Demodulator for Manchester-coded FM signals

Claim 3

The method of claim 1, wherein the determining step includes the step of selecting the phase samples nearest the centers of the symbols.

Claim 4

The method of claim 2, wherein the determining step includes the step of determining the signs of differences between the phase samples and a plurality of phase references derived from the modulated carrier signal, computed modulo 2π.

Claim 5

The method of claim 1, wherein the determining step includes the step of comparing each of the phase samples with each of a plurality of phase references derived from the modulated carrier signal.

Claim 6

The method of claim 1, further comprising the step of deriving a plurality of phase references from phase samples near boundaries between the symbols.

Claim 7

The method of claim 5, wherein the deriving step includes the step of averaging the phase samples.

Claim 8

The method of claim 6, wherein the averaging step includes the step of separately averaging cosines and sines of the phase samples.

Claim 9

The method of claim 5, wherein the deriving step is based on a moving average of phase samples near the boundaries of the symbols.

Claim 10

The method of claim 5, wherein the deriving step includes the step of applying the phase samples to a phase tracking loop.

Claim 11

The method of claim 5, wherein the deriving step includes the step of applying the phase samples to a Kalman filter.

Claim 12

The method of claim 1, wherein the determining step includes the step of determining the signs of phase differences between the phase samples and a plurality of corresponding phase references derived from the modulated carrier signal, computed modulo 2π.

Claim 13

The method of claim 11, wherein said determining step comprises the step of determining soft symbol values which are sines of said phase differences.

Claim 14

The method of claim 12, wherein soft symbol values are employed to decode redundantly coded information bits.

Claim 15

The method of claim 1, wherein the determining step includes the step of selecting one of a plurality of quality values, each quality value associated with a respective one of a plurality of phase references derived from the modulated carrier signal.

Claim 16

The method of claim 14, wherein the selecting step includes the steps of mutually comparing each of the quality values and selecting a largest value.

Claim 17

The method of claim 14, further comprising the step of determining each of the quality values associated with each of the phase references by averaging the phase samples near boundaries between the symbols to generate quality values associated with each of the phase references.

Claim 20

The method of claim 17, wherein the determining step includes the step of selecting the complex vector value samples nearest the centers of the symbols.

Claim 21

The method of claim 17, wherein the determining step includes the step of multiplying each of the complex vector value samples by each of a plurality of complex vector references derived from the modulated carrier signal.

Claim 22

The method of claim 19, wherein the determining step includes the step of determining the signs of the imaginary parts of the products of said multiplications.

Claim 23

The method of claim 19, wherein said determining step comprises the step of producing soft symbol values equal to the imaginary parts of the products of said multiplications.

Claim 24

The method of claim 21, wherein the soft symbol values are employed to decode redundantly coded information bits.

Claim 25

The method of claim 17, further comprising the step of deriving a plurality of complex vector references from complex vector value samples near boundaries between the symbols.

Claim 26

The method of claim 23, wherein the deriving step includes the step of vector averaging the complex vector value samples.

Claim 27

The method of claim 24, wherein the averaging step includes the step of de-emphasizing older complex vector value samples exponentially according to sample age.

Claim 28

The method of claim 23, wherein the deriving step is based on a moving average of complex vector value samples near the boundaries of the symbols.

Claim 29

The method of claim 23, wherein the deriving step includes the step of applying the complex vector value samples to a Kalman filter.

Claim 30

The method of claim 17, wherein the determining step includes the step of selecting one of a plurality of quality values, each quality value associated with a respective one of a plurality of complex vector references derived from the modulated carrier signal.

Claim 31

The method of claim 28, wherein the selecting step includes the steps of comparing each of the quality values and selecting a largest value.

Claim 32

The method of claim 28, further comprising the step of determining each of the quality values associated with each of the complex vector references by averaging the complex vector value samples near boundaries between the symbols and determining a magnitude of the resulting average.

Claim 33

A demodulator for recovering information bits that have been converted to Manchester-coded symbols that modulate a signal's frequency comprising: means for generating a first phase signal from the signal, the first phase signal comprising successive phase values, a plurality of phase values being generated during each symbol; means for dividing the first phase signal into a plurality of second phase signals, each second phase signal comprising respective ones of the phase values generated during successive symbols; means for averaging each of the second phase signals and for generating a plurality of candidate phase reference signals; means for comparing each of the candidate phase reference signals and selected ones of the second phase signals and for generating a plurality of estimated demodulated signals; and means for selecting one of the estimated demodulated signals and providing the selected one to an output of the demodulator as a demodulated information bit signal.

