JP2008042764A - Mobile radio terminal device - Google Patents

Abstract

A mobile radio terminal apparatus capable of preventing a decrease in throughput due to cell switching is provided.
When executing Inter Node-B handover, a control unit 100 includes a cell ID of a target cell Ct, a scrambling code (SCR) and a frequency (FREQ) used for connection with a source cell Cs. Are associated and stored in the cell list storage area 30a, and the connection time to a new node is measured. Then, when Event1D occurs, the control unit 100 is receiving data and is a node to which Target Node-B has been connected before, and the connection time t to Source Node-B is less than or equal to threshold Ts. If so, it is assumed that there is a high possibility of data loss and Inter Node-B handover, and the value of Time to Trigger is increased N times to extend the determination period of necessity of handover. I made it.
[Selection] Figure 1

Description

  The present invention relates to a radio communication system such as an automobile / mobile phone system or a wireless LAN, and more particularly to a radio communication system that performs spread spectrum communication to perform CDMA (Code Division Multiple Access) communication.

In recent years, spread spectrum communication schemes that are resistant to interference and interference have attracted attention as one of communication schemes applied to wireless mobile communication systems. The WCDMA system using this spread spectrum communication system is superior in transmitting and receiving image information, moving images, and the like because the communication band is wider than the conventional system. Further, HSDPA intended for high-speed packet transmission (High Speed Data Packet Access) scheme standardized by ^{3GPP (3 rd Generation Partnership Project)} Rel.5 ( e.g., see Non-Patent Document 1), commercial service in 2006 Is supposed to be started.

  In this HSDPA method, it is said that a maximum throughput of 14.4 Mbps can be obtained in the downlink. However, compared to Release 99, which is a conventional packet method, this HSDPA method is greatly influenced by the throughput according to the quality of the downlink. Therefore, when the reception state is not good, the throughput is not so much.

  As for handover processing that occurs at the cell boundary, conventionally, retransmission processing (in the order of several hundreds of milliseconds) was performed in the RLC layer when an error occurred while maintaining the line quality with soft handover. In the HSDPA method, Only hard handover exists from the viewpoint of effective use of system resources, and retransmission control is performed at high speed (on the order of several tens of ms) at the MAC layer.

HSDPA cell switching is roughly divided into Intra Node-B and Inter Node-B depending on the relationship between the cell before switching and the cell after switching. Since it is discarded, there is a problem that retransmission at a low-speed RLC layer occurs and throughput does not increase.
3GPP TS 25.308 V5.7.0 (2004-12) 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; High Speed Downlink Packet Access (HSDPA); Overall description; Stage 2 (Release 5) 3GPP publication, December 2004 v5. 7.0, p.21-25.

In a conventional mobile radio terminal apparatus that adopts the HSDPA method, a packet during communication when a cell is switched may be discarded, which causes retransmission at a low-speed RLC layer and does not increase throughput. There was a problem.
The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a mobile radio terminal apparatus capable of preventing a decrease in throughput due to cell switching.

  In order to achieve the above object, the present invention provides a mobile radio terminal apparatus that performs radio communication with a base station accommodated in a network, and receives signals from a first base station connected to the base station and other second base stations. Detecting means for detecting the reception level of the received radio signal, and a relationship in which the determination conditions preset by the respective reception levels of the first base station and the second base station detected by the detecting means are satisfied for a preset determination time A first determination unit that determines whether or not the handover is necessary, and a handover unit that performs a handover from the first base station to the second base station according to the determination result of the first determination unit, Second control means for determining whether or not data communication through the base station is in progress, and condition control for increasing the determination time used by the first determination means for determination when the second determination means determines that data communication is in progress hand And so that configured by including and.

  As described above, in the present invention, the determination condition in which the reception level of the radio signal received from each of the connected first base station and the other second base station is set in advance at the predetermined determination time. The necessity of handover is determined based on whether or not the relationship is satisfied, and if it is determined that data communication is in progress, it is determined that there is no need for handover by extending the above determination time. I try to make it easier.

