggered by various mechanisms including, for example, expiration of a timer, determining that the signal strength of the system in use falls below a predetermined threshold and/or determining that the signal strength of the candidate system exceeds a predetermined threshold or exceeds the signal strength of the system in use, or that the subscriber station is approaching a coverage area of a system using another mode of operation.

If it is desired to indicate the scan condition time based on the detection of proximity, the subscriber station may be equipped with a GPS, AFLT or hybrid receiver and may determine its location (or be arranged to have a location determining entity to determine its location) from the time of arrival measurements derived by the subscriber station from pilot signals from one or more reference sources visible to the subscriber station and known in location, including but not limited to GSP satellites, base stations or sectors, or a combination of GPS satellites and base stations or sectors.

Different levels of accuracy in the position estimate are also possible. If an accurate position fix is desired for the subscriber station, four or more times of arrival measurements from four or more different reference sources may be required. However, if less accuracy is required, less than four measurements are possible. For example, two measurements are sufficient to determine the distance between the subscriber station and the base station or sector. This information, in combination with the known location of the base station or sector, is sufficient for the expected proximity detection.

Regardless of how the subscriber station's location is determined, and regardless of its accuracy, the subscriber station will then compare its location to the coverage area of the system using the other modes of operation. To do so, the subscriber station may maintain and use a map database that indicates the coverage area of possible systems that may be used by the subscriber station to acquire communication services. If the two are close enough, the scan condition time may be triggered or indicated. Other examples are possible and the foregoing description should not be construed as limiting.

The time for the scan condition to occur should be spaced sufficiently to avoid undue power loss by the subscriber station. More specifically, acquisition of the desired attempted communication service requires turning on the receiver of the subscriber station and re-entering the active state. If these events occur too close together, subsequent searches will consume a significant amount of power. With this in mind, therefore, referring to fig. 2, the occurrence of the scanning condition time needs to have a sufficient interval to avoid this problem. For example, it is generally advisable to avoid indicating the time to scan condition each time the subscriber station transitions to an inactive state.

The second logic 104, in response to the scan condition time indication of the first logic 102, stores state information sufficient to allow a return to GSM mode operation without significant loss of service. Typically, the status information comprises timing information such as a GSM time reference. In addition, when the subscriber station 106 is operating in the GSM mode, the second logic 104 also determines a time until the subscriber station 106 is scheduled to transition back from the inactive state to the active state. (assuming the subscriber station 106 is in an inactive state when the second logic 104 makes the determination). Referring to FIG. 2A, for example, if the second logic 104 responds to the scan condition time at time 204, it determines that the time remaining until the next scheduled transition back to the active state is X.

In response to the remaining time X, the second logic 104 next determines one or more search or acquisition parameters to manage the subsequent at least partial acquisition of the desired CDMA service. One or more search or acquisition parameters are determined such that at least a portion of the acquisition of the desired CDMA service may be completed before a scheduled transition back to an active state in GSM mode operation. In this implementation, it is important to do this because it allows at least part of the acquisition attempt to occur transparently with respect to the GSM mode of operation.

Full acquisition of CDMA service typically requires 5-30 seconds to complete. However, when the subscriber station is operating in GSM mode, the time period available before the subscriber station is scheduled to transition back to the active state is typically on the order of hundreds of milliseconds. Thus, generally, there is not enough time to attempt a full acquisition of CDMA service, but only a partial acquisition, within the available time.

As IS well known, in an IS-95A compatible system, system acquisition includes two substates, a pilot channel acquisition substate in which a subscriber station acquires a pilot channel in a CDMA system, followed by a synchronization channel acquisition substate in which the subscriber station acquires synchronization channel information. In one implementation example, the desired at least partial acquisition includes a simplified pilot acquisition process, similar to that typically occurs in the pilot acquisition substate. This process will now be described.

In accordance with a simplified procedure, a subscriber station first tunes to a pilot channel of a CDMA system and then attempts to locate the pilot channel being transmitted by a base station or sector in the CDMA system. This is achieved by iterative correlation of the received signal with shifted versions of the identification code, where each shift of the identification code uniquely identifies a base station or sector in the CDMA system. For each shift in the code, the subscriber station determines a correlation of the shifted code and the received signal over a set of time intervals I. The process then repeats as the shift in the code is changed. The correlation value of the result may be associated with a shift value to define a correlation function. If the peak of the resulting correlation function exceeds a predetermined threshold, the pilot signal corresponding to the shift in the identification code is deemed to have been detected.

