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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Method and apparatus for quadrature multi-pulse modulation of data for spectrally efficient communication. The method of claim 23 including the step of calculating the cosine and sine demodulaton said correction angle producing first and second correction signals respectively. The base-band phase quadrature component is multiplied by the cosine theta correction signal in another multiplier US USA en 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.

## US5131008A – DSP-based GMSK coherent detector – Google Patents

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. A doubly differential detector for digital transmission with continuous phase modulation. Alternate embodiments of the invention would include coherent demodilation recovery units that factor or raise the incoming baseband signals to other mathematical powers.

The device of claim 11, wherein said matched filter sums a digitql of multiplications between a conjugated sequence indicative of said samples of a GMSK signal and a sequence derived from a sinusoidal function. The detector of claim 1 wherein the correction signal means includes 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 dm fourth product signal.

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 detector of claim 9 wherein the digitall for dividing said correction angle signal by a factor divides said signal by two producing a second correction angle signal.

Method and apparatus for obtaining initial carrier and symbol phase estimates for use in synchronizing transmitted data. 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.

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 correlation derived from a multiplication of the output of the matched filter and said at least one bit pattern combination.

The detector of claim 8 including means for dividing said correction angle signal by a factor. The coherent carrier recovery unit 20 in the preferred embodiment, as shown in FIG. The demodulator implements a non-coherent, maximum likelihood ML search over multiple bit-time intervals. rsp

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

A decision feedback multiple symbol differential demodulator for Gaussian filtered Minimum Shift Keying GMSK has a performance very close to theoretical limit even under a fading channel.

The method of demodulating recited in claim 18 wherein the step of computing a correlation output is performed by computing a first correlation by summing a sequence of multiplications of the output of vm matched filter with a first correlation function based on past bit decisions. The output of multiplier and are both added in the summer which yields the phase quadrature signal component Q, as shown.

Method and system for demodulating GMSK signals in a cellular digital packet data system. Method signalls apparatus for symbol clock recovery from signal having wide frequency possibilities. The DSP 50 also provides an AFC control back to the superheterodyne receiver front-end required to permit the radio to stay on frequency.

The base-band in-phase signal B I is also multiplied by cosine theta in the multiplier This invention relates generally to recovery of binary encoded signals, and particularly to recovery of coherent carrier signal information included therewith.

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 demoduulation signal I and the phase quadrature data signals, Q. 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.

A detector for detecting in-phase and quadrature components of an information signal comprising: A first stage in the demodulator is a coherent carrier recovery unit 20 which receives the digitized base-band in-phase component B I and the base-band quadrature component B Q and produces two new signals and which represent the magnitude of the real and which represent the magnitude of the real and imaginary components of the base-band in-phase and base-band quadrature carrier signals, B I and B Q respectively.

Trellis coded multilevel DPSK system with doppler correction for mobile satellite channels. The method of claim 26 including the step of multiplying said first signal by a first correction signal providing a first product signal and multiplying said second signal by a second correction signal providing a second product signal.

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 digita is well understood in the art. Second, it reduces the computational loads, especially if the observation interval increases.

### USA – DSP-based GMSK coherent detector – Google Patents

The method of claim 16 further including the step of mathematically squaring said first and second signals and providing in-phase and quadrature portions of said first baded second signals. The correction signal unit 40 receives the real and imaginary coherent carrier signal components, and and produces a correction factor signal, theta.

GMSK in-phase and phase signalss signals embedded in an FM signal are first generated from an IF frequency and frequency shifted down to baseband. The demodulator recited in claim 2 wherein said non-coherent correlator computes EQU The device recited in claim 11 wherein said device is implemented with a digital signal processor.

For example, the incoming baseband signals might be raised to the fourth power in the coherent carrier recovery unit The outputs of these two multipliers and are combined in a summer which yields the in-phase signal I, The detector of claim 1 including a delay means coupled between said first and second signals and said correction means for temporally delaying said first and second signals to said correction means.

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. Open-loop phase estimation methods and apparatus for coherent demodulation of phase modulated carriers in mobile channels.

Adaptive variable-gain phase and frequency locked loop for rapid carrier acquisition.

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 detector of claim 14 including means for summing said third and fourth product signals providing the quadrature corrected data signal.

The detector of claim 6 wherein the correction signal means includes means for low-pass filtering the in-phase coherent carrier component producing a sine signal and means for low-pass filtering the quadrature coherent carrier component producing a cosine signal.

According to the invention, there is provided a decision feedback multiple symbol differential demodulator which exhibits superior performance under a fading channel. 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.

The output of the divider circuit yields a signa,s angle theta which is a correction factor required to demodulate the base-band in-phase and the base-band quadrature signals. An improved method and apparatus for demodulators for MSK signals.

The demodulator algorithm realizing this idea can be described as. The method of demodulating recited in claim 7 wherein the step of computing the correlation, C Dis performed according to EQU 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 digotal uses the extracted signal phase.