JP4028356B2 - Communication system, radio communication terminal, data distribution device, and communication method - Google Patents

Communication system, radio communication terminal, data distribution device, and communication method Download PDF

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JP4028356B2
JP4028356B2 JP2002317415A JP2002317415A JP4028356B2 JP 4028356 B2 JP4028356 B2 JP 4028356B2 JP 2002317415 A JP2002317415 A JP 2002317415A JP 2002317415 A JP2002317415 A JP 2002317415A JP 4028356 B2 JP4028356 B2 JP 4028356B2
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Prior art keywords
data
rate
wireless communication
encoding
encoding rate
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JP2004153620A (en
Inventor
宏 築地
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京セラ株式会社
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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 communication system that can change a transmission rate in a radio section.
[0002]
[Prior art]
In recent years, the transmission capacity of communication lines has also increased in mobile communication networks, and mobile terminal devices such as mobile phones have become more sophisticated, and in addition to conventional voice call services, data and images, and even moving image data can be transmitted and received. What can be done has appeared, and moving picture data download services and streaming services have started to be provided in mobile phone services. With such diversification of services, mobile communication networks are required to transmit a larger amount of data on the downlink. In order to meet such needs, a high-speed packet communication network using a 1xEV-DO (1x Evolution Data Only) system in which the transmission efficiency of a downlink from a base station to a communication terminal has been proposed.
[0003]
In this 1xEV-DO system, a communication mode capable of performing high-speed packet communication most efficiently with the measured line quality is selected, and data communication is possible at a data rate of 38.4 kbps to 2.4 Mbps. The base station performs scheduling for determining transmission slot allocation according to the channel quality in each communication terminal. In consideration of improving the transmission efficiency of the entire system, the base station preferentially allocates communication resources to radio communication terminals having a high communication rate that can be communicated, thereby increasing the data transmission efficiency of the entire system.
[0004]
There is a method using a streaming technique as a moving image data distribution method, and RTP (Realtime Transport Protocol) defined by RFC1889 as a data transfer protocol and its control protocol in order to ensure real-time data reproduction during streaming. RTCP (RTP Control Protocol) is used. By using this RTCP information, the streaming server can predict the reception rate on the client side, and streaming is performed using a variable rate control method for controlling the transmission rate of the server using this information. A technique for controlling the transmission rate so as to gradually increase the transmission rate based on RTCP data from the receiving side terminal when transmitting information is known.
[0005]
When transmitting streaming data in a communication system with a large transmission rate fluctuation range, such as a 1xEV-DO system, variable-rate streaming that distributes data while changing the coding rate according to the transmission rate fluctuation Is effective. This lowers the coding rate to reduce the effective rate in the radio section to avoid delays and data discard due to buffering at the base station, and codes as much as possible to increase the effective rate in the radio section. It is intended to increase the conversion rate and provide images with good image quality. As a method for realizing a variable rate, a transcoding method for changing the encoding rate using the same video source and re-encoding, and a file switching method for selecting and transmitting a video source having a different bit rate have been proposed. Yes.
[0006]
[Patent Document 1]
JP 2002-135783 A
[0007]
[Problems to be solved by the invention]
However, in a best-effort high-speed wireless packet communication network such as a 1xEV-DO system, the bit error rate, packet loss rate, delay time, and the like are large compared to a wired network due to the characteristics of wireless communication, and its data transmission bandwidth There is a problem that the width also fluctuates rapidly. In particular, in a moving image streaming service that requires data continuity and real-time performance, the fluctuation range of the transmission band and the size of the delay time are serious problems in service.
[0008]
Further, since the transcoding technique described above needs to perform decoding processing and encoding processing, the load on the transcoder is large, and the load on the conversion processing on the server is large. In particular, in the 1xEV-DO system having a large band fluctuation width, there is a problem that the efficiency of the conversion process is deteriorated because the difference in the encoding rate for conversion becomes large. For example, if the source data is only 2.4 Mbps stream data, both stream data of 1.0 Mbps and stream data of 64 kbps will be generated based on the stream data of 2.4 Mbps. It needs to be decoded once. In particular, when the rate is lowered to 100 kbps or lower, sufficient image quality cannot be obtained by the above-described method alone, so that an image size changing process is also required before encoding. In such a case, there is a problem that it takes time to convert one image, and a desired frame rate of the converted stream data cannot be obtained, and the quality of the moving image is deteriorated.