  Therefore, according to the present invention, since it is difficult to perform handover during data communication, it is possible to provide a mobile radio terminal apparatus capable of preventing a decrease in throughput due to cell switching.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The handover in HSDPA is a hard handover triggered by Event 1d (Best Cell Change). This handover is performed according to whether the source cell Cs to which the mobile station was connected before the handover and the target cell Ct to be handed over by the mobile station belong to the same Node-B, the Intra Node-B handover, the Inter Node -B Classified as handover. In the following description, the base station BS (node) that forms the Source cell Cs is referred to as Source Node-B, and the base station BS (node) that forms the Target cell Ct is referred to as Target Node-B.

  Intra Node-B handover is shown in FIG. As shown in this figure, in the Intra Node-B handover, for example, a handover between cells formed by the same base station, the Source cell Cs and the Target cell Ct are synchronized. For this reason, the packet in the MAC-hs buffer of Node-B can be taken over.

  Inter Node-B handover is shown in FIG. As shown in this figure, the Inter Node-B handover is a handover between cells formed by different base stations, for example, so that the Source cell Cs and the Target cell Ct are not synchronized. For this reason, since the packet in the MAC-hs buffer of Node-B cannot be taken over, at the time of handover, the Source base station sends a Transport Channel Reconfiguration message to the mobile station to instruct to reset the MAC-hs data. Do. Along with this instruction, the following problems (1) to (3) occur.

(1) The mobile station must discard the retransmission data in its own MAC-hs buffer. (2) The base station must discard the MAC-hs data buffered for its own scheduling.
(3) RNC Reallocation takes time (Action Time), and data transmission / reception is not performed between the base station and the mobile station for a while.

  Therefore, if Inter Node-B handover occurs frequently due to the mobile station being located at the cell boundary, the RLC retransmissions accompanying the discard of the buffer increase rapidly, leading to a decrease in throughput. For these reasons, when using HSDPA, it should be distinguished from the viewpoint of throughput that the frequency of handover between Intra Node-B and Inter Node-B is different, but this is not the case at present.

The evaluation formula (e) for determining the necessity of Event1D handover is shown below. In this evaluation formula, M indicates a reception level of CPICH (Common Pilot Indicate Channel). CIO (Cell Individual Offset) is an offset parameter provided for each cell, and the larger the value, the more difficult the handover from the corresponding cell to another cell. H _1d is a hysteresis value for preventing fluttering due to repeated handovers that may occur near the cell boundary. Note that the suffix “S” indicates the Source cell Cs, and the suffix “T” indicates the Target cell Ct.

  If you try to add an offset with this parameter CIO, it will affect other Event1a, 1b, 1c, but Event1a, 1b, 1c is a soft handover for Release 99, and it is an Intra Node-B handover. Since there is no need to distinguish between Inter Node-B handover, CIO is normally set to 0.

  Therefore, in the present invention, as a means for distinguishing between Intra Node-B and Inter Node-B, it is not determined based on a cell-specific offset, but based on whether a Mac-hs reset request is received from the base station, Distinguish between Intra Node-B and Inter Node-B. If there is a risk of fluttering due to repeated handovers, the time required to start Cell Change after the Event1d condition is satisfied (Time to Trigger) is lengthened, and the necessity of handover is Judgment was made. Hereinafter, it will be described in detail together with a specific configuration of the mobile station.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 3 shows the configuration of a mobile radio terminal apparatus according to an embodiment of the present invention. The mobile radio terminal apparatus performs radio communication with a base station BS accommodated in a mobile communication network by a code division multiple access (CDMA) system, and includes a transmission / reception unit 10, a signal processing unit 20, a storage unit 30, and a control unit. 100.

  The transmission / reception unit 10 includes an RF reception unit 11, a baseband demodulation unit 12, a baseband modulation unit 13, and an RF transmission unit 14. The RF reception unit 11 receives a radio signal transmitted from the base station BS through an antenna, and down-converts a radio signal having a frequency specified by the control unit 100 into a baseband signal.

  The baseband demodulator 12 detects a path to a cell suitable for reception in accordance with an instruction from the controller 100, and RAKE-receives the detected path, and includes a search detector 12a and a RAKE receiver 12b. . The search detection unit 12a detects a path with a cell suitable for reception in accordance with an instruction from the control unit 100. Further, the search detection unit 12a detects the reception level of the channel designated by the control unit 100 and notifies the control unit 100 of this.

