Patent Publication Number: US-2011075758-A1

Title: Apparatus for transmitting layered data

Description:
TECHNICAL FIELD 
     The present invention relates to a technology that transmits a plurality of pieces of layer data. 
     BACKGROUND ART 
     Digital broadcasting may have a quality superior to analog broadcasting. However, digital broadcasting may not be received when a channel is degraded below a particular standard, while a receiving quality of analog broadcasting deteriorates as a channel is degraded. To overcome the disadvantage, a layered modulation may be applied. 
     Also, a digital wireless communication system has been developed after the advent of a second generation mobile communication system such as a Global System for Mobile Communication (GSM) scheme and a Code Division Multiple Access (CDMA) scheme. Currently, a convergence technology that provides a wireless multicast/broadcast service through a separate multicast/broadcast channel comes into the spotlight in a wireless communication system. Currently, a technology that provides a particular terminal with a Video On Demand (VOD) service or a multimedia service including a video through a given unicast channel is also the focus of attention.
         Scalable Video Coding (SVC), which is a multimedia compression technology for source coding required in a broadcasting or communication system, is also in the limelight since it may satisfy a variety of requirements and Quality of Service (QoS). SVC is a source coding scheme appropriate for a heterogeneous network where a broadcasting network and other communication networks are connected, and may transmit a single video source using a plurality of layers. A receiving end may receive a portion of or entire layers with a higher priority depending on conditions such as a channel state, and replay a video with variable qualities. Layering of SVC may include a temporal layering, a spatial layering, and a quality layering. The temporal layering may variably control the number of frames per second, the spatial layering may variably control a size of a replay screen, and the quality layering may variably control a video quality such as the number of bits per pixel. Also, in SVC, each layer may not be independently decoded. That is, only when layers with higher priority than a corresponding layer itself are decoded may the corresponding layer be decoded, which is known as layered decoding.       

     In a wireless broadcasting and communication system, a transmission scheme that has a number of layers is required to make the most use of SVC. 
     As an example of a wireless transmission technology supporting layer transmission of a multimedia source in a conventional art, mediaFLO of Qualcomm has proposed layered modulation. Layered modulation may first modulate multimedia data of a basic layer using a Quadrature Phase-shift keying (QPSK), and include an enhanced layer to the multimedia data of the basic layer, and transmit data of the two layers using 16-state Quadrature Amplitude Modulation (16-QAM). In this instance, a terminal with a suitable channel state may receive the two layers without error, and a terminal with an unsuitable channel state may receive only data of the basic layer. Although layered modulation may be easily embodied due to the simple structure, the number of layers may be limited. 
     Accordingly, a wireless transmission technology that may have a number of layers is required. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     An aspect of the present invention provides a transmission and receiving apparatus that may enable a number of pieces of layer data that may be received to be varied depending on a channel state of the receiving apparatus. 
     Technical Solution 
     According to an aspect of the present invention, there is provided a transmission apparatus, including: a first encoding unit to encode first layer data based on a first encoding scheme and generate first encoded data; a second encoding unit to encode both the first encoded data and second layer data based on a second encoding scheme and generate second encoded data; and a transmission unit to transmit the second encoded data to a receiving apparatus. 
     A transmission apparatus, including: a first encoding unit to encode first layer data based on a first encoding scheme and generate first encoded data; a second encoding unit to encode both the first encoded data and second layer data based on a second encoding scheme and generate second encoded data; a third encoding unit to encode third layer data based on a third encoding scheme and generate third encoded data; a fourth encoding unit to encode both the third encoded data and fourth layer data based on a fourth encoding scheme and generate fourth encoded data; a precoding unit to multiply the second encoded data and the fourth encoded data with a precoding matrix to generate a plurality of data streams; and a transmission unit to transmit the plurality of data streams to a receiving apparatus using a transmission antenna corresponding to each of the plurality of data streams. 
     A receiving apparatus, including: a receiving unit to receive first encoded data from a transmission apparatus; a first decoding unit to decode the first encoded data based on a first encoding scheme and generate second decoded data and first layer data; and a second decoding unit to decode the second decoded data based on a second encoding scheme and generate second layer data. 