In one example, each sample of the received signal S is a complex number having an in-phase (I) component and a quadrature (Q) component, and the signal S may include one or more pilot signals, each of which is modulated with a shifted version of a PN code that uniquely defines the pilot signal (and the base station or sector from which the pilot signal originated). In one implementation, a correlator in the subscriber station first determines a correlation value C based on the shift s of the PN code being used. The correlation value may be coherent, i.e. maintaining phase information. In this case, the correlation value is a complex number and can be expressed as:

where N is the (coherent) integration time in chips, s (i) is the sample of the received signal, and k is an arbitrary start time. In this implementation, the integration time I is the coherent integration time N.

In a second implementation, the correlator determines a correlation value C, another real one and derived from non-coherent, i.e. from information that does not hold the phase, combining M successive coherent integrations, each of which is performed over N chips. In this implementation, the correlation value C may be expressed as:

in this implementation, the integration time I is the product of N and M.

The range of shifts s tested is the search window W. W values C (PN, S) whose results together form a correlation function F (PN, S) that represents the degree of correlation between the signal S over the desired search window W and a shift S of the PN code, where the shift S is expressed in chips. In case the PN code is repeatedly modulated to the received signal, the correlation function F (PN, s) will be periodic.

Fig. 3 illustrates an example of a correlation function F (PN, s) of a pilot signal in a CDMA wireless communication system. The size of the window (in chips) is 8 in this example, and the window is assumed to be centered around the origin 306. The horizontal axis 302 represents a shift of the PN code (expressed in chips) and the vertical axis 304 represents the correlation function F (PN, s) (expressed in energy (dB)). As illustrated, the peak 308 of the function in this example is located at the origin 306.

If the correlation function peak 308 is high enough and sufficiently distinguishable from noise and other distortions (e.g., multipath or lack of direct line of sight), the risk of false positive (false positive) falls to an acceptable level, and a successful measurement can be obtained.

As can be seen from the foregoing description, the several parameters used in this process, the window size W, the coherent integration time N, and the non-coherent integration time M, are not the same, which affects the time at which at least part of the acquisition process occurs. In other words, the larger the window size W, the larger the coherent integration time N and the larger the non-coherent integration time M, and in general, the longer at least part of the acquisition process will take place. Thus, in this implementation, the second logic 104 will set these parameters so that the attempted acquisition process occurs within the available time until the subscriber station returns to an active state in the GSM mode of operation.

In one implementation, the energy level of the peak of the correlation function is provided to third logic 108, which determines from this information whether the acquisition attempt was successful. As previously discussed, in one implementation, an acquisition attempt will be considered successful if the energy level of the peak of the correlation function exceeds a predetermined level. A more expedited, but less reliable implementation would consider the acquisition attempt successful when the uncorrelated energy level (RSSI) exceeds a predetermined level. These techniques may be combined or selected based on the desired reliability and the available time to attempt acquisition.

If the acquisition attempt is successful, the third logic 108 in this implementation may cause the subscriber station to cease operation in the GSM mode of operation, complete service acquisition from the CDMA system and begin operation in the CDMA mode of operation.

In one configuration, this is accomplished by having the subscriber station de-register from the GSM system and completing service acquisition for the CDMA system (which may include the steps of acquiring synchronization channel information from the synchronization channel of the CDMA system to obtain the SID of the CDMA system, as well as other information needed to acquire system timing), to synchronize itself with the CDMA system, and to register itself with the CDMA system if directed by the CDMA system. In this configuration, it is important that the subscriber station first de-register from the GSM system before registering with the CDMA system to avoid confusion between the two systems or to trigger a situation where one of the systems falsely detects fraud.

In another configuration, the third logic 108 causes the subscriber station to initiate a hard or soft handoff procedure to transition into the CDMA mode of operation if the acquisition attempt is successful. In this configuration, the subscriber station may be simultaneously registered in both the GSM and CDMA systems at the time of the handoff.