  The RAKE receiving unit 12b receives the RAKE from the path detected by the search detecting unit 12a. The decoding unit 21 decodes a signal obtained by RAKE reception by the RAKE receiving unit 12b to obtain received data. Of the received data, a message transmitted from the base station BS for communication control is output to the control unit 100.

  On the other hand, the transmission data is generated by the encoding unit 22 of the signal processing unit 20. A message related to communication control addressed to the base station BS is input from the control unit 100 and output to the encoding unit 22. The baseband modulation unit 13 modulates a carrier wave signal using the transmission data, and outputs the modulated baseband signal to the RF transmission unit 14. The RF transmission unit 14 performs a spreading process on the modulated baseband signal, up-converts it to a radio frequency, and radiates it to the space from the antenna.

  The storage unit 30 stores a control program and control data of the mobile radio terminal apparatus, a message related to communication control with the base station BS, the above-described evaluation formula (e), and the like. A storage area 30a is provided. The cell list storage area 30a associates cell data C1 to Cn in which the scrambling code used for communication with the cell and the frequency identification information are associated with each other in association with the cell ID which is identification information of the connected cell. It is an area for storing. An example is shown in FIG.

  Note that there is a limit to the number of stored cell data, and when the predetermined number is reached, the control unit 100 erases the data from the oldest. When the mobile radio terminal is turned off, the information stored in the cell list storage area 30a is deleted.

  The control unit 100 controls the respective units of the mobile radio terminal device in an integrated manner, and performs radio communication with the base station BS in accordance with the CDMA system according to the control program and control data stored in the storage unit 30. Is to realize. For this purpose, the control unit 100 performs control to perform handover to the Intra Node-B or Inter Node-B base station in order to perform communication through the base station BS with good communication quality. Moreover, the control part 100 is provided with the timer function, for example, measures the time t etc. which are connected to Source Node-B continuously.

  Next, the operation of the mobile radio terminal apparatus having the above configuration will be described. Here, in particular, a description will be given of processing related to cell selection that is performed while waiting for an incoming call and during communication. Further, in the following description, in order to simplify the description, a case where 0 is set in CIO will be described as an example.

  The control unit 100 receives CPICH (Common Pilot Indicate Channel) signals respectively transmitted from the Source Node-B and its neighboring base stations BS, and controls each unit to detect the reception level M. Based on the detected reception level and system information, the detection of the Target cell Ct that satisfies the evaluation formula (e), that is, the occurrence of Event1D is monitored.

  Then, when detecting the occurrence of Event1D, the control unit 100 executes control according to the flowchart shown in FIG. 5 for Target Node-B to which the Target cell Ct belongs. This flowchart is executed by the control unit 100 according to a control program, control data, and the like stored in the storage unit 30.

  First, in step 5 a, the control unit 100 determines whether data is being received through the Source Node-B based on the operation status of the transmission / reception unit 10 and the signal processing unit 20. Here, for example, when data is being downloaded, when VoIP (Voice over Internet Protocol) is being communicated, and data is being received, the process proceeds to step 5b, and when data is not being received, such as when waiting for an incoming call, Control goes to step 5e.

  In step 5b, the control unit 100 reads out from the cell list storage area 30a cell data Cs associated with the cell ID of the source cell Cs to which the source cell Cs currently belongs, among the cells formed by the Source Node-B. Based on the data Cs, it is determined whether or not Target Node-B is a previously connected node (base station). In this determination, the scrambling code (SCR) and frequency (FREQ) included in the cell data Cs are the same as those used in Target Node-B, and whether or not the node has been connected previously. Determine whether. Here, in the case of a node that has been previously connected, the process proceeds to step 5c, whereas in the case of a node that has not been previously connected, the process proceeds to step 5e.

  In step 5c, the control unit 100 determines whether or not the connection time t to Source Node-B has elapsed below the threshold Ts. Here, if the connection time t to the Source Node-B has elapsed below the threshold value Ts, the process proceeds to step 5d. On the other hand, the connection time t to the Source Node-B has passed the threshold value Ts. To step 5e. Note that the connection time t is measured in step 5i described later by the process before the previous time.

