Digital Video Broadcasting

Published Date: 02 Nov 2017

The paper discusses about digital video broadcasting. First, a brief introduction about the definition of the term is provided. Then different types of DVB techniques are considered and discussed. The paper then considers a sample simulation model of DVB-T along with explanations of significant components involved.

Digital Video Broadcasting (DVB) is basically a set of open standards that are internationally accepted for digital television. The international industrial consortium 'DVB Project' consisting of more than 280 members maintains the DVB standards. (Reimers, 2005).

Distribution of data by DVB systems can be done using many ways. These include distribution by cable (DVBC, DVBC2); via satellite (DVBS, DVBS2, DVBSH); terrestrial television (DVBT, DVBT2); via microwave (DVB-MT, DVB-MC, DVB-MS) and terrestrial television for handheld devices (DVB-H, DVB-SH). (Jack, 2005).

The data link layer and physical layer of the distribution system are defined by these standards. These devices use synchronous parallel interface (SPI), synchronous serial interface (SSI) or asynchronous serial interface (ASI) to interact with the physical layer (Plass, 2009). These distributed systems vary from each other in the error correction codes used or modulation schemes used. For example, DVB-T uses 16-QAM or 64-QAM (or QPSK) whereas DVB-C uses 16-QAM, 32-QAM, 64-QAM, 128-QAM or 256-QAM.

DVB not only defines audio and video transmissions but also data connections (DVB-DATA) and protocols (DVB-IPTV: Internet Protocol, DVB-NPI: Network Protocol Independent) (deBruin, 1999).

Digital Video Broadcasting - Terrestrial (DVB-T)

DVB-T is the digital transmission standard for terrestrial television and is Europe consortium based. It was first broadcast in UK at 1997. The system uses COFDM modulation to transmit compressed digital audio, video and other forms of data in an MPEG transport stream. (Hanjalic, 2004).

OFDM splits the digital data into large number of slower data streams rather than carrying data on a single radio frequency (RF) carrier. Each of these digital streams modulates a set of closely spaced adjacent carrier frequencies. Based on the number of carriers there are two choices in DVB-T, namely 2K-mode and 8K-mode.

As mentioned earlier, DVB-T uses three types of modulation, namely 16-QAM, 64-QAM or QPSK. Here the system uses 64-QAM. The system delivers digital transmission data in the form of discrete blocks at the symbol rate. DVB-T uses guard interval while transmitting data using COFDM transmission technique. The receiver can make use of this guard interval during strong multipath situations. Single frequency network (SFN) operation is also supported by DVB-T systems within a geographical area where the same data is carried by two or more transmitters operating on the same frequency. Accurate time alignment of signals from each transmitter is important during such situations. The guard interval length can be chosen. Longer the guard interval length, lower will be the probability of occurrence of inter symbol interference (ISI). (deBruin, 1999).

Technical description of various parts used in the DVB-T system

RS Encoder: It is used for converting one form of code to another for various purposes such as improving security, speed etc. Reed-Solomon codes (RS) are special type of codes used for digital data transmissions, named after their inventors Reed and Solomon.

Interleavers: Interleaver is an instrument used for interleaving. Interleaving is the process of arranging data in a non-contiguous way to improve performance.

OFDM transmitter: It is a device that transmits OFDM signals. OFDM stands for Orthogonal Frequency Division Multiplexing and is a multicarrier modulation method. Data is carried using large number of closely spaced orthogonal sub-carriers.

Error rate calculation: The error rate calculation block is basically used to compare input data from a transmitter with input data from a receiver. The error rate is then calculated as a running statistic whereby total number of input data elements is divided by the total number of unequal pairs of data elements from one source.

Viterbi decoder: A viterbi decoder is basically used for decoding a bitstream using the viterbi algorithm that has been encoded based on a convolutional code using forward error correction method.

AWGN: AWGN stands for Additive White Gaussian Noise and is a channel model. The only impairment to communication while using this channel is the linear addition of white noise and a Gaussian amplitude distribution. It is one of the simplest multipath channel models.

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