Symbol rate#Symbols
As a symbol of the various character units for the transmission of the information content are referred to in the digital transmission technology and telecommunications. The number of symbols transmitted per unit time is the symbol rate and is expressed in the unit baud.
General
The finite and discrete set of symbols with the index, which can be used in a particular application, ie, symbol alphabet and symbol alphabet is ready for transmission in a constellation.
Mapping a certain number of bits to a specific symbol is performed in the coding line. The illustration of a symbol is performed in dependence of the modulation on certain physical parameters of a carrier signal.
Among the simplest and important symbol alphabets are symbols with the amount unipolar and bipolar symbols with the crowd. In these cases, a symbol can be assigned to exactly the information content of a bit. Only in this case is the bit rate expressed in bits per second, is equal to the symbol rate, expressed in bauds. For example, in a phase modulation (BPSK ), two symbols in the form of the phase angle of 0 ° and 180 ° of the carrier signal. In the field of digital technology, the two symbols by two different high voltages 0 V and 5 V are shown, as is customary in the transistor-transistor logic.
With symbol alphabets having more than two symbols, a higher information content than one bit per symbol may be achieved. For example, can be in four symbols represent two bits per symbol, as is the case with the quadrature. Non -integer bits per symbol resulting in modulations ( NIBS ), the constellations have symbol numbers that differ from the mold.
The more symbols includes a symbol alphabet, the more difficult it is to neighboring transmission systems in real symbols displayed in different amplitude values and phase angle of a carrier signal can distinguish safe because it is added also physically induced disturbances such as noise. To achieve a certain bit rate to a transmission channel, either the symbol rate can therefore be changed, it is changed to be equivalent with a change of the bandwidth of the transmission channel, or the number of symbols used. The context describes the channel capacity.
Symbol Representation
Depending on the transmission medium and transmission method An icon can be expressed by different physical sizes. Common sizes for the icon view in communications technology are:
- Electric potential, usually in the form of the amplitude.
- Frequency
- Phase ( temporal relation between two oscillations)
The actual information transmitted mainly using digital modulation techniques.