DTV ModulatorCable, satellite, and terrestrial video service providers use digital television (DTV) modulators to transform video programs (including video, audio, and ancillary data) into a format that can be broadcast over mediums such as coaxial cables or air. Modulators receive data as a single- or multi-program transport stream (SPTS or MPTS), transmitted via the digital video broadcasting (DVB) asynchronous serial interface (ASI) at 270 Mbps. The transport stream (TS) includes audio, video, and ancillary data inputs which have been encoded with compression schemes such as Moving Picture Experts Group (MPEG) -2. DTV modulators perform forward error correction (FEC) encoding and map the binary data into a modulation scheme suitable for broadcast. Different parts of the world have employed different modulation standards for the transition to DTV. Table 1 summarizes the modulation schemes employed by geography and mode of transmission. Examples of modulation schemes used for DTV broadcasting are quadrature amplitude modulation (QAM), quadrature phase shift keying (QPSK), coded orthogonal frequency division multiplexing (COFDM), and vestigial sideband (VSB).
Irrespective of the different DTV standards across geographies, all modulators have to provide some form of FEC encoding and then map the data into a modulation scheme suitable for broadcast. Figures 1, 2, and 3 show various functional blocks of the different modulation schemes based on the broadcast medium. In terrestrial broadcast, the COFDM modulation is used in Europe. The data in COFDM is distributed over many frequency carriers which are orthogonal to each other. The COFDM modulation has a based band interface to accept MPEG-TS. It employs Reed Solomon coding and Viterbi techniques to provide FEC and performs interleaving to reduce the burst type errors. The data is then QAM mapped to the signal and upconverted. Refer to Figure 1 for a DVB-T block diagram. The advanced television systems committee (ATSC) DTV broadcast standard is employed in North America for the terrestrial broadcast and uses 8-VSB for signal modulation. Figure 1. Digital Terrestrial (DVB-T) Modulator
Notes to Figure 1:
DVB-S is the satellite broadcast standard that has the baseband interface to accept single MPEG-TS or multiple MPEG-TS. FEC in DVB-S is the same as DVB-T. DVB-S2, the next-generation satellite broadcast standard, employs outer block-level coding, low-density parity check coding (LDPC), and bit interleaving for error correction. DVB-S standard supports only the QPSK modulation. However, DVB-S2 additionally supports 8PSK, 16APSK, and 32APSK modulation schemes. Figure 2 shows the block diagram for the DVB-S2 modulator. Figure 2. Digital Satellite (DVB-S2) Modulator
Notes to Figure 2:
The cable modulation schemes across all geographies are similar and employ QAM techniques for modulating the signals. For details on functional blocks and their functionalities with respect to cable modulation, refer to the QAM modulator (PDF) white paper or the Digital Cable QAM page. Figure 3 shows the digital cable modulator block diagram. Figure 3. J.83 Digital Cable Modulator
Examples of Altera intellectual property (IP) from the IP MegaStoreTM used in DTV Modulators include:
Feature-Rich Programmable Solutions for DTV ModulatorsThe feature-rich architectures of Stratix® II FPGAs (plus HardCopy® II structured ASIC migration support) and Stratix FPGAs (plus HardCopy structured ASICs migration support) provide an excellent solution for the DTV modulator's video delivery needs. These device families give you flexibility, performance, integration, and design resources that are not available in any other solution. The Stratix II devices include up to 384 18-bit x 18-bit embedded multipliers and 9 Mbits of TriMatrix™ memory. Altera’s low-cost CycloneTM II devices include an optimized set of digital signal processing (DSP) features and are supported by Altera's full set of DSP flows. Cyclone II devices include up to 150 18-bit x 18-bit multipliers, up to 1.1 Mbits of on-chip embedded memory, and high-speed interfaces to external memory to efficiently implement digital modulation schemes. | ||||||||||||||||||||||||
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