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METHOD OF SWITCHING ENABLING Field of the Invention The present invention relates generally to communication devices and more particularly to an enabling switching method in a wireless communication system. Background of the Invention Communication systems that transmit information in configurations such as time division multiplexing (TDM), time division multiple access (TDMA) or code division multiple access (CDMA) communication systems, such as digital cellular systems, can employ subscriber-assisted communication, which requires the mobile unit of the subscriber to measure the signal strengths of adjacent neighboring cells. In addition to measuring the signal strength, some systems, such as the Global System for Mobile Communications
(GSM) as established in the ETSI-GSM Technical Specification available from the European Telecommunications Standards Institute requires the positive identification of an adjacent cell which is measured by decoding an intermittently transmitted base station identification (ID) code (BSIC) . These systems typically provide a particular time for the subscriber to measure and decode the identities of the adjacent cells. Although the protocol of the GSM system ensures that it is possible to make these measurements, the process of positively identifying all adjacent cells BSICs in such systems with assisted switching to the subscriber can take considerable time. This time can also be particularly long in a system that employs synchronization between cell sites to reduce the audio interruption time when a transfer occurs. The synchronization creates a worse case of waiting for measurement for adjacent cells BSICs. Similarly, in a microcellular system, this wait in decoding becomes a significant problem since movement through a cell can occur very rapidly, thereby requiring faster acquisition of measurement information. At the beginning of a call or when the visibility of neighboring cells changes drastically (for example when a mobile turns the corner in a microcellular system), multiple neighbors may need to be verified at the same time. As the signal of the cell in service falls rapidly, the measured signal of the new cells can rise rapidly. In a conventional 7-cell reuse pattern, the measurement of adjacent BSICs for an entire set of six potential transfer candidates is increased by up to six times the amount of time to measure a single candidate. This problem is further increased by the fact that that there may be a large number of other neighboring cells in the list of neighbors that need to be decoded periodically. The accurate decoded information makes it possible to make accurate and fast transfer decisions. If the mobile is disabled to quickly decode the identity of new cells, then there is the possibility of an extension period of poor quality and call possibility even in a dropped call. For example, when a mobile phone turns a corner in a microcellular system, a cellular recognition signal can fall rapidly while a new cell can rapidly ascend. Similarly, a mobile can have a specific cell identity decoded before turning the corner. Once a mobile turns the corner, a co-channel re-user of the previously decoded cell can suddenly become very strong. Without frequent re-decoding, it is possible that the previously decoded cell will be chosen for a switchover even if it was only valid before the mobile turned the corner.
According to the above, there is a need for a method and apparatus for minimizing the switching time in a communication system that generates configurations for transmitting information. Brief Description of the Drawings Figure 1 is a plan view of a wireless communication network embodying the present invention; Figure 2 is a block diagram of a subscriber unit of Figure 1, embodying the present invention; Figure 3 is a configuration cartographic diagram showing the control channel and the traffic channel information in a TDMA system; Fig. 4 is a flow diagram showing the operation of the switching performed by the subscriber unit of Fig. 2; Figure 5 is a flow chart showing in more detail the method for switching performed by a subscriber unit according to the present invention; Figure 6 is a flow diagram showing an alternative method for switching according to the present invention; and Figure 7 is a flowchart showing the steps of verifying the signal strength of the nearby cells of steps 408, 523 and 621 of Figures 4, 5 and 6 respectively according to the present invention. Detailed Description of the Invention The method and apparatus of the present invention improves the decoding rate and the reliability of the decoding of the base stations of the adjacent cells by facilitating the decoding process if the signal quality of a traffic channel is found. within a predetermined range, such as above or below a predetermined threshold. Adjacent control channels are monitored and decoded at a fast rate by ignoring the traffic channel information. The information in the traffic channel may be voice traffic may be data, such as data in a multiple configuration data communication system. Although the remaining description generally refers to the voice, the description also applies to the data. The voice is interrupted and the channel information is decoded when, for example, the bit error rate or the traffic channel configuration error rate (TCH) is deteriorating while other channels have a better signal. The mobile unit can also interrupt the voice and immediately decode the signals when the cell in service suffers a rapid decline in the signal while a neighboring cell signal may be showing rapid improvement. When degraded conditions are detected, the facilitated process is initiated to improve the likelihood of providing the information necessary to transfer to a viable target candidate. The programming of voice channel interruptions can also occur when the information available from neighboring cells at