JP4325952B2 - Wireless communication terminal and communication method - Google Patents

Description

The present invention relates to a communication system that performs data communication, and more particularly to a wireless communication terminal that receives streaming data using a wireless communication line.

  In recent years, the transmission capacity of communication lines has also increased in mobile communication networks, and not only conventional text data and WWW data such as mail, but also data with a large amount of data such as still images has been transmitted. In the future, content data with a larger amount of data and real-time characteristics (for example, moving image data such as video) will be distributed.

  There is a method using a streaming technique as a content data distribution method. Several techniques for streaming video over wireless communication lines have also been proposed. Among them, there is a technique related to variable bit rate control. Variable bit rate control changes the coding rate of moving image data to transmit data with image quality that matches the current bandwidth of the wireless communication line whose state changes from moment to moment, and keeps the video quality as high as possible. Technology.

  In addition, when streaming video, in order to ensure real-time performance, buffering is performed to start reproduction after storing image data for a predetermined time in the memory of the receiving apparatus. Buffering is typically used to absorb variations in packet arrival delay time, but a buffer overflow where the transmission rate is faster than the playback rate and the received unplayed data exceeds the buffer's storage capacity, or There is a problem that a buffer underflow occurs in which the transmission rate is lower than the reproduction rate and the data to be reproduced is not stored in the buffer. As a conventional technique for solving this problem, there is a technique for performing transmission / reception control in a wireless IP network according to the delay time and the amount of buffer.

Further, in the mobile communication network, the terminal continues to communicate with the base station that is the communication partner while changing (handoff) while the terminal is moving, so that communication is continued. In order to absorb the influence of the packet arrival delay at the time of handoff, a technique for changing the buffer capacity of the terminal has been proposed.
Japanese Patent Laid-Open No. 11-341064

  However, even if these streaming technologies are applied, in a mobile communication network, a handoff for switching a communication partner base station occurs when a wireless communication terminal moves between control areas (cells) of the base station. Since data cannot be transmitted during the time required for this, a delay or packet loss may occur during this time. A slight increase in delay can be absorbed by the buffering described above. However, if a large delay occurs due to handoff, even if data is sufficiently accumulated in the buffer, the delay due to handoff cannot be absorbed and frames are lost. This causes a problem that the moving image is interrupted. In particular, when transmitting high-encoding rate content, if there is a large amount of data in one frame and a large delay occurs due to handoff, it is assumed that the data is sufficiently accumulated in view of the maximum capacity of the buffer. However, if the data is converted into time, there is a possibility that it will be shorter than the delayed time, and there is a high possibility that a frame will be lost.

  Even if a wireless communication terminal moves between cells of a base station, the present invention absorbs a delay caused by the handoff and continuously transmits data in a mobile communication network that continues communication by handoff that switches the base station of the communication partner. An object is to provide an unrelated communication terminal and a communication method that can be reproduced.

The first invention, when receiving the transmitted data through the first radio base station which is a communication partner from the data distribution apparatus, a radio communication line between the first radio base station Based on the difference between the quality and the quality of the wireless communication line between the second wireless base station other than the first wireless base station, a change process (handoff) of the wireless base station that is the communication partner is generated. Predicting means for predicting and, when the predicting means predicts the occurrence of the change process, to reduce the coding rate of data transmitted from the data distribution apparatus so as not to change the data transmission rate of the wireless communication line And a signal transmission means for transmitting a signal (handoff notification signal) for notifying the change processing to the data distribution apparatus .

A second invention is characterized in that, in the first invention, the predicting means predicts the occurrence of the change process when the difference is smaller than a predetermined value .

The third invention is the invention of the first or 2, further comprising a buffer for temporarily storing data from transmitted via the first radio base station the data distribution apparatus, the predicting means, less than the value the difference is predetermined, and, if less than the amount stored amount of the buffer reaches a predetermined, the change processing occurs, to predict, and wherein the.