[0009]
On the other hand, in the file switching method, a plurality of stream files with different encoding rates are prepared in advance, and variable rate control is realized by selecting and transmitting one of these stream files according to the rate change during transmission. ing. As described above, in the file switching type rate control, a stream file corresponding to each encoding rate can be prepared to cope with a wide band of the 1xEV-DO network. However, if the number of files is small, fine rate control cannot be performed, and the file If the number is large, there is a problem that the storage area of the server is compressed.
[0010]
An object of the present invention is to provide a communication system capable of transmitting data at an optimum bit rate when transmitting streaming data in a communication system having a large variation in transmission rate.
[0011]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a communication system in which content data is transmitted from a data distribution device to a wireless communication terminal via a wireless communication line. Rate information transmitting means for transmitting information necessary for determination, the data distribution apparatus, acquisition means for acquiring content source data encoded at a plurality of rates, and the wireless communication terminal transmitted from the wireless communication terminal Receiving means for receiving information; encoding rate determining means for determining an encoding rate for encoding the content data from a data distribution device based on the information; and an encoding rate determined by the encoding rate determining means Source data selection means for selecting source data based on the selected source data, and the selected source data Comprising a transcoding means for re-encoding in coding rate, a data transmission means for transmitting the re-encoded source data, the.
[0012]
According to a second aspect of the present invention, there is provided a communication system for transmitting content data from a data distribution device to a wireless communication terminal via a wireless communication line, wherein the wireless communication terminal encodes the content data by the data distribution device. Encoding rate determination means for determining the encoding rate, and rate information transmission means for transmitting the information of the encoding rate to a data distribution device, wherein the data distribution device receives content source data encoded at a plurality of rates. Obtaining means for obtaining; source data selecting means for selecting source data based on the coding rate determined by the coding rate determining means; and re-encoding the selected source data at the coding rate. Transcoding means; and data transmission means for transmitting the re-encoded source data.
[0013]
According to a third aspect of the present invention, a wireless communication terminal that receives content data transmitted from a data distribution device via a wireless communication line is necessary for the data distribution device to determine an encoding rate for encoding the content data. Transmitting means for transmitting information; source data selected based on an encoding rate determined based on the information among content source data encoded at a plurality of rates; and the determined encoding rate Receiving means for receiving the content data re-encoded and transmitted in (1).
[0014]
According to a fourth aspect of the present invention, in a wireless communication terminal that receives content data transmitted from a data distribution device via a wireless communication line, an encoding rate at which the data distribution device determines an encoding rate for encoding the content data The source data selected based on the determined encoding rate among the content source data encoded at a plurality of rates is determined and re-encoded at the determined encoding rate and transmitted. Receiving means for receiving content data.
[0015]
According to a fifth aspect of the present invention, in a data distribution apparatus for transmitting content data to a wireless communication terminal via a wireless communication line, acquisition means for acquiring content source data encoded at a plurality of rates, and encoding of the content data Receiving means for receiving information necessary for determining a rate from the wireless communication terminal; encoding rate determining means for determining a coding rate at which a data distribution apparatus encodes the content data based on the information; Source data selection means for selecting source data based on the encoding rate determined by the encoding rate determination means, transcoding means for re-encoding the selected source data at the encoding rate, and Data transmitting means for transmitting the re-encoded source data.
[0016]
According to a sixth aspect of the present invention, in a data distribution apparatus for transmitting content data to a wireless communication terminal via a wireless communication line, acquisition means for acquiring content source data encoded at a plurality of rates, and determination by the wireless communication terminal Source data selecting means for selecting source data based on the encoded rate, transcoding means for re-encoding the selected source data at the encoding rate, and transmitting the re-encoded source data Data transmitting means.
[0017]
A seventh invention is a communication method for transmitting content data from a data distribution device to the wireless communication terminal via a wireless communication line, wherein the wireless communication terminal encodes the content data by the data distribution device. The information necessary for determining the data is transmitted to the data distribution device, the data distribution device is capable of acquiring content source data encoded at a plurality of rates, and transmitted from the wireless communication terminal Receiving information, determining a coding rate at which the data distribution device encodes the content data based on the information, selecting source data based on the determined coding rate, and selecting the selected source data The content data is transmitted after being re-encoded at the encoding rate.