     According to an embodiment of the present invention, a number of pieces of layer data that may be received may vary depending on a channel state of a receiving apparatus, and thus a receiving apparatus with an unsuitable channel state may maintain basic communication and a receiving apparatus with a suitable channel state may be provided with a high quality communication service. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a conceptual diagram illustrating a data transmission method according to an embodiment of the present invention; 
         FIG. 2  is a conceptual diagram illustrating a nested coding scheme according to an embodiment of the present invention; 
         FIG. 3  conceptual diagram of a nested coding scheme according to an embodiment of the present invention; 
         FIG. 4  is a block diagram illustrating a configuration of a transmission apparatus according to an embodiment of the present invention; 
         FIG. 5  is a block diagram illustrating a configuration of the transmission unit of  FIG. 4 ; 
         FIG. 6  is a block diagram illustrating a configuration of a transmission apparatus according to another embodiment of the present invention; and 
         FIG. 7  is a block diagram illustrating a configuration of a receiving apparatus according to an embodiment of the present invention. 
     
    
    
     MODE FOR THE INVENTION 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
       FIG. 1  is a conceptual diagram illustrating a data transmission method according to an embodiment of the present invention. 
     A scalable encoder  110  may encode multimedia data for each layer. Basic layer data may include a minimum amount of data to replay the multimedia data. Enhanced layer data may include additional data to improve a sound/video quality of the multimedia data. 
     When a channel state of a receiving apparatus  150  is not suitable, the receiving apparatus  150  may receive only the basic layer data and replay a multimedia source. However, when a channel state of a receiving apparatus  160  is suitable, the receiving apparatus  160  may receive both the basic layer data and the enhanced layer data, and replay high quality multimedia data. 
     A dynamic adaptation apparatus  120  may determine layer data to be transmitted to each of the receiving apparatuses  150  and  160  based on information of the receiving apparatuses  150  and  160  receiving the layer data. That is, when the receiving apparatus  150  includes a small screen, the receiving apparatus  150  may receive only basic layer data. When the receiving apparatus  160  includes a large screen, the receiving apparatus  160  may receive both the basic layer data and the enhanced layer data. 
     The layer data which is encoded by the scalable encoder  110  and selected by the dynamic adaptation apparatus  120  may be transmitted to a transmission apparatus  140  via a communication network  130 . 
     The transmission apparatus  140  may encode the layer data of each layer based on a nested coding scheme, and transmit the encoded layer data to each of the receiving apparatuses  150  and  160 . 
     When the channel state of the receiving apparatus  150  is not suitable, the receiving apparatus  150  may receive only the basic layer data from among the layer data encoded based on the nested coding scheme. 
     When the channel state of the receiving apparatus  160  is suitable, the receiving apparatus  160  may receive both the basic layer data and the enhanced layer data from among the layer data encoded based on the nested coding scheme. 
     The receiving apparatus  150  with an unsuitable channel state may maintain a basic communication and the receiving apparatus  160  with a suitable channel state may be provided with a high quality communication service. 
       FIG. 2  is a conceptual diagram illustrating a nested coding scheme according to an embodiment of the present invention. 
     A state of digital data may be defined as one of ‘0’ and ‘1’. Accordingly, a state of n-bit data may be located in a 2 n  space  210 . Hereinafter, a concept of encoding data (w 1 , w 2 ), configured as two pieces of layer data, based on the nested coding scheme is described in detail. 
     A transmission apparatus may encode data w 2  based on an encoding scheme and generate encoded data c 2 (w 2 ). A code rate of the encoding scheme may be R 2 . Also, the transmission apparatus may encode both data w 1  and the encoded data c 2 (w 2 ) based on an encoding scheme, and generate encoded data c 1 (w 1 , w 2 ). In this instance, a code rate of the encoding scheme may be R 1  and a code rate of the encoded data c 1 (w 1 , w 2 ) may be R 1 +R 2 . 
     Although an embodiment where the data configured as the two pieces of layer data is encoded based on the nested coding scheme has been described, the nested coding scheme may be applied to a number of pieces of layer data. 
     A receiving apparatus receiving the encoded data based on the nested coding scheme may decode both the data w 1  and the data w 2  based on a channel state, or decode any one of the data w 1  and the data w 2  based on the channel state and apparatus information about the receiving apparatus. That is, the receiving apparatus may variably decode data based on the channel state or the apparatus information. Accordingly, a data transmission rate which is close to a maximum data transmission rate may be obtained depending on the channel state. 
