encoding

Transmission methods - in Anglo-Saxon literature they are referred to as coding - are methods for transmitting bit streams. Important requirements for transmission methods are freedom from direct current, bandwidth requirements and the possibility of clock recovery.

The various transmission methods differ in that the bit stream to be transmitted undergoes changes in the level of the pulses to be encoded, in their phase position, the duration or the edges. These are used on the receiving side for unambiguous bit stream recognition and thus also for clock recovery.

According to the type of transmission, a distinction is made between baseband transmission methods and wideband transmission methods. The former are unmodulated, the latter are underlaid with modulation frequencies. The most important baseband transmission methods are the single-stream method, double-stream method, ternary method with MLT coding, 8B6T coding, carrierless amplitude-phasemodulation( CAP) and others, the pseudoternary method with alternate mark inversion( AMI), Manchester coding, the bipolar method with HDB coding, high density bipolar (HDB), and the coded-diphase method.

The other methods are mostly coded modulation methods because modulation techniques and coding techniques are combined in these methods. Coded modulation works with multiple levels such as Multi Level Coding( MLC) or with multiple phase layers. These techniques include the various pulse mod ulations such as pulse amplitude mod ulation ( PAM), pulse code modulation( PCM), pulse width mod ulation( PWM), the phase modulations and the shift keying techniques such as phase shift keying( PSK), frequency shift ke ying( FSK) or amplitude shift ke ying ( ASK).

In radio and mobile communications technology, multicarrier methods such as frequency division multiplexing have become established. In some methods, several subcarriers can be distributed simultaneously to several subchannels for different mobile stations served in parallel. Frequency Division Multiple Access( FDMA) and Orthogonal Frequency Division Multiple Access( OFDMA), which works with orthogonalsubcarriers, are such methods.