MXPA98007853A - Method and apparatus for performing prefer system selection - Google Patents

Abstract

A method and apparatus for selecting a communication system according to the geographical region of the subscriber station. The subscriber station first tries to determine its geographic region. It does so by trying to acquire a system that covers the region. Once the subscriber station has determined its geographic region, then the subscriber station determines whether the system acquired is the most desirable system to use in the geographic region. If it is the most desirable system to use in the geographical region, the subscriber station is registered with the acquired system. If it is not the most desirable system to use in the geographic region, the subscriber station tries to acquire a more desirable system.

Description

METHOD AND APPARATUS FOR PERFORMING SELECTION OF PREFERRED SYSTEM BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to communication system. More particularly, the present invention relates to a novel and improved method and apparatus for selecting a preferred communication system at a subscriber station that can operate in a plurality of geographic regions.

II. Description of the Related Art. As mobile communication systems become more prevalent in society, the demands for a more sophisticated service have grown. To meet the capacity needs of mobile communication systems, multiple access techniques have been developed for a limited communication resource. The use of code division multiple access modulation (CDMA) techniques is one of the different techniques for facilitating communications, where a large number of users of the system are present. Other techniques of the multiple access communication system are known in the art, such as time division multiple access (TDMA), and frequency division multiple access (FDMA). However, the broad-spectrum code division multiple access modulation technique has significant advantages over these modulation techniques for multiple access communication systems. The use of code division multiple access techniques in a multiple access communication system is disclosed in U.S. Patent No. 4,901,307, issued February 13, 1990, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATIÓN SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS ", assigned to the assignee of the present invention and is incorporated herein by reference. The use of code division multiple access techniques in a multiple access communication system is further disclosed in U.S. Patent No. 5,103,459 issued April 7, 1992, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL AVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM "assigned to the assignee of the present invention, and is incorporated herein by reference. When the user of a subscribing station travels from one geographical region to another, the subscriber station must select a communication system on which to conduct the services. There are two means by which a user can operate his subscriber station in different geographical locations. Through the first method, the user subscribes to communications services in a variety of places. Accordingly, the subscriber station only needs to look for a communication system to which the user is subscribed, and to which he is authorized to receive services from any of the service providers. In an alternative way, the user can communicate through the search service. Mobile communications providers negotiate contracts among themselves to provide services known as "search" to their customers. A "search engine" is a subscriber station that requires service in a system that is operated by a communications service provider different from those with which the user subscribes. Currently, when a subscriber station is searching, a signal indicating the search condition to the user is provided. A search determination is made as a result of a comparison of the system identification (SID), of the subscribed system or systems, with the system identification, of the system that provides the service, which is transmitted by that system. This alerts the user of the subscribing station that the service is being provided. is accruing search fees.

Because the subscriber station is generally not aware of the user's geographic region, must determine which system is available, and then select a system that provides the optimal service to the user in terms of cost and quality of service. As the number of regions where the user wishes to operate increases, in the same way the number of different communication systems that the user should try to acquire has increased. The present invention provides a method and apparatus for selecting the most suitable communication system for the needs of the user. The present invention is described in a multi-mode subscriber station, as described in detail in the pending United States Patent Application Serial Number 08 / 509,719, entitled "METHOD AND APPARATUS FOR SYSTEM DETERMINATION IN A MULTI -MODE SUBSCRIBER STATION ", assigned to the assignee of the present invention, and is incorporated herein by reference. It should be noted that, although the present invention is described in the context of a subscriber station capable of operating in the analog and analog environments. digital, the present invention is equally applicable to subscriber stations that can only operate in an environment. In a similar manner, it should be noted that the digital operation described in the context of the code division multiple access (CDMA) operation is equally applicable to any digital communication format, such as multiple time division access, multiple access frequency division, GSM, and so on.

