Abstract:
A communication device locates a preferable wireless service provider in a multi-service provider environment using a frequency or frequency band search schedule. Initially, the communication device registers with a less preferred service provider in a first frequency. While remaining registered with the less preferred service provider, the device examines several frequencies in the order specified by the frequency search schedule. The device determines whether the last frequency used by the communication device has a more preferred service provider. If the last frequency used does not have a more preferred service provider, the device examines each of the plurality of frequencies in the predetermined order in the search schedule. The examination continues until another frequency band having a more preferred service provider is located. The communication device then registers with the more preferred service provider.

Description:
CROSS REFERENCE TO RELATED INVENTION 
     This application is related to commonly assigned and concurrently filed US patent application entitled “A Method For Selecting A Wireless Communications Service Provider In A Multi-Service Provider Environment”, Ser. No. 08/969,710. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to communications; more specifically, communications in a multi-service provider environment. 
     2. Description of the Related Art 
       FIG. 1  illustrates a portion of the radio frequency spectrum. Frequency range  10  centered around 800 MHz has historically been known as the cellular frequency range and frequency range  12  centered about 1900 MHz is a newer defined frequency range associated with personal communication services (PCS). Each range of frequencies, i.e., the cellular and PCS, are broken into two portions. In cellular frequency range  10 , there is uplink portion  14  which is used for communications from a mobile communication device to a base station such as a cellular base station. Portion  16  of cellular frequency range  10  is used for downlink communications, that is, communications from a cellular base station to a mobile communication device. In a similar fashion, Portion  18  of PCS frequency range  12  is used for uplink communications, that is, communications from a mobile communication device to a base station. Portion  20  of PCS frequency range  12  is used for downlink communications, i.e., communications from a base station to a mobile communication device. 
     Each of the frequency ranges are broken into bands which are typically associated with different service providers. In the case of cellular frequency range  10 , frequency bands  30  and  32  are designated band “a” for uplink and downlink communications, respectively. In a particular geographic area, a cellular service provider is assigned frequency band “a” in order to carry out mobile communications. Likewise, in the same geographic area another cellular service provider is assigned frequency bands  34  (uplink) and  36  (downlink) which are designated band “b”. The frequency spectrums assigned to the service providers are separated so as to not interfere with each other&#39;s communications and thereby enable two separate service providers to provide service in the same geographic area. Recently, the US Government auctioned the PCS frequency spectrum to service providers. As with the cellular frequency range, the PCS frequency range is broken into several bands where a different service provider may use a particular frequency band for which it is licensed within a particular geographical area. The PCS bands are referred to as A, B, C, D, E and F. The A band includes uplink band  50  and downlink band  52 . The B band includes uplink band  54  and downlink band  56 . Band C includes uplink band  58  and downlink band  60 . Each uplink and downlink band of the A, B and C bands are approximately 30 MHz wide. The D band includes uplink band  62  and downlink band  64 . The E band includes uplink band  66  and downlink band  68 . Likewise, band F includes uplink band  70  and downlink band  72 . The uplink and downlink bands of bands D, E and F are approximately 10 MHz wide each. It should be noted that with the cellular and PCS frequency bands, it is possible to have as many as eight different wireless communication service providers in a particular area. 
     Each of the different cellular and PCS bands consist of control channels and communication channels in both the uplink and downlink direction. In the case of analog cellular bands, there are 21 control channels for both the “a” and “b” bands. Each of the control channels include an uplink and a downlink portion. The control channels transmit information such as an SOC (System Operator Code), an SID (System Identifier Code), paging information call setup information and other overhead information such as information relating to registering with the mobile communication system. The portion of the cellular band&#39;s spectrum not occupied by the control channels is used for communication channels. Communication channels carry voice or data communications, where each channel consists of an uplink and downlink communications link. Presently there are several cellular communication standards. An analog standard known as EIA/TIA 553 was built upon the AMPS (Advanced Mobile Phone Service) standard. This standard supports  21  analog control channels (ACC) and several hundred analog voice or traffic channels (AVC). A newer standard is the EIA/TIA IS54B standard which supports dual mode operation. Dual mode operation refers to having an analog control channel, and either an analog voice/traffic channel or a digital traffic channel (DTC). The AVC or DTC are used for actual communications, and the ACC is used to transfer information relating to, for example, call set-ups, service provider identification, and the other overhead or system information. 
