JP5005798B2 - Communication terminal - Google Patents

Description

  The present invention relates to a communication terminal.

In recent years, it has become important to establish a technology for seamless communication that performs communication by adaptively switching access to a plurality of different wireless networks such as cellular and wireless LANs.
In general, since there is a large difference in transmission speed depending on communication media, it may be difficult to maintain the transmission rate before handover when performing handover between different media. In addition, due to the difference in delay time depending on media, there is a possibility that instantaneous interruption may occur during handover. Seamless communication is a technique for switching communication to an optimal communication medium according to the situation, and continuously transmitting communication by transmitting streaming data such as a moving image file and video / audio data of a videophone without interruption.

  As one of such techniques, Patent Document 1 describes a method of changing a transmission rate by converting data to be transmitted into quality suitable for communication media. However, since this method only changes the frame rate before and after the handover, the delay time difference between media and the effects of switching time and packet buffering time after rate conversion in normal handover. Can not be absorbed. Therefore, there has been a problem that video and audio are interrupted on the receiving side.

  Further, in Non-Patent Document 1, a packet loss caused by the effect of link switching time is obtained by replicating a packet in a server in the network at the time of handover and transmitting (bicasting) the packet to both the link before and after the handover. A technique has been proposed in which seamless handover is realized. However, if this method is used as it is for handover between media with greatly different transmission speeds, it is impossible to normally transmit all the packets transmitted on the medium with a high transmission speed using the medium with a low transmission speed. Therefore, there is a problem that seamless switching cannot be performed.

  Furthermore, in Non-Patent Document 2, as one method of seamless communication specialized for streaming applications, the transmission speed varies greatly by bi-casting after converting transmission data to a rate corresponding to the communication media on the content server side. A technique is described in which communication can be continued continuously even when handover is performed between networks. However, this technology has a problem that it cannot be applied to interactive and real-time applications such as videophones.

JP-A-10-126856

Karim El Malki et al., “Simultaneous Bindings for Mobile IPv6 Fast Handovers”, July 2001, IETF, Mobile IP Working Group, Internet-draft, draft-elmalki-mobileip-bicasting-v6-00.txt "Development of technology for promoting the use of user terminals in wireless LAN spots; Attachment 2 (3) Seamless handover technology", August 24, 2004, Mobile Home System Council, <URL: http: //mhsf.jeita .or.jp / pressrelease / 040824.pdf>

  The present invention has been made in view of the above points, and an object thereof is to provide a communication terminal capable of seamlessly communicating bi-directional and real-time applications without interruption even when handover is performed between different communication media. There is to do.

The present invention has been made in order to solve the above-mentioned problems, and the invention according to claim 1 is characterized in that each of the transmission / reception units individually demodulates data having different video qualities received by a plurality of transmission / reception units. A plurality of demodulating units provided in correspondence with each other, a plurality of video quality converting units provided corresponding to each of the demodulating units for converting the video quality of the input data, and a reproduction for reproducing the data The video quality conversion unit continuously converts the video quality of one demodulated data so that the video quality is the same as the video quality of the other demodulated data, and the playback unit When the other demodulated data is being played back, if the video quality of the one demodulated data is the same as the video quality of the other demodulated data, The data to the other A communication terminal, characterized in that the switching to the demodulated data of the one from the tone data.

According to the present invention, the optimum transmission rate and error resilience strength are determined in consideration of the characteristics of the communication path, and the data of different video quality transmitted by converting the data to the transmission rate or / and error resilience strength is obtained. Since the data is selectively demodulated and reproduced, communication can be performed without interrupting the video even on a medium having a low communication speed.
In addition, since data is demodulated with video quality suitable for each path using a plurality of communication paths, communication can be continued even if one of the communication paths becomes unusable.
In addition, when switching communication paths, data is relayed through a plurality of communication paths in the middle, so that video can be seamlessly communicated without interruption of video that normally occurs due to handover.
Furthermore, since data transmitted at different transmission rates is selectively reproduced or reproduced after continuously changing the transmission rate, smooth video reproduction can be performed without interruption.

1 is a configuration diagram of a wireless network according to a first embodiment. FIG. It is a block diagram which shows the structure of a bicast server. It is a block diagram of the server group which has the same function as a bicast server. It is a block diagram which shows the structure of a dual communication terminal. It is a block diagram of the wireless network by 2nd Embodiment. It is a block diagram which shows another structure of a dual communication terminal. It is a block diagram which shows another structure of a dual communication terminal. It is a block diagram which shows another structure of a dual communication terminal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<< First Embodiment >>
FIG. 1 schematically shows the configuration of a wireless network according to the first embodiment of the present invention. In the figure, this wireless network includes a bicast server 10, a cellular base station 20, a wireless LAN base station 30, a dual communication terminal 40, and a single communication terminal 50. Here, the dual communication terminals 40 correspond to “communication terminals”, respectively.