SUMMARY OF THE INVENTION In the exemplary embodiment of the present invention, the subscriber station maintains a system list, some of which are "preferred" systems (system that the subscriber station has permission to use), and some of which are 'negative' systems (system that the subscriber station does not have permission to use).

Associated with each system of the list, there is a system identification (SID), as well as acquisition parameters (band, frequency, mode, etc.). This list is referred to herein as the universal system table. The universal system table is maintained in such a way that the subscriber station can easily determine which systems (preferred or negative) cover common geographic regions. The common geographic regions are referred to herein as common radio coverage areas. Moreover, systems that cover a common geographic region have priorities, and are classified from the most desirable to the least desirable. The work of the subscribing station is to try to acquire the service in the most desirable system, in the current geographical region of the subscribing station. There is no reason to try to acquire the service in a system outside of the current geographic region of the subscribing station, since the coverage of the system is typically geographically limited. The problem is that the subscriber station does not necessarily know where it is when it is energized. Due to the search, it could be in a region entirely different from the one it was in previously. Therefore, the way to acquire any system, let alone the most desirable system, may not be obvious. In the exemplary embodiment of the present invention, the subscriber station maintains a table of systems, which are most suitable for determining the geographical region of the subscriber station. This list is referred to herein as the geographical hypothesis table. The systems in the geographic hypothesis table are selected based on the speed with which they can be acquired, and the possibility with which they can be acquired if the subscribing station is within their geographical coverage region. The subscribing station tests each of the geographical hypotheses, trying to acquire a system that operates within the geographical region. In the exemplary embodiment, the subscriber station maintains a list of the most recently used systems, and an indication of its geographic region, in a table referred to herein as the most recently used table (MRU). In the example mode, the subscriber station first selects the geographical hypotheses to be tested according to the entries in the most recently used table. That is, the regions that are going to be tested first are those where the subscriber station has recently operated. In the example mode, the following set of geographical hypotheses to be tested are those that have representative acquisition parameters. In trying to acquire one of these "representative" systems, a plurality of geographical hypotheses having identical acquisition parameters are tested simultaneously. If none of these methods is successful in acquiring a system, then the remaining systems are tested in the geographic hypothesis table. Once the subscriber station acquires a system, the subscriber station can pick up the acquired system identification from a higher message. The subscribing station uses the identification of the received system to determine its geographical region. It should be noted that the subscribing station can obtain this geographic information, whether the acquired system is preferred or negative.

The subscriber station then makes attempts to acquire a system within the geographical region that is most desirable for the needs of the user. Since the systems in the universal system table are grouped according to the geographical region, instead of being listed in sequence from the most desirable to the least desirable, that search procedure is done by going to the correct set of systems, and trying to acquire in sequence each of the preferred systems in that group, from the most desirable to the least desirable.

