MXPA00012126A - Methods for reducing channel acquisition times in a radiotelephone communications system and related mobile terminals - Google Patents

Abstract

A method of acquiring communications with a communications system having a plurality of communications channels includes storing a previously acquired communications channel in user terminal memory. The user terminal searches for the previously acquired communications channel in said user terminal memory, and acquires the previously acquired communications channel when the previously acquired communications channel is available. Channel acquisition times can thus be reduced.

Description

METHOD TO REDUCE CHANNEL ACQUISITION TIMES IN A RADIO TELEPHONE AND TERMINAL COMMUNICATIONS SYSTEM RELATED MOBILES Field of the Invention The present invention relates to the field of communications and more particularly to radiotelephone communications. BACKGROUND OF THE INVENTION Cellular communication systems are commonly employed to provide voice and data communications to a plurality of mobile units or subscribers. Analogue cellular systems such as AMPS designated ETACS, NMT450 and NMT-900, have been used successfully throughout the world. Digital cellular systems such as IS-136 designated in the U.S., and the pan-European GSM system have also been introduced. These systems and others are described, for example, in the book titled "Cellular Radio Systems" by Balston et al., Published by Artech House, Norwood, MA. , 1993. As illustrated in Figure 1, a cellular communication system 20, as in the prior art, includes one or more mobile stations or units 21, one or more base stations 23 and a mobile telephone exchange (MTSO).

= Mobile Telephone Switching Office) 25. Although only three cells 36 are illustrated in Figure 1, a typical cellular network may comprise hundreds of base stations, thousands of mobile stations and more than one MTSO. Each cell 5 will be assigned one or more dedicated control channels and one or more voice channels. A typical cell can have, for example, a control channel and 21 voice / data or traffic channels. The control channel is a dedicated channel that is used to transmit cell identification and JIJ 10 radiolocation information. Traffic channels carry voice and data information. The MTSO 25 is the central coordinating element of the total cellular network 20. Typically it includes a cellular processor 28, a cellular switch 29 and also provides the public switched telephone network (PSTN = Public Switched Telephone Network) 30 with the interface. Through the cellular network 20, a duplex radio communication link 32 can be made between two mobile stations 21 or between a mobile station 21 and a telephony user of landline 33. The function of the base station 23 is commonly handling the radio communication with the mobile station 21. In this capacity, the base station 23 functions primarily as a relay station for data and voice signals. The base station 23 also 25 monitors the quality of the link 32 and verifies the intensity signal received from the mobile station 21. Frequency reuse (multiple access with frequency division or FDMA), is commonly used in cellular technology, where frequency groups are assigned to be used in cells that define regions of limited geographical coverage. Cells that contain equivalent groups of frequencies, are geographically separated to allow mobile units in different cells to simultaneously use the same frequency without interfering with each other. By doing so, many thousands of subscribers can be served by a system of only several hundred frequencies. In the US, for example, federal authorities have assigned to cellular communications a block of the UHF frequency spectrum, subdivided further into pairs of narrow frequency bands called channels. The channel pair formation results from the duplex frequency arrangement where the transmission and reception frequencies in each pair are displaced by 45 MHz. Currently, there are 832, 30 KHz radio channels assigned to cellular mobile communications in the USA To meet the capacity limitations of this analog system, a standard transmission standard designated IS-136 has been provided, where these Frequency channels are further subdivided into time slots. The division of a frequency into a plurality of timeslots where a channel is defined by a frequency and a time slot, it is known as Multiple Access with Time Division (TDMA). Accordingly, multiple channels can be defined on a single frequency. More recently, multiple access rules with code division (CDMA = Code Division Multiple Access) have been developed in which a communication channel is defined by a carrier frequency and a pseudo-interference (PN) sequence. Accordingly, multiple communication channels can be provided on a common carrier frequency at the same time, wherein each channel on the carrier frequency has a different PN sequence. For example, a CDMA standard for a cellular radiotelephone system is provided by the Digital Cellular Multiple Access Standard with North American Code Division (CDMA) (IS-95). In any of the cellular radiotelephone systems and / or standards discussed above, it may first be necessary for a user terminal such as a radiotelephone to acquire a channel before communications services can be provided by the cellular radiotelephone system. The acquisition of a channel can require the user terminal to explore a plurality of. channels, to find a channel that can be used.

• This scan may result in a delay before communications services are provided. This delay 5 may be especially significant in a CDMA radiotelephone system where scanning through a channel requires first scanning an available carrier frequency and then scanning an available PN sequence within the carrier frequency. • 10 In a CDMA radiotelephone system (IS-95) for example, each channel on a carrier frequency is coded with a PN sequence that has a length of 32768 bits. Each of the base stations within a system can use the same carrier frequency and the same sequence PN displaced by an integer multiple of 64 bits and this displacement is known as a PN sequence offset. The combination of the carrier frequency, the PN sequence and the PN sequence offset uniquely identify the cell / base station that is verify. When attempting to acquire a CDMA channel, the user terminal may first scan a specified list of carrier frequencies in the order specified by section 6.1.1.1 of the specification.