  The cellular base station 20 is a base station to which each terminal is connected when performing communication using a mobile phone, and the wireless LAN base station 30 is a base station to which each terminal is connected when performing communication using a wireless LAN. Each of the cellular base station 20 and the wireless LAN base station 30 has a communication area determined by its radio wave output intensity and surrounding terrain environment, and each terminal is connected to the base station when it is in this communication area. And communicate. Here, in FIG. 1, it is assumed that the communication area of the cellular base station 20 and the communication area of the wireless LAN base station 30 partially overlap. Further, it is assumed that the cellular base station 20 and the wireless LAN base station 30 are both connected to the core network 60.

  The dual communication terminal 40 is a mobile phone terminal having a mobile phone communication interface and a wireless LAN communication interface. When in the communication area of the cellular base station 20, the dual communication terminal 40 uses the mobile phone interface to When in the communication area of the wireless LAN base station 30, it is possible to communicate with the wireless LAN base station 30 by using the wireless LAN interface. Further, when the communication areas of both base stations are in an overlapping area, the connection destination base station is adaptively switched according to the communication status. For example, when the dual communication terminal 40 is moving from the communication area of the wireless LAN base station 30 toward the communication area of the cellular base station 20, switching from the wireless LAN base station 30 to the cellular base station 20 (handover) Is done.

The single communication terminal 50 is a mobile phone terminal having only a wireless LAN communication interface, and the connectable base stations are limited to the wireless LAN base station 30.
Note that the dual communication terminal 40 and the single communication terminal 50 differ only in that they have a plurality of communication interfaces or only one as described above, and the other configurations and functions are the same, and both are videophones. It shall have the function of.
Hereinafter, the present embodiment will be described on the assumption that a handover is performed while videophone communication is performed between the dual communication terminal 40 and the single communication terminal 50.

  FIG. 2 is a block diagram showing a functional configuration of the bicast server 10. The bicast server 10 converts the data transmitted by a two-way real-time application such as a videophone into video quality suitable for a communication medium (in this case, communication by a mobile phone or communication by a wireless LAN) and performs bicast. And is connected to the core network 60 in the same manner as the two base stations described above.

In FIG. 2, the bicast server 10 includes a video quality conversion unit 102, a transmission quality determination unit 104, and a transmission / reception unit 106.
The video quality conversion unit 102 performs processing for converting the transmission rate and the error resilience strength on the video data (videophone video data) input from the transmission / reception unit 106 in accordance with an instruction from the transmission quality judgment unit 104. The transmission quality judgment unit 104 constantly measures the transmission rate of data input to the video quality conversion unit 102. In addition, the transmission quality determination unit 104 includes a transmission rate, a delay time, a packet loss rate, and the like for each of the wireless systems (here, the mobile phone and the wireless LAN) used in each base station connected to the core network 60. Various information about communication parameters is notified. Based on these pieces of information, the transmission quality determination unit 104 determines what transmission rate and error resistance strength it is appropriate to transmit the above video data, and sends the result to the video quality conversion unit 102. Informs and instructs to convert video data.

  Here, the transmission rate is the number of bits of data transmitted per unit time. As a method of converting the transmission rate, for example, a method of converting a frame rate that is the number of video frames per second or a method of converting the number of pixels of an image in one frame can be applied. Further, the conversion of the error resilience strength is performed by optimally adjusting the redundancy added to the data according to the packet loss rate. Then, after the error resilience process is performed, the frame rate and the number of pixels are changed, and converted to a transmission rate that can be transmitted by the wireless system used for distribution.

When the data transmission destination is the dual communication terminal 40, the video data whose transmission rate and error resilience strength are converted by the video quality conversion unit 102 is sent from the transmission / reception unit 106 to the core network 60 side together with the video data before conversion. . At this time, the two pieces of video data to be sent out may be in a synchronized state as an image or in an asynchronous state.
Also, when the data transmission destination is the single communication terminal 50, one of the video data after conversion or before conversion is sent out from the transmission / reception unit 106 based on the determination of the transmission quality determination unit 104.

  Instead of the above-described bicast server 10, as shown in FIG. 3, it is possible to adopt a configuration including separate servers (transmission quality judgment server 70 and video quality conversion server 80).

FIG. 4 is a block diagram showing a functional configuration of the dual communication terminal 40.
In the figure, the dual communication terminal 40 includes two transmission / reception units 402a and 402b, a demodulation unit 404, and a reproduction unit 406.

