JP4146708B2 - COMMUNICATION SYSTEM, RADIO COMMUNICATION TERMINAL, DATA DISTRIBUTION DEVICE, AND COMMUNICATION METHOD - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a communication system that performs data communication, and more particularly to a wireless communication system that transmits streaming data using a wireless communication line.
[0002]
[Prior art]
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.
[0003]
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.
[0004]
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.
[0005]
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.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-341064
[0007]
[Problems to be solved by the invention]
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.
[0008]
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 of the present invention is to provide a communication system that can be played back.
[0009]
[Means for Solving the Problems]
A first invention includes a wireless communication terminal, a wireless base station in which a wireless communication line is set between the wireless communication terminal, and a data distribution device that transmits content data to the wireless communication terminal. In the communication system, the wireless communication terminal includes a prediction unit that predicts the occurrence of handoff, and a signal transmission unit that transmits a handoff notification signal that notifies handoff when the prediction unit predicts the occurrence of handoff, When the data distribution device receives the handoff notice signal, the signal receiving means for receiving the handoff notice signal, Lower the encoding rate of the content data transmitted to the wireless communication terminal so as not to change the data transmission rate of the wireless communication line And a control means.
[0011]
The second invention is the first invention, The prediction means predicts the occurrence of handoff based on the result of comparing the channel quality with the base station to a predetermined value, and the signal transmission means predicts the occurrence of handoff when the prediction means In addition, a handoff notice signal is transmitted.
[0012]
The third invention is the first or second invention. The wireless communication terminal includes a buffer that temporarily stores data transmitted from the data distribution device, and the signal transmission unit stores the storage state of the buffer even when the prediction unit predicts the occurrence of a handoff. When a predetermined condition is satisfied (for example, exceeds a predetermined storage capacity), a handoff notice signal is not transmitted.
[0015]
4th invention Is a data distribution apparatus that is connected to a wireless base station that communicates with a wireless communication terminal using a wireless communication line, and that transmits content data to the wireless communication terminal, and notifies the occurrence of a handoff When receiving the handoff notice signal, signal receiving means for receiving the handoff notice signal from the wireless communication terminal, and receiving the handoff notice signal, Lowering the encoding rate of content data to be transmitted to the wireless communication terminal without changing the data transmission rate of the wireless communication line And a control means.
[0016]
5th invention Is a communication system comprising a wireless communication terminal, a wireless base station in which a wireless communication line is set between the wireless communication terminal, and a data distribution apparatus that transmits content data to the wireless communication terminal. In the applied communication method, the wireless communication terminal predicts the occurrence of handoff, and when the occurrence of handoff is predicted, the wireless communication terminal transmits a handoff notification signal for announcing handoff, and the data distribution device transmits the handoff notification signal. Is received Lower the encoding rate of the content data transmitted to the wireless communication terminal so as not to change the data transmission rate of the wireless communication line It is characterized by that.
[0017]
The sixth invention is the fifth invention, The wireless communication terminal predicts the occurrence of handoff based on the result of comparing the channel quality with the base station with a predetermined value, and transmits a handoff notice signal when the occurrence of handoff is predicted. It is characterized by that.
[0018]
The seventh invention is the fifth or sixth invention, When the storage state of the buffer that temporarily stores the data transmitted from the data distribution device satisfies a predetermined condition (for example, exceeds a predetermined storage amount), the wireless communication terminal performs handoff Even when occurrence is predicted, a handoff notice signal is not transmitted.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0020]
FIG. 1 is a block diagram showing a configuration of a wireless communication system according to an embodiment of the present invention.
[0021]
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 Assistants), or a computer terminal to which a data communication card incorporating a wireless device is added.
[0022]
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.
[0023]
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.
[0024]
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).
[0025]
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.
[0026]
In addition, although the terminal 10 of this Embodiment determined the possibility of handoff using C / I value, the result of having compared RSSI with a predetermined value by the strength of a 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.
[0027]
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 related to the signal received by the terminal (information related to the state of the wireless communication line) is acquired. 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.
[0028]
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.
[0029]
FIG. 2 is a block diagram illustrating a configuration of the distribution server according to the embodiment of this invention.
[0030]
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.
[0031]
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.
[0032]
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.
[0033]
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. Further, the number of packets transmitted from the transmission unit 23 is controlled. Note that the method of determining the data transmission rate may be a method of selecting one of contents already encoded at different rates.
[0034]
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.