IS-95 shown below in Table 1.

Table 1 • • 10 When finding a carrier frequency, the user terminal then looks for one of 512 PN sequences possible on that carrier frequency. If a valid PN frequency is not found on the carrier frequency, the user terminal then scans to find a next carrier frequency that is then searched for a PN sequence. This process can continue through the entire spectrum of carrier frequencies and PN sequences until an available channel is found. Obtaining a channel in a CDMA system, in this way can consume an excessive amount of time due to the need for adjust to new carrier frequencies and look for PN space for each carrier frequency. m The US patent. No. 5,640,675 granted to Pinault et al, entitled "Method and System 5 For Reducing The Time for Connecting to Mobile to a Cellular Base Station" (Method and System for Reducing the Time to Connect a Mobile to a Cellular Base Station) discusses a mobile that measures a first reception level for each control frequency defined in a network and compares ^ P 10 first and second reception levels for each of the control frequencies of the second list to estimate the movement of the mobile. International publication No. WO 88/10617"Methods and Apparatus for Performing Automatic Mode Selection in A Multimode Mobile Terminal" (Methods and 15 Apparatus for Performing Automatic Mode Selection in a Multi-Mode Mobile Terminal) discusses a wireless user terminal that it includes a multi-mode controller capable of bi-directional exchange of control messages and status messages to automatically switch the status of the terminal bidirectionally between primary and secondary systems. Accordingly, there continues to be a need in the art for improved methods for searching and acquiring communication channels. 25 Compendium of the Invention Therefore, an object of the present invention is to provide improved radiotelephone communication methods and terminals. Another objective of the present invention is to provide improved methods for scanning an available channel and related terminals. Still another objective of the present invention is to provide methods that reduce the time to scan an available channel and related terminals. These and other objects are provided in accordance with the present invention, when a plurality of previously acquired communication channels are stored in the user terminal memory, searching for an available one of the previously acquired communication channels in the user terminal memory and acquiring one of previously acquired communications channels when the previously acquired communications channel is available. Because radiotelephone terminals are often used at a relatively high frequency within a relatively small number of service areas (cells), the communication channels associated with those cells most frequently used, may have the highest probability of being available for use. In other words, the user terminal first You can search for channels that are more likely to be found before conducting an exhaustive search of all possible channels, thereby reducing the time required to acquire a channel by a significant number of communications. If the previously acquired channel is not available, the user terminal can search for a list of specified channels with little added delay. In addition, the user terminal may store a plurality of previously acquired communication channels i 10 in memory, such that the search stage comprises searching the previously acquired communication channels. In addition, the user terminal can store an access account for each of the channels of previously acquired communications, where the access account identifies a number of times that the respective communication channel has been acquired by the terminal of _ user. The search stage in this manner includes sequential search of the previously acquired communication channels 20 in order of a higher access account. In other words, those channels with the highest access accounts are considered to have the highest probability of being acquired, and these channels in this way are searched first. 25 The user terminal can identify in the alternates a last acquired from the previously acquired communication channels, and then first search for the last acquired communications channel. Here, it is considered that the last channel acquired is the most likely channel to acquire. In addition, the last purchased channel can be searched first followed by a channel search in order of access account as discussed above. The previously acquired channels can also be classified by geographic search identifier, so that previously acquired communication channels that have a common geographic search identifier can be searched. The methods and terminals of the present invention can be advantageously employed in a CDMA communication system, whe an exhaustive search of CDMA channels by carrier frequency and PN sequence can be time consuming. Accordingly, each of the previously acquired communication channels can be a CDMA channel, such that the user terminal stores a carrier frequency and the PN sequence for each of the previously acquired communication channels. The user terminal may also store a base station identification and a base station location for each of the previously acquired communication channels. According to this, the terminal The user can have multiple inputs of previously acquired channels with the same carrier frequency and PN sequence, but with different base station locations. In other words, the user terminal can distinguish different CDMA channels having the same carrier frequency and PN sequence by the locations of the transmitting base stations. The methods of the present invention can also be applied to dual use terminals adapted for communication with both CDMA and non-CDMA communication systems. In particular, the user terminal looks for non-CDMA