     A newer standard, the EIA/TIA IS136 standard supports communications covered by both analog and dual mode cellular, and also includes a totally digital communication scheme which was designed for the PCS frequency bands A-F and cellular frequency bands “a” and “b”. This standard allows for a digital traffic channel (OTC) and a digital control channel (DCCH). In the case of the DTC, not only is the voice or data communicated, but in addition, a digital channel locator (DL) is transmitted in the DTC. The DL enables a mobile communication device that locks onto the DTC to use the information in the DL to locate a DCCH for purposes of obtaining information such as the SOC, SID, paging information, and other system overhead information carried on the digital control channel. 
     When a mobile communication device such as a mobile telephone attempts to register with the service provider, it locks onto a control channel and reads information such as the SOC and SID. If the SOC and/or SID correspond to a service provider with which the user has a communication services agreement, the telephone may register with the service provider&#39;s mobile communication system via the up-link control channel. 
       FIG. 2  illustrates a map of the United States illustrating cities such as Seattle, Chicago and Washington, D.C. For example, in Seattle frequency band A has been licensed to SOC (Service Operator Code) 001 with a SID of 43 and band C has been licensed to SOC 003 with a SID of 37. In Chicago, suppose that frequency band C has been licensed to SOC 001 with a SID equal to 57, and that band B has been licensed to SOC 003 with a SID of 51. In Washington, D.C. suppose that frequency band “a” has been licensed to a SOC 001 with a SID of 21, and that band A has been licensed to SOC 003 with a SID of 17. It should be noted that the same SOC may be found in several different locations although on different frequency bands. It should also be noted that the same SOC will be associated with different SIDs in each geographical area and that in the same geographic area different service providers have different SIDs. If a particular subscriber to a wireless telecommunication service has an agreement with a service provider having a SOC of 001, that subscriber would prefer to use systems with a SOC of 001 because the subscriber is likely to receive a less expensive rate. When the subscriber is in Seattle he/she would prefer to be on band A, and if in Chicago on band C, and if in Washington, D.C. on band “a”. The above described situation presents a problem for a wireless communication service subscriber. As a subscriber moves from one area of the country to another, the telephone when turned on, searches for the “home” service provider, or the service provider with which the subscriber has a prearranged agreement. If for example, the subscriber travels from Seattle to Chicago, when turning the phone on in Chicago, the phone will search through the different bands of the spectrum to identify the service operator with the code 001 in order to find the desired service provider. 
     In order to find a particular service provider, the phone may have to search through both the “a” and “b” cellular bands, and through the eight PCS bands. It should be recalled that there are up to 21 different ACCs in each of the “a” and “b” cellular bands. It may be necessary to check 42 ACCS in order to find an ACC from which a SOC or SID may be obtained. Additionally, searching for a particular SOC or SID in PCS bands A through F is particularly time consuming. The digital control channels (DCCHs), which contain the SOC and SID, are not assigned to specific frequencies within a particular PCS band. As a result, the mobile communication device may find it necessary to search through the spectrum of each PCS band looking for a DCCH, or an active DTC that has a digital channel locator (DL) which will direct the mobile communication device to the DCCH. As illustrated above, the process of searching for a particular service provider is laborious and may require a period of time on the order of several minutes. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides a method for locating a particular or desirable communications service provider in an environment having a plurality of service providers. After power-up, a mobile communications device such as a cellular telephone, checks the most recently used control channel to determine whether an optimal service provider is available on that channel. If an optimal service provider is not available or if that channel is not available, the mobile communication device performs a search through frequency spectrum in a pre-determined order until an optimal or acceptable service provider is located. 
     In another embodiment of the invention, the frequency spectrum is searched in a pre-determined order that changes based on information entered by a mobile communication device distributor or mobile communication device user. In yet another embodiment of the invention, the pre-determined order for searching the spectrum for service providers is updated by over the air programming. In still another embodiment of the present invention, the pre-determined order for searching is based on the mobile communication device&#39;s operational history. 