the beginning of a call or immediately after a transfer is insufficient. According to a further aspect of the present invention, the mobile unit can determine when a voice signal is strong to interrupt traffic and obtain ID information or make additional measurements. The lost voice signal can be recovered using conventional voice extrapolation techniques. Turning now to Figure 1, a wireless communication network 100 is shown. The wireless communication network 100 preferably includes a mobile switching center 102, a plurality of cellular sites 104 each having a base station 105 coupled to site controllers. base 106. Finally, mobile communication devices 108 or portable communication devices 110 (collectively "mobile units") are adapted to communicate with base stations associated with base site controllers 106 in order to maintain communications with another mobile unit or a wired unit associated with a terrestrial network. Turning now to Figure 2, a block diagram shows a mobile unit such as a cellular radiotelephone or other wireless communication device for carrying out the method according to the present invention. In the preferred embodiment, an ASIC (Integrated Circuit for Specific Applications) 201, such as a CMOS ASIC available from Motorola, Inc. and the control circuit 203, which may comprise a microprocessor, such as a 68 HC11 microprocessor, also available from Motorola, Inc. They are combined to generate the communication protocol necessary to operate in the communication system. In the preferred embodiment, the control circuit 203 uses the RAM 205, the EEPROM 207 and the ROM 209, consolidated in a packet 211, to perform the steps necessary to generate the protocol and perform other functions, such as writing for a deployment 213, accepting the information from a numeric keypad 215, and controlling a frequency synthesizer 225. The ASIC 201 processes the audio transformed by the audio circuit 219 coming from a microphone 217 and towards a speaker 221. The transmitter 223 transmits through a antenna 229 using carrier frequencies produced by the frequency synthesizer 225. The information received by the antenna of the mobile unit 229 enters the receiver 227 which demodulates the symbols comprising the message configuration using the carrier frequencies coming from the frequency synthesizer 225. The mobile unit can optionally include a message receiver and a storage device including means for processing the digital signal. The message receiver and the storage device can be, for example, a digital answering machine or a paging receiver. Although the circuitry of Figure 2 shows an exemplary mobile unit, other circuitry may be employed within the scope of the present invention. Turning now to Figure 3, an exemplary control channel and traffic channel configurations are shown. The control channels shown in Figure 3A are subdivided into broadcast control channel (BCCH), common control channel (CCCH) configurations and blank channel (SCH) configurations. The traffic channels shown in Figure 3B comprise traffic channel configurations (TCH) and inactive configurations. Figure 2C shows two representative TCH configurations that have N slots to serve N users. In the GSM system, for example eight slots are used to provide service to eight users. In Figure 3D a representative slot is shown for the USER 2. Each slot preferably includes a synchronization slot 331, an equalizer synchronizer 332, a bit synchronizer 333, a configuration synchronizer 334, a data slot 335 and a of protection band 336. In the GSM system, for example, there are 104 logical TDMA configurations that make a TCH in a SACCH multistructure comprising 26 multistructures
configuration. The control channel has fifty-one configurations multistructures (or 102 configurations in total) for each SACCH multistructure. Because the control channel has 102 configurations as compared to 104
configurations of the traffic channel, the logical configurations of the control channel are repeated faster and "smoothly" in time with respect to the logical channels of the traffic channel TCH. The first two TDMA configurations in the control channel are started before the
SACCH multistructure ends. In the control channel configurations 102, the structure of the SCH (which
Jr contains the BSIC) occurs every ten configurations. An inactive configuration at the end makes configuration fifty-one. When the inactive configuration of the TCH
is aligned with one of the structures of the SCH, the identity of the cell can be decoded. At the moment when a decision is made to decode the identity of the cell, this can take up to 11-26 multistages or 11 x 120 milliseconds (ie 1.32 seconds) for the structures to align in conventional cellular systems such as a conventional GSM system. At the beginning of a call or when the resistance of the signals coming from the cells in service change drastically, the resistance of the signal of the multiple neighboring cells may need to be verified at the same time. The measurement of the BSICs of the adjacent cells for each of the six neighboring cells which are potential switching candidates in a conventional reuse pattern of the seventh cell, is increased to approximately eight seconds assuming no decoding error occurs. The time to measure potential switching candidates is further increased when a large number of neighboring cells in the neighbor list need to be periodically decoded, such as in a microcellular environment. According to the above, cells other than stronger cells should also be decoded periodically in the event that they become one of the strongest measured cells. Turning now to Figure 4, a flow chart shows a method for switching according to the present invention. During a step 404 when normal communication takes place between a mobile unit and a wireless communication network, the mobile unit determines whether the communication is interrupted in step 406. The communication may be interrupted for example when