communication channels when CDMA communication channels are not available. The terminal may preferably provide CDMA communications when a CDMA channel is available and provides non-CDMA communications when a CDMA channel is not available. In addition, the dual-use terminal can periodically search for available CDMA communications channel when non-CDMA communications are provided, so that CDMA communications can be provided if a CDMA channel becomes available. In accordance with the methods and terminals of the present invention, the most probable CDMA channels available are searched first, thereby reducing search times. In particular, the search may be assigned priority by the channel or channels most recently acquired, by the channel or channels most frequently acquired and / or by the location of the channel (s) previously acquired. Description of the Drawings Figure 1 is a schematic diagram of a cellular radiotelephone communication system according to the prior art. Figure 2 is a block diagram of a user terminal according to the present invention. Figures 3-7 are flow diagrams illustrating operations of a user terminal according to the present invention. Detailed Description The present invention will now be described more fully below with reference to the accompanying drawings, wherein preferred embodiments of the invention are illustrated. This invention, however, can be incorporated in very different ways and will not be considered as limited to the modalities established herein; on the contrary these modalities are provided in such a way that this description is complete and detailed, and fully transports the scope of the invention to those skilled in the art. Similar numbers refer to elements similar to through it. A block diagram of a user terminal according to the present invention is illustrated in Figure 2. As shown, the user terminal includes a transceiver 41 that transmits and receives communications to and from a radiotelephone communication system. A processor 43 is coupled to the transceiver 41, such that the processor can process communications transmitted and received by the transceiver. A user interface 45 is coupled to the processor 43 and this user interface may include a keypad 45A; a 45B visual display including a liquid crystal display (LCD = Liquid Crystal Display) and / or a light emitting diode (LED = Light Emitting Diode) display; a 45C microphone; and a 45D speaker. In addition, the user terminal can be a radiotelephone, a portable computer, a personal digital assistant or any other electronic device adapted for radiotelephone communications. Accordingly, the user terminal can provide radiotelephone communications with a radiotelephone communication system as will be understood by those skilled in the art. The user terminal may also include a memory 47 coupled with the processor 43 wherein the memory is used in accordance with the present invention to store previously acquired communication channels. In a more particular way, data referring • to each previously acquired communications channel can be stored in the user terminal memory 47, where this data can include a plurality of fields as illustrated below in Table 2. Table 2 • 10 fifteen As illustrated, the carrier frequency and the PN sequence for an acquired CDMA channel can be saved. The user terminal memory can also be used to store the system identification (SID) = System IDentification), the network identification (NID = Network IDentification), longitude / latitude, and neighbor list for the base station / cell that transmits the acquired CDMA channel. In addition, the user terminal memory can be used to store an access account by indicating a number of times that a CDMA channel has been acquired by the terminal from the base station / transmission cell; a flag indicating whether the CDMA channel transmitted by the base station / cell was the last channel acquired by the terminal; a geographic search field that indicates a region within which the base station for the channel is located; and a date on which the CDMA channel transmitted by the base station was last acquired. For a given base station, the length / altitude, the system identification and the network identification should not change often, and these fields can be used to uniquely identify a base station as well as a plurality of sectorized cells that are served by that base station. The carrier frequency and the PN sequence for a CDMA exchange transmitted by a base station can however change as channel assignments for the change of communication system to accept for example offsets in system use, and / or the addition of base stations and cells to the communications system.

In addition, geographically isolated base stations can transmit channels that have the same carrier frequency w? and PN sequence. Accordingly, the user terminal memory may include multiple entries with the same carrier frequency and PN sequence, but each of these inputs should reflect a channel transmitted by different base stations. Even more, a base station can provide service for a single cell or a base station can provide service for a (10) plurality of sectorized cells.Using the information in the user terminal memory, the processor can thus search first for the CDMA channel most likely to be acquired, based on the past use of the user terminal. in particular, the primary processor can search channels CDMAs transmitted by base stations in a given geographical region as indicated by the fields of ^ geographic search; CDMA channels transmitted by base stations that have the highest access accounts; and / or the last CDMA channel purchased as indicated by the last purchased channel flag. In addition, any channel CDMA transmitted by the base station that has not been acquired for a predetermined period of time can be removed from memory, thus freeing space of memory for new channels.