     In yet another embodiment of the invention, the communications device registers with a less preferred service provider in a first frequency band. While remaining registered with the less preferred service provider, the device examines several frequency bands in the order specified by the frequency band search schedule. A frequency band is examined by dividing the frequency band into many sub-bands, and by locating the strongest signal above a threshold within the sub-band being examined. The examination continues until a second frequency band having a more preferred service provider is located. The communication device then registers with the more preferred service provider. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the frequency spectrum used for wireless communications; 
         FIG. 2  illustrates service areas within the United States; 
         FIG. 3  is a block diagram of a mobile communication device; 
         FIG. 4  is a flow chart illustrating a spectrum searching routine; 
         FIG. 5  is a flow chart illustrating the global spectrum search routine; 
         FIG. 6  is a flow chart illustrating a periodic search routine; 
         FIG. 7  is a flow chart illustrating a received signal strength search routine; 
         FIG. 8  illustrates a search schedule; and 
         FIG. 9  illustrates a prioritized list of service providers. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  illustrates a block diagram of a mobile communication device such as a cellular telephone or personal communication device. Mobile communication device  10  includes transceiver  12  which sends and receives signals from antenna  14 . Mobile communication device  10  is controlled by control system  14  which may include a microprocessor or a microcomputer. Control system  14  uses memory  16  for storing programs that are executed and for storing information that is entered by the user, the distributor, the communication services provider or the manufacturer. Information such as user preferences, user telephone numbers, preferred service provider lists and frequency search schedules are stored in memory  16 . Memory  16  may include storage devices such as random access memory (RAM), read only memory (ROM) and/or programmable read only memory (PROM). A user communicates with control system  14  via keypad  18 . Control system  14  communicates information to the user via display  20 . Display  20  may be used to display information such as status information and items such as telephone numbers entered via keypad  18 . Sound information to be transmitted from the mobile communication device  10  is received via microphone  22 , and sound communications received by mobile communication device  10  are played to the user via speaker  24 . 
     After initially powering-up, a mobile communication device locates a service provider and registers with the service provider. Recalling  FIG. 1 , service providers are located at a plurality of frequency bands across the radio spectrum. In order to find a service provider, the communication device searches the spectrum to find service providers. The communications device examines received service provider code e.g., SOCs (Service Operator Code) or SIDs (System Identification Code) to determine whether the service provider is an optimal, preferred or prohibited service provider. 
       FIG. 4  illustrates a process or program that control system  14  executes in order to find a desirable service provider. After power-up, step  30  is executed to initialize a non-optimal flag by clearing the flag. Step  32  determines whether the last service provider, that is, the service provider used before powered down, was an optimal service provider. This is determined by checking the SOC or SID of the last service provider and determining whether that service provider&#39;s SOC or SID corresponds to the SOC or SID of an optimal service provider. The SOC or SID of the last service provider and a list of optimal and preferred service providers is stored in memory  16 . If in step  32  it is determined that the prior service provider was not optimal, a global spectrum search is executed. If the last service provider was optimal, step  34  is executed where system  14  attempts to lock onto the control signal of the service provider. If the lock is unsuccessful, which may indicate that that control channel is no longer available or out of range, the global spectrum search is executed. If a lock is successful, step  36  is executed. In step  36 , it is determined whether the control channel contains the SOC or SID of an optimal service provider. Once again, this is determined by comparing the SOC or SID from the control signal with a list of optimal service provider SOCs or SIDs. If the SOC or SID does not belong to that of an optimal service provider, the global spectrum search  33  is executed and the identity of the frequency band in which the non-optimal SOC or SID was located is passed to global search routine  33  so as to avoid unnecessarily searching this portion of the spectrum again. If in step  36  it is determined that an optimal service provider has been located, step  38  registers communication device  10  with the service provider. Step  40  is an idle state where control system  14  simply monitors the control channel of the service provider for communication system overhead information and for paging information that may indicate an incoming communication. While in idle state  40 , a timer is activated which permits a low-duty cycle search to be performed if the phone is presently registered in a non-optimal service provider system. This situation may arise if global spectrum search  33  provides a preferred but not optimal service provider. Periodically, such as every 5 minutes, step  42  is executed to determine whether the non-optimal flag has been set, if the non-optimal flag is not set, control system  14  returns to idle step  40 . If the non-optimal has been set, step  42  leads to the execution of periodic search routine  44  where a search is conducted in order to attempt to locate an optimal service provider. If periodic search routine  44  produces an optimal service provider, the non-optimal service provider flag is cleared and the mobile communication device registers with the optimal service providers while executing periodic search routine  44 . The mobile communications device then enters an idle state by executing step  40 . If an optimal service provider is not located in routine  44 , control system  14  returns to an idle state by executing step  40 . 