[0018]
According to an eighth aspect of the present invention, there is provided a communication method for transmitting content data from a data distribution device to the wireless communication terminal via a wireless communication line, wherein the wireless communication terminal encodes the content data by the data distribution device. Determining a rate, and the data distribution device is capable of acquiring content source data encoded at a plurality of rates, selecting source data based on the determined encoding rate, and selecting the selected source Content data is transmitted by re-encoding data at the encoding rate.
[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 configuration diagram of a radio communication system according to an embodiment of the present invention.
[0021]
The client terminal 10 is a data distribution device (streaming) that transmits content data (moving image, still image, music, audio, caption, etc.) having real-time properties via the radio base station 30 and the network (IP network or the like) 40. Server 20).
[0022]
The client terminal 10 is a wireless communication terminal such as a mobile phone that supports data communication, a PDA (Personal Digital Assistants), or a computer device to which a data communication card incorporating a wireless device is added.
[0023]
The client terminal 10 and the radio base station 30 are connected by a 1xEV-DO network (1x Evolution Data Only network). This 1xEV-DO network determines the bandwidth of data communication allocated to each client terminal 10 based on the quality information (DRC information) of the wireless communication line transmitted from the client terminal 10 and the number of connected client terminals 10. The transmission rate of the wireless communication line for each client terminal 10 is determined.
[0024]
Here, the high-speed packet communication performed between the radio base station 30 and the client terminal 10 in the 1xEV-DO system will be described.
[0025]
A packet used in the 1xEV-DO system is configured by adding a header including a pilot signal and control information to the head of a data portion in which data addressed to each user is time-division multiplexed. The control information includes assignment information indicating assignment of communication resources to each communication terminal.
[0026]
First, the radio base station 30 transmits a packet including the pilot signal to the client terminal 10 accommodated in its own cover area. Each client terminal 10 measures downlink channel quality (for example, desired signal to interference signal ratio (CIR)) based on a pilot signal included in the received signal. Each client terminal 10 stores a table indicating a correspondence relationship between downlink channel quality and an optimal communication mode when transmitting a packet with the channel quality. Each client terminal 10 refers to this table. Then, a communication mode capable of performing high-speed packet communication most efficiently with the measured line quality is selected. As the communication mode, a plurality of modes in which a slot length assigned to transmission data, a transmission data coding rate, a modulation method, and a spreading factor are combined are prepared. By selecting a communication mode, high-speed data communication is possible at a wide bandwidth data rate of 38.4 kbps to 2.4 Mbps. Each client terminal 10 transmits a signal (DRC signal) indicating the selected communication mode to the radio base station 30. The other client terminals 10 connected to the radio base station 30 also transmit DRC signals to the radio base station 30 in the same manner.
[0027]
Based on the DRC signal transmitted from each client terminal 10, the radio base station 30 performs scheduling for preferentially allocating communication resources from the client terminal 10 having good channel quality. As a result, since the transmission rate is increased for the client terminal 10 with good line quality and the data is transmitted, the time required for communication can be shortened, and the transmission rate is lowered for the client terminal 10 with poor line quality. Since data is transmitted, error resilience can be increased.
[0028]
The radio base station 30 allocates slots for transmission data according to communication resource allocation, performs encoding processing, modulation processing, spreading processing, etc., and configures transmission frames by time-division multiplexing transmission data addressed to each client terminal 10 The transmission frame is transmitted to each client terminal 10. At this time, control information (assignment information) indicating the assignment of communication resources to each client terminal 10 is inserted into the header of the head of the transmission frame. The client terminal 10 can demodulate data addressed to itself by knowing the communication mode by referring to the allocation information.
[0029]
Thus, in the conventional 1xEV-DO system, data transmission efficiency is enhanced as a whole system by preferentially allocating communication resources from communication terminals with good channel quality.
[0030]
FIG. 2 is a block diagram of each device constituting the wireless communication system according to the embodiment of the present invention.
