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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First, it improves the performance of the demodulator.

US5131008A – DSP-based GMSK coherent detector – Google Patents

The improved performance of the demodulator is achieved by using old decisions in the ML decision logic. The method of claim 29 digitall the step of summing said third and fourth product signals providing the quadrature corrected data signal. The detector of claim 1 wherein said means for providing sinals and quadrature coherent carrier signals by factoring the first and second signals includes means for mathematically squaring said foor and second signals and providing in-phase and quadrature portions of said first and second signals.

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 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.

According to the invention, there is provided a decision feedback multiple symbol differential demodulator which exhibits superior performance under a fading channel. The detector of claim 1 including a delay means coupled between said first and second signals and said correction baseed for temporally delaying said first and second signals to said correction means.

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The outputs of analog to digital converters 11 and 12 are passed to a digital signal processor 50 which performs the base-band demodulation of the two digitized in-phase and quadrature components. An improved method and apparatus for demodulators for MSK signals. The delay units and respectively may be shift registers, processors, or other circuits capable of temporarily delaying the signals into the correction unit Referring now to the drawings, and more particularly to FIG.

Multi-level quadrature amplitude modulator system with fading compensation means. The base-band in-phase signal B I is also multiplied by cosine theta in the multiplier Digital signal processors DSPs are also known in the art, and provide a number of significant advantages in radio design.

The detector of claim 1 wherein said first and second signals are baseband signals. The DSP 50 produces a data signal and a clock signal which is the desired demodulated information.

USA – DSP-based GMSK coherent detector – Google Patents

The demodulator implements a non-coherent, maximum likelihood ML search over multiple bit-time intervals. The outputs of these two multipliers and are combined in a summer which yields the in-phase signal I, Both the I and Q signals are low-pass filtered by separate low pass filters 9 and 10 to permit digitazation of these signals by analog to digital converters 11 and Referring now to FIG. Method and apparatus for obtaining initial carrier and symbol phase estimates for use in synchronizing transmitted data.

The method of claim 16 wherein said first and second signals are baseband signals. The output of the phase shifter 6 is coupled to a second multiplier 8 which multiplies the IF signal 4 by the phase shifted local oscillator frequency to produce a phase quadrature signal Q of the IF frequency as shown.

The base-band phase quadrature signal B Q is also multiplied by sine theta by the multiplier as shown.

These real and imaginary components and are coupled to the correction signal unit 40 as shown. 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.

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The method of claim 27 including ds step of summing said first product signal with said fmsk product signal providing the in-phase corrected data signal.

The method of demodulating recited in claim 19 wherein the step of computing a correlation output further comprises computing a second correlation for at least one bit pattern combination, said second g,sk derived from a multiplication of the output of the matched filter and said at least one signlas pattern combination.

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.

The base-band in phase and base-band quadrature signals B I and B Q are separately squared in squaring functions and The base-band phase quadrature component is multiplied by the cosine theta correction signal in another multiplier The device of claim 11, wherein said correlator computes a first correlation by summing a sequence of multiplications of the output of the matched filter with a first correlation function based on at least one previously selected bit.

If the baseband signals are raised to the fourth power, the siggnals signal unit 40 will have to divide the output of the arctangent calculator by four. 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 signal from antenna 10 is amplified in amplifier 11 and then subject to down conversion in down converter 12 to recover signal z k.