BRIEF DESCRIPTION OF THE DRAWINGS The characteristics, objects, and advantages of the present invention will become clearer from the detailed description given below, when taken in conjunction with the drawings, in which the same reference characters are they correspondingly identify therethrough, and in which: Figure 1 is a block diagram of the exemplary multiple mode subscriber station of the present invention. Figure 2 is a flow diagram illustrating the example system selection process of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Referring to Figure 1, when the multi-mode subscriber station MMSS 1 is in a sub-state of system determination, the operations are conducted by the system determination processor 8. In the system determination state, the system determination processor 8 selects the communication system over which the multi-mode subscriber station 1 attempts to perform the acquisition, and provides the necessary parameters to the acquisition circuit. In the exemplary embodiment, the multiple mode subscriber station 1 is a dual mode subscriber station which can have both analog transmission and reception, using analog modulation and demodulation, and the processing circuit (analog circuit) 4, and also transmission and code division multiple access (CDMA) reception, using code division multiple access modulation and demodulation, and processing circuit (code division multiple access circuit) 6. The design of analog circuit 4 is well known in the matter, and is described in detail in Mobile Cellular Telecommunications Systems by William CY Lee. The exemplary embodiment of the code division multiple access circuit 6 is described in detail in the aforementioned U.S. Patent Nos. 4,901,307 and 5,103,459. The most recent usage table (MRU) 9 contains a list of communication systems that have been most recently used by the multi-mode subscriber station 1. In the example mode, the most recent usage table 9 is implemented in the memory non-volatile, which is retained even after the multi-mode subscriber station is turned off 1. The Geographical Hypothesis Table 10 contains a list of system identifications (SIDs), each located in a different geographic region, and the parameters of Necessary acquisition, including band, frequency, mode, and any other parameters necessary to perform the acquisition in that system. In the exemplary embodiment, the geographic hypothesis table 9 is implemented in the non-volatile memory that is retained even after the multiple mode subscriber station 1 is turned off. It is envisioned that there may be cases where more than one may be needed. system to test a single geographical hypothesis, and in these cases, the table of geographical hypothesis 10 will contain more than one system for that region, and that geographical hypothesis will be tested trying to acquire each of the systems listed for that region. In the example mode, the systems listed in the table of geographical hypothesis 10 have been selected according to the speed and the possibility that the system can be acquired. In the example mode, the geographic hypothesis table 10 contains both the preferred and the negative system. The universal system table 11 contains the system parameters for all communication systems that the multi-mode subscriber station 1"knows" to exist. In the example mode, the universal system table 11 contains information with respect to both positive and negative systems. In the example mode, the systems stored in the universal system table 11 are grouped according to the geographical region, and each system listed within a geographic group is then ordered in sequence from the most desirable to the least desirable. For each system, the universal system table 11 contains the identification of the system, together with the necessary acquisition parameters, including the band, frequency, mode, and any other parameters necessary to perform the acquisition. In the example mode, each system listed is marked with an indication of whether the system is a system that is allowed to use the subscriber station (a preferred system), or a system that is not allowed to use the subscriber station (a negative system) .

