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Mobile narrow-band multimedia broadcast system AVIS
AVIS allows raising efficiency of using VHF band, in particular 66 – 74 MHz and 87 – 108 MHz bands, providing an opportunity to transmit more than 10 programs of high-quality stereo sound or picture of home videotape recorder quality (VHS, 352*288, 25 pictures per sec) with appropriate stereo audio in one channel of 200 or 250 KHz wide. AVIS system allows implementing reception of programs on standard pin antennas in moving transport in urban conditions with compact planning, multipathing and absence of direct visibility of transmitter antenna, as well as in complicated relief areas, in highlands and thick forestlands.
Key parameters of the system implementation:
- Modulation system – COFDM;
- Number of carriers per symbol – 279;
- QAM-constellation type – QPSK, 16-QAM;
- Protection interval length – 1/4, 1/8;
- Convolutional code rate –1/2, 2/3, 3/4;
- Hierarchical modulation –16-QAM/QPSK;
- Video encoding – Н.264 / AVC;
- Audio encoding – HE-ААС.
Preferable audio/video formats with the width of the channel of 250 KHz
Radio signal spectrum on intermediate frequency of 10,7 MHz for 250 KHz width of the channel
Theoretical studies of the system model when using 16-QAM codec showed that boundary signal/noise ratio for noise-free operation of the system made up 13.5 dB for Gaussian allocation of the noise in the channel, 14 dB – for allocation by Gauss and Rice, 17 dB – for allocation by Gauss and Relay.
During the test of on-air broadcasting of AVIS system the following parameters of transmitted signal have been used:
Number of OFDM carriers: 279
Modulation type: 16-QAM
Protection interval: 1/8
Convolutional coding rate: 3/4
Digital net bit rate: 560 kbit/s
Video parameters: 352х288 (CIF), 25 pictures/s
Signal spectrum band width: 250 KHz
During the united ITU-R conference held in Geneva in March 2006, at the 6M and 6E Work groups of the 6th Study Group from Russia there was made a presentation titled «Enhancement of efficiency of using VHF-band frequencies» (ITU-R 6Е/336-E and 6М/133-E documents), where the mobile narrow-band multimedia broadcast system AVIS (Audiovisual information system) was described.
Further development of this system is described in the Russian presentation at the 6M Work group (ITU-R 6М/150-E document) at the 6th Study Group of the ITU-R conference in Seoul (South Korea) in August 2006. At the following conference (April 2007) of the 6M Work Group the description of the AVIS system was included in the preliminary project of ITU-R BT.2049 Report change dedicated to mobile multimedia broadcast systems. |