[0035]
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.
[0036]
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.
[0037]
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.
[0038]
Furthermore, 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.
[0039]
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.
[0040]
FIG. 3 is a diagram for explaining the operation of the buffer 14 according to the embodiment of this invention.
[0041]
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.
[0042]
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.
[0043]
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.
[0044]
FIG. 4 is a flowchart of the operation of the terminal 10 according to the embodiment of this invention.
[0045]
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).
[0046]
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).
[0047]
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.
[0048]
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.
[0049]
If the amount of data stored in the buffer 14 is less than the predetermined threshold B, it is determined that handoff is to be notified because there is a possibility that reproduction data is insufficient during handoff, and the process proceeds to a 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.
[0050]
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.
[0051]
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).
[0052]
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).
[0053]
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.
[0054]
FIG. 5 is a flowchart of data transmission processing of the distribution server 20 according to the embodiment of this invention.
[0055]
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 to specify 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. Further, the transmission interval of packets transmitted from the transmission unit 23 is determined (S121).
[0056]
Then, data is transmitted to the terminal 10 according to the determined rate (S122).
[0057]
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).
[0058]
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.
[0059]
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.
[0060]
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.
[0061]
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).
[0062]
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.
[0063]
FIG. 6 is a flowchart of the handoff detection process of the distribution server 20 according to the embodiment of this invention.
[0064]
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).
[0065]
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).
[0066]
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.
[0067]
FIG. 7 is a diagram illustrating the threshold A for determining handoff notice according to the embodiment of this invention.
[0068]
The C / I values are shown when handoff is predicted to occur between Sector1 and Sector2 in three base stations and (Sector1 to Sector3) terminals. 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.
[0069]
In the state shown in FIG. 7, the terminal 10 detects three base stations, and sets a radio communication line with a 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 between the C / I value of the base station (Sector1) and the C / I value of the base station (Sector2) (d ₁₂ ) And the difference between the C / I value of the base station (Sector1) and the C / I value of the base station (Sector3) (d ₁₃ ) Then, the difference in C / I values (d ₁₂ , D ₁₃ ) And a predetermined threshold A, the difference in C / I values (d ₁₂ , D ₁₃ ) Is smaller than threshold A, a handoff notice is transmitted to distribution server 30.
[0070]
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 the three base stations and the (Sector 1 to Sector 3) terminals. The vertical dotted line indicates the detection timing of the C / I value.
[0071]
The terminal 10 sets a radio 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 the radio communication line is set is lowered. Then, the C / I value of the other detected base station (Sector2) has improved, and the C / I value is approaching before the handoff occurs between the base station (Sector1) and the base station (Sector2). , The difference in C / I values of both base stations (d ₁₂ ) Is smaller than the threshold 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).
[0072]
Thereafter, when the C / I value of the base station (Sector1) decreases and the C / I value of the base station (Sector2) improves, the C / I values of both base stations are reversed. Then, the difference between the C / I values of both base stations (d ₁₂ When the absolute value of) becomes larger than a predetermined value, handoff is executed, the connection with the base station (Sector1) is released, and a wireless communication line is set up with the base station (Sector2).
[0073]
【The invention's effect】
In the present invention, a wireless communication terminal (terminal 10), a wireless base station (wireless base station 30) in which a wireless communication line is set between the wireless communication terminal, and content data are transmitted to the wireless communication terminal. In the communication system constituted by the data distribution apparatus (distribution server 20), the wireless communication terminal predicts the handoff occurrence when the wireless communication terminal predicts the handoff occurrence, and the handoff for notifying the handoff when the prediction means predicts the handoff occurrence. Signal transmission means for transmitting a notice signal, and the data distribution device receives the handoff notice signal and a signal receiving means for receiving the handoff notice signal, Lower the encoding rate of the content data transmitted to the wireless communication terminal so as not to change the data transmission rate of the wireless communication line Control means (control unit 25). Therefore, with handoff predictions, In order not to change the transmission rate of the wireless communication line, The encoding rate can be reduced. According to such control, buffer underflow is unlikely to occur, and content data (image data or the like) that is longer than before the change can be stored in the wireless communication terminal. Therefore, it is possible to reproduce a moving image that is not easily interrupted. Further, the user can continuously watch the moving image without being aware of handoff. Further, by detecting handoff in advance, processing after the occurrence of handoff (recovery processing such as complementing data when a packet is delayed and does not meet the reproduction time) is not required.
