Abstract:
A mobile station can be used in both public cellular systems and private cellular systems, the private cellular system using select allocated frequency bands from the public cellular systems. There is disclosed herein a system for manually searching for one of the private cellular systems. The system comprises a memory storing information on select frequency bands. A transmitter and receiver is provided for communicating in the public cellular systems and the private cellular systems. An input initiates a manual search for one of the private cellular systems using the stored information on one of the select frequency bands. A programmed processor is operatively coupled to the memory, the transmitter and receiver and the input for operating the transmitter and receiver to search for the one private cellular system using the one of the select frequency bands.

Description:
FIELD OF THE INVENTION 
     This invention relates to autonomous private cellular systems operating in public cellular system frequency bands and, more particularly, to a system and method for manually searching for autonomous private systems. 
     BACKGROUND OF THE INVENTION 
     A wireless communication system, in the form of a cellular system, is designed to cover a large geographic area. The system is divided into numerous cells providing air interface between mobile stations and land-based systems. Each cell includes a base station for communicating with mobile stations. These wireless communication systems maintain a set of frequencies that are used for traffic channels and control channels. Frequency planning is necessary in order to determine which of the frequencies should be used at any given time. 
     Recently, cellular-based system design is used as a foundation for smaller systems, such as private cellular or wireless office systems. These private cellular systems may share the frequency spectrum with the public cellular systems. The private cellular system user must be defined as a normal cellular subscriber in the subscriber database of the public cellular system, and the user&#39;s mobile station must be defined in both the private cellular system and the public cellular system. These are preconditions to enable the mobile station to roam between the public and private cellular system and to perform authentication. It will also be required for the mobile station to find the private cellular system. Use of neighbor cell pointers from the public system to the private system is not desirable, since it will increase the administration of the public system. Instead, a mechanism based on stored information in the terminal is preferred. Such a mechanism is defined in ANSI-136. 
     A frequency re-plan is usually performed to give more capacity or to improve coverage. Since the public cellular systems have a limited spectrum based on the licensed frequency band, capacity is increased by increasing the number of frequencies in each cell site and/or installing more cell sites. Both methods bring new frequencies in use in the area affected. Since frequencies are re-used, other cell sites frequency use is also affected and they may have to re-tune their transceivers to other frequencies to accommodate the first change. This produces a rippling effect. The private cellular systems monitor the public cellular system and avoid frequencies used nearby in the public cellular systems. A change in the public cellular system&#39;s frequency use thus changes the frequency use of the private cellular systems. 
     A mobile station will not automatically find an autonomous private cellular system if a frequency re-plan of the control frequency has taken place in either the private or public cellular systems. Also, the first time a mobile station wants to acquire service from a private cellular system, the appropriate parameters, such as the public service profile/private operating frequency (PSP/POF) parameters in the ANSI 136, Rev. A standard are not defined in the mobile station and it will not automatically find the private cellular system. 
     If the mobile station cannot automatically find the private cellular system, due to, e.g., the stored PSP/POF information is not correct due to a frequency re-plan, then a manual search must be invoked. Presently, the ANSI-136 Rev. A standard outlines a manual search procedure to find a private cellular system. However, the search is limited to the frequency band the mobile station is presently camping on. As a result, autonomous private cellular systems operating on other bands cannot be found. In a publication entitled “Global Operators Forum  Implementation Guide: Non - Public Mode Operation in TIA/EIA -136- A Compliant Mobile Stations ”, Version 4, December 1998, a modified manual search is proposed. In this proposal, the mobile station searches all bands if the private system is not found in the frequency band the mobile station was last camping on. Searching all bands can take more than fifteen minutes, resulting in substantial inconvenience for the end user. A mobile station designed according to ANSI-136 Rev. A can also be configured to find a private cellular system during a power-up scan. However, doing so limits the usage of the intelligent roaming database (IRDB) for public cellular system and provides undesirable behavior, such as long scanning times whenever a power-on is performed in the public cellular system and limited roaming capabilities. 
     The present invention is directed to solving one or more of the problems discussed above in a novel and simple manner. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention there is provided a unique and more robust manually initiated search procedure for private cellular systems in a mobile station, independent of the frequency band the mobile station was last camping on. 
     Broadly, there is disclosed herein in a mobile station for use in both public cellular systems and private cellular systems, the private cellular system using select allocated frequency bands from the public cellular systems, a system for manually searching for one of the private cellular systems. The system comprises a memory storing information on select frequency bands. A transmitter and receiver is provided for communicating in the public cellular systems and the private cellular systems. An input initiates a manual search for one of the private cellular systems using the stored information on one of the select frequency bands. A programmed processor is operatively coupled to the memory, the transmitter and receiver and the input for operating the transmitter and receiver to search for the one private cellular system using the one of the select frequency bands. 
