# Digital signals

 ♦Avishka RJ ♦™ · February 9, 2015 What doesbit duration mean ??

## Replies

 Pere Garau Burguera · February 9, 2015 It's the inverse of the bit rate. For example, you have 1000 bits/s, aka 1 kb/s, so the bit duration, or bit time or bit period will be 1/1000, which is 1 ms (milisecond). This is directly the time from when the signal changes to the current bit until it changes to the following bit (in a binary modulation, and that's because a symbol only contains one bit (it's the same)). For a non-binary modulation, there's no a bit time directly, because each symbol contains more than one bit. But the analogy is the same. You have for example a QPSK modulation, where m=2 bits/symbol. The symbol rate is 1000 baud (symbols/second). Since each symbol contains two bits, you will have a bit rate equal to 2kb/s. Then you take the inverse of this and you'll get that the bit time is 0'5 ms. (With a QPSK you can thing as 2 individual ASK signals at the same time, one for the in-phase component and the other for the quadrature component (each one represents one bit).
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