It is also possible for a subscriber station to dynamically switch from CDMA to GSM mode of operation using a similar format as used in dynamically switching from GSM mode of operation to CDMA mode of operation. In particular, in a CDMA operating system, a slotted paging scheme may be used in which the subscriber station need only monitor the paging channel for paging messages at intervals of each paging cycle. The duration of the paging cycle is a system parameter, typically from 1.28 to 163.84 seconds, and may use 2ⁱX 1.28 seconds, where the index i is from 0 to 7. The index i refers to the index of the slot cycle. CDMA systems using the quick paging channel use the slot activity indication as an optimum to indicate whether the subscriber station should listen for messages in the next interval. The quick paging channel provides a periodic indication including a similar period of inactivity.

The subscriber station need only listen for paging messages during the intervals in the paging cycle. For the remainder of the paging cycle, the subscriber station may turn off its receiver and enter an inactive state. This situation is illustrated in fig. 2B, which illustrates time periods 206a, 206B, 206c during which the subscriber station remains in an active state. For the remainder of the paging cycle T, the receiver in the subscriber station may be turned off and the subscriber station is in an inactive state.

When the subscriber station is in the inactive state, either after or when the scan condition time is indicated, the second logic 104 may once again store state information sufficient to allow the subscriber station to return to the CDMA mode of operation without significant loss of service, determine the time remaining until the subscriber station is scheduled to transition back to the active state, and, in response thereto, determine parameters of the acquisition attempt such that the attempt can be scheduled to end before the transition. When these parameters are determined, the second logic 104 may initiate an acquisition attempt.

However, here with respect to a transition from the GSM mode of operation, there may be sufficient time from the paging cycle to complete acquisition of GSM service, and thus the available time for an acquisition attempt may be as high as 163.84 seconds in duration, which is much greater than the typical time required to acquire GSM service. Thus, full acquisition of GSM service may be attempted upon transition out of CDMA mode of operation.

Some of the work that may be done during an acquisition attempt includes using a frequency dependent channel (FSSH) to synchronize the local oscillator of the subscriber station with the reference frequency of the base transceiver station in the GSM system, to obtain timing information from the Synchronization Channel (SCH) and to synchronize the subscriber station with GSM frames and multi-frame timing structures, and to obtain other important system information broadcast by the base transceiver station on the Broadcast Control Channel (BCCH).

If the acquisition attempt is successful as before, the third logic 108 causes the subscriber station to cease operation in the CDMA mode of operation and to begin operation in the GSM mode of operation. In one configuration, these operations are performed by logging off from the CDMA system, and if necessary, completing service acquisition from the GSM system and registering with the GSM system. In another configuration, these operations are performed by initiating a hard or soft handoff from the CDMA to the GSM system.

An example of one implementation of a multi-mode wireless communication device including a system in accordance with the present invention is illustrated in fig. 4. In this particular example, the components of the wireless communication device include a CPU402 for executing software instructions; a memory 404 holding software instructions and data; a persistent memory 406; a keyboard 408 and a display 410, both of which are typically provided as part of the user interface; a microphone 412 and speaker 414 are typically provided to support the device for transceiving voice; a radio transceiver (Tx/Rx)416 capable of receiving and transmitting information over a wireless communication link in multiple modes; a modem 418 for modulating baseband information, such as voice or data, onto an RF carrier and demodulating the modulated RF carrier to obtain baseband information; and an antenna 422 for transmitting the modulated RF carrier over a wireless communication link. These components are standard elements in many wireless communication devices and need no further explanation.

In this particular implementation example, the wireless communication device is capable of switching between first and second modes of operation, which are different modes, each selected from the group consisting of 1x, 1xEV, AMPS, CDMA, GSM, TDMA, and WCDMA.

Further, in this particular implementation example, the functionality of the first, second, and third logic 102, 104, and 106 has been described previously and will be discussed further below in connection with FIG. 6 in a software implementation executed by the CPU in FIG. 4. The software may be embodied in the form of a series of instructions stored in memory 404, persistent storage 406, or both.