Figure 2 is a flow diagram illustrating the exemplary method of selecting the preferred system of the present invention. Upon energization (block 20), the multi-mode subscriber station 1 enters the system determination sub-state, and the control is transmitted to the system determination processor 8. In block 22, the system determination processor 8 selects the initial system on which to try the acquisition. This system tests a geographical hypothesis. For example, if the multiple mode subscriber station 1 is going to determine if it is operating in San Diego, then the system determination processor 8 selects the system or systems from the geographic hypothesis table 10, covering the region of San Diego, and have been selected to test that hypothesis. In the exemplary embodiment, the system determination processor 8 initially determines the geographic region to be tested according to the systems listed in the most recent usage table 9. In the example mode, the system determination processor selects, as the system for initial acquisition, the geographic region of the last system used to provide the service to the subscriber station in multiple modes 1. In an alternative mode, the system determination processor 8 selects the region where the station is most frequently used. Subscriber of multiple modes 1. Having determined which region should be tested, the system determination processor 8 retrieves the system to test the hypothesis from the table of geographical hypothesis 10. In the example mode, the table of geographical hypothesis 10 contains the acquisition parameters required for the selected system. In an alternative embodiment, the system determination processor retrieves the identity of the system from the geographical hypothesis table 10, and then retrieves the acquisition parameters for the system selected from the universal system table 11. If the system selected for the initial acquisition is an analog system, the system determination processor 8 provides the system parameters to the analog circuit 4, and provides the necessary frequency information to the transceiver 3. In block 24, the transceiver 3 converts down and amplifies the signal (if present), and provides the signal to the analog circuit 4, which demodulates the received signal, and determines whether the acquisition was successful. In block 22, if the preferred system is a code division multiple access system, the system determination processor 8 provides the system parameters to the code division multiple access circuit 6, and provides the necessary frequency information to the system. transmitter-receiver 3. In block 24 transmitter-receiver 3 converts downward and amplifies the signal (if present), and provides the signal to the code division multiple access circuit 6, which demodulates the received signal, and determines if the acquisition was successful. In block 26, if the acquisition attempt was not successful, then the control is returned to the determination processor of system 8 in block 25. The system determination processor 8 selects the next system to be acquired. In the exemplary embodiment, the multi-mode subscriber station 1 first tests all geographic regions where the multi-mode subscriber station 1 has recently operated. This is determined according to the information in the most recent usage table 9. If the tests of these regions are unsuccessful, then the multi-mode subscriber station 1 tries to acquire a "representative" system. A representative system is one that has acquisition parameters that are common to a plurality of other systems. Therefore, when attempting to acquire on a representative system, the multiple mode subscriber station 1 is actually testing a plurality of geographical hypotheses in a simultaneous manner. If neither of these systems can be acquired, then the multi-mode subscriber station 1 exhaustively attempts the acquisition over the remaining regions of the geographical hypothesis table 10. When, in block 26, the acquisition of the system selected by the processor of determination of system 8 is unsuccessful, the operation moves to block 28. Block 28 determines whether all geographic regions where it is known that the multiple mode subscriber station 1 has recently operated have been tested. If there are regions where the multiple mode subscriber station 1 has recently operated, which have not been tested, then the system determination processor 8 selects a region to be tested, according to the information from the most recent usage table 9. Then, in block 30, the system determination processor 8 retrieves the acquisition parameters to test the geographical hypothesis from the geographical hypothesis table 10. The system determination processor 8 selectively provides the acquisition parameters of the system. system to the analog circuit 4, to the code division multiple access circuit 6, and to the transmission-receiver 3, as described above. The acquisition is then attempted on the selected system in block 24 as described above. If all the geographic regions where the multiple mode subscriber station 1 has recently operated have been tested, then the multi-mode subscriber station 1 attempts acquisition over the "representative" systems. In block 34, if the multi-mode subscriber station 1 has not attempted to acquire all the representative systems then, in block 36, the system determination processor 8 selects a representative system from the table of geographical hypothesis 10. The The system determination processor 8 selectively provides the system acquisition parameters to the analog circuit 4, the code division multiple access circuit 6, and the transceiver 3, as described above. The acquisition is then attempted on the selected system in block 24 as described above. If acquisition attempts have been made on all "representative" systems in block 42, then the multi-mode subscriber station 1 exhaustively attempts acquisition over the remaining systems in the table of geographical hypothesis 10. In block 44, if there is geographic assumptions in the table of geographical hypothesis 10 that have not been tested, then the flow moves to block 38. In block 38, the system determination processor 8 selects a remaining geographical hypothesis, and retrieves the acquisition parameters to Starting from the table of geographical hypothesis 10, and selectively providing the system acquisition parameters to the analog circuit 4, the code division multiple access circuit 6, and the transmission-receiver 3, as described above. The acquisition is then attempted on the selected system in block 24 as described above. Attempts to test all geographical hypotheses have failed, then, in the example mode, in block 40, the multi-mode subscriber station 1 is temporarily turned off to save battery