  Of the two transmission / reception units, one transmission / reception unit 402a is a mobile phone communication interface, and the other transmission / reception unit 402b is a wireless LAN communication interface. These transmission / reception units 402 a and 402 b independently receive data transmitted in each wireless system and output the data to the demodulation unit 404. Each received data has video quality (transmission rate, error tolerance strength) suitable for each system of a mobile phone or a wireless LAN.

The demodulator 404 selects one of the input received data based on the communication state and the video quality, performs a demodulation process on the selected data, and extracts video data. This video data is sent to the playback unit 406 to play back the video.
Here, regarding the above data selection performed by the demodulator 404, specifically, for example, when the communication state in the wireless LAN is poor, the data received by the mobile phone system is selected, or the wireless LAN is also portable. If the telephone can be received in the same communication state, a determination is made to select data having a higher transmission rate. When the demodulator 404 switches data from one to the other, a buffer (not shown) provided in the preceding stage of the demodulator 404 is used to synchronize the data and the reproduced video is interrupted. Control shall be performed so as not to occur.

Next, a handover operation in this embodiment will be described.
As a premise, it is assumed that the dual communication terminal 40 moves from point A to point B to point C (see FIG. 1), and points A to C are in the communication area of the wireless LAN base station 30, respectively. It is assumed that the point B is located in an area where the communication area of the cellular base station 20 and the communication area of the wireless LAN base station 30 overlap, and the point C is located in the communication area of the cellular base station 20. In addition, the transmission speed when using a wireless LAN system is 2 Mbps, and the transmission speed when using a mobile phone system is 200 kbps. Further, it is assumed that the transmitted data is always communicated via the bicast server 10 regardless of the position of the dual communication terminal 40.

  First, when the dual communication terminal 40 exists at the point A, communication between the dual communication terminal 40 and the single communication terminal 50 is performed using the wireless LAN system via the wireless LAN base station 30. In this case, since the same communication system (wireless LAN) is used and the transmission speed is the same, the bicast server 10 does not convert the transmission rate and transfers the data to the destination as it is. That is, communication is performed at a transmission rate of 2 Mbps in any direction.

  Next, when the dual communication terminal 40 moves to the point B, the data of 2 Mbps transmitted from the single communication terminal 50 is copied by the video quality conversion unit 102 and converted to a transmission rate of 200 kbps of the mobile phone. The bicast server 10 transmits the copy source 2 Mbps data and the converted 200 kbps data to the dual communication terminal 40 that is the communication partner. At this time, 2 Mbps data is sent from the wireless LAN base station 30, and 200 kbps data is sent from the cellular base station 20 to the dual communication terminal 40. The dual communication terminal 40 performs the above-described selection as appropriate for two pieces of received data having different transmission rates to perform data demodulation and video reproduction.

  The dual communication terminal 40 transmits 2 Mbps data to the wireless LAN base station 30 and 200 kbps data to the cellular base station 20, respectively. Both of these two data are delivered to the bicast server 10. The bicast server 10 sends out data at a transmission rate suitable for the communication system used by the single communication terminal 50 that is the transmission destination. Here, since the single communication terminal 50 is capable of 2 Mbps communication, the received data Of these, 2 Mbps data is sent out as it is. However, if the communication state of the wireless LAN in the dual communication terminal 40 is poor and 2 Mbps data cannot be received, the data of 200 kbps is used as an exception. The single communication terminal 50 receives the data from the bicast server 10 via the wireless LAN base station 30, and reproduces the video after demodulation.

Thus, at point B, for both directions of communication, the transmission rate between the single communication terminal 50 and the bicast server 10 is 2 Mbps (except for the above exception), and the transmission rate between the bicast server 10 and the dual communication terminal 40 is Control is performed so as to be 2 Mbps or 200 kbps depending on the situation.
If communication of the single communication terminal 50 is limited to a transmission rate of 500 kbps, the bicast server 10 converts 2 Mbps data received from the dual communication terminal 40 to a transmission rate of 500 kbps, and the converted data Is transmitted to the single communication terminal 50.

  When the dual communication terminal 40 further moves and reaches point C, the bicast server 10 converts 2 Mbps data from the single communication terminal 50 into 200 kbps and sends it out. This data is received by the dual communication terminal 40 via the cellular base station 20. The 200 kbps data transmitted by the dual communication terminal 40 is sent to the single communication terminal 50 at the same transmission rate by the bicast server 10.

  As described above, according to the present embodiment, in an environment where a cellular system and a wireless LAN system coexist, the bicast server 10 converts the transmission rate and error resilience strength for the video data of the transmitted videophone. The bicast communication with the quality suitable for each system of cellular and wireless LAN is performed. At the time of handover, the dual communication terminal 40 receives data of two different video qualities to be bicast and reproduces one of the video data depending on the situation. As a result, communication can be continued seamlessly even when handover is performed.

