Symbols
A symbol can be described as either a pulse (in digital baseband transmission) or a "tone" (in passband transmission using modems) representing an integer number of bits. A theoretical definition of a symbol is a waveform, a state or a significant condition of the communication channel that persists for a fixed period of time. A sending device places symbols on the channel at a fixed and known symbol rate, and the receiving device has the job of detecting the sequence of symbols in order to reconstruct the transmitted data. There may be a direct correspondence between a symbol and a small unit of data (for example, each symbol may encode one or several binary digits or 'bits') or the data may be represented by the transitions between symbols or even by a sequence of many symbols.
The symbol duration time, also known as unit interval, can be directly measured as the time between transitions by looking into an eye diagram of an oscilloscope. The symbol duration time Ts can be calculated as:
where fs is the symbol rate.
- A simple example: A baud rate of 1 kBd = 1,000 Bd is synonymous to a symbol rate of 1,000 symbols per second. In case of a modem, this corresponds to 1,000 tones per second, and in case of a line code, this corresponds to 1,000 pulses per second. The symbol duration time is 1/1,000 second = 1 millisecond.
Read more about this topic: Symbol Rate
Famous quotes containing the word symbols:
“My image is a statement of the symbols of the harsh, impersonal products and brash materialistic objects on which America is built today. It is a projection of everything that can be bought and sold, the practical but impermanent symbols that sustain us.”
—Andy Warhol (1928–1987)
“If the Americans, in addition to the eagle and the Stars and Stripes and the more unofficial symbols of bison, moose and Indian, should ever need another emblem, one which is friendly and pleasant, then I think they should choose the grapefruit. Or rather the half grapefruit, for this fruit only comes in halves, I believe. Practically speaking, it is always yellow, always just as fresh and well served. And it always comes at the same, still hopeful hour of the morning.”
—Johan Huizinga (1872–1945)
“The use of symbols has a certain power of emancipation and exhilaration for all men. We seem to be touched by a wand, which makes us dance and run about happily, like children. We are like persons who come out of a cave or cellar into the open air. This is the effect on us of tropes, fables, oracles, and all poetic forms. Poets are thus liberating gods.”
—Ralph Waldo Emerson (1803–1882)