     The encoded data c 2 (w 2 ) may be mapped to a center point of each of data spaces  220  and  230  divided within the 2 n  space  210 . When both the encoded data c 2 (w 2 ) and the data w 1  are encoded together, the data (w 1 , w 2 ) may be mapped to any one point of sub data spaces  241 ,  242 , and  243  in the data spaces  230  and  240 . 
       FIG. 3  conceptual diagram of a nested coding scheme according to an embodiment of the present invention. An embodiment where basic layer data is modulated based on a Quadrature Phase-shift keying (QPSK) modulation scheme in a high power and enhanced layer data is modulated based on a QPSK modulation scheme in a low power is illustrated in  FIG. 3 . 
       FIG. 3  ( a ) illustrates a modulation of the basic layer data. An embodiment where a power of a symbol  310  where the basic layer data is mapped is P 1  is illustrated in  FIG. 3  ( a ). 
       FIG. 3  ( b ) illustrates a modulation of the enhanced layer data. An embodiment where a power of a symbol  320  where the enhanced layer data is mapped is P 2  is illustrated in  FIG. 3  ( b ). When comparing  FIG. 3  ( a ) and  FIG. 3  ( b ), it may be ascertained that the power of the basic layer data, P 1 , is greater than the power of the enhanced layer data, P 2 . 
       FIG. 3  ( c ) illustrates that the modulated basic layer data and the modulated enhanced layer data are superposed. When a receiving apparatus accurately detects a symbol  340  where the basic layer data and the enhanced layer data are superposed, the receiving apparatus may determine the basic layer data and the enhanced layer data, respectively. The receiving apparatus may first determine the basic layer data  330 , and determine the enhanced layer data through a successive cancellation of the determined basic layer data  330  from the superposed symbol  340 . 
     Since the power of the enhanced layer data, P 2 , is relatively insignificant, the receiving apparatus may not receive the enhanced layer data when a channel state is not suitable. The receiving apparatus may receive only the basic layer data transmitted in the power of the basic layer data, P 1 . 
       FIG. 4  is a block diagram illustrating a configuration of a transmission apparatus according to an embodiment of the present invention. The transmission apparatus may include at least one data division unit, that is, a first data division unit  410  and a second data division unit  440 , a first encoding unit  420 , a second encoding unit  430 , a third encoding unit  450 , a fourth encoding unit  460 , and a transmission unit  470 . 
     The first encoding unit  420  may encode first layer data based on a first encoding scheme and generate first encoded data. The first encoding scheme may include a convolutional coding scheme, a turbo encoding scheme, and a low density parity check (LDPC) encoding scheme. 
     The second encoding unit  430  may encode both the first encoded data and second layer data based on a second encoding scheme and generate second encoded data. The second encoding scheme may include the convolutional encoding scheme, the turbo encoding scheme, and the LDPC encoding scheme. 
     According to an embodiment of the present invention, the first encoding scheme may be different from the second encoding scheme. Also, a code rate of the first encoding scheme may be different from a code rate of the second encoding scheme. A receiving apparatus which receives the second encoded data may compare a channel state of the receiving apparatus to each of the code rate of the first encoding scheme and the code rate of the second encoding scheme. Also, the receiving apparatus may selectively decode any one of the first layer data and the second layer data. 
     The third encoding unit  450  may encode third layer data based on a third encoding scheme and generate third encoded data. The third encoding scheme may include the convolutional encoding scheme, the turbo encoding scheme, and the LDPC encoding scheme. 
     The fourth encoding unit  460  may encode both the third encoded data and fourth layer data based on a fourth encoding scheme and generate fourth encoded data. The fourth encoding scheme may include the convolutional encoding scheme, the turbo encoding scheme, and the LDPC encoding scheme. 
     According to an embodiment of the present invention, the first data division unit  410  may divide 1 st  original data into the first layer data and the second layer data. For example, the first data division unit  410  may divide particular multimedia data into basic layer data and enhanced layer data. Here, the basic layer data may be a minimum amount of data to replay the multimedia data, and the enhanced layer data may be data to improve a sound quality or a video quality of the multimedia data. The first data division unit  410  may generate the basic layer data as the first layer data, and generate the enhanced layer data as the second layer data. 
     Also, the second data division unit  440  may divide 2 nd  original data into the first layer data and the second layer data in a similar manner as the first data division unit  410 . The second data division unit  440  may generate the basic layer data as third layer data, and the enhanced layer data as fourth layer data. 
