Technologies
COFDM
Robust digital radio transmission for demanding environments
COFDM stands for Coded Orthogonal Frequency Division Multiplexing.
It combines parallel data transmission over many orthogonal subcarriers with Forward Error Correction (FEC).
This enables reliable digital transmission under difficult radio conditions, within the limits of the particular system and configuration.
COFDM is particularly suitable for mobile video applications involving reflections, multipath propagation and changing reception conditions.
Why COFDM?
Conventional single-carrier radio systems transmit information on one modulated carrier.
Interference or frequency-selective fading can significantly affect the transmission channel.
COFDM distributes data across many narrowband subcarriers. Combined with error correction and suitable receiver technology, this can reduce the effects of such impairments.
This can be useful in cities, stadiums, production halls and with moving cameras.
COFDM compared with other radio methods
| Property | Single-carrier methods | OFDM | COFDM |
|---|---|---|---|
| Multiple orthogonal subcarriers | No | Yes | Yes |
| Forward error correction | Optional | Optional | Part of the method |
| Resilience to multipath propagation | Depends on equaliser | Good with suitable design | Good with suitable design |
| Frequency-selective interference | Can be critical | Individual subcarriers affected | Additional protection from FEC |
| Mobile applications | System-dependent | System-dependent | Particularly suitable with appropriate design |
| Data rate | System-dependent | Flexible | Flexible, with FEC overhead |
Important distinction: OFDM and COFDM are not fundamentally competing radio technologies.
OFDM describes the division of a signal into orthogonal subcarriers.
COFDM refers to OFDM transmission with additional channel coding for error correction. Many modern OFDM-based standards also use FEC and are therefore technically coded OFDM systems.
The benefit comes from the combination of modulation, error correction, interleaving, synchronisation and receiver architecture, rather than from the COFDM label alone.
Modulation and transmission capacity
COFDM systems can use different modulation methods.
QPSK offers comparatively high robustness at a lower data rate.
16-QAM provides a compromise between data rate and required signal quality.
64-QAM offers higher transmission capacity but requires better reception conditions.
The appropriate configuration depends on the required picture quality, range, movement and available radio bandwidth.
Diversity reception
Diversity technology can further improve reception reliability.
Multiple antennas or receiver branches are used to evaluate different propagation paths.
Depending on the system, signals can be selected or combined.
This is especially relevant to mobile cameras, motorsport productions and changing line-of-sight conditions.
Typical applications
COFDM is used for wireless broadcast cameras, sports and motorsport production, mobile vehicle cameras and professional video links for public safety organisations.
Elbstone supports the planning of professional COFDM links, from selecting transmitters and receivers to antenna planning and system integration.