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GMS Inc. doing business as Cobham Tactical Communications and Surveillance
www.cobham.com/tcs
devices. The second operating mode is the Encoder-Only Mode. In this mode the COFDM RF
transmission chain is disabled and only the ASI and LAN ports are active.
There are two COFDM operating modes available; standard 2K DVB-T compliant and a Cobham
unique 4K mode
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. The 4K mode provided twice the data throughput than 2K mode (2x RF
bandwidth) and allows the transmission of high quality dual HD video in a robust 16-QAM format.
COFDM 2K Carrier Mode
In 2K Mode the M2TE uses standard DVB-T coding and modulation. DVB-T stands for Digital Video
Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast
transmission of digital terrestrial television that was first broadcast in the UK in 1997. This system
transmits compressed digital audio, video and other data in an MPEG transport stream, using coded
orthogonal frequency-division multiplexing (COFDM or OFDM) modulation.
The
OFDM
scheme works by splitting the digital data stream into a large number of slower digital
streams each of which digitally modulate a set of closely spaced adjacent carrier frequencies. COFDM
goes a step further by using a “Coding” scheme to map the data onto the multiple carriers in a way
that maximizes recovery from link errors. This coding includes Forward Error Correction with
Convolution Interleaves’ and Reed Solomon encoding along with careful distribution of the data onto
the multiple carriers. COBHAM CS has chosen to use 2K carrier in which 1,705 carriers actually carry
the payload that are approximately 4KHz apart. DVB-T offers three different modulation schemes
(QPSK, 16QAM, 64QAM).
4K Carrier Mode
The 4K HIGH-THROUGHPUT OPTION enables user-selectable options to set bandwidths from 6 MHz
to 16 MHz and to double the throughput of our standard M2T (Up to 63 Mbps!). In 2K carrier mode
the system would need to operate in 64-QAM to support dual program/video operations. Using 4K
carriers and the 16 MHz bandwidth, the link can support dual program/video HD operation using 16
QAM. This increases link robustness and provides an additional 13.5 dB of gain with a link margin
increase greater than 4.7 x in operating range! For the same throughput rate in a standard HD MPEG-
2 DVB-T system! With the 4 K HIGH-THROUGHPUT OPTION you can run with fully DVB-T compliant
2K carriers and bandwidths of 6, 7, or 8 MHz. When you switch to 4K carriers you can select 12, 14
or 16 MHz bandwidth.
4.2
Video Quality and 2K or 4K Transmission
The M2TE uses Advanced Coding Standard (AVC) also known as h.264 or MPEG-4 Part 10. It is 30-
40% more compression efficient than MPEG-2 which helps achieve high quality HD or SD video
through a standard 2K DVB-T wireless link.
Video quality depends on many complex factors including;
Video resolution and frame rate
Single or dual video processing
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With 4K High-Throughput Option on M2TE or Encoder Mode
