JP4256022B2 - Mobile communication terminal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention includes, for example, PDC (Personal Digital Cellular) and PHS (Personal Handyphone System).As a wireless access method, time division multiple access (TDMA; Time Division Multiple Access ) Adopted the methodThe present invention relates to a mobile communication terminal apparatus used in a cellular mobile communication system, and more particularly to a mobile communication terminal apparatus having a seamless handover function.
[0002]
[Prior art]
In general, in a cellular mobile communication system, a large number of base stations are distributed in a service area and cells are formed by these base stations, and a mobile communication terminal apparatus is connected to a base station of a cell in which the mobile communication terminal apparatus exists. Wireless communication is possible by connecting through the network. When the mobile communication terminal apparatus moves to another cell during communication, the communication can be continued by performing a handover.
[0003]
In handover, for example, the reception quality of a radio signal arriving from a base station during communication by the mobile communication terminal apparatus is monitored, and communication with the base station is interrupted when the reception quality deteriorates below a predetermined level. In this state, all the surrounding base stations are searched, the base station transmitting the radio wave with the highest received electric field strength is selected as the switching destination, and a link channel establishment request is transmitted to the selected base station. Then, the base station that has received the request assigns a link channel to the requesting mobile communication terminal device, and uses the assigned link channel between the mobile communication terminal device and the switching destination base station. A procedure is set so that a new wireless link is formed and a connection base station is switched after a predetermined connection switching procedure is performed between the mobile communication terminal device and the switching destination base station.
[0004]
This normal handover procedure used in the past can interrupt the communication with the switching source base station and select the optimum base station as the switching destination from among the surrounding base stations. The handover can be completed with a high probability. However, on the other hand, since communication is interrupted for a relatively long time during the handover period, there is a problem that communication quality is deteriorated.
[0005]
On the other hand, recently, a new handover procedure called seamless handover has been proposed. Seamless handover selects a switching destination base station using an idle slot period while maintaining communication with the switching source base station. Then, after executing the link channel establishment procedure and the connection control procedure with the switching destination base station, the new base station is switched to the connection destination.
[0006]
In this seamless handover, since communication with the switching source base station is maintained during the handover period, the communication quality can be kept high. However, since the base station to be selected as a switching destination is limited to a base station that transmits a control signal during the idle slot period, there is a probability that handover cannot be performed without selecting an appropriate base station as the switching destination. This is higher than the normal handover described above.
[0007]
[Problems to be solved by the invention]
As described above, both the normal handover and the new seamless handover that are conventionally used have advantages and disadvantages.
[0008]
  The present invention has been made paying attention to the above circumstances, and its first object is that of normal handover andseamlessIt is an object of the present invention to provide a mobile communication terminal apparatus that can effectively use different handovers and thereby achieves both improvement in communication quality and increase in handover success probability.
[0009]
  The second purpose isseamlessWhen a communication channel that uses the same slot as the communication channel in use is allocated between the switch-destination base station and the switch-source base station during the handover, the optimum radio depending on the reception quality at that time It is to provide a mobile communication terminal apparatus that enables selection and execution of a connection procedure, thereby achieving both maintenance of communication quality and successful handover.
[0010]
  The third purpose isseamlessIt is an object of the present invention to provide a mobile communication terminal apparatus that can always select a base station having better reception quality than a switching source base station in handover.
[0011]
[Means for Solving the Problems]
  In order to achieve the first object, the first invention selects, as a handover procedure, a switching destination base station in a state where communication with the switching source base station is interrupted, In the state in which the communication between the first handover control means for switching the connection destination base station after executing the predetermined connection control procedure and the switching source base station is maintained,Use a period other than the slot assigned to your device,A mobile communication terminal apparatus comprising a second handover control means for switching a connection destination base station after executing a connection control procedure including an operation of selecting at least a switch destination base station,
  It comprises reception quality detection means for detecting reception quality of a radio signal coming from a connected base station, and handover selection means. Then, when switching the connection-destination base station by handover, the handover selection unit selectively selects the first handover and the second handover based on the reception quality detected by the reception quality detection unit. It is made to run.
[0012]
Specifically, a first reception quality determination level and a second reception quality determination level set higher than the first reception quality determination level are set, and the detection value of the reception quality is the first reception quality. The second handover is mainly selected and executed when the quality determination level is higher than the second reception quality determination level and lower than the second reception quality determination level, and when the reception quality detection value is lower than the first reception quality determination level, The first handover is mainly selected and executed.
[0013]
  Therefore, according to the present invention, the following operational effects are exhibited. That is, in the first handover, the communication with the switching source base station is interrupted, and the switching destination base station is selected from all the base stations. Therefore, the probability that an appropriate base station can be selected as the switching destination. However, on the other hand, communication quality is deteriorated due to interruption of communication. In contrast, the second handover can maintain high communication quality in order to maintain communication with the switching source base station during the handover period.There is a possibility of failure.
[0014]
  Therefore, if the first and second handovers are selected and executed according to the reception quality of the radio signal arriving from the switching source base station as in the present invention, the communication quality is improved when the reception quality is relatively good, for example. Since the second handover is preferentially performed, relatively good communication can be maintained in most of the handover period, and even if an appropriate base station is not found as a switching destination, communication can be performed directly with the switching source base station. It is unlikely that handover will fail due to continuing.
On the other hand, when the reception quality deteriorates, the first handover is performed with priority given to the success of the handover, so the communication interruption time becomes long, but it is suitable as a switching destination from among a larger number of neighboring base stations. Since a simple base station can be selected, the handover can be successful with a high probability.
That is, it is possible to achieve both improvement in communication quality and improvement in the probability of successful handover.
In addition, since the second reception quality determination level for activating the second handover is set higher than the first reception quality determination level for activating the first handover, The second handover is executed in a state in which the communication quality during the period is ensured to some extent, and as a result, the second handover can be used effectively.
[0017]
As a more specific configuration, the reception field strength is used as the reception quality, and the first handover and the second handover are selected by determining the reception field strength with a plurality of threshold values. The reception error rate is used to select the first handover and the second handover by determining the reception error rate with a plurality of threshold values, and the reception field strength and the reception error rate are combined as reception quality, It is conceivable that the first handover and the second handover are selected by determining the reception field strength and the reception error rate with a plurality of threshold values.