     It is a feature of the invention that the memory stores a directory of the private cellular systems including identification information and a frequency band for each private cellular system. The input selects from the directory of private systems and the programmed processor operates the transmitter and receiver to search for the one of the private cellular systems on the stored frequency band for the selected private cellular system. It is another feature of the invention that the input can be used to update the directory. 
     It is another feature of the invention that the memory stores plural predefined frequency bands. The input selects from the plural predefined frequency bands and the programmed processor operates the transmitter and receiver to search for the one of the private cellular systems on the selected predefined frequency band for one of the private cellular systems. 
     It is another feature of the invention that the programmed processor is operated to initially search using strongest control channels found in the selected predefined frequency band. 
     There is disclosed in accordance with another aspect of the invention the method of operating a mobile station used in both public cellular systems and private cellular systems, the private cellular systems using select allocated frequency bands from the public cellular systems, for manually searching for a private cellular system. The method comprises the steps of storing information on select frequency bands; initiating a manual search for one of the private cellular systems using the stored information on one of the select frequency bands; and operating a transmitter and receiver communicating in the public cellular systems and the private cellular systems to search for the one private cellular system using the one of the select frequency bands. 
     Further features and advantages of the invention will be readily apparent from the specification and from the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a generalized block diagram illustrating a mobile station communicating in both a public cellular system and a private cellular system; 
     FIG. 2 is a block diagram of the mobile station of FIG. 1; 
     FIG. 3 is a flow diagram illustrating a manually initiated search procedure in accordance with one aspect of the invention; 
     FIG. 4 is a flow diagram illustrating operation of a manually initiated search procedure in accordance with another aspect of the invention; and 
     FIG. 5 is a flow diagram illustrating updating of private cellular system information in a mobile station in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to FIG. 1, a telephone communication system  10  is generally illustrated. The communication system  10  consists generally of the public switched telephone network (PSTN)  12  shown connected to a private business premises  14  and the public land mobile network  16 . The business premises  14  includes a private branch exchange (PBX)  18  for communicating with the PSTN  12  in the conventional manner. A digital wireless office system (DWOS)  20  is a fully digital mobile communication system that provides a mobile extension to the PBX  18 . The DWOS  20  allows use of digital cellular phones based on cellular or PCS standard within an office environment. It operates on either one of the cellular bands (850 MHz) or one of the personal communication services (PCS) bands (1900 MHz). 
     While the ANSI-136 standard is used as an exemplary embodiment in this application, the invention as described herein is applicable to all cellular standards where support for autonomous private cellular systems is provided. 
     The DWOS  20  is a private cellular system that coexists with a public cellular system  26  in the PLMN  16  and uses the frequencies that are licensed to the operator of the particular network. The DWOS  20  automatically finds usable frequencies. 
     A digital wireless office system mobile station  22  is adapted for communication both with the DWOS  20  and the public cellular system  26 . The mobile station  22  must be defined in both the DWOS  20  and the public cellular system  26 . The DWOS  20  interacts with a home location register (HLR)  24  using the ANSI- 41  protocol. A WOS SS 7  gateway (WGW)  28  is used for interworking between SS 7  and TCP/IP if TCP/IP is not used by the HLR  24  for communicating via an SS 7  network  30 . Other elements of the PLMN  16  connected to the SS 7  network are a conventional mobile switching center (MSC)  32  which is connected to the PSTN  12 , and a message center  34 . The MSC  32  is in turn connected to a base station  36  that communicates with the mobile station  22  in the conventional manner for public cellular systems. 
     The DWOS mobile station  22  is reached either through its PLMN telephone number or a DWOS user number. The general communication principles involving the mobile station  22  and the DWOS  20  and PLMN  16  are known and are not specifically described herein. The present invention relates particularly to the system and method for conducting a robust manual search for an autonomous private cellular system, such as the DWOS  20 . Such a search might be necessary if a frequency re-plan of control frequencies has taken place in either the private or public cellular systems, or the first time the mobile station  22  wants to acquire service from the DWOS  20 . This search is independent of the system the mobile station  22  was last camping on. 