[0031]
The client terminal 10 includes an antenna 11 that receives a radio wave (downlink signal) from the radio base station 30 and transmits a radio wave (uplink signal) to the radio base station 30, and the antenna 11 is connected to the radio unit 12. It is connected. The radio unit 12 includes a transmission unit and a reception unit. The transmission unit generates a high-frequency signal to be transmitted from the antenna 11, and the reception unit performs amplification, frequency conversion, and the like on the high-frequency signal received by the antenna 11, thereby generating a baseband signal. To the transmitter / receiver 13.
[0032]
The transmission / reception unit 13 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 13 and modulated. The modulated signal is converted into a high-frequency signal by the transmission unit and transmitted from the antenna 11.
[0033]
The transmission / reception unit 13 is connected to the reception buffer 14 and temporarily stores the streaming data received by the client terminal 10, so that the streaming data can be stored even if the transmission rate is reduced for a short time or the line is disconnected. Is played without interruption. The data read from the reception buffer 14 is sent to the decoding unit 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 the display unit 16 and the moving image data is reproduced.
[0034]
The control unit 17 controls each unit of the client terminal 10 such as the radio unit 12, the transmission / reception unit 13, the reception buffer 14, and the decoding unit 15. Specifically, a channel is designated for the radio unit 12 to control the transmission / reception frequency and transmission / reception timing. In addition, according to a predetermined communication protocol, various control signals such as setting, releasing, and location registration of a wireless communication line between the client terminal 10 and the wireless base station 30 are generated, and transmission / reception of these signals is controlled.
[0035]
Further, in the embodiment of the present invention, since the wireless communication network is a 1xEV-DO network, the client terminal 10 receives and obtains a signal (for example, a pilot signal, a control packet, etc.) transmitted from the wireless base station 30. Based on the CIR, DRC information, which is a signal indicating a communication mode selected as one capable of efficiently performing data communication, is transmitted to the radio base station 30 as radio communication line quality information. That is, the control unit 17 obtains the CIR obtained from the received signal and refers to the conversion table stored in advance to determine the transmission rate. Based on the determined transmission rate, DRC information is generated and sent to the radio unit 12. In this way, detection means for detecting the quality of the wireless communication line is configured by the wireless unit 12 or the like. The control unit 17 and the radio unit 12 constitute a line quality information transmission unit that transmits the line quality information detected by the detection unit to the streaming server 20.
[0036]
In addition, the control unit 17 monitors a packet of data transmitted from the streaming server 20 and acquires a change state of the reception rate during streaming. That is, the reception report (RR) 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 is transmitted to the streaming server 20 as data reception status information (feedback information). In this way, detection means for detecting the data reception status is configured by the control unit 17 or the like. The control unit 17, the wireless unit 12, and the like constitute reception status information transmission means for transmitting data reception status information transmitted from the streaming server 20 to the streaming server 20.
[0037]
Further, the buffer occupation amount information of the reception buffer 14 may be transmitted as feedback information.
[0038]
The control unit 17 instructs the decoding unit 15 on information for decoding.
[0039]
The radio base station 30 has an antenna 31 connected to the radio unit, receives radio waves (upstream signals) from the client terminals 10, and transmits radio waves (downstream signals) to the client terminals 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.
[0040]
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 the 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.
[0041]
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.
[0042]
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 30. Specifically, this control unit controls a transmission / reception frequency and transmission / reception timing by designating a channel to the radio unit. Further, in response to a connection request from the client terminal 10, the permission of the connection and the number of connections of the client terminal 10 are controlled.
[0043]
Furthermore, in the embodiment of the present invention, since the wireless communication network is a 1xEV-DO network, each client terminal 10 is assigned to each client terminal 10 based on the quality information of the wireless communication line transmitted from the client terminal 10 and the number of connected client terminals. The bandwidth of data communication to be allocated is determined, and the transmission rate of the wireless communication line for each client terminal 10 is determined.
[0044]
That is, the channel quality information receiving means for receiving the radio communication channel quality information (DRC information) and the reception status information (reception report: RR) transmitted from the client terminal 10 by the control unit and the radio unit of the radio base station 30. The transmission rate determining means configured to determine the data transmission rate of the wireless communication line is configured by the control unit or the like.