[0018]
Among these, the following specific configuration is conceivable for selecting the type of handover by combining the received field strength and the reception error rate. For example, when the received electric field strength is relatively high and the reception error rate is relatively good, the communication quality is still sufficient, so the second handover is attempted, and as a result, an appropriate base station cannot be found as the switching destination. In this case, the handover is stopped and communication with the switching source base station is continued as it is.
[0019]
On the other hand, when the reception electric field strength decreases or the reception error rate deteriorates even if the reception electric field strength is relatively high, first, the second handover is executed with an emphasis on the call quality, which is suitable as a switching destination. When a new base station is not found, the first handover is executed in order to find the switching destination with certainty.
[0020]
In addition, in a state where the reception error rate is degraded even if the reception electric field strength is high, there is a high possibility that it is caused by interference with other PHS terminals, etc., so it is possible to connect without selecting any handover procedure. Control to switch to another communication channel held by the base station is executed.
[0021]
With the configuration described above, it is possible to select and execute an optimal handover procedure in the state of the wireless environment at that time.
[0022]
On the other hand, in order to achieve the second object, the present invention is a mobile communication terminal apparatus having a so-called seamless handover procedure,
As a connection control means executed when a communication channel that uses the same slot as the communication channel used between the switching destination base station and the switching source base station is allocated, The communication between the first connection control means for executing the connection control procedure using the communication channel assigned from the switching destination base station and the switching source base station was maintained by interrupting the communication of If the communication channel is requested to be reassigned to the switching destination base station in the state and a communication channel using a different slot is assigned from the switching destination base station in response to this request, the communication channel is used to Second connection control means for executing a connection control procedure.
[0023]
Then, when executing the connection control procedure, the first control means and the second control means are selectively executed based on the reception quality detection result of the radio signal coming from the switching source base station. It is made to let you.
[0024]
Therefore, according to the present invention, in seamless handover, when the communication channel assigned from the switching destination base station uses the same slot as the communication channel used with the switching source base station, switching is performed. When the radio reception quality from the former base station is deteriorated, communication with the switching source base station is interrupted, and a radio link is formed by the communication channel assigned from the switching destination base station. For this reason, the handover can be completed quickly and reliably.
[0025]
On the other hand, when the reception quality from the switching base station is relatively good, the mobile communication terminal device is requested to reassign the communication channel to the switching destination base station, and another slot is used from the switching base station. Wait for the communication channel to be assigned. For this reason, communication with the switching source base station is not interrupted during the handover period, and as a result, the communication quality is maintained at a high quality.
[0026]
The request for reassignment of communication channels by the second connection control means may be configured to be repeated up to a predetermined number of times until a communication channel using a different slot is assigned from the switching destination base station. In this way, the problem that the communication channel reassignment request is repeated indefinitely is prevented.
[0027]
Further, when the second connection control means repeats the reassignment request of the communication channel, it is determined whether or not the reception quality detected by the reception quality detecting means is maintained at a predetermined level or more, and the reception quality is The communication channel reassignment request may be repeated when the predetermined level or higher is maintained, and the first connection control unit may be executed when the predetermined level is not maintained.
[0028]
With this configuration, when the reception quality from the switching source base station deteriorates during the execution of the second connection control means, the communication channel is not allocated to the switching destination base station, but is allocated. A wireless link is established by the communication channel. For this reason, it becomes possible to complete the handover before communication with the switching source base station becomes impossible during the connection control, whereby the reliability of the handover can be kept high.
[0029]
Furthermore, in order to achieve the third object, the third invention is the first invention, wherein the first handover control means is set to be equal to or higher than the first reception quality judgment level and lower than the second reception quality judgment level. Having a base station selection level of 1
The second handover control means includes a second base station selection level set to be equal to or higher than the second reception quality determination level, and switches a base station whose reception quality exceeds the second base station selection level to a switching destination. Is selected as a base station.
[0030]
Therefore, according to the third invention, in the second handover, it is possible to prevent a problem that a base station whose reception quality is deteriorated compared to the switching source base station is selected as a switching destination. A station can be handed over.
[0031]
Incidentally, if the base station selection level for the second handover is set in common with the base station selection level for the first handover, the first base station selection level is lower than the reception quality determination level for starting the second handover. In this case, there is a possibility that a base station whose reception quality is deteriorated as compared with the switching source base station is selected as the switching destination.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is a circuit block diagram showing a configuration of a PHS terminal which is a first embodiment of a mobile communication terminal apparatus according to the present invention.
[0033]
The PHS terminal (PS) includes a radio unit 1 equipped with an antenna 11, a modem unit 2, a TDMA unit 3, a call unit 4, a control unit 5, an information storage unit 6, a data communication unit 7, a key communication unit, An input unit 8 having a pad and a display unit 9 using a liquid crystal display (LCD) are provided.
[0034]
That is, a radio carrier signal arriving from a base station (CS) (not shown) is received by the antenna 11 and then input to the receiving unit 13 via the high frequency switch (SW) 12 of the radio unit 1. In the receiving unit 13, the received radio carrier signal is mixed with a local oscillation signal generated from the frequency synthesizer 14 and down-converted to a received intermediate frequency signal. The frequency of the local oscillation signal generated from the frequency synthesizer 14 is set to a value corresponding to the radio channel frequency according to an instruction from the control unit 5. The wireless unit 1 is provided with a received electric field strength detecting unit 16. The reception field strength detection unit 16 detects a reception field strength (RSSI) of a radio carrier signal that has arrived from a base station in communication or a neighboring base station, and the detected value is used for, for example, determination and display of reception quality. Is notified to the control unit 5.
[0035]
The received intermediate frequency signal output from the receiving unit 13 is input to the demodulating unit 21 of the modem unit 2. The demodulator 21 digitally demodulates the received intermediate frequency signal, thereby reproducing the digital demodulated signal.