       FIG. 5  illustrates a flowchart of global spectrum search routine  33  which is executed by control system  14 . At step  60  it is determined whether the last control channel used by the mobile communication device was a personal communication services related control channel, that is, a control channel in the bands A through F. If the last control channel was not a PCS control channel, step  62  is executed. In step  62  it is determined whether the mobile communication device can lock onto, or receive and decode the last ACC (Analog Control Channel) that was used. If the mobile communication device can successfully lock onto the last ACC, step  64  is executed. If the communication device cannot lock onto the last ACC, step  66  is executed. In step  66 , an RSS (Received Signal Strength Scan) is performed. This step involves the mobile communication device tuning to each of the 21 ACCs associated with the cellular band of the last used ACC, and attempting to lock onto the strongest received signal. In step  68 , it is determined whether a lock has been achieved. In step  68  if a lock is not obtained, a predetermined search schedule is executed in order to find a service provider, if in step  72  a lock is obtained, step  64  is executed where the SOC or SID obtained from the control channel is compared to a list of optimal SOCs or SIDs. In step  70  if the received SOC or SID is associated with an optimal service provider, step  72  is executed where the mobile communication device clears the non-optimal flags, registers with the communication service provider, and then enters an idle state by executing step  40  of  FIG. 4 . If, in step  70  it is determined that an optimal service provider SOC or SID was not received, step  74  is executed where the identity of the frequency band just searched is stored in memory  16 . Step  78  is executed after step  74 , after  68  if a lock is not obtained, or after step  60  if the last control signal was from a PCS frequency band. In step  78 , a search schedule is downloaded using a master search schedule. When downloading the search schedule in step  80 , frequency bands previously searched are removed from the downloaded schedule so as to avoid searching bands that have already been searched. For example, bands searched in the search routine discussed with regard to  FIG. 4  and the cellular band search discussed with regard to step  74  are removed from the search schedule. After the modified search schedule has been loaded, a search pointer is initialized to point to the first band identified by the modified search schedule. The first band identified on the modified schedule is searched with regard to received signal strength (RSS) in step  79 &#39;s RSS routine. In the case of bands “a” and “b”, the ACC with the strongest signal is selected. In the case of the PCS bands, that is the bands A through F, 2.5 MHz sections of each band are searched in 30 kilohertz steps. The mobile communication device tunes to the strongest signal that crosses a minimum threshold, e.g., −110 dBm, within the 2.5 MHz band being examined. In step  80  it is determined whether the signal is valid, that is, conforms to one of the above mentioned standards. If it is not valid, the search pointer is incremented in step  96 , and if the signal is valid, step  82  is executed. In step  82  it is determined whether the signal is an ACC. If the signal is an ACC, the SOC or SID is decoded in step  90 . If the signal is not an ACC, step  84  determines whether the received signal is a digital traffic channel (DTC) or a digital control channel (DCCH). If the signal is an DCCH the SOC or SID is extracted in step  90 . If it is determined that the received signal is a DTC, step  86  is executed where the DL (digital channel locator) is extracted to identify the location of the DCCHs associated with the DTC that has been received. In step  88 , the mobile communication device tunes to the strongest DCCH of the digital control channels identified by the DL. In step  90 , the SOC or SID of the received DCCH is extracted and in step  91 , it is determined whether the SOC or SID is associated with an optimal service provider. If the SOC or SID is associated with an optimal service provider, step  92  clears the non-optimal flag and step  96  registers the mobile communication device with the service provider. After step  96 , the communication device enters the idle state in step  40  of  FIG. 4 . If in step  92  it is determined that the SOC or SID does not belong to that of an optimal service provider, step  94  is executed where the SOC or SID is stored in memory  16  indicating whether the SOC or SID was at least a preferred rather than an undesirable or prohibited service provider with the spectral location of the SOC&#39;s or SID&#39;s control channel. In step  96  the search pointer that identifies the band being searched is advanced to identify the next band in the schedule for searching. In step  98  it is determined whether the pointer has reached the end of the search schedule. If the end of the search schedule has not been reached, step  82  is executed to perform another received signal strength search routine as discussed above, and if the last frequency band has been searched, step  100  is executed. In step  100  the mobile communication device registers with the best stored SOC or SID, that is, an SOC or SID that has at least been associated with a preferred service provider. The best service provider can be identified by comparing the stored SOCs or SIDs with a list of preferred SOCs or SIDs. The list of preferred SOCs or SIDs can include the optimal SOC(s) or SID(s) and a prioritized list of preferred SOCs or SIDs where the higher priority will get preference for registration. The listing also includes undesirable or prohibited SOC(s) or SID(s) that are used only in emergencies (e.g., 911 calls) or if the user enters an override command. After registering with the service provider in step  100 , step  102  is executed to set the non-optimal flag, and then step  40  of  FIG. 4  is executed where the mobile communication device enters the idle state. 