     Referring to FIG. 2, the mobile station  22  is illustrated in block diagram form. The mobile station  22  includes an antenna  40  for sending and receiving radio signals between itself and the communication system  10  see FIG.  1 . The antenna is connected to a transmitter receiver  42  to broadcast and receive on the same antenna  40 . particularly the transmitter/receiver  42  includes a receiver that demodulates. demultiplexes, and decodes the radio signals into one or more channels. Such channels include a control channel and a traffic channel for speech or data. The speech or data are delivered to an output device of an input-output circuit  44 , such as speaker. The receiver delivers messages from the control channel to a processor  46 . The processor  46  controls and coordinates the functioning of the mobile station  22  responsive to messages on the control channel using programs and data stored in a memory  48 , so that the mobile station  22  can operate within the wireless network. The processor  46  also controls the operation of the mobile station  22  responsive to input from the input-output circuit  44 . This input may utilize a keypad or the like as a user-input device and a display to give the user information, as is well known. The transmitter/receiver  42  also includes a transmitter that converts analog electrical signals into digital data, encodes the data with error detection and correction information and multiplexes this data with control messages from the processor  46 . This combined data is modulated and broadcast via radio signal through the antenna  40 , as is conventional. 
     The memory  48 , in accordance with the invention, stores a record or directory of private cellular systems. This directory includes an alphanumeric system name, system identity, such as PSID and SID in the ANSI-136 standard, and frequency band and hyperband for each such private cellular system. This record could be an extension of the record in IS-136 mobile stations used for automatic searching. The end user is able to edit the information in the record and to add information regarding new private systems using the input-output circuit  44 , see FIG.  2 . 
     With reference to FIG. 3, a flow diagram illustrates a program for implementing a system name initiated manual search in accordance with the invention. At a block  50 , the mobile station  22  is on. However, the mobile station need not be camping on any particular cellular system. If the user wishes to initiate a manual system name search, then the user enters the directory or record of private cellular systems via an appropriate menu at a block  52 . A decision block  54  determines whether the user has requested to perform a manual search for a private cellular system or to edit the record. If the user selects the edit function, then at a block  56  the user edits the record of private systems. For each existing or new private system, the user must enter an alphanumeric name, the PSID, SID, and frequency band. The control then returns to the block  50 . 
     If the user wishes to conduct a manual search from the block  54 , then at a block  58  the mobile station lists the available private cellular system names. A decision block  60  waits for the user to select one of the private cellular system names and then advances to a block  62 . The mobile station  22  uses the stored information for the selected private cellular system to attempt to obtain service via the transmitter-receiver  42 , see FIG. 2, on the selected system. If the mobile station  22  finds the private cellular system, then it starts camping on that private cellular system. Otherwise, the program returns to the start node. 
     In addition to the system name initiated manual search, the mobile station  22  in accordance with the invention utilizes a band initiated search. This search is illustrated in the flow diagram of FIG.  4 . From a start node, a user selects a band initiated search via a menu at a block  70 . With the band initiated search, the end user specifies the band to search by choosing one band from a set of predefined bands, such as a, b, A, B, C, D, E, F in IS-136. A decision block  72  displays the available bands. The user then selects from these bands and at a block  74  the mobile station  22  searches all frequencies where a system can be found within the specified band. Conventionally, the mobile station  22  searches the whole band. The procedure can be accelerated by looking only at the two strongest control channels found in a sub-band. The mobile station then evaluates the rest of the band if a private cellular system is not found by the accelerated procedures. Two types of searches may be implemented using the band initiated search procedure. The first is a search for a private system identified by its PSID and SID and/or SOC. The second is a search for new private systems that accept a test registration in ANSI-136. If a band initiated search is initiated, or if no PSID, SID or SOC is defined for a system name initiated search, then a search procedure for new private systems is used. 
     Referring to FIG. 5, a flow diagram illustrates a procedure for updating a private cellular system record at registration. This update procedure begins at a block  80  when the mobile station  22  has successfully registered on a private cellular system. This may be done, for example, after a new system search, and if the PSID is not in the phone&#39;s private cellular system record. Particularly, a decision block  82  determines if the PSID is in the record. If so, then the routine ends. If not, then at a decision block  84  the phone asks the user if the private cellular system should be stored in the record. If not, then the routine ends. If so, then the record is updated at a block  86  by storing the alphanumeric name, PSID, SID and frequency band in the private system record. This routine then ends. 
     Thus, in accordance with the invention, the memory  48  stores information on both the select frequency bands available in the system and the record of private systems. This information can be used to manually search for a private cellular system using a system name initiated search, as illustrated relative to FIG. 3, or a frequency band initiated search, as illustrated in FIG.  4 .