Channel coding improves mobile communication link performance by adding redundant data bits in the transmitted message.Channel coding is used by the receiver to detect or correct some (or all) of the errors introduced by the channel in a particular sequence of message bits. Because decoding is performed after the demodulation portion of the receiver, coding can be considered to be a post detection technique.
Fundamentals of Channel Coding:
There are two general types of channel codes:
- Block codes
- Convolutional codes.
- Shannon demonstrated that by proper encoding of the information, errors induced by a noisy channel can be reduced to any desired level without sacrificing the rate of information transfer.
Shannon's channel capacity formula is applicable to the AWGN channel and is given by
- C is the channel capacity (bits per second),
- B is the transmission bandwidth(Hz),
- P is the received signal power (watts), and
- N0 is the single-sided noise power density (watts/Hz).
The received power at a receiver is given as
- Where Eb is the average bit energy, and R b is the transmission bit rate
- Equation 1 can be normalized by the transmission bandwidth and is given by
Where C/B denotes bandwidth efficiency.
- The basic purpose of error detection and error correction techniques is to introduce redundancies in the data to improve wireless link performance.
- It providesexcellent BER performance at low SNR values. But increases the bandwidth requirement.
- Error correction coding offers advantages in bandwidth limited applications and also provides link protection in power limited applications.