The persistent memory 406 is configured to hold provisioning information for acquiring wireless communication services in multiple modes and may be implemented as a combination of non-volatile EEPROM devices, such as in conjunction with a SIM card.

In one example, the provisioning information includes a Preferred Roaming List (PRL), which is a CDMA structure including a list of system IDs, network IDs (SID, NID) for identifying CDMA systems and networks in the CDMA system, a geographic indicator for indicating, for each pair of SID, NID, the coverage area of the system or network specified by the SID, NID pair, an indicator of a preference that other systems or networks in the list are to give to the system or network specified by the SID, NID pair, or of a non-preference of the system or network specified by the SID, NID pair, and a frequency or channel to be used to attempt to acquire service from the system or network specified by the SID, NID pair. The provisioning information may also include a Most Recently Used (MRU) list, which is a list of SID, NID pairs that specify the system or network most recently used by the subscriber.

In another example, the Preferred Roaming List (PRL) also includes records that identify the CDMA system and networks in the CDMA system using 1xEV subnet ID sums, or instead of system ID, network ID (SID, NID) pairs. The provisioning message may also include a Most Recently Used (MRU) list, which is a network ID and, or alternatively, a list of SID, NID pairs to specify the system or network most recently used by the subscriber. Alternatively, the MRU entities for subnet ID and SID, NID pairs may be split into two lists, one for each mode.

In another example, the Preferred Roaming List (PRL) also includes identifying the GSM system or networks in the GSM system using a PLMN or PLMN + LAC group (both described below) and, or instead, a 1xEV subnet ID or system ID, network ID (SID, NID) pair. The provisioning information may also include a Most Recently Used (MRU) list, as explained above.

In addition, the provisioning information may also include a Public Land Mobile Network (PLMN) list, which is a GSM structure including a PLMN list, i.e., mobile country code, mobile network code (MCC, MNC) pairs that identify the country and GSM networks in the country, and for each MCC, MNC pair, a geographic indicator indicates the coverage area of the system or network specified by the MCC, MNC pair, an indicator of a preference that other systems or networks in the list are to give to the system or network specified by the MCC, MNC pair, or a preference that is not to be given to the system or network specified by the MCC, MNC pair, and a frequency or channel to be used in an acquisition attempt service from the system or network specified by the MCC, MNC pair. The MCC, MNC pair may be associated with one or more Local Area Code (LAC) values to further specify the area of the system or network.

This provisioning information may be used by a protocol stack executing on CPU402 to dynamically determine an acquired candidate system or network that is preferred by the subscriber station as compared to the current system or network. And at least some of the acquisition parameters are used to make attempted service acquisitions from the candidate system or network. When the scan condition time is detected, the protocol stack that maintains communication with the current system or network may be put on hold while another protocol stack will be invoked to make attempted service acquisitions from other networks or systems. As discussed above, the search/acquisition parameters to be used in an acquisition attempt are determined so that the attempt can be completed before the next scheduled transition to the active state of the previous mode of operation. This would allow the attempted acquisition to be transparent to the previous protocol stack.

In one implementation, the preferred roaming list includes a sequential list of system records, each having the format shown in FIG. 5A. In this record, the SID field is a 15-bit system identifier associated with the system of this record, and the value "000000000000000" matches any SID and is used as a SID wildcard.

The NID INCL field is a 1-bit field indicating whether the system record includes the NID field. If the field is set to "1", then the record includes the NID field; otherwise, the field is set to "0".

The NID field, if indicated as present by the NID INCL field, is a 16-bit field that identifies the record associated with the record. The value "1111111111111111" matches any NID and is a NID wildcard.

NEG PREF is a 1-bit field that indicates whether the subscriber station is allowed to operate in the system or network associated with the record. The field is set to "1" indicating that the subscriber station is allowed to operate in the system and network associated with the record, and is set to "0" otherwise.

The GEO field is a 1-bit geographical area indicator. This field is set to "0" if the record is the first in the list. If the record is not the first in the list and the system or network associated with the record is in the same geographic area as the system or network associated with the previous record, this field is set to the same value as the GEO field of the previous record. Otherwise, this field is set to the complement (completion) of the value of the GEO field of the previous record.