<< Second Embodiment >>
Next, another embodiment will be described. FIG. 5 schematically shows the configuration of a wireless network according to the second embodiment of the present invention. The difference between this embodiment and 1st Embodiment exists in the place which distributed the function of the bicast server 10 to the some server provided in the network in this embodiment. That is, the transmission quality determination server 70 corresponds to the transmission quality determination unit 104 in the first embodiment, and the video quality conversion servers 81 to 84 all correspond to the video quality conversion unit 102 in the first embodiment.

  In FIG. 5, data transmitted and received by each dual communication terminal 41 and 42 is transmitted via video quality conversion servers 81 and 82 that are present at the closest locations in the network. The video quality conversion servers 81 to 84 measure the transmission rates of those data passing through and notify the transmission quality judgment server 70 of the measurement results as needed. The transmission quality judgment server 70 instructs each of the video quality conversion servers 81 to 84 to convert the transmission rate based on the notified transmission rate value.

  As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to

For example, the functional configuration of the dual communication terminal 40 is not limited to the configuration described in the first embodiment (FIG. 4), and may be configured as shown in FIGS.
That is, in FIG. 6, the dual communication terminal 43 has separate demodulation units 405a and 405b corresponding to the transmission / reception units 402a and 402b. In the case of this configuration, the received data is demodulated by the demodulating units 405a and 405b, and then one is selected and reproduced by the reproducing unit 406.

  Further, the dual communication terminal 44 in FIG. 7 is obtained by providing video quality conversion units 103a and 103b in the subsequent stage of the demodulation units 405a and 405b in the dual communication terminal 43 in FIG. In this dual communication terminal 44, when a handover is performed from a wireless LAN (using the transmission / reception unit 402a and the demodulation unit 405a) communicating at a transmission rate of 2 Mbps to a mobile phone of 200 kbps (using the transmission / reception unit 402b and the demodulation unit 405b), The video quality conversion unit 103a gradually changes the transmission rate from 2 Mbps to 200 kbps, and switching of communication media (from wireless LAN to mobile phone) is performed when the rate reaches 200 kbps. By doing in this way, it becomes possible to switch an image | video smoothly.

  In the case of FIG. 8, the dual communication terminal 45 includes two demodulation units 405c and 405d corresponding to the transmission / reception unit 402c (wireless LAN communication interface) and one demodulation corresponding to the transmission / reception unit 402d (communication interface of the mobile phone). Part 405e. In a wireless network in which the dual communication terminal 45 is used, in a handover from a wireless LAN (transmission speed is 2 Mbps) to a mobile phone (transmission speed is 200 kbps), the bicast server 10 changes the transmission rate from 2 Mbps to, for example, 500 kbps and 200 kbps. First, bicast is performed at 2 Mbps and 500 kbps while the communication medium is a wireless LAN, and then bicast is performed at 500 kbps for the wireless LAN and 200 kbps for the mobile phone. Corresponding to such bicast communication, the dual communication terminal 45 performs demodulation by the demodulation units 405c and 405d at the first bicast and switches the video from 2 Mbps to 500 kbps, and at the next bicast, the demodulation unit Demodulate at 405d and 405e and further switch the video to 200 kbps.

In addition, the dual communication terminals 40 to 45 described so far each have two transmission / reception units, and the communication media correspond to mobile phones and wireless LANs, but are limited to such a configuration. Needless to say, it may be configured to have three or more transmission / reception units and to support other communication media (including wired communication).
Further, the bicast server 10 may always perform bicast not only when the dual communication terminal 40 exists at the B point in FIG. 1 but also at the A point or the C point.

  DESCRIPTION OF SYMBOLS 10 ... Bicast server 20 ... Cellular base station 30 ... Wireless LAN base station 40-45 ... Dual communication terminal 50 ... Single communication terminal 60 ... Core network 70 ... Transmission quality judgment server 80-84 ... Video quality conversion server 102, 103 ... Video quality conversion unit 104 ... transmission quality judgment unit 106 ... transmission / reception unit 402 ... transmission / reception unit 404, 405 ... demodulation unit 406 ... reproduction unit

Claims (1)

A plurality of demodulating units provided corresponding to each of the transmitting / receiving units, individually demodulating different data of video quality received by a plurality of transmitting / receiving units;
A plurality of video quality conversion units provided corresponding to each of the demodulation units for converting the video quality of the input data;
A playback unit for playing back the data;
With
The video quality conversion unit continuously converts the video quality of one demodulated data so that the video quality is the same as the video quality of the other demodulated data ,
When the reproducing unit reproduces the other demodulated data, the video quality of the one demodulated data is the same as the video quality of the other demodulated data. In this case, the communication terminal switches the data to be reproduced from the other demodulated data to the one demodulated data .

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