     The transmission unit  470  may transmit the second encoded data or the fourth encoded data to the receiving apparatus. The transmission unit  470  may transmit the second encoded data in a first transmit power, and transmit the fourth encoded data in a second transmit power. The transmission unit  470  may change a value of the first transmit power and the second transmit power depending on a channel state. An operation of the transmission unit  470  is described in greater detail with reference to  FIG. 5 . 
       FIG. 5  is a block diagram illustrating a configuration of the transmission unit  470  of  FIG. 4 . The transmission unit  470  may include power control units  510  and  520 , and a precoding unit  530 . 
     The first power control unit  510  may control a transmit power of the second encoded data, and the second power control unit  520  may control a transmit power of the fourth encoded data. The first power control unit  510  and the second power control unit  520  may control the transmit power of each of the second encoded data and the fourth encoded data depending on a channel state of each of the receiving apparatuses  551  and  552 , a data rate of original data, and the like. 
     According to an embodiment of the present invention, the first power control unit  510  and the second power control unit  520  may control the transmit power of each of the second encoded data and the fourth encoded data based on a receiving priority order of layer data included in each of the second encoded data and the fourth encoded data. 
     The precoding unit  530  may multiply the power-controlled second encoded data and the controlled fourth encoded data with a precoding matrix, and generate a plurality of data streams. 
     According to an embodiment of the present invention, the precoding unit  530  may control the precoding matrix to obtain a diversity gain, or to obtain a spatial multiplexing gain. 
     The transmission unit  470  may transmit the plurality of data streams to the receiving apparatuses  551  and  552  using transmission antennas  541  and  542  corresponding to each of the plurality of data streams. 
       FIG. 6  is a block diagram illustrating a configuration of a transmission apparatus according to another embodiment of the present invention. The transmission apparatus may include layer encoding units  610  and  630 , layer modulation units  620  and  640 , power control units  651  and  652 , and a precoding unit  660 . 
     The layer encoding units  610  and  630  may generate encoded data using a layer encoding scheme. The layer encoding scheme may be an encoding scheme to generate the encoded data using a plurality of encoding schemes. In this instance, a code rate of each of the plurality of encoding schemes may be different. 
     The first layer encoding unit  610  may include a first encoding unit  611 , a second encoding unit  612 , a third encoding unit  613 , and a fourth encoding unit  614 . 
     The first encoding unit  611  may encode first layer data based on a first encoding scheme, and generate first encoded data. The second encoding unit  612  may encode the first encoded data and second layer data based on a second encoding scheme, and generate second encoded data. 
     Also, the third encoding unit  613  may encode third layer data based on a third encoding scheme, and generate third encoded data. The fourth encoding unit  614  may encode the third encoded data and fourth layer data based on a fourth encoding scheme, and generate fourth encoded data. 
     The second layer encoding unit  630 , that is, a second nested coding unit  630 , may encode pieces of layer data and generate pieces of encoded data in a similar manner as the first layer encoding unit  610 . 
     The first layer modulation unit  620  may include a plurality of modulation units  621  and  623  and a plurality of power control units  622  and  624 . The first modulation unit  621  may modulate the second encoded data generated by the second encoding unit  612 . The second modulation unit  623  may modulate the fourth encoded data generated by the fourth encoding unit  614 . The first power control unit  622  may control a transmit power of the modulated second encoded data. The second power control unit  624  may control a transmit power of the modulated fourth encoded data. 
     The second layer encoding unit  630  and the second layer modulation unit  640  may encode and modulate pieces of layer data in a similar manner as the first layer encoding unit  610  and the first layer modulation unit  620 . 
     A multiple-input and multiple-output (MIMO) antenna system may provide diversity for a lower error rate and spatial multiplexing for a high transmission rate. The MIMO antenna system may enable a layered spatial multiplexing. 
     According to an embodiment of the present invention, pieces of independent encoded data may be transmitted. Also, a basic layer with a higher priority may be transmitted in a relatively high transmit power, a relatively low code rate, and/or using a low-level modulation scheme to enable a receiving apparatus to perform a layer receiving. 
     According to another embodiment of the present invention, an enhanced layer with a relatively low priority may be transmitted in a relatively low transmit power, a relatively high code rate, and/or using a high-level modulation scheme. Accordingly, a terminal with a suitable channel state may receive the enhanced layer. 