  In step 5d, the control unit 100 considers that the possibility of data loss and the possibility of Inter Node-B handover is high, and multiplies the value of Time to Trigger by N times and starts the processing. Until that time elapses, it is monitored whether the above-described evaluation formula (e) continues to hold. Then, when the time has passed by the value of Time to Trigger multiplied by N, the process proceeds to step 5e.

  In step 5e, the control unit 100 monitors whether the above-described evaluation formula (e) continues to hold until the preset default Time to Trigger elapses after the processing is started. Then, when the time has elapsed by the value of Time to Trigger, the process proceeds to step 5f.

In step 5d and step 5e, the control unit 100 controls the RF reception unit 11, the baseband demodulation unit 12, and the decoding unit 21 to receive CPICHs transmitted from Intra Node-B and Inter Node-B, respectively. Then, each reception level M of Intra Node-B and Inter Node-B is detected. In addition, the CIO and H _1d of Intra Node-B and Inter Node-B are read from the system information recorded in the storage unit 30 and used for the monitoring.

  In step 5f, the control unit 100 determines whether or not the evaluation formula (e) continues to be established from the start of the process, that is, the evaluation formula (e) until the step. If the evaluation formula (e) continues to hold, the process proceeds to step 5g. On the other hand, if the evaluation formula (e) does not continue to hold, that is, the evaluation formula (e) does not hold. If it is found, the process is terminated.

  In step 5g, the control unit 100 controls the encoding unit 22, the baseband modulation unit 13, and the RF transmission unit 14 to transmit a Measurement Report Message addressed to Source Node-B, and to Source Node-B. The cell switching is requested and the process proceeds to step 5h.

  In step 5h, the control unit 100 controls the RF reception unit 11, the baseband demodulation unit 12, and the decoding unit 21 to receive the Reconfiguration Message from Source Node-B. And the control part 100 acquires the parameter of Target cell Ct from the said message, and transfers to step 5i. The parameters include the cell ID of the target cell Ct, the handover execution timing, the scrambling code used for the handover, and the frequency identification information.

  In step 5i, the control unit 100 determines whether the parameter acquired in step 5h includes a Mac-hs reset request. Here, if a Mac-hs reset request is included in the above parameters, Target Node-B is regarded as Intra Node-B, and the process proceeds to step 5j. On the other hand, a Mac-hs reset request is included in the parameters. Is not included, Target Node-B is regarded as Inter Node-B, and the process proceeds to step 5k.

  In step 5j, the control unit 100 detects the cell ID of the target cell Ct from the parameters of the target cell Ct acquired in step 5h, and detects cell data Ct corresponding to this cell ID from the cell list storage area 30a. Then, scrambling code (SCR) and frequency (FREQ) identification information used in connection with the source cell Cs is recorded in association with the detected cell data Ct. In addition, the measurement of the connection time to Source Node-B that had been measured up to this point is terminated, and instead the measurement of the connection time to Target Node-B is started as the connection time to the new Source Node-B. Control goes to step 5k.

  In step 5k, the control unit 100 controls each unit of the transmission / reception unit 10 and the signal processing unit 20, and performs handover to Target Node-B based on the parameters acquired in step 5h according to a predetermined procedure. Then, the system information of the target node-B and its neighboring base stations is acquired from the target node-B, recorded in the storage unit 30, and the process ends.

  As described above, in the mobile radio terminal having the above-described configuration, when a handover with a Mac-hs reset request, that is, an Inter Node-B handover is executed, the cell ID of the target cell Ct and the source cell Cs The scrambling code (SCR) and frequency (FREQ) used for connection are stored in association with each other, and measurement of the connection time to a new node is started.

  Then, when Event1D occurs, if data is being received and Target Node-B is a previously connected node, and connection time t to Source Node-B is less than or equal to threshold value Ts, Considering that the possibility of loss and the possibility of Inter Node-B handover are high, the value of Time to Trigger is increased N times to extend the determination period of necessity of handover.

