DSP BASED DIGITAL FM DEMODULATION FOR GMSK SIGNALS PDF

This is the traditional discrete signal FM demodulation method, and it is based on copyrighted material from “Understanding Digital Signal. this with digital signal processing. In an earlier semester project, four FM demodulation algo- are are implemented on the DSP (TMSCDSK). radio provider organizations are planning to replace their traditional analog FM-based. the demodulation of signals that follow the AM-FM model. Traditional such as CPM, CPFSK, FSK, MSK, GMSK and other forms of digital modulation, can be reformulated as digital FM mod- ulation and component AM-FM signal demodulation. The ESA and . threshold around Yo = dB the MESA-based demodu-.

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The correction factor signal, theta is indicative of the angle between the in-phase and quadrature components of the GMSK signal from a reference coordinate system, orthogonal real and imaginary axes representing the phase angle between the I and Q signals of a GMSK signal.

Digital signal processors DSPs are also known in the art, and provide a number of significant advantages in radio design. The demodulatikn signal is used to demodulate the in-phase and quadrature signals at base-band to produce the data and clock signals which are thereafter digitally decoded.

A detector for detecting in-phase and quadrature components digita, an information signal comprising: Method of rapidly controlling the frequency of a coherent radio receiver and apparatus for carrying out the method.

The method of claim 26 including the step of multiplying said second signal by a first correction signal providing a third product signal and multiplying said second signal by a second correction signal providing a fourth product signal. The method of claim 22 further including the step of calculating the arctanagent of the sine signal divided by the cosine signal producing a first correction angle signal. According to the invention, there is provided a decision feedback multiple symbol differential demodulator which exhibits superior performance under a fading channel.

In some applications a delay circuit 80 gor between the input of the base-band in-phase and base-band quadrature components and the correction unit 60 may be required to accommodate Rayleigh fading, a phenomenon frequently observed in land demodukation radio applications of GMSK demodulation.

The method of demodulating recited in claim 19 wherein the step of computing a correlation output further comprises computing a second correlation for at digltal one bit pattern combination, said second correlation derived from a multiplication of the output of the matched filter and said at least one bit pattern combination. The detector of claim 1 wherein said first and second signals are baseband signals. Note that these functions are performed per bit interval.

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The method of claim 23 including the step of calculating the cosine and sine of said correction angle producing first and digitak correction signals respectively. The demodulator recited in claim 1 wherein said matched filter filters the sampled received signal according to EQU13 where EQU A base-band phase quadrature signal is produced by multiplying the IF by a ninety degree shifted signal from the local oscillator 5.

Second, it reduces the computational sognals, especially if the observation interval increases. The base-band in-phase signals as well as the base-band phase quadrature signals B I and B Q are also multiplied together in a multiplier to produce a signal that is the magnitude of the imaginary component of the GMSK signal, The output of the correlator 14 is supplied to Maximum Likelihood ML decision logic 15 which outputs decision d i and feeds back d demodulatoin to the correlator.

Dgiital divider circuit is required because the squaring functions wignals in the coherent carrier recovering unit 20 generates a frequency twice that of the desired signal. The method of demodulating recited in claim 18 digitao the step of computing a correlation output is performed by computing a first correlation by summing a sequence of demoduulation of the output of the matched filter with a first correlation function based on past bit decisions.

This invention relates generally to recovery of binary encoded signals, and particularly to recovery of coherent carrier signal information included therewith. Squaring the baseband signals in the coherent carrier recovery unit 20 necessitates dividing the output of the arctangent calculator by a factor of two to cancel-out the frequency doubling that results when sine or cosine functions are squared.

The detector of claim 12 including means for summing said first product signal with said second product signal providing the in-phase corrected data signal. In function block 22, the samples are subjected to matched filtering with a matched filter.

USA – DSP-based GMSK coherent detector – Google Patents

The detector of claim 7 wherein the correction signal means bases means for calculating the arctangent of the sine signal divided by the cosine signal producing a first correction angle signal. The output of multiplier and are both added in the summer which yields the phase quadrature signal component Q, as shown.

The method of demodulating recited in claim 6 wherein said matched filter filters the sampled received signal according to EQU17 where EQU The method of demodulating recited in claim 18 wherein the step of filtering said GMSK signal is performed by summing a sequence of multiplications between digltal conjugated sequence indicative of said GMSK signal and a sequence derived from a sinusoidal function.

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First, it improves the performance of the demodulator.

The foregoing and other objects, aspects and advantages will be better understood from the following derailed description of a preferred embodiment of vor invention with reference to the drawings, in which:. An improved method and apparatus for demodulators for MSK signals.

The device recited in claim 11 further comprising logic for performing differential decoding and bit mapping on said selected bit. The method of claim 24 including gm step of dividing said correction angle signal by a factor of two producing a second correction angle signal.

The device of claim 11, wherein said matched filter sums a sequence of multiplications between a conjugated sequence indicative of said samples of demodulaiton GMSK signal and a sequence derived from a sinusoidal function. The method of claim 16 wherein said first and second signals are IF signals.

Referring now to FIG. And, p t is a pulse shaping function described as EQU2. Field of the Invention The present invention generally relates to demodulators for communication systems and, more particularly, to a new non-coherent demodulator for a digital communication system which exhibits superior performance in a fading channel. And, p t is a pulse shaping function described as EQU2 For the demodulator design according to baeed present invention, the second interpretation is used.

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Method and apparatus for obtaining initial carrier and symbol phase estimates for use in synchronizing transmitted vor. Year of fee payment: The signals output from low pass filters and being the sine and cosine representations of a reference angle, are passed to an arc tangent calculator in the correction signal unit Method and apparatus for signala clock recovery from signal having wide frequency possibilities.

The detector of claim 9 wherein the means for dividing said correction angle signal by a factor divides said signal by two producing a second correction angle signal. The device of claim 12, wherein said correlator further computes a second correlation for at least one bit pattern combination, said second correlation derived from a multiplication of the output of the matched filter and said at least one bit pattern combination.

The method of claim 16 further including the step of multiplying said in-phase coherent and quadrature coherent signals by said clock signal producing, respectively, an in-phase coherent carrier component and a quadrature coherent carrier component.

The demodulator implements a non-coherent, maximum likelihood ML search over multiple bit-time intervals.