[0036]
The TDMA decoding unit 31 of the TDMA unit 3 separates the digital demodulated signal for each reception time slot. If the data in the separated slot is audio data, the audio data is input to the interface unit 4. On the other hand, if the data of the separated slot is packet data or control data, these data are input to the data communication unit 7.
[0037]
The call unit 4 includes an ADPCM (Adaptive Differential Pulse Code Modulation) transcoder 41, a PCM codec 42, a speaker 43, and a microphone 44. The ADPCM transcoder 41 decodes the audio data output from the TDMA decoding unit 31. The PCM codec 42 converts the digital audio signal output from the ADPCM transcoder 41 into an analog signal, and outputs the audio signal from the speaker 43 in a loud sound.
[0038]
The data communication unit 7 receives the data supplied from the TDMA decoding unit 31 and supplies this data to the control unit 5. If the received data is control data, the control unit 5 analyzes the control data and performs necessary control. On the other hand, if the received data is packet data coming from a server or the like, the packet data is depacketized and then stored in the information storage unit 6 and supplied to the display unit 9 for display.
[0039]
On the other hand, the user's voice signal input to the microphone 44 is PCM-encoded by the PCM codec 42 and further compressed and encoded by the ADPCM transcoder 41. The encoded audio data is input to the TDMA encoding unit 32. Control data and packet data output from the control unit 5 are input to the TDMA encoding unit 32 via the data communication unit 7.
[0040]
The TDMA encoding unit 32 multiplexes the digital audio data output from the ADPCM transcoder 41 and the control data and packet data output from the data communication unit 7 by inserting them into the transmission time slot designated by the control unit 5. Turn into. The modulation unit 22 digitally modulates the transmission intermediate frequency signal with the multiplexed digital communication signal output from the TDMA encoding unit 32 and inputs the modulated transmission intermediate frequency signal to the transmission unit 15.
[0041]
The transmission unit 15 mixes the modulated transmission intermediate frequency signal with a local oscillation signal generated from the frequency synthesizer 14, up-converts it to a radio carrier frequency, and further amplifies it to a predetermined transmission power level. The radio carrier signal output from the transmitter 15 is transmitted from the antenna 11 to a base station (CS) (not shown) via the high frequency switch 12.
[0042]
By the way, the control unit 5 includes, for example, a microcomputer as a main control unit, and has a normal handover control unit 51, a seamless handover control unit 52, and a handover selection control unit 53 as main functions related to the present invention. ing. In the figure, handover is indicated by H.264. Abbreviated as O.
[0043]
The normal handover control means 51 interrupts communication with the communicating base station (switching source base station), searches for a neighboring base station in this state, and has the highest received electric field strength (RSSI). As the switching destination. Then, a link channel establishment request is transmitted to the selected base station, a link channel is allocated from the base station, and a predetermined connection is established with the switch-destination base station using the allocated link channel. After executing the control procedure, the connection destination base station is switched.
[0044]
The seamless handover control means 52 searches for neighboring base stations using the idle slot period and selects an appropriate base station as a switching destination while maintaining communication with the switching source base station. Then, a link channel establishment request is transmitted to the base station of the switching destination, the allocation of the link channel is received from the base station, and a predetermined channel is established with the base station of the switching destination using the allocated link channel. After executing the connection control procedure, the connection destination base station is switched.
[0045]
The handover selection control means 53 determines the reception quality of the radio carrier signal arriving from the communicating base station, the thresholds X1 and X2 for determining the received electric field strength (RSSI), and the threshold for determining the reception error rate (FER). The determination is made using the values Y1 and Y2, and the handover to be activated is selected and executed based on the determination result and a preset selection table. FIG. 8 shows an example of the configuration of the selection table.
[0046]
Next, a handover operation of the PHS terminal configured as described above will be described. FIG. 2 is a flowchart showing the procedure and contents of handover selection control in the control unit 5.
[0047]
During communication, the control unit 5 detects the received electric field strength (RSSI) at step 2a and detects the reception error rate (FER) at step 2b. In step 2c, the reception quality is determined by comparing the RSSI detection value and the FER detection value with threshold values X1, X2 and Y1, Y2, respectively. The determination result and the selection table shown in FIG. Based on the above, the handover control means to be activated is determined.
[0048]
For example, if RSSI ≧ X2 and FER <Y2, it is determined that the reception quality is good and no handover is performed. On the other hand, if FER ≧ Y1, it is determined that the handover is necessary immediately regardless of the detected value of the RSSI, the normal handover control means 51 is selected in step 2d, and the normal handover control is performed in step 2e. Is executed.
[0049]
In this normal handover control, as described above, communication with the communicating base station (switching source base station) is interrupted, and in this state, the neighboring base stations are searched to receive field strength (RSSI). The base station with the highest connection is selected as a switching destination, a link channel is established with the selected base station, and a predetermined connection control procedure is executed to switch the connecting base station.
[0050]
On the other hand, for example, assume that the reception quality is X1 ≦ RSSI <X2 and FER <Y2. In this case, the handover selection control means 53 first selects the seamless handover control means 52 in step 2f, and executes seamless handover.
[0051]
That is, as shown in FIG. 3, the seamless handover control means 52 maintains the communication with the base station in communication (switching source base station) as shown in FIG. Search for neighboring base stations by receiving Logical Control Channel). At this time, the search for the neighboring base stations is performed using an idle slot period. For this reason, the peripheral base station that transmits the LCCH during the idle slot period is a search target. For example, in FIG. 7, since the PHS terminal (PS) communicates using the slots T1 and R1, the base stations CS14 and CS15 that transmit the LCCH during the slots T1 and R1 are excluded from the search targets. The base stations CS11, CS12, CS13 that transmit the LCCH in other slot periods are to be searched.
[0052]
Subsequently, the handover selection control means 53 determines whether or not there is an effective peripheral base station as a switching destination in step 2h based on the search result of the peripheral base station. Here, whether or not the switching destination is valid is determined by comparing the level of the RSSI of the LCCH received from the neighboring base station with the switching destination base station selection level set separately from the normal handover for seamless handover. The peripheral base station whose RSSI is higher than the switching destination base station selection level is selected as an effective base station as the switching destination. If there are a plurality of neighboring base stations that satisfy this condition, the base station with the largest RSSI is selected as the switching destination.