Claim 34

A demodulator for recovering information bits that have been converted to Manchester-coded symbols that modulate a signal's frequency comprising: means for generating a first phase signal from the signal, the first phase signal comprising successive phase values, a plurality of phase values being generated during each symbol; means for dividing the first phase signal into a plurality of second phase signals, each second phase signal comprising respective ones of the phase values generated during successive symbols; means for averaging each of the second phase signals and for generating a plurality of candidate phase reference signals; means for comparing each of the candidate phase reference signals and selected ones of the second phase signals and for generating a plurality of estimated demodulated signals; and means for selecting one of the estimated demodulated signals and providing the selected one to an output of the demodulator as a demodulated information bit signal.

Claim 35

The demodulator of claim 31, wherein the dividing means comprises an electronic memory.

Claim 36

The demodulator of claim 31, wherein the averaging means comprises a Kalman filter.

Claim 37

The demodulator of claim 31, wherein the averaging means comprises means for circular averaging each of the second phase signals.

Claim 38

The demodulator of claim 31, wherein the averaging means comprises means for averaging with exponential forgetting each of the second phase signals.

Claim 39

The demodulator of claim 31, wherein the averaging means generates a plurality of quality values corresponding to respective ones of the candidate phase reference signals and the selecting means comprises means for determining the largest quality value and for generating a control signal and means, responsive to the control signal, for providing the estimated demodulated signal corresponding to the largest quality value to the output.

Claim 40

The demodulator of claim 31, wherein the selecting means comprises means for detecting a predetermined bit pattern in each of the estimated demodulated signals.

Claim 41

The demodulator of claim 37, wherein the predetermined bit pattern detecting means comprises means for determining a respective number of mismatching bits between the predetermined bit pattern and each respective estimated demodulated signal and the selecting means selects one of the estimated demodulated signals based on the numbers of mismatching bits.

Claim 42

A demodulator for recovering information bits that have been converted to Manchester-coded symbols that modulate a signal's frequency comprising: means for generating a first signal from the signal, the first signal comprising successive complex vector values, a plurality of complex vector values being generated during each symbol; means for dividing the first signal into a plurality of second signals, each second signal comprising respective ones of the complex vector values generated during successive symbols; means for averaging each of the second signals and for generating a plurality of candidate reference signals; means for generating products of complex conjugates of each of the candidate reference signals and selected ones of the second signals and for generating a plurality of estimated demodulated signals; and means for selecting one of the estimated demodulated signals and providing the selected one to an output of the demodulator as a demodulated information bit signal.

Claim 43

A demodulator for recovering information bits that have been converted to Manchester-coded symbols that modulate a signal's frequency comprising: means for generating a first signal from the signal, the first signal comprising successive complex vector values, a plurality of complex vector values being generated during each symbol; means for dividing the first signal into a plurality of second signals, each second signal comprising respective ones of the complex vector values generated during successive symbols; means for averaging each of the second signals and for generating a plurality of candidate reference signals; means for generating products of complex conjugates of each of the candidate reference signals and selected ones of the second signals and for generating a plurality of estimated demodulated signals; and means for selecting one of the estimated demodulated signals and providing the selected one to an output of the demodulator as a demodulated information bit signal.

Claim 44

The demodulator of claim 39, wherein the dividing means comprises an electronic memory.

Claim 45

The demodulator of claim 39, wherein the averaging means comprises a Kalman filter.

Claim 46

The demodulator of claim 39, wherein the averaging means comprises means for averaging with exponential forgetting each of the second signals.

Claim 47

The demodulator of claim 39, wherein the averaging means generates a plurality of quality values corresponding to respective ones of the candidate reference signals and the selecting means comprises means for determining the largest quality value and for generating a control signal and means, responsive to the control signal, for connecting the estimated demodulated signal corresponding to the largest quality value to the output.

Claim 48

The demodulator of claim 39, wherein the selecting means comprises means for detecting a predetermined bit pattern in each of the estimated demodulated signals.

Claim 49

The demodulator of claim 44, wherein the predetermined bit pattern detecting means comprises means for determining a respective number of mismatching bits between the predetermined bit pattern and each respective estimated demodulated signal and the selecting means selects one of the estimated demodulated signals based on the numbers of mismatching bits.