the bit error rate or proportion The configuration error calculated by the control circuit 203 exceeds a certain value. If communication is interrupted, the mobile unit interrupts the voice to decode the BSIC of the nearby cells in a step 408. The mobile or base in service (in conjunction with the cellular network) then determines whether a stronger base is available in a step 410. As will be described in more detail with reference to the remaining figures, the mobile unit can determine that a stronger base station is available by maintaining a list of signal strength of new base stations. Alternatively, the base station can send a signal to the mobile unit informing the mobile unit of the strongest base station. If a stronger base is available, then the mobile unit sends a message to the network requesting a switch in step 412. A switch is then performed in step 414 which is well known in the art. Turning now to FIG. 5, a flow chart shows in greater detail a method for requesting a switch performed by a mobile unit according to the present invention. At the start of normal communication in the traffic channel assigned in step 502, the control circuit 203 of the mobile receives a frequency list of the control channel, commonly called the BCCH Assignment (BA), coming from the network through the receiver 227 in a step 504, to monitor them as potential switching candidates. Although in normal communication the control circuit measures or determines the resistance of the signal of the frequencies BA in a step 506, and orders the signal resistances of the BAs from the strongest to the weakest in a step 508. The mobile then wait for either the configuration of the TCH or the inactive configuration of the traffic channel to align it with the SCH configuration of the desired control channel in a step 510. If the mobile unit is operating in the system and has already tracked the station Based on this, the mobile unit can predict when the configuration of the TCH or the inactive of the traffic channel will be aligned with the SCH configuration of the control channel. The mobile control circuit then determines whether the inactive configuration of the traffic channel is aligned with the configuration of the SCH (which has the identity of the cell) of the control channel in a step 512. If the inactive configuration of the traffic channel is is aligned with the SCH configuration of the control channel, the mobile control circuit decodes the BSIC in a step 514 and rearranges the signal strength list of the BAs in a step 516 if necessary based on the decoding of the BSIC . However, if the configurations are not aligned and a decoding of a strong BA frequency is required, the mobile then determines whether the traffic channel configuration TCH is aligned with the desired control channel SCH configuration in a step 518. If the configuration of the TCH and the SCH configuration of the desired control channel are not aligned, the mobile waits for the next configuration alignment of either a TCH traffic channel configuration or an inactive configuration of the traffic channel with the SCH configuration of the desired control channel, whichever comes first, in a step 510. Since the TCH traffic channel configurations are repeated 24-25 times more frequently than the inactive configurations, many new opportunities are available for the alignment of the configuration with the SCH configuration of the control channel. If a configuration of the traffic channel TCH is aligned with the SCH configuration of the desired control channel in a step 518, the mobile control circuit determines whether the communication is interrupted in a step 520 by monitoring the bit error rate. or the error rate of configuration of the signal received by the receiver 227. If the communication is not interrupted, the control circuit determines whether the current traffic channel assignment was only recently established as a result of a new call that was made or received or a recent switchover in a step 522. If the communication is interrupted in a step 520, or a new call is initiated or a recent switch has occurred in a step 522, the mobile interrupts the voice in a step 524. In In particular, the control circuit ignores the data that could be received in the data slot 335 of the slot assigned to the mobile and tunes to the monitor receiver a control channel. The control circuit then attempts to decode the BSIC transmitted in the control channel in a step 526. The mobile will report the measurements of any frequency of the control channel found in the BA to the network, provided that the identity of the cell of those neighboring have recently been decoded by mobile. The mobile will preferably decode the BSIC of the cell having the highest signal strength (or some other criteria) to increase the probability that the decoded BSIC cells have the strongest signal and are selected for a switch. The control circuit will rearrange the list of BAs according to the signal strength if necessary in a step 528. The mobile or base station in service determines which neighbor cell measured and decoded is the strongest and in conjunction with the cellular network determines if this strongest neighbor identified in a 530 stage is available. If a stronger base is not available, the mobile continues normal communication on the same channel. However, if a base station is available the mobile makes a request in a step 532 to allow a switch in a step 534. The mobile then preferably recovers the voice lost in step 536. The interpolation of the digital voice carried out in Step 536 for recovering the lost voice is well known in the art, as described for example in "Design and Test of a Spectrally Efficient
Land Mobile Communications Systems using LPC Speech "
