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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In one embodiment, a delay ddemodulation is incorporated to accommodate for certain types of fading of the receive signal as the receiver travels through various geographic areas. The device of claim 11, wherein said matched filter sums a sequence of multiplications between a conjugated sequence indicative of said samples of a GMSK signal and a sequence derived from a sinusoidal function.

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 output of the phase shifter 6 is coupled to a second multiplier 8 which multiplies the IF signala 4 by the phase shifted local demodulztion frequency to produce a phase quadrature signal Q of the IF frequency as shown.

The demodulator recited in claim 2 wherein said non-coherent correlator computes EQU What is claimed is: Adaptive demodulatioh phase and frequency locked loop for rapid carrier acquisition.

The method of claim 16 wherein said first and second signals are baseband signals. For digital matched filter implementations, z t should be appropriately sampled; i. Method and apparatus for symbol clock recovery from signal having wide frequency possibilities.

It is therefore an object of the present invention to provide a demodulation scheme for GMSK having a performance very close to theoretical limit even under fading channel.

The divider circuit is required because the squaring functions performed in the coherent carrier recovering unit 20 generates a frequency twice that of the desired signal. Even though coherent demodulation is generally considered the best demodulation for GMSK modulated signals, the performance is not guaranteed under fading channel conditions. And, p t is a pulse shaping function described as EQU2. Raising the baseband signals to other powers will change the division required of the divider circuit accordingly.

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The method of demodulating recited in claim 6 wherein said matched filter filters the sampled received signal according to EQU17 where EQU The arc tangent calculator yields a signal which represents the angle between the base-band information signal and the reference axes used to demodulate GMSK.

The detector of claim 1 wherein the correction signal means includes means for multiplying said first signal by a first correction signal providing a first product signal and means for multiplying said second signal by a second correction signal providing a second product signal. The base-band in-phase signal B I is also multiplied by cosine theta in the multiplier The first multiplier 7 receives the IF 4 and multiplies it by a signal obtained from a local oscillator 5 running at the IF frequency.

The demodulator recited in claim 1 wherein said matched filter filters the sampled received signal according to EQU13 where EQU The digital signal processor receives two signals, an in-phase component and a phase quadrature component and recovers from these a coherent carrier error signal from these two components. Time acquisition system using a single synchronization word and method of using same.

The detector of claim 7 wherein the correction signal means includes means for calculating the arctangent of the sine signal divided by the cosine signal producing a first correction angle signal.

In the preferred embodiment, the coherent carrier recovery unit 20 squared the baseband in-phase and phase-quadrature signals B I and B Q to recover the phase coherent carrier and The baseband in-phase and phase quadrature signal components are digitized and coupled to a digital signal processor, DSP where the clock and data signals are recovered.

Method of demodulation in digital communication systems with multipath propagation.

US5131008A – DSP-based GMSK coherent detector – Google Patents

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. This signal is first passed though matched filter 13 before being supplied to non-coherent correlator The method of demodulating recited in claim 7 wherein the step of computing the correlation, C Dis performed according to EQU In some applications a delay circuit 80 inserted 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 mobile radio applications of GMSK demodulation.

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The method of claim 16 including the step of temporally delaying said first and second signals before producing detected in-phase and quadrature components. The detector of claim 1 wherein said first and second signals are baseband signals.

The demodulator recited in claim 4 wherein said matched filter, said non-coherent correlator and said maximum likelihood decision logic are implemented with a digital signal processor.

The method of claim 23 including the step of dividing said correction angle signal by a factor. And, p t is a pulse shaping function described as EQU2 For the demodulator design according to the present invention, the second interpretation demorulation used. The output of multiplier and are both added in the summer which yields the phase quadrature signal component Q, as shown.

An incoming signal is received at an antenna 2 and processed in an superheterodyne receiver 3 which produces a first intermediate frequency IF 4.

USA – DSP-based GMSK coherent detector – Google Patents

The detector of claim 1 wherein the correction signal means ffor means for multiplying said second signal by a first correction signal providing a third product signal and means for multiplying said second signal by a second correction signal providing a fourth product signal. The method of demodulating GMSK signals recited in claim 18 further comprising the steps of differentially decoding and bit mapping the decision output to produce demodulated bit stream output.

In one embodiment the delay provided by the delay circuits and equal the propagation delay through the coherent carrier recovery unit 20 and the correction signal unit Method and apparatus for obtaining initial carrier and symbol phase estimates for use in synchronizing transmitting data. The delay units and respectively may be shift registers, processors, or other circuits capable of temporarily delaying the signals into the correction unit