Patent Application
20100086087
Digital Video Broadcasting (DVB) systems distribute data using a variety of approaches, including by satellite (DVB-S, DVB-S2 and DVB-SH), DVB-SMATV for distribution via SMATV), cable (DVB-C), terrestrial television (DVB-T, DVB-T2), and digital terrestrial television for handhelds (DVB-H, DVB-SH). The associated standards define the physical layer and data link layer of the distribution system. Devices interact typically with the physical layer through a synchronous parallel interface (SPI), synchronous serial interface (SSI), or asynchronous serial interface (ASI). Data is typically transmitted in MPEG-2 transport streams with some additional constraints (DVB-MPEG).
The distribution systems for the different DVB standards differ mainly in the modulation schemes used and error correcting codes used, due to the different technical constraints.
For example, DVB-S (SHF) uses QPSK, 8PSK or 16-QAM. DVB-S2 uses QPSK, 8PSK, 16APSK or 32APSK, based as a broadcaster's option. QPSK and 8PSK are the only versions regularly used. DVB-C (VHF/UHF) uses QAM: 16-QAM, 32-QAM, 64-QAM, 128-QAM or 256-QAM. DVB-T (VHF/UHF) uses 16-QAM or 64-QAM (or QPSK) in combination with COFDM and can support hierarchical modulation.
The DVB-T2 standard (e.g., “Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2),” DVB Document A122, June 2008) is an update for DVB-T to provide enhanced quality and capacity. It is expected that the DVB-T2 standard will provide more-robust TV reception and increase the possible bit-rate by over 30% for single transmitters (as in the UK) and is expected to increase the maximum bit rate by over 50% in large single-frequency networks (as in Germany, Sweden). However, there are real market needs to further enhance capacity in order to support additional services for mobile devices with the available broadcast spectrum.
An aspect provides apparatuses, computer-readable media, and methods for supporting the broadcast of signaling data over a network. Error detection and protection as well as modulation mechanisms enhance the flexibility and robustness of signaling data for digital broadcasting of video, audio or other media. By separately encoding different portions of the signaling data, a data frame may be utilized even though a portion of the signaling data contains an error while another portion of the signaling data does not.
According to another aspect of the invention, a first error detection code for a first portion of signaling data and a second error detection code for a second portion of the signaling data are determined. The signaling data is combined with data symbols and transmitted as a digital stream through a digital terrestrial television broadcasting system. A portion of the signaling data may include a configurable part and a dynamic part or may include different dynamic parts of the signaling data.
According to another aspect of the invention, different portions of the signaling data may be separately modulated and encoded.
According to another aspect of the invention, a portion of the signaling data is divided over a plurality of code words and evenly distributed over a transmission period.
A more complete understanding of the present invention and the advantages thereof may be acquired by referring to the following description in consideration of the accompanying drawings, in which like reference numbers indicate like features and wherein:
In the following description of the various embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention.
Each frame 101 contains one P1 symbol 103, P2 symbols 105, and data symbols 107. (Each frame typically includes only one P1 symbol, although embodiments may include a plurality of P1 symbols.) P1 symbol 103 is fixed pilot symbol that carries P1 signaling information 109 and is located in the beginning of frame 101 within each RF-channel. P1 symbol 103 is typically used for a fast initial signal scan. P2 symbols 105 are pilot symbol located right after P1 symbol 103 with the same FFT-size and guard interval as the data symbols. P2 symbols carry L1 pre-signaling information 111 and L1 post-signaling information 113. The number of P2 symbols depends on the FFT-size. P2 symbols 105 are typically used for fine frequency and timing synchronization as well as for initial channel estimates. Data symbols 107 are OFDM symbols in frame 101 that are not P1 or P2 symbols. Data symbols 107 typically convey data content that are associated with different physical layer pipes (PLPs). T2 frames are further grouped into super frames, consisting of selected number of frames.
In DVB-T2, data is transmitted through PLPs (Physical Layer Pipes) where different PLPs may have different coding and modulation parameters. Signaling at the physical layer indicates how to decode the different PLPs. This L1 signaling is transmitted in a preamble, consisting of P2 OFDM symbols.
As discussed above, L1 signaling is divided into pre-signaling (L1-pre) 111 and post-signaling (L1-post) 113, where L1-pre 111 acts as a key for receiving L1 post-signaling 113 including the PLP mappings.