     According to the present invention, a layer encoding scheme, a layer modulation scheme, and an MIMO may be combined, and thus a greater number of layers may be transmitted/received. A number of layers that may be transmitted by the transmission apparatus of  FIG. 6  may be determined by multiplying a number of layers supported by the layer encoding scheme, a number of layers supported by the layer modulation scheme, and a number of layers supported by the MIMO. 
     When the layer encoding scheme supports three layers, the layer modulation scheme supports two layers, and the MIMO supports two layers, the transmission apparatus may transmit total 12 layers. 
     The number of layers supported by the MIMO may be determined by a smaller number of a number of transmission antennas and a number of receiving antennas. 
     Receiving apparatuses  671  and  672  may selectively receive at least one layer from a plurality of layers based on a channel state or apparatus information of the receiving apparatuses  671  and  672 . Accordingly, even when the transmission apparatus transmits same data, a number of layers that may be received by each of the receiving apparatuses  671  and  672  may be different. Therefore, a data rate of multimedia data that each of the receiving apparatuses  671  and  672  replays may vary. 
       FIG. 7  is a block diagram illustrating a configuration of a receiving apparatus according to an embodiment of the present invention. The receiving apparatus may include an MIMO detector  710 , a channel estimator  720 , a channel decoder  730 , and a data combination unit  740 . 
     A process of receiving a signal transmitted as illustrated in  FIG. 6  is described in detail. The signal, multiplexing-transmitted as described above, may first be separated from multiplexing antenna signals through the MIMO detector  710 . For example, the MIMO detector  710  may first detect a basic layer in a first stream for layered modulation. The detected signal may be restored as a transmission signal through the channel decoder  730  in a decoding rate corresponding to a channel state. Here, it may be assumed that the restored signal is accurate. When the restored signal is removed from the receiving signal, a subsequent layer of the layered modulation may be restored in a same manner as the above-described process, and thus the first stream may be completely decoded. A decoding operation with respect to remaining streams may be the same as the above-described decoding. 
     The decoding operation is described in greater detail with reference to  FIG. 7 . A characteristic of a channel code according to the present invention is that layer multimedia data of various levels may be supported, and code words for each layer may have a layered structure. For example, the layered structure may indicate that, when code word sets for two layers, C 1  and C 2 , exist, the code word set C 2  of a basic layer may be a subset of the code word set C 1  of an upper layer. Accordingly, a characteristic that uses the single code word set C 1  to decode the two layers may be efficiently used for the decoding operation. As illustrated in  FIG. 7 , when a decoding rate is determined in the channel estimator  720 , the channel decoder  730  may completely decode layer data to a corresponding layer through a single decoding operation. That is, the decoding operation may be simultaneously performed with respect to decodable layers, while encoding may be performed through a plurality of operations depending on a number of layers. The above-described characteristic may be different from the layered modulation which requires an additional layered decoding for each layer. 
     The data combination unit  740  may combine first layer data and second layer data and generate receiving data. According to an embodiment of the present invention, the receiving data may be multimedia data, the first layer data may be basic layer data of the multimedia data, and the second layer data may be enhanced layer data of the multimedia data. 
     A receiving apparatus may replay the multimedia data using the basic layer data of the multimedia data. However, the receiving apparatus may improve a sound/video quality of the multimedia data by additionally using the enhanced layer data. 
     The receiving apparatus may receive a portion of layer data from among pieces of layer data based on apparatus information of the receiving apparatus or a channel state. For example, when the channel state is not suitable, the receiving apparatus may receive only the basic layer data. Also, when a small screen is included in the receiving apparatus, the receiving apparatus may receive only the basic layer data. 
     According to an embodiment of the present invention, the basic layer data may be transmitted in a higher transmit power than the enhanced layer data. Accordingly, a receiving apparatus, that may not receive the enhanced layer data due to a long distance from the transmission apparatus, may receive the basic layer data. The receiving apparatus located far away from the transmission apparatus may replay the multimedia data using only the basic layer data. 
     A receiving apparatus located closed to the transmission apparatus may receive the enhanced layer data as well as the basic layer data. Accordingly, the receiving apparatus located closed to the transmission apparatus may replay the multimedia data with an improved sound/video quality. 
     Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.