If a previously acquired CDMA channel of the user terminal memory can not be acquired, the processor can then perform an exhaustive search of CDMA channels specified as in the prior art. Alternatively, available communications may be sought by interspersing specified communication channels (such as those listed in Table 1), with preferred communication channels (such as previously acquired communication channels). In addition, if the user terminal is a dual-use terminal that provides communications with both CDMA and non-CDMA communication systems, the processor may attempt to acquire a non-CDMA channel if a CDMA can not be acquired over a period of time. reasonable time. In addition, an interleaved scan can be performed where alternating periods of time of predetermined length are used to search respectively for CDMA and non-CDMA channels. As will be appreciated by those skilled in the art, the above described aspects of the present invention in Figure 2 may be provided by hardware, software or a combination of the foregoing. While the components of the apparatus of the present invention such as the processor, memory, transceiver and user interface have been illustrated in part as discrete elements in the figure, in practice it can be implemented totally or partially by a microcontroller that includes input and output ports and running software code by customized microcircuits (chips) or hybrids, by described components or by a combination of the above. In particular, the memory 47 and the processor 43 can be implemented with an existing memory segment and execution of additional code in an existing processor of the user terminal, respectively. In addition, the means used to search for CDMA channels can be defined as a portion of the processor. Alternatively, the search means may be defined to include portions of the processor, transceiver, memory and / or user interface. Operations of a user terminal according to the present invention are illustrated in the flow diagrams of Figures 3 to 7. In particular, the flow chart of Figure 3 illustrates operations for acquiring a CDMA channel according to the present invention . When the user terminal is turned on, it will attempt to acquire a previously acquired CDMA channel, using the information from the user terminal memory. If a geographic search option is established in block 101, the processor can classify the stored channels according to the geographic search field, so that previously purchased channels transmitted by the Base stations within a predetermined geographic region are searched first in block 103. If a CDMA channel is in block 105, the access account for the CDMA channel is incremented in block 117 and the channel is acquired in the block 119. Otherwise, the search for a CDMA channel may continue. The geographic search option can be adjusted manually by the user, for example when the user travels with the user terminal to an area where the terminal has been used before. Alternatively, the user terminal can set the geographic search option automatically, for example, to search for previously purchased channels in the geographic region where the user terminal was most recently used. The search for previously acquired channels in a predetermined geographical region can be done in sequential order, in order account values of access and / or in order of the most recently acquired channels. If no channel is acquired during the search for previously acquired channels in the predetermined geographic region, the search may continue in block 109 as indicated in Figures 3A-3B. Alternatively, the search can proceed directly to block 109 if the geographic search option is not adjusted in block 101. In addition, the geographic information regarding the channel Acquired can be used to classify telephone numbers in a requested user terminal directory using that channel. Accordingly, the directory of telephone numbers can be classified alphabetically and / or geographically. In block 109, the processor identifies the last purchased channel using the last channel flag acquired from the user terminal memory and attempts to acquire the channel in block 111. If the channel is in block 113, the processor increases the access account for the channel in block 117 and acquires the channel in block 119. If the last purchased channel is not in block 113, the processor determines whether the carrier frequency for the last purchased channel can be found in block 121 If the carrier frequency can be found, the processor searches for the list of neighboring channels corresponding to the last channel acquired in block 123. The neighbor list provides the PN sequences of channels for the base stations neighboring the base station of the last acquired channel. If a channel of the neighbor list is found in block 125, the channel is acquired in block 127. If the carrier is not found in block 121, or a channel is not found in block 125, the previously acquired channels are found. of the user terminal memory they are sorted by access account in block 129. The processor then chooses the previously purchased channel with (¡? the highest access account in block 131 and searches for the selected channel in block 133. If the selected channel is found 5 in block 135, the processor increases the access amount for the select channel in block 117 and acquires the select channel in block 119. If the select channel is not in block 135, the processor tries to find the frequency f 10 carrier for the select channel in block 137. If the carrier frequency is found, the processor looks for channels identified by the neighbor list for the select channel in block 139. If one of the channels identified by the neighbor list is in he block 141, the channel is acquired in block 119. If the carrier for the select channel is not in block 137 or if a channel identified by the neighbor list is not in block 141, the processor determines whether all the previously acquired channels are have searched in block 143. If all previously acquired channels have not been searched, the processor chooses the previously acquired channel that has the next highest access account and repeats the search in block 133. 25 If all channels previously acquired are have searched without finding one, the processor can move forward with an exhaustive search of all possible CDMA channels in block 141. The processor can start with the specified channel that is previously provided in Figure 1, and then proceed sequentially through all the remaining possible channels. Alternatively, the processor can progress sequentially through all remaining possible channels. In a dual-use terminal, the terminal may proceed with non-CDMA operation, such as AMPS operation if a CDMA channel can not be found or if a predetermined period of time passes without finding a CDMA channel. In addition, an interleaved scan may be performed where alternate time periods of predetermined length are used to search respectively for CDMA and non-CDMA channels. Dual-use user terminals will be discussed in more detail with reference to Figures 6 and 7. When a CDMA channel is acquired as discussed above with respect to blocks 107, 119 and 127, an entry for the purchased channel should already be added to the user terminal memory or an existing entry for the acquired channel should be updated as discussed below with respect to Figure 4. Accordingly, when a CDMA channel is acquired by the user terminal in block 401 , the processor looks for the memory of user terminal for previously acquired channels that are transmitted by base stations that have the same • location as the base station transmitting the channel acquired in block 405. As will be understood by those 5 with skill in the specialty, the length and altitude of a base station are transmitted by the base station in a CDMA IS-95 system , such that the location of the base station can be determined by the receiving user terminal. The location of the channel base station • 10 acquired is verified against the base station locations of previously acquired channels because the carrier frequency and PN sequence of a base station of a previously acquired channel may have changed and thus require updating. 