[0053]
Note that the switching destination base station selection level for seamless handover is set as follows, for example. FIG. 12 to FIG. 16 each show an example. That is, FIG. 12 shows that the switching destination base station selection level for seamless handover is set to the same level as the RSSI determination level for starting seamless handover, and FIG. 13 shows a level higher by Δ than the seamless handover starting level. It is set. In FIG. 14, the value of Δ is set to the same value as the increase Δ1 of the normal handover switching destination base station selection level with respect to the normal handover activation level. Further, FIG. 15 shows the level used when seamless handover is activated based on the RSSI determination result and the level used when seamless handover is activated based on the FER determination result as the switching destination base station selection level for seamless handover. The level to be set is set separately. FIG. 16 shows a case where the normal handover switching destination base station selection level and the seamless handover switching destination base station selection level are both set higher than the normal handover activation level and the seamless handover activation level.
[0054]
Even when any of the above setting examples is used, the problem that the base station whose RSSI is lower than the seamless handover activation level is selected as the switching destination is prevented, and thus an appropriate base station can always be selected as the handover destination. it can.
[0055]
Incidentally, when the seamless handover switching destination base station selection level is also used as the normal handover switching destination base station selection level as shown in FIG. In this area, a base station whose RSSI is lower than the seamless handover activation level is selected as a switching destination, which is very undesirable.
[0056]
Note that the activation level for normal handover and the switching destination base station selection level may be changed by an instruction from the base station. To cope with this, when the activation level and switching destination base station selection level for normal handover are changed, the activation level and switching destination base station selection level for seamless handover are changed and set in conjunction with the change settings. You may make it do.
[0057]
When an effective base station is found as a switching destination, the handover selection control means 53 proceeds to step 2i and continues the seamless handover control here. FIG. 3 is a sequence diagram showing the control procedure. In this control procedure, since a signal specified in RCR STD-28 is exchanged, description thereof is omitted.
[0058]
On the other hand, if a valid base station is not found in the search for the neighboring base stations, the handover selection control means 53 proceeds to step 2j and stops the handover here. FIG. 4 is a sequence diagram showing the control procedure. In this case, the PHS terminal continues to communicate with the switching source base station. However, the reception quality determination condition at this time is X1 ≦ RSSI <X2 and FER <Y2 as shown in FIG. 8, and the reception quality is relatively good. For this reason, even if the handover is canceled, there is no fear that a serious trouble is caused in communication.
[0059]
On the other hand, for example, it is assumed that the reception quality is RSSI <X2 and Y2 ≦ FER <Y1, or X1 <RSSI and FER <Y2. In this case, the handover selection control means 53 proceeds to step 2k and selects the seamless handover control means 52 here to execute the seamless handover. This seamless handover control is performed in steps 21 to 2n, and the procedure and contents thereof are the same as those described in steps 2g to 2i.
[0060]
However, if no effective base station is found as a switching destination in step 2m, the process proceeds to step 2o where normal handover is executed. Therefore, in this case, although communication is temporarily interrupted, the PHS terminal is handed over to another neighboring base station with higher probability, and communication can be continued. FIG. 5 is a sequence diagram showing a control procedure in this case.
[0061]
If the reception quality determination result is RSSI ≧ X2 and Y2 ≦ FER <Y1, it is determined that there is a high possibility of causing interference, and the control unit 5 has the same base station in step 2p. Try switching to another communication channel (TCH). By doing so, communication failure due to interference is eliminated. FIG. 6 shows the control sequence. In this control procedure, since the signal specified in RCR STD-28 is exchanged, the description thereof is omitted.
[0062]
As described above, in the first embodiment, the communication between the switching source base station and the normal handover control means 51 that executes the handover procedure by interrupting the communication with the switching source base station is maintained. And seamless handover control means 52 for executing the handover procedure as it is, determining the reception quality of the signal arriving from the switching source base station, and based on the determination result and a selection table prepared in advance The normal handover control means 51 and the seamless handover control means 52 are selectively executed.
[0063]
Therefore, for example, seamless handover is performed when the reception quality is relatively good, so that high quality communication can be maintained with a short interruption time of communication, and even if a suitable base station is not found as a switching destination, Returning to communication with the station or executing a normal handover makes it difficult to fail a handover.
[0064]
On the other hand, when reception quality deteriorates, normal handover is performed with priority given to successful handover from the beginning, so the communication interruption time becomes longer, but it is suitable as a switching destination from among a larger number of neighboring base stations. Since a simple base station can be selected, the handover can be successful with a high probability.
[0065]
In the first embodiment, the reception quality is determined using both the reception field strength and the reception error rate, and the reception field strength and the reception error rate are set to two threshold values X1, X2 and Y1, Y2, respectively. It is made to judge using. Therefore, the reception quality can be determined more finely and precisely, and more appropriate handover can be selected by using the determination result. In particular, when the reception quality is relatively good, the seamless handover is positively selected, so that a high-quality handover with a short interruption of communication can be performed while the success probability of the handover is kept high. On the other hand, in a state where the reception error rate (FER) is remarkably deteriorated, by selecting normal handover unconditionally, handover can be completed with a high success probability, thereby promptly and reliably degrading communication quality. Can be recovered.
[0066]
Furthermore, in the first embodiment, in order to determine a base station that is effective as a switching destination, a switching destination base station selection level for seamless handover is provided in addition to the switching destination base station selection level for normal handover. The switching destination base station is selected using these different selection levels according to the type of handover. For this reason, it is possible to eliminate the problem of selecting a base station whose reception quality is deteriorated as compared with the switching source base station as a switching destination, and it is possible to always select an appropriate base station.
[0067]
The following various modifications can be considered in the first embodiment described above. For example, the selection table for selecting the type of handover can be configured as shown in FIGS. 9 to 11 in addition to FIG.
[0068]
9 is the same as that shown in FIG. 8 in that the determination of reception quality is performed by combining both RSSI and FER, but an area for stopping handover when seamless handover fails, and The area in which normal handover is executed when seamless handover fails is different from that in FIG.