A fourth invention is a communication method in a radio communication terminal that communicates with a radio base station , and receives data transmitted from a data distribution device via a first radio base station that is a communication partner. when and, obtaining a quality of the wireless communication channel between the first radio base station, a quality of the wireless communication channel between the second radio base station other than the first radio base station Based on the difference between the quality of the radio communication line between the acquisition step and the first radio base station acquired in the acquisition step and the quality of the radio communication line with the second radio base station. Predicting the occurrence of the change process of the base station serving as a communication partner, and predicting the occurrence of the change process in the prediction step, the encoding rate of the data transmitted from the data distribution device is set to the wireless Change the data transmission rate of the communication line To let no way lowered, characterized in that it comprises a transmission step of transmitting a signal to notice the change processing to the data distribution apparatus.

For example, with respect to the data distribution apparatus via the radio base station, by transmitting a signal to notice the change process as a communication partner radio base station (handoff warning signal) it is transmitted from the data distribution apparatus It is possible to change the coding rate of data. Therefore, it occurs change processing of the radio base station as a communication partner (handoff) also to hardly cause buffer underflow, and, the long-time image data as compared to before the change is to be stored in the wireless communication terminal Can do. Therefore, it is possible to reproduce a moving image that is not easily interrupted. The processing (a packet of the change process (handoff) after the occurrence by detecting changing process of the non linear base station as a communication partner (handoff) prior to complement the data if not in time for reproduction time delayed Recovery process) is not required.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a wireless communication system including a wireless communication terminal according to an embodiment of the present invention.

  The terminal 10 is connected to a data distribution apparatus (distribution server 20) that transmits content data (moving image, still image, music, audio, caption, etc.) having real-time properties via the radio base station 30. The terminal 10 is a wireless communication terminal such as a mobile phone that supports data communication, a PDA (Personal Digital Assistant), or a computer terminal to which a data communication card incorporating a wireless device is added.

  The terminal 10 includes an antenna (not shown) that receives radio waves (downlink signals) from the radio base station 30 and transmits radio waves (uplink signals) to the radio base station 30. It is connected to the. The radio unit includes a reception module 11 and a transmission module 12, and the reception module 11 includes a reception circuit, a demodulation circuit, and a CODEC unit. The reception circuit amplifies and converts a high frequency signal received by an antenna. To generate a baseband signal. Then, the baseband signal is demodulated by the demodulation circuit, decoded into a data signal by the CODEC unit, and sent to the buffer 14.

  The transmission module 12 includes a transmission circuit, a modulation circuit, and a CODEC unit. The CODEC unit encodes a data signal, the encoded signal is modulated by the modulation circuit, and a high-frequency signal is generated by the transmission circuit. Is generated and transmitted from the antenna.

  A buffer 14 is connected to the receiving module 11, and the streaming data received by the terminal 10 is temporarily stored, and the streaming data is interrupted even if the data rate is reduced for a short time, the line is disconnected, or the like. To be played without any problems. The data read from the reception buffer 14 is sent to the decoding module 15, and the data encoded as a moving image file such as MPEG is decoded into a video signal. The decoded video data is displayed on a display unit (not shown).

  The radio information acquisition module 13 receives a desired wave to interference wave ratio (C / I) received by the receiving module 11 and obtained from a signal from the radio base station 30. Then, based on the result of comparing the C / I value with a predetermined value, it is determined whether or not handoff may occur in the near future. When it is determined that there is a possibility of handoff, a handoff notice signal to be transmitted to the distribution server 20 is generated, the signal is sent to the transmission module 12, and the handoff notice signal is transmitted from the transmission module 12.

  The terminal 10 of the present embodiment determines the possibility of handoff using the C / I value, but the result of comparing the RSSI with a predetermined value depending on the strength of the received signal strength (RSSI: Received Signal Strength Indicator). May be configured to determine the possibility of handoff). In the case of a CDMA system, it is preferable to use a C / I value. Thus, the wireless information acquisition module 13 constitutes a handoff necessity determination unit.

