Pulse shaping

Pulse shaping (English pulse shaping), a method in telecommunications, in which the impulse response of the symbols used for a transmission is adapted to the channel.

The pulse shaping is realized with pulse shaping filters. This may be for example, analog filter circuits or also to digital filtering to improve virtually any impulse responses can be formed. In the selection of the filter for a given channel is typically tries to find a compromise between transmission rate and of the necessary bandwidth. Therefore, it is practically desirable, (ie, an impulse response ) to find the filter, the maximum transmission rate can be achieved with a given channel. It can be reached by the filter converts the value discrete symbol sequence of the transmitter to a signal with the least possible symbol crosstalk. In addition to the other limitations of the channel bandwidth with appropriate filters can be maxed, as echoes of the radio channels.

Within the signal processing, the pulse shaping is usually performed after the line coding and before modulation.

Example

The maximum transfer rate for a value-and time-discrete (ie digital ) signal is achieved entirely without signal conditioning. This means will transmit on the channel a sequence of rectangular pulses, such as a square wave signal. Between the discrete steps of the signal are then, however, infinitely steep transitions, since changing from one stage without delay to the next stage. However, these infinitely steep transitions also mean that the signal is infinitely more bandwidth occupied. The less bandwidth of the channel is available, the more grind the transitions - the slope of the signal decreases and the symbol crosstalk increases.

Many electronic channels have low-pass characteristic, ie they are bandwidth- limited. A square wave signal of (relatively) low frequency can happen such a channel well, as the signal frequency increases, more and more approaching a DC voltage. The symbol crosstalk is at a maximum, because the symbols can not be distinguished.

Examples of pulse shaping filter

  • Trivial rectangle filter
  • Sinc filter
  • Raised cosine filter and root raised cosine filter
  • Gaussian filter
Telecommunications engineering Bandwidth (signal processing) Root-Raised-Cosine-Filter Pulse (signal processing)
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