[0069]
The one shown in FIG. 10 is used when the reception quality is determined only by RSSI. In this example, two threshold values X1 and X2 are used. When the RSSI detection value is equal to or greater than the threshold value X2, handover is performed. If the RSSI detection value is less than the threshold value X2 and greater than or equal to X1, seamless handover is executed. If this fails, the handover is stopped. When the RSSI detection value falls below the threshold value X1, first, seamless handover is attempted. If this fails, normal handover is executed.
[0070]
The one shown in FIG. 11 is used when the reception quality is determined only by FER. In this example, two threshold values Y1 and Y2 are used. When the FER detection value is equal to or higher than threshold value Y2, handover is performed. If the FER detection value is less than the threshold value Y2 and greater than or equal to Y1, seamless handover is executed. If this fails, the handover is stopped. When the FER detection value deteriorates below the threshold value Y1, the normal handover is executed unconditionally.
[0071]
Note that in the PHS terminal (PS) according to the present embodiment, in order to realize seamless handover, channel search for other frequencies is performed during communication, so that the frequency synthesizer 14 can switch and set at least two frequencies. Composed.
[0072]
Further, in the present embodiment, it is appropriate that the mobile communication terminal has a single radio unit, and the normal handover control unit and the seamless handover control unit can be selectively executed by one radio unit. Is.
[0073]
In addition, the reception quality determination level for starting normal handover and seamless handover is not limited to two, but may be three or more or one, and the value of the switching destination base station selection level can be set to various values. . Furthermore, various modifications can be made to the procedure and contents of handover selection control.
[0074]
(Second Embodiment)
In the second embodiment according to the present invention, during execution of seamless handover, the communication channel assigned from the base station selected as the switching destination is the same slot as the communication channel in use with the switching source base station. Communication channel assigned by the switching destination base station by interrupting communication with the switching source base station based on the reception quality from the switching source base station at that time. To select whether to execute the first connection procedure for connecting the radio link or to execute the second connection procedure for requesting reassignment of the communication channel to the switching destination base station. is there.
[0075]
FIG. 18 is a circuit block diagram showing the configuration of the PHS terminal according to the second embodiment. In the figure, the same parts as those in FIG.
[0076]
The control unit 5 'includes a first connection control means 54 for executing the first connection procedure and a second connection control means for executing the second connection procedure as main control functions according to the present invention. 55 and a connection procedure selection control means 56 are provided.
[0077]
The first connection control means 54 uses the same slot as the communication channel in use with the switching source base station when the communication channel assigned from the base station selected as the switching destination is used during seamless handover. If so, the communication with the switching source base station is interrupted at that time, and a procedure for connecting the radio link through the communication channel assigned by the switching destination base station is executed.
[0078]
During the seamless handover, the second connection control means 55 uses the same slot as the communication channel used by the base station selected as the switching destination for the communication channel assigned to the switching source base station. If so, a procedure for requesting reassignment of the communication channel to the switching destination base station and receiving assignment of the communication channel using another slot is executed.
[0079]
The connection procedure selection control means 56 uses the same slot as the communication channel in use with the switching source base station as the communication channel assigned from the base station selected as the switching destination during the seamless handover. If so, the reception quality from the switching source base station at that time is determined, and if the reception quality is equal to or higher than a predetermined level, the second connection control means 55 is selected and executed. If not, the first connection control means 54 is selected and executed.
[0080]
Next, the seamless handover operation in the PHS terminal configured as described above will be described. 19 and 20 are flowcharts showing the control procedure and control contents.
[0081]
For example, when seamless handover is selected by the handover selection control means 53 described in the first embodiment, the control unit 5 ′ maintains the communication with the switching source base station in step 19a, A search process for neighboring base stations is performed in 19b, and it is determined whether there is a valid base station as a switching destination based on the search result. The search for the neighboring base station detects the RSSI of the LCCH arriving from the neighboring base station using the idle slot period in the same manner as described in the first embodiment, and uses the detected RSSI value. This is done by comparing with the switching destination base station selection level set for seamless handover.
[0082]
If no effective base station is found as a result of the search for the neighboring base stations, communication with the switching source base station is interrupted in step 19d, and normal handover control is executed. Note that the normal handover control may not be executed and the handover may be stopped to continue communication with the switching source base station.
[0083]
On the other hand, it is assumed that an effective base station is found by the search processing of the neighboring base stations. Then, in step 19e, the control unit 5 ′ determines whether or not the reception quality from the switching source base station at the present time is good. This determination is made by comparing at least one of RSSI and FER of the radio signal coming from the switching source base station with a preset threshold value. When the reception quality is maintained at a relatively good level equal to or higher than the threshold value, the second connection control procedure is selected and executed as follows.
[0084]
In other words, when the second connection control procedure is selected, the control unit 5 ′ continues to maintain the communication with the switching source base station in step 19 f, and the link channel is transmitted to the base station selected as the switching destination. An establishment request is transmitted and a link channel is allocated from the base station. Then, it is determined in step 19h whether or not the allocated communication channel (TCH) uses the same slot as the communication channel being used with the switching source base station.
[0085]
As a result of this determination, if the assigned communication channel uses another slot, such as the base stations CS11, CS12, CS13 shown in FIG. 21, the control unit 5 ′ It is determined that the wireless link connection procedure can be executed while maintaining the communication between the two, and the process proceeds to step 20c in FIG. Then, the process for connecting the radio link by the assigned communication channel is executed, and when the radio link is formed with the switching destination base station, the connection control procedure shown in FIG. 3 is executed. After that, in step 20d, the communication channel with the switching source base station is released. Thus, the handover is completed, and thereafter the PHS terminal can continue communication with the switching destination base station.