The control module 17 controls each part of the terminal 10 such as the reception module 11, the transmission module 12, the wireless information acquisition module 13, the buffer 14, and the decoding module 15. Specifically, the storage amount of the streaming data stored in the buffer 14 is monitored, and the transmission / reception frequency and transmission / reception timing are controlled by specifying a channel for the reception module 11 and the transmission module 12. Also, information about the signal received by the terminal (the state of the wireless communication line)

Status information). Further, according to a predetermined communication protocol, various control signals such as setting, releasing, and location registration of a wireless communication line between the terminal and the wireless base station are generated, and transmission / reception of these signals is controlled. That is, the control unit 17 and the transmission module 12 constitute a signal transmission unit. Also, the decoding module 15 is instructed with information for decoding.

  The radio base station 30 is connected to the terminal 10 by a radio communication line. One or a plurality of sectors are formed for each radio base station, and the terminal 10 performs communication by selecting a sector (radio base station) that gives the best communication state. The radio base station 30 is connected to a distribution server 20 that transmits streaming data to the terminal 10.

  FIG. 2 is a block diagram showing the configuration of the distribution server.

  The data distribution device is a device that transmits (distributes) content data to a wireless communication terminal, and stores content data. The data distribution device is a device on the service providing side, and is a computer device such as a server, for example, and will be described as a server in the present embodiment. Note that a storage device that stores content such as content data may be provided inside the server or outside the server.

  The distribution server 20 is a computer device that transmits data to the terminal 10. The terminal 10 stores the video source 21 in a storage device (storage device, hard disk, etc.). This video source is read from the storage device and sent to the encoding unit 22. In the encoding unit 22, the video source is encoded based on a moving image encoding standard such as MPEG and sent to the transmission unit 23. The transmission unit 23 transmits the data encoded based on the communication protocol to the network (IP network) 40 as a packet.

  The control unit 25 controls each unit of the distribution server 20 such as the encoding unit 22 and the transmission unit 23. The distribution server 20 predicts a data transmission band that varies from time to time for the terminal, and performs variable bit rate control for transmitting data at a bit rate that matches the predicted band. Specifically, when a handoff notice signal transmitted from the terminal 10 is received, the encoding rate of data transmitted to the terminal 10 is changed to a low rate. That is, the control unit 25 monitors packets received by the distribution server 20, and when a handoff notice signal from the terminal 10 is detected, the control unit 25 sets the encoding rate for reducing the transmission rate to the encoding unit 22. Send change instructions. At this time, for example, the encoding unit 22 reduces the encoding rate by changing the encoding method (from MPEG1 to MPEG2) or changing the encoding coefficient (for example, DCT coefficient, quantization coefficient, etc.). Let Thus, the coding rate changing means is configured by the action of the control unit 25.

Further, the data transmission rate is determined by predicting the optimum rate of data transmitted from the distribution server 20. That is, in the present invention, the terminal 10 receives a reception report including the packet loss rate, the number of lost packets, the maximum value of the sequence number of the received packet, the arrival interval jitter, and the like as the reception status information of the data transmitted from the distribution server 20. (RR) is transmitted to the distribution server 20. In addition, the terminal 10 transmits DRC information as quality information of a wireless communication line between the terminal 10 and the wireless base station 30. This DRC information is a signal indicating a communication mode selected as one capable of performing efficient data communication based on a C / I value obtained by receiving a signal transmitted from the radio base station 30 by the terminal 10 It is. The control unit 25 determines a rate at which data is transmitted from the distribution server 20 based on the received reception report and DRC information, and instructs the encoding unit 22 and the transmission unit 23 on the data transmission rate. That is, the encoding unit 22 is controlled by instructing the encoding unit 22 of an encoding method and information for encoding (for example, DCT coefficients, quantization coefficients, etc.) that match the determined data transmission rate. Moreover, it is transmitted from the transmitter 23.

Control the number of packets Note that the method of determining the data transmission rate may be a method of selecting one of contents already encoded at different rates.

  The radio base station 30 has an antenna 31 connected to the radio unit, receives radio waves (uplink signals) from the terminal 10, and transmits radio waves (downlink signals) to the terminal 10. The radio unit is composed of a transmission unit and a reception unit. The transmission unit generates a high-frequency signal to be transmitted from the antenna 31, and the reception unit performs amplification, frequency conversion, etc. on the high-frequency signal received by the antenna 31 as a baseband signal. Output to the transceiver.

