What is Symbols
Thursday, 4. January 2007, 15:56:10
Like just about any form of digital transmission, the receiver has to know the rate at which the transmitter is sending information. In the computer world, we call this the bit rate. For example, PCs can transmit from their serial ports at up to 115,200 bits per second. Bit rate and baud rate are not the same, despite the fact that some people will turn blue trying to tell you that they are. The bit rate specifies how many bits per second are carried across the channel (phone line, serial cable or satellite transponder), however, the baud rate describes the rate that data is sent within the channel.
For example, suppose you invented a simple modem that transmitted at 50 bps by using two tones. One tone could signal a 1 needed to be sent and the other would signal 0. Now imagine that you wanted to double the transfer rate across the channel. By using four tones instead of two, you could signal two sets of bits at the same time by switching various combinations of the four tones. The baud rate is still 50 baud (i.e. the tone pairs change 50 times per second), however, the bit rate is now 100 bps. The combination of the sets of tones is called a "symbol" because too many people are confused by the term baud.
For example, suppose you invented a simple modem that transmitted at 50 bps by using two tones. One tone could signal a 1 needed to be sent and the other would signal 0. Now imagine that you wanted to double the transfer rate across the channel. By using four tones instead of two, you could signal two sets of bits at the same time by switching various combinations of the four tones. The baud rate is still 50 baud (i.e. the tone pairs change 50 times per second), however, the bit rate is now 100 bps. The combination of the sets of tones is called a "symbol" because too many people are confused by the term baud.
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