[0074]
Also The prediction means predicts the occurrence of handoff based on the result of comparison between the channel quality with the base station and a predetermined value, and the signal transmission means performs handoff when the prediction means predicts the occurrence of handoff. Since a warning signal is transmitted, the occurrence of handoff is predicted on the wireless communication terminal side, Delivery The server can identify the occurrence of a handoff.
[0075]
The Furthermore, even when the prediction means predicts the occurrence of handoff, when the storage state of the buffer satisfies the predetermined condition, Since the handoff notice signal is not transmitted, an unnecessary handoff notice signal is not transmitted, and the traffic of the wireless communication line is not increased.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a wireless communication system according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a distribution server according to the embodiment of this invention.
FIG. 3 is an operation explanatory diagram of a buffer of the terminal according to the embodiment of this invention.
FIG. 4 is a flowchart of the operation of the terminal according to the embodiment of this invention.
FIG. 5 is a flowchart of data transmission processing of the distribution server according to the embodiment of this invention.
FIG. 6 is a flowchart of a handoff detection process of the distribution server according to the embodiment of this invention.
FIG. 7 is an explanatory diagram of a threshold A for determining handoff notice in the wireless communication system according to the embodiment of this invention.
FIG. 8 is an explanatory diagram of handoff notice timing of the wireless communication system according to the embodiment of this invention.
[Explanation of symbols]
10 terminals
11 Receiver module
12 Transmission module
13 Wireless information acquisition module
14 buffers
15 Decoding module
17 Control module
20 Distribution server
21 Video source
22 Encoding unit
23 Transmitter
25 Control unit
30 radio base stations
31 Antenna
40 network

Claims (7)

In a communication system including a wireless communication terminal, a wireless base station in which a wireless communication line is set between the wireless communication terminal, and a data distribution apparatus that transmits content data to the wireless communication terminal,
The wireless communication terminal includes prediction means for predicting occurrence of handoff, and signal transmission means for transmitting a handoff notice signal for announcing handoff when the prediction means predicts occurrence of handoff,
The data distribution device includes:
Signal receiving means for receiving the handoff notice signal;
Upon receiving the handoff warning signal, so as not to change the data transmission rate of the wireless communication line, a communication, characterized in that a control means for reducing the coding rate of the content data to be transmitted to the wireless communication terminal system.   The prediction means predicts the occurrence of handoff based on the result of comparing the channel quality with the base station with a predetermined value,
  The communication system according to claim 1, wherein the signal transmission unit transmits a handoff notice signal when the prediction unit predicts the occurrence of a handoff.   The wireless communication terminal includes a buffer for temporarily storing data transmitted from the data distribution device,
  3. The signal transmission unit does not transmit a handoff notice signal when the storage state of the buffer satisfies a predetermined condition even when the prediction unit predicts the occurrence of a handoff. The communication system according to any one of the above.   A data distribution device that is connected to a wireless base station that communicates with a wireless communication terminal using a wireless communication line, and that transmits content data to the wireless communication terminal,
  A signal receiving means for receiving a handoff notice signal for notifying the occurrence of handoff from the wireless communication terminal;
  Data distribution comprising: control means for reducing the coding rate of content data to be transmitted to the wireless communication terminal without changing the data transmission rate of the wireless communication line when receiving the handoff notice signal apparatus.   The present invention is applied to a communication system including a wireless communication terminal, a wireless base station in which a wireless communication line is set between the wireless communication terminal, and a data distribution apparatus that transmits content data to the wireless communication terminal. In the communication method
  The wireless communication terminal is
  Predict the occurrence of handoffs,
  When a handoff is predicted, a handoff warning signal will be sent to notify the handoff.
  The data distribution device includes:
  When the handoff notice signal is received, a communication method characterized by lowering a coding rate of content data to be transmitted to the wireless communication terminal so as not to change a data transmission rate of the wireless communication line.   The wireless communication terminal is
  Predicting the occurrence of handoff based on the result of comparing the line quality with the base station with a predetermined value,
  6. The communication method according to claim 5, wherein a handoff notice signal is transmitted when occurrence of a handoff is predicted.   The wireless communication terminal transmits a handoff notice signal even when the occurrence of a handoff is predicted when the storage state of a buffer that temporarily stores data transmitted from the data distribution device satisfies a predetermined condition The communication method according to claim 5 or 6, wherein the communication method is not performed.

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