[0045]
The data distribution device is a device that transmits (distributes) moving image data to a wireless communication terminal, and stores moving image data. The data distribution apparatus is an apparatus on the service providing side, and is a computer apparatus 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 moving image data may be provided inside the server or outside the server.
[0046]
The streaming server 20 is a computer device that transmits data to the client terminal 10. The streaming server 20 stores video sources 21 a to 21 e in a stream data storage unit (storage device such as a storage device or a hard disk) that stores a plurality of stream data as sources. This video source divides a wide band of the 1xEV-DO network into a plurality of levels, and stores stream data encoded at a bit rate set for each level. In this embodiment, the range from 38.4 kbps to 2.4 Mbps is divided into five levels, and the bit rates are set from the highest to 2.4 Mbps, 1.2 Mbps, 600 kbps, 300 kbps, and 100 kbps. Prepare a stream file.
[0047]
The stream data selection unit 26 selects video sources 21 a to 21 e having appropriate bit rates from the stream data storage unit in accordance with the effective rate of the wireless section predicted by the rate prediction unit 24. For example, if the prediction rate is 400 kbps, 600 kbps stream data is selected, and if the prediction rate is 100 kbps or less, 100 kbps stream data is selected. Then, the video source is read from the storage device and sent to the transcoding unit 22.
[0048]
In the transcoding unit 22, the read video source is re-encoded based on a moving image encoding standard such as MPEG at a bit rate different from that of the read video data, and is sent to the transmission unit 23. That is, the transcoding unit 22 reads a bit stream from the stream data (video source) selected by the stream data selection unit 26, performs re-encoding (transcoding) at a coding rate that matches the prediction rate, To change.
[0049]
Specifically, in the transcoding unit 22, for example, after moving image content stored in a data format such as MPEG-1 or MPEG-2 is temporarily decoded into image data, another encoding scheme (for example, MPEG- 4) Re-encode with another image format or encoding rate. In order to obtain the necessary bit rate for re-encoding, the frame rate is changed by thinning out the frame to be processed, the quantization coefficient is changed during re-encoding, the compression rate is increased, and the DCT coefficient to be transmitted The amount of data is reduced to reduce the amount of data. With this technology, stream data of a plurality of rates can be transmitted from one image source in accordance with rate fluctuations in the wireless section.
[0050]
The transmission unit 23 segments the stream data based on a communication protocol and transmits the data as a packet to a network (IP network or the like) 40.
[0051]
The rate prediction unit 24 predicts the encoding rate of the data encoded by the streaming server 20 and determines the encoding rate of the data. In other words, in the present invention, the client terminal 10 receives, as the reception status information of the data transmitted from the streaming server 20, the packet loss rate, the number of lost packets, the maximum value of the sequence number of the received packet, the arrival interval jitter, etc. The report is transmitted to the streaming server 20. In addition, the client terminal 10 transmits DRC information to the streaming server 20 as quality information of a wireless communication line between the client terminal 10 and the wireless base station 30. Then, the streaming server 20 predicts the effective rate of the radio section based on the received feedback information (reception report (reception status information) and DRC information (line quality information)), and the data encoded by the streaming server 20 Is determined.
[0052]
The prediction of the effective rate may use only the feedback information recently received from the client terminal 10, or the feedback rate received in the past or the predicted rate from the feedback information is stored, and the transmission time is determined from the fluctuation. You may comprise so that the future rate which considered may be estimated. Also, other known prediction methods using various information can be taken. Also, the rate prediction interval and the coding rate switching interval are not particularly limited. However, it is desirable to switch the stream data at the start point of the I frame (I-VOP) in the stream data.
[0053]
The control unit 25 controls each unit of the streaming server 20 such as the transcoding unit 22 and the transmission unit 23. Specifically, the data encoding rate is acquired from the rate prediction unit 24, and an encoding method and encoding information (for example, DCT coefficient, quantization coefficient, etc.) suitable for the data encoding rate are transcoded. 22 is instructed. Further, the number of packets transmitted from the transmission unit 23 is controlled.