  In the example shown in FIG. 6, since the evaluation formula (e) is satisfied at the timing of Reporting event 1D (Time to Trigger), conventionally, it is considered that the condition for performing the handover at this time is satisfied. On the other hand, in the mobile radio terminal having the above-described configuration, when the process proceeds to step 5d, the evaluation formula (e) continues to hold for the determination period five times as long as Time to Trigger from the timing of Reporting event 1D. The condition for performing the handover is considered to be satisfied.

  For this reason, in the example shown in FIG. 6, since the evaluation formula (e) is not continuously established, handover is not performed. Thereafter, in the example shown in FIG. 6, the situation that satisfies the evaluation formula (e) does not continue, and even if handover is performed at the timing of Reporting event 1D, it is highly likely that the handover will be performed again, and flapping occurs. However, the mobile radio terminal device having the above-described configuration can prevent such a situation from occurring.

  That is, according to the mobile radio terminal apparatus having the above configuration, when receiving data, when the Target Node-B is a previously connected node, or when the connection time t to the Source Node-B is short, the handover is performed. If there is a risk of frequent occurrence of handover, conditions for performing handover become severe, and frequent occurrence of handover can be suppressed. Thereby, it is possible to prevent a decrease in throughput due to cell switching.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. Further, for example, a configuration in which some components are deleted from all the components shown in the embodiment is also conceivable. Furthermore, you may combine suitably the component described in different embodiment.

  As an example, for example, in the above-described embodiment, as shown in FIG. 5, when all the conditions of steps 5a, 5b, and 5c are satisfied, step 5d is executed. It is not a thing. That is, step 5d may be executed when one or two of steps 5a, 5b, and 5c are satisfied.

  In the above embodiment, for the sake of simplicity, it is assumed that CIO is set to 0, and in step 5d, the value of Time to Trigger is increased N times to determine the necessity period of handover. However, the present invention is not limited to this. In step 5d, the CIO value of the evaluation formula (e) used by the control unit 100 may be varied to make conditions for performing handover more stringent.

  FIG. 7 shows a flowchart for performing such processing. The process shown in FIG. 7 is substantially the same as the process shown in FIG. 5, except that the control unit 100 performs step 7d instead of step 5d and performs step 7e instead of step 5e. Different. Similarly to the flowchart shown in FIG. 5, the control unit 100 starts the process when the evaluation formula (e) is satisfied. Only differences from FIG. 5 described above will be described below.

  In step 7d, the control unit 100 increases the value of CIO (second term on the left side) of the Target cell Ct included in the evaluation formula (e) by X [dB], and proceeds to step 5f. On the other hand, in step 7e, the control unit 100 does not change the evaluation formula (e) and proceeds to step 5f.

That is, in step 7d, the control unit 100 increases the value of the CIO (second term on the right side) of the Target cell Ct included in the evaluation formula (e), thereby making the conditions for performing the handover stricter. Can be suppressed. Thereby, it is possible to prevent a decrease in throughput due to cell switching.
In addition, it goes without saying that the present invention can be similarly implemented even if various modifications are made without departing from the gist of the present invention.

The figure for demonstrating Intra Node-B handover. The figure for demonstrating Inter Node-B handover. The circuit block diagram which shows the structure of one Embodiment of the mobile radio | wireless terminal apparatus concerning this invention. The figure which shows an example of the cell data memorize | stored in the cell list storage area of the memory | storage part shown in FIG. 6 is a flowchart for explaining processing related to cell selection of the mobile radio terminal apparatus shown in FIG. 3. The figure for demonstrating an example of the cell selection by the process shown in FIG. 6 is a flowchart for explaining processing related to cell selection of the mobile radio terminal apparatus shown in FIG. 3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Transmission / reception part, 11 ... RF reception part, 12 ... Baseband demodulation part, 12a ... Search detection part, 12b ... RAKE reception part, 13 ... Baseband modulation part, 14 ... RF transmission part, 20 ... Signal processing part, 21 Decoding unit 22 Encoding unit 30 Storage unit 30a Cell list storage area 100 Control unit BS Base station

Claims (6)

