Digital TV & Video Broadcasting: Key Concepts & Technologies
1. Define an LDA: Duration and Content
An LDA (Line Double Alternate) is digitizing only the signal bits containing information. It lasts 53.33 microseconds, contains 720 samples, and 360 luminance and color difference signals.
2. What Types of Images Can Be Transmitted in the MPEG System?
The MPEG system can transmit in VCD format and can store 78 minutes of video with two channels of sound on a 700 MB CD-ROM.
3. Explain the Interface Characteristics of a Firewire Connection
- Supports connection of up to 63 devices.
- Maximum cable length of 4.25 meters.
- Tree topology.
- Supports Plug and Play.
- Peer-to-peer communication.
- Enables the link between devices without using system memory or the CPU.
- Supports hot connection.
4. What Profiles Can Be Transmitted in DVB?
- DVB-S: Designed for satellite transmission.
- DVB-C: Designed for cable transmission.
- DVB-T: A variant for terrestrial transmissions.
5. What Does the Constellation Represent in Digital TV Measurement?
It represents the possible phases that the carrier signal can take.
6. Advantages of Digital Television
- Ability to transmit a large number of television programs through a single channel with standard bandwidth capacity.
- Transmission of radio and digital information via radio.
- Flexible election of video and audio quality of broadcast.
- Contemplates the transmission of High Definition Television (HDTV).
- Encoding systems for high security and restricted programs, improving pay-per-view.
- Notably improved image quality compared to analog broadcasting, using systems more immune to interference.
7. What Types of Redundancy Are Present in Television Images?
Temporal and spatial redundancy are present in television images.
Temporal redundancy means that in a video image, it is not necessary to send again and again the parts that do not change for a long time.
8. Explain the COFDM Modulation System
COFDM (Coded Orthogonal Frequency Division Multiplexing) is a management method that operates with transmission mode signals and modulated transmission. This system uses a high number of carriers distributed along the channel, so as not to interfere with each other. There is a multiplexed transmission system. Often the result is a large group of thousands of carriers modulated in QAM or QPSK, while digital signals individually use a low binary flow rate. Therefore, they are highly susceptible to possible phase shifts caused by bouncing the signal during propagation.
9. List the Parameters Measured in a Field Meter for Digital TV
- Digital Channel Power: This is vitally important and is the first step in assessing the quality of a facility. Specific margins are 45 to 70 dBµV and an impedance of 75Ω.
- Carrier to Noise (C/N): The received signal must have a good relationship between power and noise. It is better to have some level of power and a low noise level than to have a lot of power and too much noise.
- Channel State Information (CSI): Channel State Information percentage is a parameter that serves as a complementary measure of the quality of the system. Factors above 50% can decode the digital frame, allowing viewing of the programs.
- Constellation Measures: The accuracy with which the symbols are transmitted, detecting the amplitudes and phases of the signals displayed on the screen of the measuring equipment, indicates the limits within which the different points can move. We can have a visual indication of reception quality based on the degree of sharpness of this figure.
10. Explain the Principle of Intra Coding
Intra coding is a method used to encode the points corresponding to the same semi-image. It is based on reducing the amount of information that can be achieved by comparing sets of points that contain similar information. A group of 8×8 pixels is sampled separately.
11. What is the BER of a Digital TV Transmission?
BER stands for Bit Error Rate.
12. What is the Sampling Frequency of the Luminance Signal?
The sampling frequency of the luminance signal is 13.5 MHz.