  The transmission / reception unit includes a modulation / demodulation circuit and a CODEC unit, and demodulates the baseband signal by the modulation / demodulation circuit. The demodulated signal is sent to the CODEC unit and decoded into a data signal by the CODEC unit. The CODEC unit encodes a data signal, and the encoded signal is sent to the transmission / reception unit and modulated. The modulated signal is converted into a high-frequency signal by the transmission unit and transmitted from the antenna 31.

  An interface unit is connected to the transmission / reception unit, and the radio base station 30 is connected to a network 40 (such as an IP network) such as the Internet via the interface unit.

  In addition, the radio base station 30 includes a control unit that controls each unit (a radio unit, a transmission / reception unit, an interface unit, and the like) of the radio base station. Specifically, this control unit controls a transmission / reception frequency and transmission / reception timing by designating a channel to the radio unit. In addition, in response to a connection request from the client terminal 10, the permission of the connection and the number of terminals connected are controlled.

  Further, in the embodiment of the present invention, since the wireless communication network is a 1xEV-DO network (1x Evolution Data Only network), based on the quality information of the wireless communication line transmitted from the terminal 10 and the number of connected terminals, The bandwidth of data communication allocated to each client is determined, and the transmission rate of the wireless communication line is determined.

  That is, the control unit and the radio unit of the radio base station 30 constitute reception means for receiving the reception status information and the channel quality information transmitted from the radio communication terminal, and the control unit sets the data transmission rate of the radio communication channel. Transmission rate determining means for determining is configured.

  FIG. 3 is a diagram for explaining the operation of the buffer 14 according to the embodiment of this invention.

  The streaming data output from the receiving module 11 is temporarily stored in the buffer 14 and stored and read out by first-in first-out. The streaming data read from the buffer 14 is decoded into a video signal by the decoding module 15.

  As described above, the buffer 14 is a temporary storage area for buffering the difference between the speed at which the receiving module 11 receives from the wireless communication network and the decoding speed of the decoding module 15. Used because timing is not affected. That is, the amount of data stored in the buffer 14 varies depending on the difference between the reception speed and the decoding speed.

  The use status of the storage area of the buffer 14 is monitored by the control module 17, and a predetermined percentage of the total storage capacity is set as the threshold value B. As will be described later, this threshold value B is used to determine whether or not the amount of data required for reproduction while data reception is interrupted during handoff is sufficiently stored.

  FIG. 4 is a flowchart of the operation of the terminal 10 according to the embodiment of this invention.

  When receiving the streaming data from the radio base station 30, the terminal 10 sends the data to the decode module 15 via the buffer 14 and reproduces it as a video signal (S101).

  Then, the terminal 10 obtains a reception profile by sequentially changing the spreading code, and counts the number of base stations that can be detected from the reception profile (S102). If only one base station can be detected (“No” in S103), the process returns to step S101 and continues to receive and reproduce streaming data. On the other hand, if two or more base stations can be detected (“Yes” in S103), the desired signal-to-interference wave ratio of each base station (including the currently captured base station) received by the receiving module 11 is calculated. Take out (S104).

  Whether the difference between the C / I value of the base station that is currently captured and the wireless communication line is set and the C / I value of another receivable base station is smaller than a predetermined threshold A It is determined whether or not (S105). If the difference between the C / I values is smaller than a predetermined threshold A, a handoff may occur in the near future, and the process proceeds to determination of the use state of the buffer 14 (S106 to S107). On the other hand, if the difference between the C / I values is greater than or equal to a predetermined threshold A, there is no possibility of handoff in the near future, and there is no need to notify handoff. Continue. That is, the difference between the C / I value of the base station that is currently captured and the wireless communication line is set and the C / I value of another receivable base station is obtained, and the difference between the C / I values is obtained. And whether or not to notify the handoff notice is determined based on the result of comparing the predetermined threshold A with a predetermined threshold A.