(Design and Test of Spectrally Efficient Land Mobile Communications Systems Using Voice of the LPC) by Michael McLaughlin, Donald Linder and Scott Carney published in I.E.E.E. Journal On Selected Areas In Communications, Vol. SAC-2, No. 4, July 1984, or US Pat. No. 4,868,981 entitled "Interrupted Audio Fill-In System For Noise Reduction And Intelligibility Enhancement In Multi-Channel Scanning Receiver Applications" (Complete Interrupted Audio System for Noise Reduction and Intelligent Improvement in Multi-Channel Tracking Receiver Applications) by Jhon D. Ide, Jhon P. Fussell, Aaron S. Rogers, the complete application of which is incorporated for reference. Turning now to Figure 6, a flow chart shows the method for performing a switch according to an alternative embodiment of the present invention. At the start of a normal communication in the traffic channel assigned in step 602, the mobile receives a list of the frequencies of the control channel in step 604, to monitor them, as potential switching candidates. Although in normal communication the control circuit determines the resistance of the signal of the frequencies BA in a step 606, and orders the signal resistances of the BAs from the strongest to the weakest in a step 608. The mobile then waits by any of the configurations of the TCH or of the inactive traffic channel configurations to align it with the SCH configuration of the desired control channel in a step 610. The control circuit then determines whether the inactive traffic channel configuration is aligned with the configuration of the SCH of the control channel in a step 612. If the inactive configuration of the traffic channel is aligned with the SCH configuration of the control channel, the mobile decodes the BSIC in a step 614. The mobile reorders the list of signal strength of the BAs in a step 616 if necessary, based on the decoding of the BSIC. However, if the configurations are not aligned and a decoding of a strong frequency BA is required, the mobile then determines whether the configuration of the traffic channel TCH is aligned with the SCH configuration of the desired control channel in a step 618. If the configuration of the TCH and the configuration of the SCH are not aligned, the mobile expects the following configuration alignment of any configuration of the traffic channel TCH or the inactive configuration of the traffic channel with the SCH configuration of the desired control channel, either come first, in a step 610. If a traffic channel configuration TCH is aligned with the SCH configuration of the desired control channel in a step 618, the mobile determines whether a valid voice is predicted in step 620. The voice valid can be predicted by monitoring the bit error rate, the configuration error rate or some - l
other criteria to determine the quality of the signal. If a valid voice is predicted, the control circuit interrupts the voice in a step 622. The control circuit then attempts to decode the identity of the cell contained in the control channel in a step 624. The mobile will report the measurements of any frequency control channel found in the BA to the network, provided that the identity of the cell of that neighbor has been recently decoded by the mobile. The control circuit will rearrange the list of BAs based on the signal strength if necessary in a step 626. The mobile or the base in service determines which neighbor cell measured and decoded is the strongest and in conjunction with the cellular network determines if this identified stronger neighbor is available, in a step 630. If a stronger base is available, the mobile requests a switchover in a step 632 and the network performs a switch in a step 634. Because the voice is valid, the mobile recovers the lost voice according to the techniques well known in the art in a step 620. Although the modalities of figures 5 and 6 are shown in separate flowcharts, the two modalities may be used concurrently according to the present invention. Turning now to Figure 7, a method for verifying the signal strength of neighboring cells according to the present invention is shown. The mobile unit first determines whether the cell sites are synchronized in a step 704. If the cells are synchronized, the mobile unit can intelligently interrupt the voice when it knows a SCH configuration of the control channel that can be decoded. If the cell sites are not synchronized, the mobile control circuit determines if a prior configuration alignment is known, in a step 705. A prior configuration alignment can be detected during a previous scan of a base station and can also be used to delay the interruption of the voice to decode the identities of the adjacent cells. If the cell sites are synchronized or the alignment of the previous configuration is known, the control circuit continues to decode until a predetermined configuration having the identity of the cell is reached, in a step 706. The control circuit then interrupts the voice in a step 708 and monitor a control channel to send a BSIC when the configuration having the identity of the cell is reached. By interrupting the voice when an SCH configuration is detected, the mobile unit will minimize the loss of voice. Finally, the mobile unit decodes the BSIC of the neighbor cell when the inactive configuration is aligned with the configuration of the SCH in step 710. Although the invention has been described and illustrated in the description and drawings above, it is understood that this description is only a example and that numerous changes and modifications can be made by those skilled in the art without departing from the true spirit and scope of the invention. For example, although a GSM system has been described by way of example, the method and apparatus of the present invention can be applied to any TDM or TDMA mobile and system, or other device or system that decodes information configurations. Although the present invention finds particular application in portable cellular radiotelephones, the invention can be applied to any wireless communication device, including pagers, electronic organizers or computers. Our invention should only be limited by the following claims.