The PRI field is a 1-bit relative priority indicator. This field is set to "0" if the record is the first record in the list. If the record is not the first record in the list and the value of the GEO field in that record is not the same as the value in the previous record, this field is set to "0". If the record is not the first record in the list and the value of the GEO field of the record is the same as the value in the previous record and the system or network associated with the record is the same as the expected degree of the system or network associated with the previous record, the field is set to the value of the PRI field in the previous record; otherwise, the complement of the value of the PRI field to the previous field will be set.

The ACQ _ INDEX field is an INDEX of a 6-bit acquisition record specifying acquisition parameters of the system or network associated with the record. The format of these acquisition records will be discussed below.

The ROAM _ IND field exists only when the NEG _ PREF field is set to "1". If present, is a 3-bit field set to a roaming indicator value for the system or network associated with the record. If the field is set to "000," it indicates that the subscriber station is not roaming and the roaming indicator is off. If the field is set to "001", it indicates that the roaming indicator of the subscriber station is turned on. If the field is set to "010", it indicates that the roaming indicator is blinking (flashing).

Examples of some possible formats for the acquisition record are illustrated in fig. 5B-5D. Fig. 5B illustrates the format of an acquisition record for a cellular CDMA system or network. The ACQ _ TYPE field is a 4-bit field indicating the TYPE of acquisition record. In this case, the record type is set to "0010", indicating cellular CDMA.

The a _ B field is a 2-bit field indicating whether the system or network associated with the record is allocated to the a band or the B band. The value "00" specifies the a band; the value "01" specifies the B band; and a value of "11" designates either the a or B band.

The PRI _ SEC field is a 2-bit field indicating which of the primary or secondary channels is preferred. The primary channel in band a is 283 and the secondary channel in band a is 691. The primary channel in the B band is 384 and the secondary channel in the B band is 777. The value "00" indicates that the primary channel is preferred; a value of "01" indicates that the second channel is preferred; and a value of "11" indicates that either the primary channel or the secondary channel is preferred.

Fig. 5C illustrates the format of an acquisition record for a PCS CDMA system or network, where the record specifies one or more frequency blocks.

The ACQ _ TYPE field is a 4-bit field that specifies the acquisition record TYPE again. In this case, the field value is "0100" which indicates a PCS CDMA acquisition record in the form of a frequency block.

The NUM _ BLOCK field specifies a 3-bit field for the number of PCS frequency BLOCKs included in the acquisition record.

The BLOCK field is a 3-bit field that specifies the PCS frequency BLOCK. This field may be duplicated and the number of times this field occurs is given by the value of the NUM BLOCK field. The value "000" specifies A blocks; the value "001" specifies the B block; the value "010" specifies a C block; the value "011" designates a D block; the value "100" specifies an E block; the value "101" specifies an F block; and the value "111" specifies any block.

Fig. 5D illustrates the format of an acquisition record for a PCS CDMA system or network that specifies one or more CDMA channels.

The ACQ _ TYPE field is set to a value of "0101" to indicate a PCS CDMA acquisition record in the form of a channel.

The NUM _ CHANS field is a 5-bit field indicating the number of CDMA channels included in the record.

The CHAN field is an 11-bit field indicating the number of PCS CDMA channels. This field may be duplicated and the number of occurrences of this field is given by the value of the NUM _ CHANS field.

The MRU list and PLMN list may have similar formats as before. Further, where the current system spans multiple geographic areas, it may be desirable to use a different, previously referred to as an Alternative Scan List (ASL), which is derived from the PRL and includes a collection of records associated with more preferred systems or networks in all geographic areas spanned by the current system.

Returning to fig. 4, the (optional) geographic database 424 is a database that indicates the coverage areas of the systems or networks specified in one or more of the preferred roaming list, MRU list, and PLMN list. This information may be used to detect that the subscriber station is near one of the coverage areas of these systems or networks and may trigger a scan condition time. The database may be implemented in the manner of provisioning information previously discussed, wherein a geographic indicator corresponding to the coverage area of a system or network of SID, NID pair, MCC, MNC pair or MCC, MNC, LAC group is provided. Alternatively, the geographic database 424 may be contained in a separate database from the provisioning data. Regardless of the implementation, the geographic database 424 should indicate the coverage area of a system or network that is accessible by subscriber stations for obtaining communication services.