[0086]
On the other hand, as a result of the above determination, it is assumed that the assigned communication channel uses the same slot as the communication channel in use with the switching source base station as in the base station CS14 shown in FIG. In this case, the control unit 5 ′ transmits a communication channel reassignment request to the switching destination base station in step 19j. Then, when another communication channel is assigned from the switching destination base station in response to this request, the control unit 5 'indicates that the reassigned communication channel is the same slot as the communication channel in use with the switching source base station. It is determined in step 19h whether or not it is used. If the assigned communication channel uses another slot, the process proceeds to step 20c as described above, and a wireless link connection procedure using the assigned communication channel is executed.
[0087]
However, in response to the above communication channel reassignment request, if only the communication channel using the same slot as the communication channel being used with the switching source base station can be assigned, the control unit 5 'repeats again. A communication channel assignment request is sent and a communication channel assignment is received. Thereafter, the communication channel allocation request procedure is repeated until a communication channel using another slot is allocated from the switching destination base station.
[0088]
However, the number of times the communication channel reassignment request procedure is repeated (the number of retries) is counted in step 19k, and when the number of retries exceeds 3, the control unit 5 'gives up on the retry and from step 19i to step 20e. Migrate to Then, after the communication with the switching source base station is interrupted in step 20e, the procedure for connecting the radio link by the communication channel allocated from the switching destination base station is executed in step 20f. Then, when the communication link is formed with the switching destination base station, the communication link with the switching source base station is released in step 20g, and the wireless link formed with the switching destination base station is subsequently released. Continue to communicate.
[0089]
Further, when repeating the communication channel reassignment request procedure, the control unit 5 ′ determines whether or not the reception quality from the switching source base station maintains a predetermined level in step 19g. If the reception quality is maintained at a predetermined level or higher, the communication channel reallocation request procedure is executed. On the other hand, when the reception quality falls below a predetermined level, the control unit 5 ′ proceeds from step 19g to step 20e, and thereafter executes the same procedure as when the number of retries exceeds three.
[0090]
On the other hand, if it is determined in step 19e that the reception quality from the switching source base station has dropped below the threshold, the control unit 5 ′ determines that it is necessary to complete the handover as soon as possible. 1 connection control procedure is selected and executed as follows.
[0091]
That is, when detecting the deterioration of the reception quality, the control unit 5 ′ proceeds from step 19e to step 20a. Then, while maintaining communication with the switching source base station, a link channel establishment request is transmitted to the base station selected as the switching destination, and allocation of the link channel is received from the base station. Then, in step 20b, it is determined whether or not the allocated communication channel (TCH) uses the same slot as the communication channel being used with the switching source base station.
[0092]
As a result of this determination, if the assigned communication channel uses another slot, the control unit 5 ′ proceeds to step 20c to connect the radio link by the assigned communication channel. Execute the process. Then, when a radio link is formed with the switching destination base station, after performing the connection control procedure shown in FIG. 3, the communication channel with the switching source base station is released in step 20d. Thus, the handover is completed, and thereafter the PHS terminal can continue communication with the switching destination base station.
[0093]
On the other hand, as a result of the above determination, it is assumed that the assigned communication channel uses the same slot as the communication channel in use with the switching source base station. In this case, the control unit 5 ′ does not perform the communication channel reassignment request procedure, moves to step 20 e, immediately interrupts communication with the switching source base station, and then assigns from the switching destination base station. In step 20f, a procedure for connecting a wireless link through the designated communication channel is executed. Then, when the communication link is formed with the switching destination base station, the communication link with the switching source base station is released in step 20g, and the wireless link formed with the switching destination base station is subsequently released. Continue to communicate.
[0094]
As described above, in the second embodiment, during execution of seamless handover, the communication channel assigned from the base station selected as the switching destination is the same slot as the communication channel in use with the switching source base station. Is used, it is determined whether or not the reception quality from the switching source base station at that time holds a predetermined level or higher. When the reception quality is maintained at a predetermined level or higher, the second connection control procedure is selected, and the communication channel of the switching destination base station is maintained while maintaining communication with the switching source base station. A reassignment request is made, and a wireless link is connected by the communication channel assigned thereby. On the other hand, when the reception quality deteriorates below a predetermined level, the first connection control procedure is selected, the communication with the switching source base station is interrupted, and the communication allocated from the switching destination base station. Procedures are executed to connect wireless links by channel.
[0095]
Therefore, when the reception quality from the switching source base station is relatively good, the communication channel reassignment procedure for the switching destination base station is executed, thereby waiting for the communication channel using another slot to be allocated, Since the wireless link connection control procedure is performed, the communication with the switching source base station is not interrupted during the handover period, and as a result, the communication quality is maintained at a high quality. That is, high quality handover can be performed while maintaining communication with the switching source base station as much as possible.
[0096]
On the other hand, when the reception quality from the switching source base station deteriorates, the communication with the switching source base station is interrupted, and a radio link is formed by the communication channel allocated from the switching destination base station. . For this reason, the handover can be completed quickly and reliably.
[0097]
The present invention is not limited to the above embodiment. For example, although cases have been described with the above embodiments as examples where the PHS terminal activates handover, there are also cases where handover is activated in accordance with an instruction from the base station. In this case, it is preferable to perform control so that seamless handover is executed first, and normal handover is executed when this fails. However, if the reception quality from the base station is remarkably deteriorated and there is no point in executing seamless handover, immediate normal handover may be selected and executed without selecting seamless handover.
[0098]
In addition, the function of selectively executing the first and second connection controls described in the second embodiment may be applied to the seamless handover control procedure described in the first embodiment.
[0099]
Furthermore, in each of the above embodiments, the PHS terminal has been described as an example. However, if the mobile communication terminal apparatus is used in a cellular mobile communication system adopting the TDMA system as a radio access system, PDC (Personal Digital Cellular) or GSM ( The present invention can also be applied to terminal devices used in other cellular mobile communication systems such as Global System for Mobile Communication.
[0100]
In addition, the circuit configuration at the end of the mobile communication terminal apparatus, the procedure and contents of handover selection control and connection procedure selection control, the setting value of the reception quality judgment level (handover activation level), and the like are within the scope of the present invention. Various modifications can be made.