15 If the location of the channel base station CDMA acquired corresponds to one or more CDMA channels previously acquired, the processor verifies the system identification and network identification of the acquired channel against that of the acquired channel (s) previously, with the corresponding base station location in block 409. The system identification and network identification can be used to identify one of a plurality of sectorized cells, when a single base station is used to define a plurality of sectorized cells. If the location of the base station, the identification of the system and the network identification of the acquired channel correspond to that of a previously acquired channel in block 409, the cell where the user terminal is located may have changed service of the carrier frequency and the PN sequence previously acquired at the carrier frequency and PN sequence currently acquired. Accordingly, a new entry in the user terminal entry is not desired. In contrast, the carrier frequency, the PN sequence and the neighbor list must be undated for memory entry with the corresponding base station location, and the system identification and network identification in block 411. In addition, the Access account for this entry should be increased in block 413, to reflect the fact that the user terminal has received service within this cell before, and the last employee flag should be adjusted for this channel in block 415. If the The location of the base station for the acquired CDMA channel does not correspond to that of any previously purchased CDMA channels in block 405, or if the system identification and network identification does not correspond to that of any CDMA channels previously purchased in block 409. , the user terminal has acquired a channel in a new cell. From According to this, a new entry for this channel must be made in the user terminal memory, as indicated in blocks 417, 419, 421. In particular, the access account for the new entry is set to one in the block 417; the carrier frequency, the PN sequence, system identification, network identification, location (longitude / latitude), neighbor list and the data that the system is accessed, are supplied in block 419; and the last employee flag is adjusted for the new entry in block 421. As discussed above, entries are added to memory when the channels for the new cells are acquired. Conversely, an entry for a previously acquired channel in the user terminal memory may deteriorate by aging (removed) if the previously acquired channel has not been acquired within a predetermined period of time as illustrated in Figure 5. In In particular, the processor may periodically (when the terminal is turned on for example) search the memory for previously acquired channels that have not been acquired within a predetermined period of time (six months for example) in block 501. This period can be adjusted by the user. If any channels are in block 503, the entries for these previously acquired channels can be deleted in the block 505. If no channels are found in block 503, no channels are deleted. By reducing the number of previously acquired channels, memory space can be made available for newly acquired channels. In addition, when deteriorating due to aging, the less recently acquired channels, those channels that are not currently used, are eliminated. In other words, the processor considers that less recently purchased channels that are acquired in the future are less likely. In addition, memory may age or age when the memory space is almost complete. In this situation, the processor may age a predetermined number of the last recently acquired channels, to make room for newly acquired channels. The user terminal in this way can adapt its channel searches based on changing usage patterns. In accordance with another aspect of the present invention, the CDMA channel acquisition operations of the present invention can be employed in a user terminal adapted to communicate with both CDMA and non-CDMA communication systems (such as AMPS). Accordingly, the user terminal may first attempt to obtain communication services from a CDMA system to obtain advantages in CDMA system performance, and then try to obtain communications services from a non-CDMA system, such as an AMPS system, if a CDMA system is not available. This hierarchy of operations provides that CDMA communications are obtained, if they are available and that non-CDMA communications are obtained as a backup. In addition, an interleaved scan can be performed where alternate time periods of predetermined length are used for respective search by CDMA and non-CDMA channels. As illustrated in Figure 6, the user terminal attempts to establish CDMA communications in block 601, as discussed in more detail with respect to Figure 2. If a CDMA channel is acquired in block 603, the user terminal provides CDMA communication with the CDMA communication system in block 605. Provided that CDMA communications are not lost, the user terminal processor periodically re-scans the CDMA channels in blocks 609 through 611 to ensure communications are maintained in the channel strongest available. If a CDMA channel is not acquired in block 603 or if CDMA communications are lost in block 607, the user terminal attempts to acquire a non-CDMA channel such as an AMPS channel in block 613. If an AMPS channel is acquired in block 615, are provided AMPS communications in block 617. If they are lost AMPS communications in block 629, the user terminal can again try to acquire a CDMA channel • in block 601. During AMPS communications, processor 5 determines if it is time for a periodic re-scan in block 619 and if it is time for a re-scan, the processor determines whether an AMPS re-scan is to be performed or a partial search for CDMA channels in block 621. In particular, a user terminal that • 10 operate in an AMPS system periodically re-scans AMPS channels to ensure that the strongest available AMPS channel is being used. In accordance with the present invention, partial CDMA channel searches are interleaved with conventional AMPS re-scans, so such that CDMA communications can be provided, if a CDMA channel becomes available. Accordingly, the processor periodically initiates a scan in block 619 and any predetermined number of scans performs a partial CDMA channel search in the block 623. The other scan periods are used to perform AMPS re-scans in block 625. If a CDMA channel is acquired in block 627 in response to