  Thereafter, it is determined whether or not to check the storage amount of the streaming data stored in the buffer 14 (S106). When the amount of streaming data stored in the buffer 14 is confirmed, it is determined whether or not the capacity of the streaming data stored in the buffer 14 is smaller than a predetermined threshold B (S107). In the case of a fixed-rate streaming data communication system, the amount of data is proportional to the playback time, so it is easy to determine how much delay the data amount stored in the buffer 14 can withstand when handoff occurs. Predictable. On the other hand, in the case of a variable-rate streaming data communication system, it is necessary to record the bit rate of streaming data stored in the buffer 14 or the playback time of streaming data stored in the buffer 14.

  If the amount of data stored in the buffer 14 is less than the predetermined threshold B, there is a possibility that the reproduction data may be insufficient during the handoff, so it is determined that the handoff is notified, and the process proceeds to the detection notification phase (S108 to S111). On the other hand, if the amount of data stored in the buffer 14 is equal to or greater than the predetermined threshold B, there is no possibility that the reproduction data is insufficient during the handoff, and there is no need to notify the handoff. Is continued to be received and reproduced (S107). That is, whether or not to notify the handoff notice is determined based on the result of comparing the data amount of the streaming data stored in the buffer 14 with a predetermined threshold value B.

  Note that in a variable rate streaming data communication system, it is difficult to predict how much delay the data amount stored in the buffer 14 can withstand when a handoff occurs. Regardless of whether or not there is data enough to absorb the delay ("NO" is determined in S106), a handoff notice signal is transmitted based on C / I (S108), and the code of the data to be distributed from the distribution server 30 By reducing the conversion rate and shortening the transmission interval, the amount of data stored in the buffer 14 can be increased, and the possibility of absorbing the data delay that occurs when handoff occurs can be increased.

  If it is determined by the above handoff detection phase processing (S101 to S107) that the handoff notice is notified, the handoff notice is notified to the distribution server 20 (S108).

  Then, the streaming data from the radio base station 30 is received, the data is sent to the decoding module 15 via the buffer 14, and is reproduced as a video signal (S109).

  Thereafter, the capacity of the streaming data stored in the buffer 14 is confirmed, and it is determined whether or not the capacity of the streaming data stored in the buffer 14 is smaller than a predetermined threshold B (S110). If the amount of data stored in the buffer 14 is less than the predetermined threshold B, the process returns to step S109 to continue receiving and reproducing streaming data. On the other hand, if the amount of data stored in the buffer 14 is equal to or greater than a predetermined threshold B, the distribution server 20 is notified that the reproduction data is sufficiently accumulated in the buffer 14 during handoff (S111). That is, based on the comparison result between the amount of data stored in the buffer 14 and a predetermined threshold B, the distribution server 20 is notified that the data has been sufficiently accumulated in the buffer 14.

  FIG. 5 is a flowchart of data transmission processing of the distribution server 20.

  The distribution server 20 uses the DRC information as quality information of the wireless communication line between the terminal 10 and the radio base station 30 transmitted from the terminal 10, and the rate at which the distribution server 20 encodes data to the terminal 10 And the encoding unit 22 and the transmission unit 23 are instructed of the encoding rate. That is, an encoding method that matches the determined encoding rate and information for encoding (for example, DCT coefficient, quantization coefficient, etc.) are instructed to the encoding unit 22, and the encoding rate in the encoding unit 22 is set. decide. Moreover, the transmission interval of the packet transmitted from the transmission part 23 is determined (S121).

  Then, data is transmitted to the terminal 10 according to the determined rate (S122).

  Then, it is detected whether or not the handoff detection flag is set (standing) (S123). This handoff detection flag is set in step S133 of the handoff detection process (FIG. 6).

  If the handoff detection flag is not set, there is no need to transmit in advance the data to be reproduced during the time required for handoff, so the process returns to step S121 to determine the encoding rate of the streaming data (S121). The data is transmitted to (S122). On the other hand, if the handoff detection flag is set, the process proceeds to the processing after step S124 in order to transmit in advance data to be reproduced during the time required for handoff.