[0054]
Thus, in the streaming server 20 according to the embodiment of the present invention, the stream data selection unit 26 and the transcoding unit 22 use a combination of the file switching method and the transcoding method. The wide bandwidth (38.4 kbps to 2.4 Mbps) of the 1xEV-DO network is divided into a plurality of levels, and bit stream data (video sources 21a to 21e) as sources are stored for each level, and stream data selection is performed. The unit 26 selects stream data to be transmitted based on feedback information from the client, and switches files. Further, the transcoding unit 22 provided between the transmission unit 23 performs transcoding at a rate predicted based on the feedback information, thereby adjusting a difference from the effective rate after the file is switched. Further, when the fluctuation range of the effective rate is small, control is performed so that rate control is performed only by transcoding.
[0055]
With this configuration, the change rate of the bit rate when converting from the source stream data to the stream data to be actually transmitted is reduced, the deterioration in image quality from the source data is reduced, and the time required for the conversion process Can also be shortened.
[0056]
In the embodiment described above, the streaming server 20 calculates the rate at which the streaming server 20 encodes the streaming data, but the client terminal 10 calculates the rate at which the streaming server 20 encodes the streaming data. The client terminal 10 may notify the streaming server 20.
[0057]
FIG. 3 is a flowchart illustrating transmission processing of the streaming server 20 according to the embodiment of this invention.
[0058]
In this flowchart, the streaming server 20 starts data distribution from the lowest settable rate when streaming data distribution starts, and then uses the feedback information (reception report) to predict the effective rate and control the encoding rate. To do.
[0059]
The transcoding unit 22 detects a start code in the bit stream (S1).
[0060]
Then, it is determined whether the start code is a sequence end code (S2). If the start code is a sequence end code, the data transmission process is terminated (S10).
[0061]
On the other hand, if the start code is not a sequence end code, the process proceeds to an effective rate prediction process (S3). The rate prediction unit 24 predicts the effective rate of the wireless communication line based on the feedback information from the client terminal 10 and performs an effective rate prediction process (S3). At this time, only the feedback information recently received from the client terminal 10 may be used, or the feedback rate received in the past or the predicted rate from the feedback information is stored, and the future rate considering the transmission time from the fluctuation May be configured to predict. Other known prediction methods using various information can be used.
[0062]
After prediction of the effective rate, the predicted value of the effective rate is compared with the encoding rate of the transcoding unit 22 to determine whether or not the encoding rate needs to be changed (S4). If there is no difference between the prediction value of the effective rate (that is, the rate at which data is transmitted from the streaming server 20) and the encoding rate of the read video sources 21a to 21e, the encoding rate is changed by the transcoding unit 22. It is determined that it is not necessary to proceed to step S9, and re-encoding (transcoding) is continued while maintaining the current encoding rate.
[0063]
On the other hand, if the encoding rate of the video sources 21a to 21e read out from the predicted value of the effective rate is larger, it is determined that the encoding rate needs to be changed. Then, it is determined whether or not it is necessary to switch the video source (stream data) in order to match the encoding rate of the data transmitted from the streaming server 20 with the effective rate (S5).
[0064]
That is, if the data coding rate is greatly changed in the transcoding unit 22, the quality of the stream data (image quality, sound quality, etc.) deteriorates. Therefore, the video source input to the transcoding unit 22 is re-encoded. It is desirable to use the one closest to the coding rate. Therefore, in step S5, it is determined whether or not it is necessary to switch the video source. If it is not necessary to switch the stream data, the process proceeds to step S8 to set the encoding rate of the transcoding unit (S8). Coding is performed (S9).
[0065]
On the other hand, when it is necessary to switch the stream data (video source), it is determined from the header information of the bit stream data whether the encoding type of the data to be transcoded next is intra-frame encoding (S6). In the case of intra-frame coding, the stream data selection unit selects stream data with an appropriate bit rate from this prediction rate, and switches the stream data (video source) (S7).
[0066]
For example, if the prediction rate is 400 kbps, 600 kbps stream data is selected. Subsequently, the transcoding unit 22 is set to an encoding rate for generating 400 kbps stream data from 600 kbps source data, and transcoding is performed. If the prediction rate is 100 kbps or less, 100 kbps stream data is selected, and the transcoding unit 22 is set to an encoding rate for generating stream data at a target rate from 100 kbps source data.