[0101]
【The invention's effect】
  As described in detail above, in the first invention, as a handover procedure, a switching destination base station is selected in a state where communication with the switching source base station is interrupted, and a predetermined connection is established with the base station. In a state where the communication between the first handover control means for switching the connection destination base station after executing the control procedure and the switching source base station is maintained,Use a period other than the slot assigned to your device,A mobile communication terminal apparatus comprising: a second handover control unit that selects a switching destination base station, executes a predetermined connection control procedure with the base station, and then switches the connecting base station; A reception quality detection means for detecting the reception quality of a radio signal coming from a destination base station; and a handover selection means. When the connection destination base station is switched by handover, the reception quality detection is performed by the handover selection means. The first handover and the second handover are selectively executed based on the reception quality detected by the means.
[0102]
  Therefore, according to the first invention,For example, when the reception quality is relatively good, the second handover can be selected and executed with priority on the communication quality. On the other hand, when the reception quality deteriorates, the first handover is given priority on the success of the handover. Can be selected and executed. That is,To provide a mobile communication terminal device that can effectively use a normal first handover and a seamless second handover, thereby achieving both improvement in communication quality and increase in handover success probability. Can do.
[0103]
On the other hand, in the second invention, in a mobile communication terminal apparatus having a seamless handover procedure, communication using the same slot as the communication channel used between the switching destination base station and the switching source base station. As connection control means to be executed when a channel is assigned, communication with the switching source base station is interrupted and the connection control procedure is executed using the communication channel assigned by the switching destination base station. Requesting the switching destination base station to reallocate the communication channel while maintaining communication between the first connection control means and the switching source base station, and in response to this request, the switching destination base station And a second connection control means for executing the connection control procedure using the communication channel when a communication channel using a different slot is assigned.
[0104]
Then, when executing the connection control procedure, the first control means and the second control means are selectively executed based on the reception quality detection result of the radio signal coming from the switching source base station. I try to let them.
[0105]
Therefore, according to the second invention, when a communication channel using the same slot as the communication channel being used is allocated between the switching destination base station and the switching source base station during the seamless handover, An optimal wireless connection procedure can be selected and executed in accordance with the reception quality at that time, thereby providing a mobile communication terminal apparatus that achieves both maintenance of communication quality and successful handover.
[0106]
In the third invention, when the first handover control means has the first base station selection level set to be equal to or higher than the first reception quality determination level and lower than the second reception quality determination level, The second handover control means includes a second base station selection level set to be equal to or higher than the second reception quality determination level, and selects a base station whose reception quality exceeds the second base station selection level as a switching destination. The base station is selected.
[0107]
Therefore, according to the third invention, in the second handover, it is possible to prevent a problem that a base station whose reception quality is deteriorated compared to the switching source base station is selected as a switching destination. It is possible to provide a mobile communication terminal apparatus capable of performing handover to a station.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a configuration of a PHS terminal according to a first embodiment of the present invention.
FIG. 2 is a flowchart showing the procedure and contents of handover selection control by the PHS terminal shown in FIG. 1;
FIG. 3 is a sequence diagram showing a procedure for seamless handover.
FIG. 4 is a sequence diagram showing a procedure when a handover is canceled during execution of a seamless handover procedure.
FIG. 5 is a sequence diagram showing a procedure when a transition is made to a normal handover procedure during execution of a seamless handover procedure.
FIG. 6 is a sequence diagram showing a procedure when switching communication channels with the same base station.
FIG. 7 is a diagram for explaining a search operation of neighboring base stations during execution of seamless handover.
FIG. 8 is a diagram showing a first configuration of a selection table used for selecting a handover type.
FIG. 9 is a diagram showing a second configuration of a selection table used for selecting a handover type.
FIG. 10 is a diagram showing a third configuration of a selection table used for selecting a handover type.
FIG. 11 is a diagram showing a fourth configuration of a selection table used for selecting a handover type.
FIG. 12 is a diagram showing a first setting example of a switching destination base station selection level.
FIG. 13 is a diagram showing a second setting example of a switching destination base station selection level.
FIG. 14 is a diagram showing a third setting example of a switching destination base station selection level.
FIG. 15 is a diagram showing a fourth setting example of a switching destination base station selection level.
FIG. 16 is a diagram showing a fifth setting example of a switching destination base station selection level.
FIG. 17 is a diagram illustrating a conventional setting example of a switching destination base station selection level.
FIG. 18 is a circuit block diagram showing a configuration of a PHS terminal according to a second embodiment of the present invention.
FIG. 19 is a flowchart showing the first half of a seamless handover control procedure in the PHS terminal shown in FIG. 18;
FIG. 20 is a flowchart showing the latter half of the seamless handover control procedure in the PHS terminal shown in FIG. 18;
FIG. 21 is a diagram showing an example of a communication channel assigned from a switching destination base station.
[Explanation of symbols]
1 ... Radio section
2. Modem part
3 ... TDMA section
4 ... Calling part
5, 5 '... control unit
6. Information storage unit
7. Data communication part
8 ... Input section
9 ... Display section
11 ... Antenna
12 ... High frequency switch (SW)
13: Receiver
14 ... Synthesizer
15 ... Transmitter
16: Received electric field strength detection unit
21. Demodulator
22: Modulation section
31 ... TDMA decoding unit
32 ... TDMA encoding section
41 ... ADPCM transcoder
42 ... PCM codec
43 ... Speaker
44 ... Microphone
51. Normal handover control means
52. Seamless handover control means
53. Handover selection control means
54. First connection control means
55. Second connection control means
56. Connection procedure selection control means

Claims (11)

In a mobile communication terminal used in a cellular mobile communication system adopting a time division multiple access method,
In a state where communication with the switching source base station is interrupted, a switching destination base station is selected after selecting a switching destination base station and executing a predetermined connection control procedure with the base station. First handover control means for executing handover of
After performing a connection control procedure including at least an operation of selecting a switching destination base station using a period other than the slot allocated to the own device while maintaining communication with the switching source base station. A second handover control means for executing a second handover for switching a connection destination base station;
Reception quality detection means for detecting the reception quality of the radio signal coming from the connected base station;
And a handover selection means for selectively executing the first handover and the second handover based on a detection result of the reception quality detection means when switching a connection destination base station. Mobile communication terminal device. The handover selection means includes
A first reception quality determination level and a second reception quality determination level set higher than the first reception quality determination level;
Said receiving the selected to execute the second handover state reception quality detected is less than the the first reception quality determination level or more and the second reception quality determination level by the quality detection unit, the reception quality mobile communication terminal apparatus according to claim 1, characterized in that said first handover the selected executed when the reception quality detected by the detecting means is lower than said first reception quality determination level. When the reception quality detection means has a function of detecting the received electric field strength of the radio signal coming from the switching source base station,
The handover selection means includes
As a threshold value for determining the received electric field strength, a first threshold value and a second threshold value set higher than the first threshold value,
When the received electric field strength detected by the received quality detecting means is not less than the first threshold and less than the second threshold, the second handover is selected and executed, and the detected received electric field is detected. When the strength is less than the first threshold, the second handover is first selected and executed, and when the second handover fails, the first handover is continuously selected and executed. The mobile communication terminal device according to claim 1. When the reception quality detection means has a function of detecting a reception error rate of a radio signal coming from a switching source base station,
The handover selection means includes
As a threshold value for determining the reception error rate, a third threshold value, and a fourth threshold value set lower than the third threshold value,
When the reception error rate detected by the reception quality detection means is equal to or higher than the fourth threshold value and lower than the third threshold value, the second handover is selected and executed.