Correlator 420 is provided for acquiring the CDMA system among other functions. For a given PN code shift, it produces a correlation function in a search window W defined by defined coherent and non-coherent integration times (N, M).

Referring to fig. 6, one embodiment of a method of dynamically acquiring communication services in a subscriber station in accordance with the present invention is illustrated. The method may be tangibly embodied as a series of instructions stored in a memory, such as, but not limited to, the subscriber station's memory 404 and/or persistent memory 406 in fig. 4.

The method begins at step 602, which includes determining if this is a scan time for another service. (in one embodiment, this step is performed while the subscriber station is in the current operating mode.) if so, control proceeds to step 604. If not, the method returns to the beginning of step 602.

Step 602 may be performed in a variety of ways. In one implementation, this is done in accordance with the expiration of a timer, which is a sufficient interval between the occurrence of timed scan times so that battery life is not unduly consumed for attempted new service acquisitions. In another embodiment, this step includes determining whether the signal strength from the candidate system is above a predetermined threshold and/or whether the signal strength from the in-use system falls below a predetermined threshold and/or whether the signal strength from the candidate system is sufficiently above the in-use system. In a third implementation, this step includes determining whether the distance between the location of the subscriber station and the coverage area of the candidate system is close enough to permit scanning for new services.

In step 604, the method determines a candidate system or network and possibly a scan type that gives the time allowed before the subscriber station in the current mode of operation is scheduled to transition back to the active state. (in one embodiment, this step is assumed to occur when this subscriber station is in the inactive state of the current mode of operation). In one implementation, candidate systems or networks are determined based on provisioning information reflecting user preferences. In one example, if the new system is intended to be a CDMA system, this step includes setting the search window W, and coherent and non-coherent integration times N, M, so that there is sufficient time to perform acquisition within the allowed time.

From step 604, control proceeds to optional step 606, which is to check whether there is sufficient time to scan before the subscriber station in the current mode of operation is scheduled to transition back to the active state. This step is optional because it is at least partially redundant with step 604, which is setting the search parameters so that the scan can be completed within the allowed time. If so, this step may include confirming that the scan can be performed within the allowed time. If true, control proceeds to step 608. If not, control returns to the start of step 602.

At step 608, the timing and state information for the current mode of operation is saved and the scan determined in step 604 is performed. The timing and state information that is saved should be sufficient to allow for later return to the current mode of operation without significant loss of service. In one example, this step is performed based at least in part on provisioning information specifying a preferred frequency and channel for acquisition attempts. This is followed by step 610, where a query is made whether the scan was successful or not, step 610. If so, control proceeds to step 612. If not, control returns to the beginning of step 602.

At step 612, the subscriber station logs off from the current service. Step 614 follows step 612. In step 614, the subscriber station completes service acquisition from the new system, if necessary, and registers with the new system. Control next passes to the start of step 602.

In another embodiment, the method performs a hard or soft handoff from the current system to the new system instead of steps 612 and 614. Note that in this embodiment, it may be, but is not required that the subscriber station register with both systems at the same time.

While various embodiments of the invention have been described above, it will be apparent to those of ordinary skill in the art that many more possible embodiments and implementations are possible that are within the scope of the invention.

Claims (21)

1. A system for providing a dynamic multi-mode service acquisition capability to a subscriber station, the subscriber station capable of operating in two or more modes of operation, the system comprising:

first logic means for indicating when a subscriber station is operating in a current mode of operation having active and inactive states a time for a scanning condition in response to detecting sufficient proximity between the subscriber station and a coverage area of a candidate system using another mode of operation, wherein detection of proximity is accomplished based on consideration of an estimated position of the subscriber station relative to the coverage area of the candidate system;

second logic means, responsive to the first logic means indicating a time for the scanning condition, for storing state information of the current mode of operation and for attempting at least partial acquisition of communication services in accordance with another mode of operation, the at least partial acquisition attempt being initiated when the subscriber station is in an inactive state of the current mode of operation and being scheduled to be completed before the subscriber station reverts to an active state of the current mode of operation; and

third logic means for causing the subscriber station to cease operation according to the current mode of operation and commence operation according to the other mode of operation if the at least partially acquired attempt is successful, and for allowing the subscriber station to resume operation in the current mode of operation using the stored state information if the at least partially acquired attempt is unsuccessful.