the partial CDMA channel search in block 623, CDMA communications are provided in the block 605 Alternatively, if CDMA channel is not acquired, operations AMPS are continued in block 617. In accordance with the present invention, CDMA channels are periodically searched during non-CDMA operations, so that CDMA communications can be provided if a CDMA channel becomes available. By interspersing partial CDMA searches between AMPS re-scans that occur normally, the impact on AMPS operations can be reduced. The partial CDMA search of block 623 will now be discussed in more detail with reference to Fig. 7. Because the time allocated for the interleaved search of CDMA channels may not be sufficient to search all CDMA channels, it may be convenient to coordinate CDMA scans interspersed, so that different CDMA channels are searched in consecutive scans. For example, an AMPS re-scan period may be in the range of 42.6 ms to 83.2 ms. In addition, because a previously acquired CDMA channel scan was supposedly unsuccessful in blocks 601 and 603 of FIG. 6 before providing AMPS communications, it may be convenient to search for CDMA channels that have not been previously acquired by the user terminal during some of the CDMA searches interspersed. Accordingly, when an interleaved CDMA search is chosen in block 701 of FIG. 7, the processor decides in block 703 to perform either a partial search for previously acquired CDMA channels or a partial search for CDMA channels specified as indicated in table 1. Partial CDMA searches may alternate between the two. Alternatively, the list of previously purchased CDMA channels can be searched partially once for each predetermined number of CDMA searches, with the remaining CDMA searches being used to search the specified list of CDMA channels. fB 10 If the list of previously purchased CDMA channels is chosen in block 703 for a partial search, the next channel in the list is chosen in block 705 and the processor looks for this selected channel in block 707. If this is the first partial search for list of CDMA channels previously acquired since the acquisition of AMPS communications, the first selected CDMA channel may be the first channel in the list. If this partial search has been preceded by a previous partial search of the list, the first selected CDMA channel can be the CDMA channel that follows the last CDMA channel searched in the previous search of the list. If the select channel is in block 709, the user terminal provides CDMA communications in block 711. If the selected channel is not found, the processor checks if there is time left to search during the re-scan period in block 715 and if there is time remaining, it selects the next CDMA channel from the list of previously purchased CDMA channels in block 717. The processor searches for the next selected CDMA channel in block 707 and the cycle continues until a CDMA channel is already found or the time for the re-exploration period is over. When the time for the re-scan period ends in block 715 without finding a CDMA channel, the processor stores the last CDMA channel searched in memory, and returns to AMPS communications in block 719. Accordingly, the processor You can start the next partial CDMA channel search previously acquired where the last partial search stayed. Alternatively, if the processor selects to perform a partial search of the specified list of CDMA channels in block 703 during the reexploration period, the processor chooses the next channel from the CDMA channel specific list in block 721 and searches for the channel selected in block 723. If the select channel is in block 725, the processor provides CDMA communication in block 727. As before, if this is the first partial search of the specified list of CDMA channels since operations are provided AMPS, the processor chooses the first channel of the list. If this search has been preceded by a previous partial search of CDMA channels, since the AMPS operations are provided, the processor chooses the next channel in the list following the last channel searched in the previous search. If the selected channel is not found, the processor determines if there is time remaining in the re-scan period in block 725. If there is still time, the processor chooses the next CDMA channel from the list in block 731 and looks for the channel in block 723. The partial search of the specified list of CDMA channels continues until a CDMA channel is already found or the time for the re-scanning period is over. If the time runs out without finding a CDMA channel, the processor stores the last searched channel of the specified list, and returns to AMPS operations in block 719. Accordingly, the following partial search of the specified list may begin where the previous search was left. As discussed above, a portion of the AMPS re-scan periods can be used to search for CDMA channels during AMPS operations in a dual-use terminal. Accordingly, CDMA communications can be provided if a CDMA channel becomes available during AMPS operations. Because the list of CDMA channels specified is likely to be longer that the list of CDMA channels previously acquired, it may be convenient to perform partial searches of the list • more frequently specified to search the list of previously purchased channels. The present invention has been described with respect to Figs. 3-7, with reference to flow charts illustrating operations of the present invention. It will be understood that each block of the flow chart and combinations of blocks in the flow chart can implemented by computer program instructions. These program instructions can be provided to a processor to produce a machine, such that the instructions running on the processor create means to implement the functions specified in the processor (s). flow chart blocks. The computer program instructions can be executed by a processor to cause a series of operational steps to be performed by the processor, to produce a process implemented by computer, in such a way that Instructions that are executed on the processor provide steps to implement the functions specified in the flowchart block (s). Accordingly, blocks of flowchart illustrations support combinations of means for perform the specified functions, combinations of stages to perform the specified functions and means of program instructions to perform the specified functions. It will also be understood that each block of the flowchart illustration and combinations of blocks in the flowchart illustration may be implemented by systems based on special purpose physical equipment that perform the specified functions or steps or combinations of hardware and instructions of special purpose computer. In the drawings and specifications, typical preferred embodiments of the invention have been described. The scope of the invention is set forth in the following claims. While the present invention has been discussed above in a satellite radiotelephone communication system, the methods, systems and terminals of the present invention can also be applied in a terrestrial cellular radio telephone communication system. The methods, systems and terminals of the present invention can also be applied with dual mode terminals capable of providing communications with both satellite radiotelephone communication systems and terrestrial radiotelephone systems.