L1-post 113 is further divided into configurable part 115 and dynamic part 117, where configurable parameters comprise static signaling data that may change only at super frame border. Configurable parameters change only when the system configuration is changed (e.g., when PLPs are added or removed). Dynamic parameters refer to the mapping of each PLP to T2 frame 101 and may change from frame to frame. Configurable and dynamic parts 115 and 117 of L1 post-signaling 113 are transmitted in the same code words.
L1 post signaling 113 may also include optional extension field 119 that allows for expansion of L1 post-signaling. CRC (cyclic redundancy check) 121 provides error detection of any errors that may occur in L1 post-signaling 113. A 32-bit error detection code is applied to the entire L1 post-signaling 113 including configurable part 115, dynamic part 117, and extension part 119. L1 padding 123 is a variable-length field that is inserted following the L1-post CRC field 121 to ensure that multiple LDPC blocks of the L1 post-signaling have the same information size when the L1 post-signaling is segmented into multiple blocks and when these blocks are separately encoded. The values of the L1 padding bits, if any, are set to “0”.
L1-dynamic part 203 and 205 can signal PLP to frame mappings either for only the current frame or optionally for both the current frame and the next frame. In the former case only the L1-dynamic part 203 is present, whereas in the latter case also the L1-dynamic part 205 is included. In both cases, the entire L1 post-signaling is handled as one block as shown in
For example, if the receiver is only interested in dynamic information corresponding to a set of PLPs for a desired service, the receiver may use L1 dynamic information received as part of a L1 post-signaling block containing some errors if the receiver could ascertain that the error is in other parts of L1 post-signaling. Similarly, in case the dynamic part includes signaling for both current and next frame PLP to frame mapping, the receiver could continue receiving data from current frame if the error were known to be in the part of signaling associated with the next frame.
The approach shown in
The scheme shown in
Cyclic redundancy check codes (CRC-codes) allow the detection of transmission errors at the receiver side. For this purpose, CRC words are included in the transmitted data. A cyclic redundancy check may be referred as a redundancy check or checksum. The CRC calculation may be performed by means of a shift register containing register stages in accordance with the corresponding CRC polynomial. An error detection code includes a checksum, CRC, and other error detection/correction mechanisms.
As shown in
Alternatively, a CRC covering an extension and one or more parts of the L1 post signaling may be supported. For example, if a single extension is used and is placed after the L1-conf, a common CRC may be used to cover both L1-conf and the extension field following it.
With an embodiment of the invention, BCH field 427 and LDPC field provide further error protection for fields 403-425.
In the embodiment shown in
Because separate BCH/LDPC fields are associated with each signaling part, BCH fields 509, 523, and 537 may be used as an error correction mechanism as well as an error detection mechanism. Consequently, embodiments of the invention may include BCH OK fields 507, 521, and 535 that indicate whether the corresponding signaling part contains errors or not. In embodiments employing the BCH OK field, the CRC field may or may not be included. In one embodiment BCH OK fields 507, 521, and 535 may be part of the data transmitted as L1 post-signaling. In another embodiment, BCH OK fields 507, 521, and 535 may be added in the receiving end to be used in the subsequent processing. In embodiments that transmit the BCH OK field, the received value of this field can be ignored and replaced with a value indicating weather the received frame was corrupted or not. The sender can set the BCH OK field to any value, for example to a value indicating valid data.
While BCH and LDPC coding may be used to provide error protection, embodiments of the invention may utilize other codes such as Turbo codes.
Dynamic parts 601 and 621 may be differently modulated, for example corresponding to BPSK modulation 619 and QPSK modulation 639, respectively, as illustrated in the example of
Processor 701 may execute computer executable instructions from a computer-readable medium, e.g., memory 703. Computer storage media may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media include, but is not limited to, random access memory (RAM), read only memory (ROM), electronically erasable programmable read only memory (EEPROM), flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by processor 701.
A user (not shown) chooses a service through user interface 809 to generate service selection indication 861 to processor 801. Accordingly, processor 801 selects PLPs 857 and 859 that are associated with the selected service in order to render the service on device 807.
Processor 801 may execute computer executable instructions from a computer-readable medium, e.g., memory 803 as described above in connection with
While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.