2. The system of claim 1, wherein the estimated position of the subscriber station is determined based on signals received from one or more reference sources.

3. The system of claim 2, wherein the at least one reference source comprises a GPS satellite.

4. The system of claim 2, wherein at least one reference source is a base station or a sector.

5. The system of claim 2, wherein at least one reference source is a GPS satellite and another is a base station or sector.

6. A system for providing a dynamic multi-mode service acquisition capability to a subscriber station, the subscriber station capable of operating in two or more modes of operation, the system comprising:

first logic means for indicating a time for a scan condition when the subscriber station is operating in a current mode of operation having active and inactive states;

second logic means responsive to the first logic means indicating a time for the scanning condition for storing state information for the current mode of operation and for attempting at least partial acquisition of communication service in accordance with another mode of operation, said at least partial acquisition attempt being initiated when the subscriber station is in an inactive state of the current mode of operation and being arranged to be completed before the subscriber station reverts back to an active state of the current mode of operation, wherein said second logic means determines when the subscriber station is arranged to transition to the active state in the current mode of operation the next time and, responsive to that determination, determines said at least partially acquired one or more parameters; and

third logic means for causing the subscriber station to cease operation according to the current mode of operation and commence operation according to the other mode of operation if the at least partially acquired attempt is successful, and for allowing the subscriber station to resume operation in the current mode of operation using the stored state information if the at least partially acquired attempt is unsuccessful.

7. The system of claim 6, wherein the one or more parameters include a coherent integration time.

8. The system of claim 6, wherein the one or more parameters include a non-coherent integration time.

9. The system of claim 6, wherein the one or more parameters include coherent and non-coherent integration times.

10. The system of claim 6, wherein the one or more parameters include one or more energy levels.

11. A method of dynamically acquiring service in a subscriber station, the subscriber station being capable of operating in two or more modes of operation, the method comprising the steps of:

indicating a time of a scanning condition while the subscriber station is operating in a current mode of operation having active and inactive states, wherein the time of the scanning condition is indicated in response to detecting sufficient proximity between the subscriber station and a coverage area of a candidate system using another mode of operation, and the detection of proximity is done based on considering that an estimated location of the subscriber station cell is relative to the coverage area of the candidate system;

storing state information for the current mode of operation in response to the indication of the scan condition time;

attempting at least partial acquisition of communication services in the other mode of operation in response to the indication of the time to scan condition, the attempt to at least partially acquire being scheduled to initiate when the subscriber station is in an inactive state of the current mode of operation and to complete before the subscriber station reverts to an active state of the current mode of operation;

if the at least partial acquisition attempt is successful, causing the subscriber station to end operation in accordance with the current mode of operation and begin operation in accordance with the other mode of operation; and

if the at least partially acquired attempt is unsuccessful, the subscriber station is allowed to resume operation in the current mode of operation using the stored state information.

12. The method of claim 11, wherein the estimated position of the subscriber station is determined based on signals received from one or more reference sources.

13. The method of claim 12, wherein the at least one reference source comprises a GPS satellite.

14. The method of claim 12, wherein at least one reference source comprises a base station or sector.

15. The method of claim 12, wherein at least one reference source comprises a GPS satellite and another comprises a base station or sector.

16. The method of claim 11, wherein the step of attempting comprises the steps of: the received signal is correlated with an identification code uniquely identifying the candidate system to obtain a correlation function having a peak value, and it is determined whether the peak value of the correlation function exceeds a predetermined threshold.

17. The method of claim 11, further comprising the steps of: determining when the subscriber station is scheduled to transition to an active state in a current mode of operation, and, in response to the determination, determining the at least partially acquired one or more parameters.

18. The method of claim 17, wherein the one or more parameters comprise a coherent integration time.

19. The method of claim 17, wherein the one or more parameters comprise a non-coherent integration time.

20. The method of claim 17, wherein the one or more parameters include coherent and non-coherent integration times.

21. The method of claim 17, wherein the one or more parameters comprise one or more energy levels.