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GMSK Modulation: Overview & Applications

This document summarizes a student paper on Gaussian Minimum Shift Keying (GMSK) modulation. It introduces GMSK as a form of continuous phase frequency shift keying used in wireless communications. It then discusses generating a GMSK waveform through pulse shaping, summing, and integration of Gaussian pulses. The document also covers the power spectrum, bit error rate, advantages, disadvantages, and applications of GMSK modulation. Key applications mentioned are GSM networks, CDPD, and GPRS/EDGE systems.

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209 views17 pages

GMSK Modulation: Overview & Applications

This document summarizes a student paper on Gaussian Minimum Shift Keying (GMSK) modulation. It introduces GMSK as a form of continuous phase frequency shift keying used in wireless communications. It then discusses generating a GMSK waveform through pulse shaping, summing, and integration of Gaussian pulses. The document also covers the power spectrum, bit error rate, advantages, disadvantages, and applications of GMSK modulation. Key applications mentioned are GSM networks, CDPD, and GPRS/EDGE systems.

Uploaded by

hiri
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Higher Institute for Applied Science and Technology

Telecommunication department
Fifth year
2015-2016

Gaussian Minimum Shift Keying


(GMSK)
Raafat Ali Raafat Ali & Dr. Nizar Zarka

Supervisor: Dr. Nizar Zarka

Jan 2016
Raafat Ali & Dr. Nizar
Zarka

Outlines:

• Introduction to GMSK.
• Generation of GMSK & its Waveform.
• GMSK Demodulator
• Power spectrum of GMSK
• Advantages.
• Disadvantages.
• Applications.
Raafat Ali & Dr. Nizar
Zarka

Introduction To GMSK (1)


Gaussian Minimum Shift Keying (GMSK) is a
form of continuous-phase FSK (CPFSK)

That Mean: the phase is changed between symbols


to provide a constant envelope.
So: GMSK allows efficient class C non-linear
amplifiers to be used.
The RF bandwidth is controlled by the Gaussian
low-pass filter.
Raafat Ali & Dr. Nizar
Zarka

Introduction To GMSK (2)


The degree of filtering:
It is expressed by multiplying the filter 3dB
bandwidth (B) by the bit period of the
transmission(T).
BT = 0.3 for GSM networks.
Data rate: 270.8 kbps.
Raafat Ali & Dr. Nizar
Zarka

GENERATING A GMSK WAVEFORM(1)


• GMSK as implemented by quadrature signal processing
at baseband followed by a quadrature modulator

1-2

 

Time

2T T 0 T 2T
Raafat Ali & Dr. Nizar
Zarka

GENERATING A GMSK WAVEFORM(2)


Modulation
Raafat Ali & Dr. Nizar
Zarka

Generation of GMSK & its Waveform(3)


Pulse Shaping
• Input: Binary pulse train (+1/-1)
• Each binary pulse goes through a LPF with a Gaussian
impulse response
• This process results in a train of Gaussian shaped pulses
Raafat Ali & Dr. Nizar
Zarka

Generation of GMSK & its Waveform(4)


Summing and Integration
• The pulses are summed together (left)
• The signal is integrated over time to obtain a
continuous waveform which captures the bit
transition information (right)
Raafat Ali & Dr. Nizar
Zarka

Generation of GMSK & its Waveform(5)


I&Q Signals
• The resulting waveform is divided into In-Phase
and Quadrature components
▫ In-phase: Left
▫ Quadrature: Right

• The two signal components are then up-converted


to the carrier frequency
Raafat Ali & Dr. Nizar
Zarka

GMSK Demodulator
Raafat Ali & Dr. Nizar
Zarka

Power Spectrum Of GMSK(1)

• GFilter Is a Partial Response So it increases ISI.


Raafat Ali & Dr. Nizar
Zarka

Power Spectrum Of GMSK(1)


GMSK Spectra

• Improved spectral efficiency


• Requires more power to transmit data than
many comparable modulation schemes
Raafat Ali & Dr. Nizar
Zarka

GMSK Bit Error Rate


• Bit error probability for GMSK is:

Notice that: BER Is a Function of BT.


Raafat Ali & Dr. Nizar
Zarka

Advantages
• High spectral efficiency.
• Reducing sideband power.
• Excellent power efficiency due to constant
envelope.
• reducing the interference between signal carriers
in adjacent frequency channels.
• Self synchronizing capability
• Good choice for voice modulation.
Raafat Ali & Dr. Nizar
Zarka

Disadvantages
• causes (inter symbol interference[ISI])
• Higher power level than QPSK.
• Requiring more complex channel equalization
algorithms such as an adaptive equalizer.
Raafat Ali & Dr. Nizar
Zarka

Applications
• Most widely used in the Global System for
Mobile Communications (GSM).
• Used for CDPD (cellular digital packet data)
overlay network.
• Used for GPRS & EDGE systems.
Raafat Ali & Dr. Nizar
Zarka

THANK YOU

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