[0067]
If it is not intra-frame coding, control is performed only by changing the coding rate of the transcoding unit 22 without changing the stream data serving as the source. For example, when streaming is currently performed using 600 kbps stream data as a source and the prediction rate is 200 kbps, if the coding type is intraframe coding, the stream data is switched to 300 kbps and then transcoded. 200 kbps data is transmitted, but if it is not intra-frame coding, the source data of 600 kbps is converted into stream data of 200 kbps, and the data is transmitted. Then, the stream data is switched at the timing of the next intra-frame encoded frame.
[0068]
On the other hand, if the prediction rate is higher than the encoding rate of the source data, transmission is performed at the highest rate that can be converted with the stream data until the timing of the next intraframe encoded frame, and the next frame is transmitted. The stream data is switched at the timing of the inner encoded frame.
[0069]
FIG. 4 is a diagram showing changes in the coding rate when the present invention is applied. The horizontal axis represents the elapsed time from the start of communication, and the vertical axis represents the predicted rate.
[0070]
When the predicted rate exceeds 100 kbps and is 300 kbps or less, the stream data selection unit 26 selects the 300 kbps video source 21d, and the transcoding unit 22 re-encodes the streaming data to 100 kbps to 300 kbps. When the prediction rate increases to a value exceeding 300 kbps (600 kbps or less), the stream data selection unit 26 selects the 600 kbps video source 21c, and the transcoding unit 22 re-encodes the streaming data to 300 kbps to 600 kbps. It becomes. Further, when the prediction rate increases to a value exceeding 600 kbps (1.2 Mbps or less), the stream data selection unit 26 selects the 1.2 Mbps video source 21b, and the transcoding unit 22 selects 600 kbps to 1.2 Mbps. Re-encoded to streaming data. Further, when the predicted rate increases to a value exceeding 1.2 Mbps, the stream data selection unit 26 selects the 2.4 Mbps video source 21a, and the transcoding unit 22 selects the streaming data from 1.2 Mbps to 2.4 Mbps. Is re-encoded. Thus, the video data 21a to 21e having different encoding rates are selected depending on the encoding rate of the streaming data transmitted from the streaming server 20. It should be noted that it is convenient to provide a hysteresis characteristic for switching between the prediction rate and the video source because switching of the video source does not frequently occur for a short time change.
[0071]
Further, when the fluctuation range of the effective rate is small, control is performed so that rate control is performed only by transcoding.
[0072]
【The invention's effect】
In the first invention, source data selection means (stream data selection unit 26) for selecting source data based on a coding rate determined based on a predicted rate (reception report and / or DRC information), and the selection And a transcoding means (transcoding unit 22) for changing the encoding rate of the source data, and the bit rate is controlled by combining the transcoding method and the file switching method, so that feedback information from the client Since switching between multiple stored files and adjusting the difference from the effective rate after switching files is based on transcoding, even in communication systems with large fluctuations in transmission rate, Rate can be controlled. Also, the load on the conversion process for the streaming server and the load on the storage area can be reduced. And the quality of the streaming service in a high-speed packet communication network can be improved.
[0073]
In the second invention, the wireless communication terminal (client terminal 10) determines the coding rate at which the server determines the coding rate for coding the content data based on the predicted rate (reception report and / or DRC information). Means (control unit 17), and the server (streaming server 20) has source data selection means (streaming data selection unit 26) for selecting source data based on the coding rate determined by the wireless communication terminal; Transcoding means (transcoding unit 22) for changing the encoding rate of the selected source data, and the server determines the encoding rate at which the content data is encoded at the wireless communication terminal. Can be mitigated, and detailed judgment can be made.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a radio communication system according to an embodiment of the present invention.
FIG. 2 is a block diagram of devices included in the wireless communication system according to the embodiment of this invention.
FIG. 3 is a flowchart of transmission processing of the streaming server 20 according to the embodiment of this invention.
FIG. 4 is a diagram showing a change in coding rate when the present invention is applied.
