In the IEEE 802.16m (next generation WiMAX (Worldwide Interoperability for Microwave Access)), which is one of the standards of next generation wireless communication technology, or the MPEG (Moving Picture Experts Group), which is one of video data compression methods, cross layer optimization has been considered as new technology for achieving high-efficiency and high-quality video transmission (refer to NPL 1). The cross layer optimization is a method of improving the overall performance by mutual notification of information between different layers and sharing the information between different layers so that protocols of respective layers cooperate with each other. As the cross layer optimization in video transmission, a video encoding process in a layer (video encoding layer) in which encoding of the video content (including a moving image and a still image) is performed, such as an application layer, is linked to an error correction coding (channel coding) process, which is performed to correct errors occurring at the time of wireless transmission (or cable transmission) of the video content in a physical layer (or a data link layer), for optimization of video transmission efficiency and the transmitted video quality.
FIG. 19 is a view showing a layer structure at the time of transmission of the multimedia content in the related art. In the related art, according to the OSI reference model which defines a hierarchical structure of a network, data is exchanged between layers corresponding to a physical layer, a data link layer, a network layer, a transport layer, and an application layer so that the process at the time of transmission is performed.
The cross layer optimization described above mainly includes the following two approaches (refer to NPL 2). In addition, although a case where wireless transmission is applied as a transmission channel in the physical layer is described below, the transmission means is not limited to this, and similar application may also be made in cable transmission.
(1) Exchange of quality information and parameter information is performed between a layer in which video encoding is performed and a layer in which channel coding is performed. The following two methods may be considered as the method for information exchange between the application layer and the physical layer (wireless layer). The first method is a method of introducing a direct interface between layers over a plurality of layers. The second method is a method of performing information exchange between cross-layer through the network layer (IP layer) in the middle with the addition of header information that can be recognized. FIG. 20 is a view showing a layer structure at the time of transmission of the multimedia content under investigation in the MPEG. The example shown in FIG. 20 corresponds to the first method described above. In this example, an MPEG media transport layer is provided between a multimedia application and a data link layer, and information exchange is performed between the MPEG media transport layer and the data link layer and a physical layer.
(2) A quality evaluation measure (including the quality information of video encoding and the quality information of a transmission section) specific to video transmission is introduced, the transmission rate of a transmission section (wireless transmission section) of a physical layer and the video encoding rate are determined, and an operation to link these is performed. The quality evaluation measure specific to video transmission is disclosed in NPL 2. Here, video distortion D(R) when the transmission rate R of a physical layer and the video encoding rate are variable (under the conditions in which the used wireless resources are fixed) is included in the quality evaluation measure. The video distortion D(R) is related to the video encoding rate. The video distortion D(R) is small when the video encoding rate is high, and the video distortion D(R) is large when the video encoding rate is low. The quality evaluation measure MCSSELECTED including the video distortion D(R) is expressed by the following Expression (1).
                              [                      Expression            ⁢                                                  ⁢            1                    ]                ⁢                                                                                                MCS          SELECTED                =                              arg            ⁢                                                  ⁢                                          min                MCS                            ⁢                                                D                  ⁡                                      (                    R                    )                                                  *                                  (                                      1                    -                    PER                                    )                                                              +                                    D                              ma                ⁢                                                                  ⁢                x                                      *            PER                                              (        1        )            
On the basis of this quality evaluation measure, the transmission rate and the video encoding rate of the transmission section of the physical layer are selected. In this manner, not only is the efficiency of video transmission increased, but also the effect of maintaining the video quality satisfactorily is obtained.