     It should be noted that the searching operation of  FIGS. 4 and 5  may be carried out in a simplified manner. With regard to  FIG. 4 , control system  14  may execute step  33  after step  30  while always skipping steps  32 ,  34 ,  36  and  38 . With regard to  FIG. 5 , control system  14  may start the global spectrum search with step  78  while always skipping steps  60 - 74 . 
       FIG. 6  illustrates a flowchart for the periodic search routine executed by control system  14 . In step  120  it is determined whether the periodic search flag has been set. If the periodic search flag has not been set, step  122  is executed where periodic search flag is set and the search schedule is initialized by loading the master search schedule into the search schedule used by the periodic search routine; however, the frequency band currently being received is not included in the search schedule used for the periodic search routine. Step  122  also sets a search pointer to the first band in the search schedule. In step  124  a received signal strength search (RSS) routine is conducted. As in step  79  of the global spectrum search routine of  FIG. 5 , step  124  is a RSS routine of any PCS and cellular bands that are in the search schedule. In the case of a cellular band search, the 21 ACCs are searched using a received signal strength search i.e., the transceiver tunes to the strongest ACC. In the case of a PCS frequency band search, as discussed earlier, each band is broken into segments of approximately 2.5 MHz where a search of each segment is conducted in 30 kilohertz steps. The strongest signal within the 2.5 MHz segment and above a minimum threshold, such as −110 dBm, is selected. In step  126  the selected signal is examined to determine if it is valid by conforming to one of the previously referenced standards. If the signal is invalid, step  144  is executed and if the signal is valid, step  129  is executed. Step  129  determines whether the signal is an ACC. If the signal is an ACC, step  130  is executed when the SOC or SID is extracted and if the signal is not an ACC, step  132  is executed. Step  132  determines whether a DTC signal has been received. If the signal is not a DTC signal (therefore it is a DCCH signal), step  130  is executed to extract the SOC or SID from the DCCH signal. If in step  132  it is determined that a DTC has been received, step  134  is executed to extract the DL to enable tuning to a DCCH. In step  136  a received signal strength search is conducted of the DCCHs where the strongest signal is selected, and then step  130  is executed to extract an SOC or SID from the signal. In step  138  it is determined whether the SOC or SID is an optimal SOC or SID. If the SOC or SID is optimal, step  140  clears the non-optimal flag and in step  142  the mobile communication device registers with the service provider associated with the optimal SOC or SID. Step  40  of  FIG. 4  is then executed to enter the idle state. If in step  138  it is determined that the SOC or SID was not an optimal service provider, step  144  is executed. In step  144  the search pointer is incremented to the next band to be searched. In step  146 , it is determined whether the entire search schedule has been completed. If the schedule has not been completed, step  40  is executed so that the mobile communication device can be returned to the idle state. If in step  146  it is determined that the search schedule has been completed, step  148  clears the periodic search flag and then step  40  is executed so that the mobile communication device can enter the idle state. 