The mobile communication terminal apparatus according to claim 1, wherein when the detected reception error rate is equal to or greater than the third threshold value, the first handover is selected and executed. When the reception quality detection means has a function of detecting the reception field strength and the reception error rate of the radio signal arriving from the switching source base station,
The handover selection means includes
The threshold value for determining the received electric field strength includes a first threshold value and a second threshold value set higher than the first threshold value, and determines the reception error rate. A threshold value for the third threshold value and a fourth threshold value set lower than the third threshold value,
In a state where the detection value of the reception error rate obtained by the reception quality detection means is not less than the third threshold value, the first handover is selected and executed regardless of the detection value of the reception electric field strength,
The detection value of the reception error rate obtained by the reception quality detection means is not less than the fourth threshold value and less than the third threshold value, and the detection value of the reception electric field strength is a second threshold value. If the detected value of the reception error rate is less than the fourth threshold value and the detected value of the received electric field strength is less than the first threshold value, the second handover is selected. And if the second handover fails, select and execute the first handover,
In a state where the detection value of the reception error rate is less than the fourth threshold value and the detection value of the reception electric field strength is greater than or equal to the first threshold value and less than the second threshold value, The mobile communication terminal apparatus according to claim 1, wherein when the second handover fails by selecting and executing the handover, the handover is stopped. When the reception quality detection means has a function of detecting the reception field strength and the reception error rate of the radio signal arriving from the switching source base station,
The handover selection means includes
The threshold value for determining the received electric field strength includes a first threshold value and a second threshold value set higher than the first threshold value, and determines the reception error rate. A threshold value for the third threshold value and a fourth threshold value set lower than the third threshold value,
In a state where the detection value of the reception error rate obtained by the reception quality detection means is not less than the third threshold value, the first handover is selected and executed regardless of the detection value of the reception electric field strength,
When the detection value of the reception error rate obtained by the reception quality detection means is less than the third threshold value and the detection value of the received electric field strength is less than the first threshold value, the second handover If the second handover fails, the first handover is selected and executed.
The detection value of the reception error rate detected by the reception quality detection means is less than the fourth threshold value, and the detection value of the received electric field strength is greater than or equal to the first threshold value and less than the second threshold value. 2. The mobile communication terminal apparatus according to claim 1, wherein, in the state, the second handover is selected and executed, and the handover is stopped when the second handover fails.   The reception error rate detected by the reception quality detection means is not less than the fourth threshold value and less than the third threshold value, and the received electric field strength is not less than the second threshold value. The communication channel switching control means for executing control for switching to another communication channel held by the base station to which the communication channel is connected without activating handover is further provided. Or the mobile communication terminal device of 6. Used in cellular mobile communication systems that employ a time division multiple access method, and when switching the connection destination base station, keeps communication with the switching source base station, except for the slot assigned to the own device. In a mobile communication terminal device having a handover function for switching a connection destination base station after performing a connection control procedure including at least an operation of selecting a switching destination base station using the period of
During execution of the handover function, when the communication channel assigned from the switching destination base station is the same slot as the communication channel being used with the switching source base station, the switching source base station First connection control means for executing the connection control procedure using a communication channel assigned by the switching destination base station by interrupting communication between
During execution of the handover function, when the communication channel assigned from the switching destination base station is the same slot as the communication channel being used with the switching source base station, the switching source base station When the communication channel is requested to be reassigned to the switching destination base station while maintaining the communication between the switching destination base station and the communication channel using a different slot is assigned from the switching destination base station in response to the request, the communication is performed. Second connection control means for performing the connection control procedure using a channel;
Reception quality detecting means for detecting the reception quality of the radio signal coming from the switching source base station;
A selection unit that selectively executes the first connection control unit and the second connection control unit based on a detection result of the reception quality detection unit when executing the connection control procedure; A mobile communication terminal device.   The second connection control means repeats the communication channel reassignment request up to a predetermined number of times until a communication channel using a different slot is assigned from the switching destination base station. The mobile communication terminal device according to claim 9.   The second connection control means determines whether or not the reception quality detected by the reception quality detection means maintains a predetermined level or more when repeating the request for reassignment of the communication channel, and the reception quality is 11. The mobile communication terminal apparatus according to claim 10, wherein a request for reassigning a communication channel is repeated when a predetermined level or more is maintained, and the first control unit is executed when the request is not maintained. . When the first handover control means has a first base station selection level that is set to be equal to or higher than the first reception quality determination level and relatively lower than the second reception quality determination level,
The second handover control means includes a second base station selection level set higher than the second reception quality determination level, and switches a base station whose reception quality exceeds the second base station selection level to a switching destination. The mobile communication terminal apparatus according to claim 2, wherein the mobile communication terminal apparatus is selected as a base station.

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