What Is Channel Coding?

A channel is also called a channel. A channel is a channel through which a signal is transmitted in a communication system. It is a transmission medium through which a signal is transmitted from a transmitting end to a receiving end. The definition of generalized channels includes not only transmission media, but also related equipment for signal transmission.

narrow sense

Block diagram of modulation and coding channels. for

A channel is a channel through which information is transmitted. The channel capacity describes the maximum capacity of the channel to transmit information without errors. It can be used to measure the quality of the channel. Shannon gave the definition and calculation of channel capacity in his famous paper "The Mathematical Principles of Communication", that is, the channel capacity is the upper bound of the mutual information amount of the channel input signal and output signal.

For an additive Gaussian white noise channel with a signal-to-noise ratio of S / N and a bandwidth of B, the channel capacity is

log2 (1 + S / N) is the spectral efficiency of the channel transmission information, that is, the amount of information that can be transmitted per unit time and unit bandwidth, the unit is. Increasing the signal-to-noise ratio can increase the capacity of the channel, which can be achieved by suppressing noise or increasing the transmission power. If the signal-to-noise ratio is infinite, the channel capacity will also be infinite. However, because there is always noise in the channel, and the power of the transmitter cannot be unlimited, this situation does not occur. Increasing channel bandwidth can also increase channel capacity, but this increase is not unlimited. Let the noise power spectral density of the channel be N0, then as the channel bandwidth B increases, the noise power N = BN0 also increases. Remember that the maximum signal power is Es, when the bandwidth is infinite, the limit of the channel capacity is

It can be seen that increasing bandwidth is not a good way to increase channel capacity.

Channel capacity is the theoretical limit of the channel's ability to transmit information. In various communication technologies, the actual channel throughput that can be achieved is far less than this limit ^[3] .