       FIG. 7  illustrates a flow chart of the RSS routine or received signal strength search routine which is carried out, for example, in steps  79  of  FIGS. 5 and 124  of  FIG. 6 . Step  170  determines whether the band being searched is one of the “a” or “b” cellular bands. If a cellular band is being searched, step  172  is executed where the 21 ACCs are searched to determine which is the strongest, the strongest ACC is tuned to by transceiver  12  under the control of control system  14  and then the RSS routine is exited. If in step  170  it is determined that a cellular band is not being searched, step  178  tunes transceiver  12  to the beginning of the first 2.5 MHz band in the PCS band being searched. Step  178  also clears a search scratch pad memory location in memory  16 . The search scratch pad is used to record the amplitude or strength and location of a received signal in step  180  it is determined whether the signal being received is greater than a threshold. If the signal is greater than the threshold, step  182  is executed, if the signal is not greater than the threshold, step  184  is executed. In step  182  it determined whether the received signal strength is greater than the signal strength value stored in the search scratch pad. If the received signal is not greater, then step  184  is executed. If the received signal strength is greater, step  186  is executed and the present signal strength is recorded in the search scratch pad with the received signal&#39;s location in the spectrum. In step  184 , transceiver  12  is tuned to a frequency 30 kilohertz higher than the frequency at which it was tuned. Step  188  determines whether the new frequency extends beyond the 2.5 MHz band currently being searched. If the new frequency does not exceed the 2.5 MHz band, step  180  is executed to once again examine received signal strength relative to the signal strength or amplitude value stored in the search scratch pad. If in step  188  it is determined that the 30 kilohertz increment extends beyond the 2.5 MHz band being examined, step  190  is executed. In step  190 , the transceiver tunes to the signal location specified in the search scratch pad. If the signal is a valid signal and can be decoded, the RSS routine is exited. If the signal is not valid or cannot be decoded, (e.g., the signal does not conform to the above-referenced standards) step  192  is executed. In step  192 , the transceiver is tuned to the beginning of the next 2.5 MHz band within the PCS band being searched. Step  194  determines whether the new 2.5 MHz band extends beyond the PCS band currently being searched. If the new increment extends beyond the PCS band being searched, the periodic search routine is exited. If the 2.5 MHz increase does not result in extending beyond the PCS band being searched, step  196  is executed. In step  196 , the search scratch pad containing signal strength measurements and signal location information is cleared to prepare for searching another band. After step  196 , step  180  is executed as described above. 
       FIG. 8  illustrates a master search schedule. The master schedule is used to initialize search schedules used in the above described search routines. The master search schedule is stored in a memory such as memory  16 . The master search schedule can be initially programmed by the mobile communication device&#39;s manufacturer, distributor or user. It should be noted that the first location in the search schedule is left unprogrammed. If left blank, the blank is ignored when initializing the search schedules for the search routines. It is desirable for the first location to be programmed with the band in which the user&#39;s home service provider resides. For example, if the user has a service agreement with a service provider who is licensed to operate in PCS band B within the SID or geographical area in which the user most frequently is located, band B is programmed into the first slot of the master search schedule. If, for example, band B is programmed in the first slot, the slot originally containing band B is made blank. This avoids searching the same band twice. It should also be noted that the user can vary the master search schedule through keypad  18 . Additionally, the master search schedule may be reprogrammed using signals received over the wireless communication channel. For example, the mobile communication device may be restricted to accepting new programming for the master search schedule only from a service provider transmitting the home SID and an optimal SOC. It is also possible to accept over the air programming if the service provider sends a prearranged code. It is desirable to restrict the over the air programming through the use of codes, home SIDs and/or optimal SOCs to avoid unintentional or undesirable altering of the master search schedule. Over the air programming may be implemented using for example, logical sub-channels of a digital control channel. The logical sub-channels have the capability to transmit data addressed to a particular mobile communication device and to receive data, such as confirmation data, from the mobile communications device. 
     When the search schedules are initialized using the master search schedule, it is also possible to precede the first location in the master search schedule with other frequency bands based on, for example, the prior history of the mobile communication device&#39;s use. For example, the first location searched may be the location where the phone was last turned off (powered down) or the location where the phone was last turned on (powered up). 
       FIG. 9  illustrates a table stored in memory  16  defining the optimal service provider&#39;s SOC and SIDs, and preferred service provider&#39;s SOCs and SIDs. The SOC or SID with the lowest number has the highest priority and is preferred over service providers with higher numbers and therefore a lower priority. For example, an SOC or SID with a priority level  2  would be preferred over an SOC or SID with a priority level of 5. The table may also include SOCs or SIDs that are undesirable or prohibited. In the case of SOCs or SIDs that are prohibited, it is desirable to permit connection to the prohibited SOCs or SIDs when an emergency call, such as a 911 call, is attempted or when the user enters an override command. The table in  FIG. 9  may be programmed by the manufacturer, by the distributor when the phone is purchased or by the user. It is also possible to program the table of  FIG. 9  over the air using restrictions similar to those used when programming the master search schedule over the air.