power, and then starts the system selection process preferred again at a later time previously determined in block 20. There are several possible alternative courses of action. A possible alternative is that the multi-mode subscriber station 1 simply shuts down. A second possible alternative is that the multi-mode subscriber station 1 starts the preferred system selection process again immediately. A third possible alternative, is that the multi-mode subscriber station 1 indicates the fault and waits for the user to intervene. Upon successful acquisition, the acquired system transmits a system identification (SID), which is received in block 27, by antenna 5, and transmitter-receiver 3 is provided, wherein the message signal is converted to down and amplified. If the acquired system is analog, the message is provided to the analog circuit 4, which demodulates the signal in accordance with an analog demodulation format, and provides the system identification information to the system determination processor 8. If the system acquired is code division multiple access, the message is provided to the code division multiple access circuit 6, which demodulates the signal according to a code division multiple access demodulation format, and provides the identification information from the system to the system determination processor 8. In block 35, the system determination processor 8 determines whether the identification of the received system is one of the systems stored in the universal system table 11. If the acquired system is not known for the multi-mode subscriber station 1, then the flow is returned to block 25, and the subscriber in multiple modes 1 tries to acquire a different system. In a preferred embodiment, the acquisition parameters of the acquired but unknown system are retained by the system determination processor 8, and the system is used if the multiple mode subscriber station 1 can not acquire a preferred system. If the received system identification (SID) is listed in the universal system table 11, then the determination process of system 8 determines whether this is a more desirable system for the geographic region in block 48. If the acquired system is the most desirable system for the geographic region, then the service is provided using the system acquired in block 50. Upon termination of the service, the system determination processor 8 updates the most recent usage table 9, in block 52. If the identification of the received system is not of the preferred system for the geographical region, then the system determining processor 8 selects the most desirable system for the geographical region, and selectively provides the acquisition parameters of the system to the analog circuit 4, to the access circuit Code 6 division multiple, and transceiver 3, as described above. Block 56, the multiple mode subscriber station 1 attempts acquisition on the most desirable system in the geographic region as described above. If the acquisition is successful, the service is provided using the system acquired in block 60. In block 62, the system determination processor 8 updates the most recent usage table 9. If the acquisition is unsuccessful, then the block 64, the system determination processor 8 selects the next most desirable system to use in the geographic region. If there are remaining preferred systems on which to attempt acquisition, in block 66, then the system determination processor 8 selectively provides the system acquisition parameters to the analog circuit 4, to the code division multiple access circuit 6, and to the transceiver 3, as described above. If attempts to acquire all of the preferred systems in the geographic region have failed, then, in the example mode, in block 68, the multiple-subscriber-1 subscriber station is temporarily turned off to save battery power, and then start the process of selecting the preferred system again at a later time previously determined, in block 20. There are several possible alternative courses of action. A possible alternative is that the multi-mode subscriber station 1 simply shuts down. A second possible alternative is that the multi-mode subscriber station 1 starts the preferred system selection process again immediately. A third possible alternative is that the multiple mode subscriber station 1 indicate the failure and wait for the user's intervention. In an alternative modality, upon successful acquisition in block 48, the system determination processor 8 determines whether the system is preferred. If it is a preferred system, then the multi-mode subscriber station 1 immediately provides the service, using the acquired system, and intermittently re-enters the system determination sub-state, to verify if a further system can be acquired. desirable in the region. In an alternative embodiment, a central communication station may assist the multiple mode subscriber station 1, transmitting an indication of the geographical region in addition to its system identification. This would make it possible for a subscriber station to immediately move to the system section within the geographic region by acquiring a system that provides this information. The above description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Those skilled in the art will be able to see different modifications to these modalities easily, and the generic principles defined herein may be applied to other modalities without the use of the inventive faculty. Accordingly, the present invention is not intended to be limited to the embodiments shown herein, but should receive the broadest scope consistent with the principles and novel features disclosed herein.

Claims (4)

NOVELTY OF THE INVENTION Having described the above invention, it is considered as a novelty, and therefore, the content of the following is claimed as property: CLAIMS

1. A method for acquiring a system in a subscriber station, which comprises the steps of: transmitting an acquisition signal according to a geographical hypothesis; receive a system identification from a central communication station; determine the geographical region based on the identification of the received system; and perform the acquisition of the system according to the geographical region.

2. The method according to claim 1, characterized in that the step of transmitting an acquisition signal is carried out according to the most recently used systems.

3. The method according to claim 1, characterized in that, in addition, the step of transmitting an acquisition signal is carried out in accordance with the generality of the acquisition parameters.

4. The method according to claim 1, characterized in that in addition the step of transmitting an acquisition signal is carried out in accordance with the remaining preferred systems.