Coded Orthogonal Frequency Division Multiplexing

What Does Coded Orthogonal Frequency Division Multiplexing Mean?

Coded Orthogonal Frequency Division Multiplexing (COFDM) is a modulation form that is ideal for the requirements of terrestrial broadcasting channels. COFDM has the ability to deal with high levels of multi-path propagation. It uses a wide spread of delays between the received signals.

COFDM is an innovative approach with numerous intriguing features used in Digital Video Broadcasting – Terrestrial (DVB-T) and WLAN. It transforms blocks of thousands of modulated signal samples through iFFT into the frequency domain and also inserts guard intervals into the spectrum.

Techopedia Explains Coded Orthogonal Frequency Division Multiplexing

COFDM is a substitute for a single carrier waveform. In addition to the ability to deal with high levels of multi-path propagation, COFDM handles co-channel narrowband interference very well. Therefore, COFDM has been preferred for two new broadcasting standards, namely:

• Digital Audio Broadcasting (DAB): DAB was specifically built to handle the rigors of signal reception in moving cars – particularly the issue of multi-path reception which, in the above case, is time varying.
• Digital Video Broadcasting – Terrestrial (DVB-T): DVB-T requires a higher capacity when compared with DAB. Multi-path tolerance is crucial due to the extensive usage of set-top television antennas.

In order to accommodate the specific requirements of DAB and DVB-T, COFDM is used, with proper adjustments in parameters. The overall performance of COFDM with respect to multi-path propagation and interference can be achieved only by a sensible choice of parameters. A successful implementation also demands attention to detail about how the forward error-correction coding is used.

COFDM involves the modulation of data into a multitude of carriers with the help of the FDM technique. The key features that make it ideal for terrestrial channels include:

• Orthogonality
• Use of guard intervals
• Use of error coding, channel-state information (CSI) and interleaving