  In step S124, the distribution server 20 uses the DRC information as quality information of the radio communication line between the terminal 10 and the radio base station 30 transmitted from the terminal 10 and sends it to the terminal 10 as in step S121. The distribution server 20 determines the rate at which the data is encoded. In addition, using the reception report transmitted from the terminal 10, the rate at which the distribution server 20 encodes data in the terminal 10 (the encoding rate in the encoding unit 22 and the packet transmission interval in the transmission unit 23) is determined. May be.

Then, the encoding unit 22 is instructed to an encoding rate that further decreases the encoding rate predicted in S124 (S125). Then, data is transmitted to the terminal 10 (S126). At this time, the transmission unit 23 is instructed to shorten the transmission interval of packets transmitted from the transmission unit 23.

(S126). That is, the amount of data required for reproduction of unit time is reduced, the number of packets transmitted per unit time is increased, and the amount of data transmitted per unit time is not changed, so that the buffer 14 can be quickly Image data with a low coding rate is accumulated. Therefore, since image data of a longer time is accumulated in the buffer than before the change of the coding rate, it is possible to withstand a delay at the time of handoff and a packet loss.

  Then, it is detected whether or not the handoff detection flag is cleared (down) (S127). The handoff detection flag is cleared in step S136 of the handoff detection process (FIG. 6).

  If the handoff detection flag is cleared (if not set), the accumulation of data to be played back in the buffer 14 is completed in the time required for handoff, and the process returns to step S121 to determine the encoding rate of the streaming data. Then, data is transmitted to the terminal 10 (S122). On the other hand, if the handoff detection flag is not cleared (if set), accumulation of data to be played back during the time required for handoff has not ended, and the process proceeds to step S124.

  FIG. 6 is a flowchart of the handoff detection process of the distribution server 20.

  The distribution server 20 monitors notification of handoff notice from the terminal 10 (S131). When a handoff notice notification is detected from the terminal 10 (“Yes” in S132), a handoff detection flag is set (set up) (S133), and streaming data required during the handoff is transmitted (FIG. 5). 5 of S124 to S126).

  Thereafter, the distribution server 20 monitors a notification from the terminal 10 that data has been sufficiently accumulated in the buffer 14 (S134). When the notification that the data is sufficiently accumulated in the buffer 14 from the terminal 10 is detected (“Yes” in S135), the handoff detection flag is cleared (lowered) (S133) and is required during the handoff. The transmission of streaming data is terminated (S127 in FIG. 5).

  It should be noted that the amount of data stored in the buffer when a handoff occurs can be predicted by a fixed rate system, but in the case of a variable rate system, all received data can be predicted. It is necessary to record the bit rate. Therefore, regardless of whether the buffer has enough data to absorb the delay at the time of handoff, the encoding rate of the data distributed from the server is lowered and the transmission interval is shortened to increase the temporal accumulation amount of the buffer. Thereby, it is possible to increase the possibility of absorbing the delay when the handoff occurs.

  FIG. 7 is a diagram illustrating the threshold A for determining handoff notice according to the embodiment of this invention.

  The C / I values when handoff is predicted to occur between Sector1 and Sector2 in three base stations and (Sector1-Sector3) terminals are shown. In FIG. 7, the horizontal axis represents time, and dotted lines provided at equal intervals with respect to the horizontal axis (vertical lines drawn perpendicular to the horizontal axis) indicate monitoring timing. In the case of FIG. 3, the levels of Sector 1 and Sector 2 are approaching, and this is predicted as the occurrence of handoff. For this prediction, a “threshold value A” is set, and when the difference is smaller than A as shown in FIG.

  In the state shown in FIG. 7, the terminal 10 has detected three base stations, and has set up a radio communication line with the base station (Sector 1) that gives the maximum C / I value. At this time, the difference between the C / I value of the base station that is currently captured and the wireless communication line is set and the C / I value of the other detected base station is obtained. The difference is compared with a predetermined threshold A. That is, the difference (d12) between the C / I value of the base station (Sector 1) and the C / I value of the base station (Sector 2) is obtained, and the C / I value of the base station (Sector 1) and the C / I value of the base station (Sector 3) are obtained. The difference (d13) from the / I value is obtained. Then, the C / I value difference (d12, d13) is compared with a predetermined threshold A, and if the C / I value difference (d12, d13) is smaller than the threshold A, a handoff notice is sent to the distribution server 30. To send.