In a mobile wireless terminal device that wirelessly communicates with a base station accommodated in a network,
Detecting means for detecting a reception level of a radio signal received from each of the connected first base station and the other second base station;
The necessity of handover depends on whether or not the reception conditions of the first base station and the second base station detected by the detection means satisfy a predetermined determination condition for a predetermined determination time. First determination means for determining
A handover means for performing a handover from the first base station to the second base station according to a determination result of the first determination means;
Second determination means for determining whether data communication through the base station is in progress;
A mobile radio terminal apparatus comprising: a condition control unit that lengthens a determination time used by the first determination unit when the second determination unit determines that data communication is being performed. In a mobile wireless terminal device that wirelessly communicates with a base station accommodated in a network,
Detecting means for detecting a reception level of a radio signal received from each of the connected first base station and the other second base station;
The necessity of handover depends on whether or not the reception conditions of the first base station and the second base station detected by the detection means satisfy a predetermined determination condition for a predetermined determination time. First determination means for determining
A handover means for performing a handover from the first base station to the second base station according to a determination result of the first determination means;
Second determination means for determining whether the second base station is a base station connected in the past;
A mobile radio terminal apparatus comprising: a condition control unit that lengthens a determination time used for determination by the first determination unit when the second determination unit determines that the base station has been connected in the past. In a mobile wireless terminal device that wirelessly communicates with a base station accommodated in a network,
Detecting means for detecting a reception level of a radio signal received from each of the connected first base station and the other second base station;
The necessity of handover depends on whether or not the reception conditions of the first base station and the second base station detected by the detection means satisfy a predetermined determination condition for a predetermined determination time. First determination means for determining
A handover means for performing a handover from the first base station to the second base station according to a determination result of the first determination means;
Measuring means for measuring time connected to the first base station;
Second determination means for determining whether the time measured by the measurement means is equal to or less than a preset time;
A mobile radio terminal apparatus comprising: a condition control unit configured to increase a determination time used by the first determination unit when the second determination unit determines that the time is equal to or less than a preset time. In a mobile wireless terminal device that wirelessly communicates with a base station accommodated in a network,
Detecting means for detecting a reception level of a radio signal received from each of the connected first base station and the other second base station;
First determination means for determining the necessity of handover according to whether or not the reception levels of the first base station and the second base station detected by the detection means are in a relationship satisfying a predetermined determination condition;
A handover means for performing a handover from the first base station to the second base station according to a determination result of the first determination means;
Second determination means for determining whether data communication through the base station is in progress;
A condition control unit configured to change a determination condition used for determination by the first determination unit so that it can be easily determined that there is no need for handover when the second determination unit determines that data communication is in progress; A mobile radio terminal apparatus. In a mobile wireless terminal device that wirelessly communicates with a base station accommodated in a network,
Detecting means for detecting a reception level of a radio signal received from each of the connected first base station and the other second base station;
First determination means for determining the necessity of handover according to whether or not the reception levels of the first base station and the second base station detected by the detection means are in a relationship satisfying a predetermined determination condition;
A handover means for performing a handover from the first base station to the second base station according to a determination result of the first determination means;
Second determination means for determining whether the second base station is a base station connected in the past;
Condition control means for varying the determination condition used for determination by the first determination means so that it can be easily determined that there is no need for handover when the second determination means determines that the base station has been connected in the past. A mobile radio terminal apparatus comprising: In a mobile wireless terminal device that wirelessly communicates with a base station accommodated in a network,
Detecting means for detecting a reception level of a radio signal received from each of the connected first base station and the other second base station;
First determination means for determining the necessity of handover according to whether or not the reception levels of the first base station and the second base station detected by the detection means are in a relationship satisfying a predetermined determination condition;
A handover means for performing a handover from the first base station to the second base station according to a determination result of the first determination means;
Measuring means for measuring time connected to the first base station;
Second determination means for determining whether the time measured by the measurement means is equal to or less than a preset time;
A condition control unit configured to change the determination condition used for the determination by the first determination unit so that it can be easily determined that there is no need for handover when the second determination unit determines that the time is equal to or less than a preset time; A mobile radio terminal apparatus comprising:

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