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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US5131008A – DSP-based GMSK coherent detector – Google Patents

The DSP implements interpolation and phase rotation which can be considered as a part of down converter 12, the matched filter 13, the non-coherent correlator 14 and the ML decision logic These real and imaginary components and are coupled to the correction signal unit 40 as shown. The improved performance of the demodulator is achieved by using old decisions in the ML decision logic.

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. The base-band in phase and base-band quadrature signals B I and B Q are separately squared in squaring functions and 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 sine theta and cosine theta correction signals are coupled to the correction unit 60 which takes the base-band in-phase and base-band phase quadrature signals B I and B Q and processes these signals together to yield the in-phase data signal I and the phase quadrature data signals, Q. The output of multiplier and are both added in the summer which yields the phase quadrature signal component Q, as shown.

The detector of claim 1 wherein said first and second signals are IF 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.

Adaptive variable-gain phase and frequency locked loop for rm carrier acquisition. On the sinals and performance of single and double differential detection schemes. 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.


Alternate embodiments of the invention would include coherent carrier recovery units that factor or raise the incoming baseband signals to other mathematical powers. In the preferred embodiment, the coherent carrier recovery unit 20 squared the basef in-phase and phase-quadrature signals B I and B Q to recover the phase coherent carrier and This invention relates generally to recovery of binary encoded signals, and particularly to recovery of coherent carrier signal information included therewith.

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.

Method of demodulation in digital communication systems with multipath propagation. The output is d k which is fed back via a one bit period delay 26, T, as d k-1 to function block 23 to compute the next correlation C D. Open-loop phase estimation methods and apparatus for coherent demodulation of phase modulated carriers in mobile channels.

CA CAC en The output of the divider circuit yields a phase angle theta which is a correction factor required to demodulate the base-band in-phase and the base-band quadrature signals.

The DSP 50 also provides an AFC control back to the superheterodyne receiver front-end required to permit the radio to stay on frequency. Method and apparatus for symbol clock recovery from signal having wide frequency possibilities.

USA – DSP-based GMSK coherent detector – Google Patents

The base-band in-phase signal B I is also multiplied by cosine theta in the multiplier The method of demodulating recited in claim 7 wherein the step of computing the correlation, C Dis performed according to EQU The detector of claim 1 wherein said first and second signals are baseband signals.

The correction signal unit 40 receives the real and imaginary coherent carrier signal components, and and produces a correction factor signal, theta. 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.

The past bit decisions are fed back to the ML decision logic. The method of demodulating recited in claim 6 wherein said matched filter filters the sampled received signal according to EQU17 where EQU Such binary signals are typically detected through use of coherent signal detectors that use the phase of the signalling tones to facilitate detection of the transmitted bits.

The method of claim 24 including the step of dividing said correction angle signal by a factor of two producing a second correction angle signal. The correction signal is derived from the in-phase coherent carrier signal and the quadrature carrier signal to produce a correction signal representative of a correction angle required to demodulate the GMSK. While the invention has been described in terms of a single preferred embodiment, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.


Parallel correlator architecture for synchronizing direct sequence spread-spectrum signals. The correction factor signal, theta is indicative of the angle between the in-phase and quadrature components of the GMSK digitall from a reference coordinate system, orthogonal real and imaginary axes representing the phase angle between the I and Q signals of a GMSK signal. This type of receiver usually includes two parts; a first portion that extracts the bit clock and phase of the signalling tones, and a detector that uses the extracted signal phase.

The transmission of angle modulated carrier signals having substantially constant amplitude and continuous phase such as FSK, MSK, and GMSK signalsand of similar signals having nonconstant amplitudes, to convey binary data over a radio frequency communication resource cor well understood in the art.

Vsp acquisition system using a single synchronization word and method of using same. Method and apparatus for combined frequency offset and timing offset estimation. Referring now to the drawings, and more particularly to FIG. An improved method and apparatus for demodulators for MSK deodulation.

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The output d k is also fed to function block 27 where differential decoding and bit mapping are performed to derive output d kwhich is the demodulated information bit stream. And, p t is a pulse shaping function described as EQU2.

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. In one embodiment, a delay element is incorporated to accommodate for certain types of fading of the receive signal as the receiver travels dejodulation various geographic areas.

And, p t is a pulse shaping function described as EQU2 For the demodulator design according to the present invention, the second interpretation is used.

The method of demodulating recited in claim 9 further comprising the steps of differentially decoding and bit mapping d k to generate a demodulated bit stream. The method of claim 21 further including the step of low-pass filtering the in-phase coherent carrier component producing a sine signal and low-pass filtering the quadrature coherent carrier component producing a cosine signal.

This is a realization of equation demodulationn where the digital filter performs EQU6 where EQU7 Note that match filtering is done over a 2-bit time period.