  FIG. 8 is a diagram for explaining the handoff notice timing according to the embodiment of the present invention, and shows the time change of the C / I value between three base stations and (Sector 1 to Sector 3) terminals. The vertical dotted line indicates the detection timing of the C / I value.

  The terminal 10 sets a wireless communication line with the base station (Sector 1) that gives the maximum C / I value, but the C / I value of the base station that is currently captured and has the wireless communication line set is low. Then, the C / I value of the other detected base station (Sector 2) has improved, and the C / I value is approaching before the hand-off occurs between the base station (Sector 1) and the base station (Sector 2). When the difference (d12) between the C / I values of both base stations becomes smaller than the threshold value A, it is determined that a handoff will occur in the near future, and a handoff notice is transmitted to the distribution server 30 (Detected).

  Thereafter, when the C / I value of the base station (Sector 1) decreases and the C / I value of the base station (Sector 2) improves, the C / I values of both base stations are reversed. When the absolute value of the difference (d12) between the C / I values of both base stations becomes larger than a predetermined value, the handoff is executed, the connection with the base station (Sector 1) is released, and the base station (Sector 2) is disconnected. Set up a wireless communication line between them.

It is a block diagram which shows the structure of the radio | wireless communications system provided with the radio | wireless communication terminal of embodiment of this invention. It is a block diagram which shows the structure of a delivery server. It is operation | movement explanatory drawing of the buffer of the terminal of embodiment of this invention. It is a flowchart of operation | movement of the terminal of embodiment of this invention. It is a flowchart of the data transmission process of a delivery server. It is a flowchart of the handoff detection process of a delivery server. It is explanatory drawing of the threshold value A of the determination of the handoff notice of embodiment of this invention. It is explanatory drawing of the handoff notice timing of embodiment of this invention.

Explanation of symbols

10 terminal 11 receiving module
12 Transmission module 13 Wireless information acquisition module
14 Buffer 15 Decode module
17 Control module 20 Distribution server
21 Video source 22 Encoding unit
23 Transmitter 25 Control Unit
30 Radio base station 31 Antenna
40 network

Claims (4)

When receiving data transmitted from the data distribution apparatus via the first wireless base station that is the communication partner, the quality of the wireless communication line with the first wireless base station, and the first and on the basis of the difference between the quality of the wireless communication network, predicting means for predicting the occurrence of change processing of the communication partner wireless base station between the first except the wireless base station 2 of the radio base station,
When the prediction means predicts the occurrence of the change process, the data distribution apparatus is configured to reduce the encoding rate of data transmitted from the data distribution apparatus so as not to change the data transmission rate of the wireless communication line. a signal transmitting means for transmitting a signal to notice the change process for,
A wireless communication terminal comprising:   The wireless communication terminal according to claim 1, wherein the prediction unit predicts the occurrence of the change process when the difference is smaller than a predetermined value. A buffer for temporarily storing data from the data distribution apparatus transmitted via the first radio base station;
Said predicting means, wherein the difference is smaller than a predetermined value, and, if less than the amount stored amount of the buffer reaches a predetermined, the change processing occurs, to predict,
The wireless communication terminal according to claim 1, wherein the wireless communication terminal is a wireless communication terminal. A communication method in a wireless communication terminal that performs communication with a wireless base station,
When receiving data transmitted from the data distribution apparatus via the first wireless base station that is the communication partner, the quality of the wireless communication line with the first wireless base station, and the first an acquisition step of acquiring the quality of the wireless communication channel between the other than the wireless base station the second radio base station,
Based on the difference between the quality of the wireless communication line with the first wireless base station acquired in the acquisition step and the quality of the wireless communication line with the second wireless base station, A prediction step for predicting the occurrence of the change process of the base station,
When the occurrence of the change process is predicted in the prediction step, the data distribution apparatus is configured to reduce the encoding rate of data transmitted from the data distribution apparatus so as not to change the data transmission rate of the wireless communication line. a transmission step of transmitting a signal to notice the change process for,
A communication method comprising:

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