# Difference between revisions of "Quadrature Phase Shift Keying"

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− | + | The '''Quadrature Phase Shift Keying''' or '''QPSK''' is a [[Modulation Scheme]] where the [[Phase]] of the modulated signal is shifted depending on the incoming bitstream by an angle of -135°, -45°, +45° or +135°. Thus 4 states (a two-digit binary symbol) can get expressed in every transition: | |

− | [[Image:Qpsk.jpg|QPSK in | + | [[Image:Qpsk.jpg|QPSK Sample points in the Phase Plot]] |

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+ | The resulting waveform looks like if it would be assembled of several sine wave segments from 4 phase-shifted base sine signals. | ||

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+ | [[Image:Principle_QPSK.jpg|picture of a sine signal with shifted phase]] | ||

In order to minimize the used [[Bandwidth]] allocated on the [[Transponder]] the outgoing signal is usually filtered using digital low-pass [[FIR Filter]]s with smooth roll-off so that the high-order noise of the sudden state changes gets removed. | In order to minimize the used [[Bandwidth]] allocated on the [[Transponder]] the outgoing signal is usually filtered using digital low-pass [[FIR Filter]]s with smooth roll-off so that the high-order noise of the sudden state changes gets removed. | ||

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+ | ''here we may show the smoothed version of the sine sigal with shifted phase. Maybe also the spectrum diagrams?'' | ||

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+ | ''Has anybody the standard number of the paper that specifies usage of QPSK in DVB-S handy? Any more useful information in there?'' | ||

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+ | ''a few words about allocated bandwidth and noise sensitivity of QPSK modulated signals would be great.'' | ||

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+ | [[Category:Technology]] |

## Latest revision as of 22:16, 2 April 2005

The **Quadrature Phase Shift Keying** or **QPSK** is a Modulation Scheme where the Phase of the modulated signal is shifted depending on the incoming bitstream by an angle of -135°, -45°, +45° or +135°. Thus 4 states (a two-digit binary symbol) can get expressed in every transition:

The resulting waveform looks like if it would be assembled of several sine wave segments from 4 phase-shifted base sine signals.

In order to minimize the used Bandwidth allocated on the Transponder the outgoing signal is usually filtered using digital low-pass FIR Filters with smooth roll-off so that the high-order noise of the sudden state changes gets removed.

*here we may show the smoothed version of the sine sigal with shifted phase. Maybe also the spectrum diagrams?*

*Has anybody the standard number of the paper that specifies usage of QPSK in DVB-S handy? Any more useful information in there?*

*a few words about allocated bandwidth and noise sensitivity of QPSK modulated signals would be great.*