[Explanation of symbols]
10 Client terminal
11 Antenna
12 Radio section
13 Transceiver
14 Receive buffer
15 Decryption unit
16 Display section
17 Control unit
20 Streaming server
21 Video source
22 Transcoding section
23 Transmitter
24 Rate prediction unit
25 Control unit
26 Stream data selector
30 radio base stations
31 Antenna
40 network

Claims (8)

  1. In a communication system for transmitting content data from a data distribution device to a wireless communication terminal via a wireless communication line,
    The wireless communication terminal is
    The data distribution device comprises rate information transmission means for transmitting information necessary for determining an encoding rate for encoding content data,
    The data distribution device includes:
    Acquisition means for acquiring content source data encoded at a plurality of rates;
    Receiving means for receiving the information transmitted from the wireless communication terminal;
    An encoding rate determining means for determining an encoding rate for encoding the content data from a data distribution device based on the information;
    Source data selection means for selecting source data based on the coding rate determined by the coding rate determination means;
    Transcoding means for re-encoding the selected source data at the encoding rate;
    And a data transmission means for transmitting the re-encoded source data.
  2. In a communication system for transmitting content data from a data distribution device to a wireless communication terminal via a wireless communication line,
    The wireless communication terminal is
    An encoding rate determining means for determining an encoding rate at which the data distribution apparatus encodes the content data;
    Rate information transmitting means for transmitting the information of the coding rate to a data distribution device,
    The data distribution device includes:
    Acquisition means for acquiring content source data encoded at a plurality of rates;
    Source data selection means for selecting source data based on the encoding rate determined by the encoding rate determination means;
    Transcoding means for re-encoding the selected source data at the encoding rate;
    And a data transmission means for transmitting the re-encoded source data.
  3. In a wireless communication terminal that receives content data transmitted from a data distribution device via a wireless communication line,
    Transmitting means for transmitting information necessary for the data distribution apparatus to determine an encoding rate for encoding content data;
    Of the content source data encoded at a plurality of rates, the source data selected based on the encoding rate determined based on the information is re-encoded at the determined encoding rate and transmitted. A wireless communication terminal comprising: a receiving unit configured to receive content data.
  4. In a wireless communication terminal that receives content data transmitted from a data distribution device via a wireless communication line,
    An encoding rate determining means for determining an encoding rate at which the data distribution apparatus encodes the content data;
    Among the content source data encoded at a plurality of rates, the source data selected based on the determined encoding rate is received and the content data re-encoded at the determined encoding rate is received. A wireless communication terminal.
  5. In a data distribution apparatus for transmitting content data to a wireless communication terminal via a wireless communication line,
    Acquisition means for acquiring content source data encoded at a plurality of rates;
    Receiving means for receiving information necessary for determining an encoding rate of the content data from the wireless communication terminal;
    An encoding rate determining means for determining an encoding rate at which the data distribution apparatus encodes the content data based on the information;
    Source data selection means for selecting source data based on the coding rate determined by the coding rate determination means;
    Transcoding means for re-encoding the selected source data at the encoding rate;
    And a data transmission means for transmitting the re-encoded source data.
  6. In a data distribution apparatus for transmitting content data to a wireless communication terminal via a wireless communication line,
    Acquisition means for acquiring content source data encoded at a plurality of rates; source data selection means for selecting source data based on an encoding rate determined in the wireless communication terminal;
    Transcoding means for re-encoding the selected source data at the encoding rate;
    And a data transmission means for transmitting the re-encoded source data.
  7. In a communication method for transmitting content data from a data distribution device to the wireless communication terminal via a wireless communication line,
    The wireless communication terminal transmits information necessary for determining an encoding rate at which the data distribution apparatus encodes content data to the data distribution apparatus,
    The data distribution apparatus is capable of acquiring content source data encoded at a plurality of rates, receives the information transmitted from the wireless communication terminal, and encodes the content data by the data distribution apparatus Determining an encoding rate based on the information, selecting source data based on the determined encoding rate, re-encoding the selected source data at the encoding rate, and transmitting content data. A characteristic communication method.
  8. In a communication method for transmitting content data from a data distribution device to the wireless communication terminal via a wireless communication line,
    The wireless communication terminal determines an encoding rate at which the data distribution apparatus encodes the content data,
    The data distribution device can acquire content source data encoded at a plurality of rates, selects source data based on the determined encoding rate, and encodes the selected source data A communication method characterized by transmitting content data after re-encoding at a rate.
JP2002317415A 2002-10-31 2002-10-31 Communication system, radio communication terminal, data distribution device, and communication method Expired - Fee Related JP4028356B2 (en)

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