Understanding Coded Orthogonal Frequency Division Multiplexing (COFDM)


Advanced wireless communication we see these days makes it possible to send radio frequency signals over very long distances. Through Wireless communication, we can comfortably relay crucial information over hundreds of miles without the need of expensive infrastructure like installation of physical cables, which are prone to all kinds of damage either through vandalism or through extreme climate.

Wireless signal transmission on the other hand also suffers certain limitations. Engineers have come up with different ways to counter these limitations in order to make signal transmission and reception as flawless as possible. This has led to the development of different types of broadcasting techniques that seek to overcome the difficulties associated with wireless end-to-end signal distribution.

These broadcasting techniques include Coded Orthogonal Frequency Division Multiplexing.

COFDM is a type of digital radio frequency modulation that makes it possible to divide a single digital signal across over 1,000 carriers and transmit it simultaneously. It is an alternative modulation method used instead of a single carrier wave form. This modulation scheme was developed in on order to overcome the various limitations associated with the use of single carrier systems.

The term Orthogonal’ describes the manner in which the signals are sent out at right angles to each other. Such signals do not interfere with each other in way. In most instances where a single waveform is used, the signal is often scattered by obstacles such as buildings, people, hills and canyons along its path. These obstacles scatter the signal causing it to take different paths to arrive at its final destination, your television.

In Television sets, it is the scattered portions of the signals arriving late that results in what we usually see as ghost images. In order to avoid such signal degradation especially in metropolitan areas where signals face numerous obstacles, cable and satellite television are better alternatives that offer better quality pictures as opposed to relying on UHF antennas for signal reception.

In Coded Orthogonal Frequency Division Multiplexing, multiple carriers transmitting the same signal at right angles to each other makes it possible for signals to go round obstacles in the same way water flows round an obstacle on its path. The transmitted signal takes the form of an artificial multipath’ and works in the same way single-frequency networks with several individual transmitting stations do.

The signal therefore travels free of any form of signal attenuation. The result is a perfect picture at the receiving end. The signals are also multiplexed at right angles to each other to prevent them from interfering with each other resulting in perfect clean signal at the receiving end. This form of modulation is able to with stand the limitations associated with terrestrial broadcasting channels.
This is also the most common modulation scheme in Europe. It is compliant with Digital Video Broadcasting (DVB) standards. The U.S on the other hand has opted for the 8-level Vestigial Sideband as an equivalent modulation standard.

In Digital broadcasting, COFDM is eliminates the problem of inter-symbol interference that usually occurs when signals arrive via different paths at different intervals. In such a case, the first signal is received and demodulated while the delayed signal only acts as interference during reception of the second signal. Very small signal delays are tolerated in digital broadcasts and should therefore be kept at a bare minimum. Coded Orthogonal Frequency Division Multiplexing scheme is the best way to achieve error free digital Radio Signal communication.