Claims (34)

1. CLAIMS 1. A method to provide communications of • radiotelephony for a user terminal with a radiotelephone communication system having a communication channel priority 5, the method is characterized by: storing a plurality of previously acquired communication channels in a user terminal memory; find an available from the plurality of previously acquired communication channels stored in the • 10 user terminal memory; acquire one of the previously acquired communications channels when one of the previously acquired communication channels is available; and providing radiotelephone communications between the user terminal and the communications system 15 of radiotelephony over the previously acquired communications channel available, when the previously acquired communications channel is available.
2. 2. A method according to claim 1, characterized in that the storage step comprises 20 save an access account for each of the previously acquired communication channels, where the access account identifies a number of times that the respective communications channel has been acquired by the user terminal, and where the search stage understands 25 Sequentially search the communication channels previously acquired in order of a higher access account.
3. 3. A method according to claim 1, characterized in that the step of storing comprises identifying a last acquired one of the previously acquired communication channels and wherein the search stage comprises first searching for the last acquired communications channel.
4. A method according to claim 1, characterized in that the step of storing comprises saving a geographical search identifier for each of the previously acquired communication channels, and wherein the search step comprises searching the previously acquired communication channels. that have a geographic search identifier.
5. 5. A method according to claim 1, characterized in that each of the plurality of previously acquired communication channels comprises a communication channel of Multiple Access with Code Division (CDMA = Code Division Multiple Access) and wherein the stage of storing comprises storing a carrier frequency and a PN sequence for each of the previously acquired communication channels.
6. 6. A method according to claim 5, characterized in that the storage step comprises store a base station identification and a base station location for each of the channels of • previously acquired communications.
7. 7. A method according to claim 5, further comprising the steps of: obtaining a base station location for an acquired communications channel; compare the base station location for the acquired communications channel with the base station locations for the communication channels • 10 previously acquired; identifying a previously acquired communications channel having a corresponding base station location with the base station of the acquired communications channel; and update the carrier frequency and PN sequence for the channel 15 communications previously acquired that has the corresponding base station location.
8. 8. A method according to claim 5, further comprising the steps of: searching a channel of • CDMA communications available not previously acquired 20 when previously purchased CDMA communication channels are not available; look for non-CDMA communication channels when CDMA communication channels are not available; and acquire a non-CDMA communications channel when one of the channels of 25 non-CDMA communications searched is available.
9. 9. A method according to claim 8, further comprising the steps of: providing communications over the acquired non-CDMA communications channel; and periodically search channels 5 CDMA communications available. A method according to claim 9, characterized in that the periodic search step comprises searching the previously acquired CDMA communication channels.
10. 10
11. 11. A method of compliance with • claim 10, characterized in that the periodic search step further comprises searching for CDMA communication channels that have not been previously acquired.
12. 12. A method of compliance with 15 claim 1, characterized in that it also comprises the step of eliminating one of the previously acquired communications channels when the previously acquired communications channel has not been reacquired within a • predetermined time period.
13. 13. A method according to claim 1, characterized in that the step of storing comprises saving a list of neighboring communication channels for cells neighboring the previously acquired communications channel, the method furthermore 25 comprises the stage of: searching the communication channels neighbors when the previously identified communications channel is not available.
14. 14. A method according to claim 1, characterized in that it further comprises the step of: acqug a new communication channel when the previously acquired communication channels are not available.
15. 15. A user terminal for use with a radiotelephone communication system having a plurality of communications channel, the user terminal comprises a transceiver for transmitting and receiving radiotelephone communications to and from the radiotelephone communication system, the method is characterized by: user terminal memory for storing a plurality of previously acquired communication channels; and search means coupled to the transceiver and user terminal memory, when the search means searches for an available one of the previously acquired communication channels in the user terminal memory and acquires one of the previously acquired communication channels when it is available the previously acquired communications channel.
