Gaussian minimum shift keying or GMSK is a kind of continuous phase frequency-shift keying. The baseband modulation is generated by starting with a bitstream 0/1 and a bit-clock giving a timeslice for each bit. This is the type of modulation used in Global System for Mobile Communications (GSM). This article or section is in need of attention from an expert on the subject. ... Modulation is the process of varying a carrier signal, typically a sinusoidal signal, in order to use that signal to convey information. ... A bitstream or bit stream is a time series of bits. ... BIT is an acronym for: Bangalore Institute of Technology Bilateral Investment Treaty Bhilai Institute of Technology - Durg Birla Institute of Technology - Mesra Battles in Time (Doctor Who magazine) Category: ... This article or section may be confusing or unclear for some readers, and should be edited to rectify this. ...

How it works

The baseband signal is generated by first transforming the zero/one encoded bits into -1/+1 encoded bits. This -1/+1 signal is then filtered in such a way that the "boxcar" shaped +1/-1 pulses are transformed into Gaussian-shaped signals. The baseband signal is then modulated using frequency modulation, producing a complete GMSK signal. If the Gaussian shapes do not overlap, then the modulation form is called 1-GMSK. If the slots overlap 50% (½), the modulation is called 2-GMSK, and so on. In information theory, a signal is the sequence of states of a communications channel that encodes a message. ... Television signal splitter consisting of a hi-pass and a lo-pass filter. ... In medicine, a persons pulse is the throbbing of their arteries as an effect of the heart beat. ... The normal distribution, also called Gaussian distribution (although Gauss was not the first to work with it), is an extremely important probability distribution in many fields. ... When used in supervisory signaling in telephony, the term frequency-change signaling has been used to describe frequency modulation. ...

The more the bits overlap, the more significant intersymbol interference (ISI) from adjacent bits will be, and for 4-GMSK and up, the ISI seen at any particular point in time is stronger than the signal from the bit currently being decoded. By looking at greater parts of the signal using advanced decoder techniques (including Viterbi algorithm decoders), high density codings can be decoded efficiently. Currently the highest density coding being used is 5-GMSK. In telecommunication, the term intersymbol interference has the following meanings: 1. ... The Viterbi algorithm, named after its developer Andrew Viterbi, is a dynamic programming algorithm for finding the most likely sequence of hidden states – known as the Viterbi path – that result in a sequence of observed events, especially in the context of hidden Markov models. ...

Spectral efficiency

GMSK has high spectral efficiency, but it needs higher power level than for instance Quadrature phase-shift keying (QPSK) to reliably communicate the same amount of data. Spectral efficiency is a measure of the performance of encoding methods that code information as variations in an analog signal. ... Transmission lines in Lund, Sweden Electric power, often known as power or electricity, involves the production and delivery of electrical energy in sufficient quantities to operate domestic appliances, office equipment, industrial machinery and provide sufficient energy for both domestic and commercial lighting, heating, cooking and industrial processes. ... Quadrature phase-shift keying (quadriphase, quaternary phase-shift keying) is a form of modulation in which a carrier is sent in four phases, 45, 135, 225, and 315 degrees, and the change in phase from one symbol to the next encodes two bits per symbol. ... Quadrature phase-shift keying (quadriphase, quaternary phase-shift keying) is a form of modulation in which a carrier is sent in four phases, 45, 135, 225, and 315 degrees, and the change in phase from one symbol to the next encodes two bits per symbol. ... Communication is the process of exchanging information usually via a common system of symbols. ... Data is the plural of datum. ...

See also

• Phase-shift keying

Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave). ...

External links

• Document from the University of Hull giving a thorough description of GMSK.
  Note: Section D5 appears to state that MSK replaces a rectangular amplitude pulse shape with a sinusoidal shape and that GMSK replaces the sinusoidal shape with a Gaussian shape. But an important distinction is that the GMSK shaping is applied to the instantaneous frequency [not amplitude].
• Another good discussion (University of Toronto)
• PSK/GMSK comparison & illustrations (Aerospace)