16. 16. A user terminal according to claim 15, characterized in that the memory of The user terminal stores an access account for each of the previously acquired communication channels, wherein the access account identifies a number of times that the respective communications channel has been acquired by the user terminal, and wherein the search queries sequentially search the previously acquired communication channels in order of a higher access account.
17. A user terminal according to claim 15, characterized in that the user terminal memory identifies a last acquired one of the previously acquired communication channels and wherein the search means first searches for the last acquired communications channel.
18. 18. A user terminal according to claim 15, characterized in that the user terminal memory stores a geographic search identifier for each of the previously acquired communication channels and wherein the search means look for previously acquired communication channels. that have a common geographic search identifier.
19. 19. A user terminal according to claim 15, characterized in that each of the plurality of previously acquired communication channels comprises an Access communications channel. Multiple with Code Division (CDMA) and wherein the user terminal memory stores a carrier frequency and a PN sequence for each of the previously acquired communication channels.
20. 20. A user terminal according to claim 19, characterized in that the user terminal memory also stores a base station identification and a base station location for each of the previously acquired communication channels.
21. 21. A user terminal according to claim 20, characterized in that the search means obtains a base station location for an acquired communications channel, compares the base station location with the acquired communications channel with the base station locations. for the previously acquired communication channels and identifies a previously acquired communications channel having a corresponding base station location that couples with the base station of the acquired communications channel, and where the user terminal memory updates the carrier frequency and the PN sequence for the previously acquired communications channel having the corresponding base station location.
22. 22. A user terminal according to claim 19, characterized in that the means of search look for an available CDMA communications channel that was not previously acquired when previously acquired CDMA communications channels are not • available, when the search means look for non-CDMA communications channels 5 when the CDMA communication channels are not available and where the search means acquire a non-CDMA communication channel when one of the non-CDMA communication channels searched is available.
23. 23. A user terminal according to claim 22, characterized in that the transceiver provides communications over the acquired non-CDMA communications channel and wherein the search means periodically searches for available CDMA communication channels. 15 while maintaining communications over the non-CDMA communications channel acquired.
24. 24. A user terminal according to claim 23, characterized in that the means of • search periodically search for channels 20 CDMA communications previously acquired.
25. 25. A user terminal according to claim 24, characterized in that the search means periodically searches for CDMA communication channels that have not been previously acquired.
26. 26. A user terminal in accordance with the claim 15, characterized in that the user terminal memory stores a list of neighboring communication channels for neighboring cells of the • previously acquired communications and where the search means search for the neighboring communication channels when the previously identified communications channel is not available.
27. 27. A user terminal according to claim 15, characterized in that the means of ^ ¡^ B 10 search acquire a new communication channel when * f previously acquired communication channels are not available.
28. 28. A user terminal according to claim 15, characterized in that the terminal of The user removes one of the previously acquired communication channels, when the previously acquired communications channel has not been reacquired within a predetermined period of time.
29. 29. A method for acquiring communication channels for a user terminal with a radiotelephone communication system having a plurality of communication channels, the method is characterized by: storing a list of previously acquired communication channels in a memory of 25 user terminal; store a list of channels of communications specified in the user terminal memory wherein the previously acquired communication channels are a subset of the specified communication channels; and searching through an available communication channel using the list of previously acquired communication channels, where partial searches of the specified communication channels are interspersed with partial searches of the previously acquired communication channels.
30. 30. A method according to claim 29, characterized in that the search step is followed by the steps of: acquiring one of the communication channels; and providing radiotelephone communications between the user terminal and the radiotelephone communication system over the acquired communications channel.
31. 31. A method according to claim 30, characterized in that the step of acquiring is followed by the step of: adding the acquired communications channel to the list of previously acquired communication channels.
32. 32. A user terminal for providing communications with a radiotelephone communication system having a plurality of communication channels, the user terminal comprises a transceiver for transmitting and receiving radiotelephony communications to and from the radiotelephone communication system, the user terminal is characterized by: user terminal memory for storing a list of previously acquired communication channels and for storing a list of specified communication channels , where the previously acquired communication channels are a subset of specified communication channels; and search means coupled with the transceiver and the user terminal memory, wherein the search means search for an available communications channel, using the lists of previously acquired and specified communication channels where the specified communication channels are interleaved with the previously acquired communication channels.
33. 33. A user terminal according to claim 32, characterized in that it further comprises: means for acquiring one of the communication channels and providing radiotelephone communications between the user terminal and the radiotelephone communication system over the acquired communications channel. .
34. 34. A user terminal according to claim 33, characterized in that it further comprises: means for adding the acquired communications channel to the list of previously acquired communication channels.