Digital block processor for processing a plurality of transmission channels in a wireless radiotelephony system

• US 5,367,539 A
• Filed: 12/31/1991
• Issued: 11/22/1994
• Est. Priority Date: 12/31/1991
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Original Assignee: AT&T, Inc.
• Inventors: Copley, Terry W.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): TSE, YOUNG TOI
• Application Number:
  US07/815,683
• Time in Patent Office: 1,057 Days
• Field of Search: 375/38, 375/40, 375/55, 375/87, 375/100, 375/102, 379/58, 379/63, 364/726, 455/33.1, 455/33.2, 455/33.3, 455/66
• US Class Current: 375/347
• CPC Class Codes: H04B 1/0003 Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain digital baseband systems H04L25/00; digital modulation/demodulation H04L27/00; CDMA H04B1/707; TDMA H04B7/2643; image transmission H04N5/00
• CPC Class Codes: H04B 1/001 Channel filtering, i.e. selecting a frequency channel within the SDR system multiplexing of multicarrier modulation signals being represented by different frequencies H04L5/06; multiplexing of multicarrier modulation signals H04L5/023
• CPC Class Codes: H04B 1/0017 Digital filtering H04B1/001 takes precedence; digital filters per se H03H17/00
• CPC Class Codes: H04B 1/26 for superheterodyne receivers multiple frequency-changing H03D7/16
• CPC Class Codes: H04B 7/2621 using frequency division multiple access [FDMA] H04B7/2615 takes precedence

Abstract

A digital block receiver system, in a cellular/wireless FM radiotelephony system, receives and heterodyne a block of cellular/wireless receive channels to a very low block IF signal by analog processing. This block IF signal is applied to a precision high speed A/D converter and converted to a digitized time series. A window function is applied to the digitized time series and a high speed FFT is applied to frequency isolate the individual channels. The active channels are digitally processed by a DSP to recover the FM channel modulation.

Claims

1. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, a method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels;

comprising the steps of;

receiving a block of receive channels as a plurality of analog RF signals to be processed;

converting the plurality of analog RF signals into a digitized time series;

windowing the digitized time series into a plurality of defined frequency ranges equal to the number of defined channels;

including;

defining a window time span having an effective time duration less than a time duration of 1/4 cycle of a present baseband modulating frequency, and

restricting frequency domain sidelobes produced by windowing to a value less than a minimum acceptable post detection signal to noise ratio,

generating Fourier coefficients with fast Fourier transforms in response to the windowing in order to identify the information signals of the individual channels of the digitized time series by recovering from the Fourier coefficients instantaneous frequencies from each FM carrier in each individual frequency defined channel;

including;

performing at least a first moment calculation that incorporates power spectra offset from a channel center frequency by an amount at least equal to a sum of a peak frequency deviation of FM modulation and a highest value of a modulating frequency, and

excluding from the first moment calculation power spectra offset from a channel center frequency by an amount that exceeds a sum of a peak frequency, deviation of FM modulation and a highest value of a modulating frequency,

recovering the individual voice channels from the instantaneous frequencies of each FM carrier.

2. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, the method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels, as claimed in claim 1:

comprising the further step of;

converting the block of RF signals into a very low frequency block IF signal by heterodyning techniques such that its low end frequency is coincident in frequency with a Fourier coefficient and its high end frequency is coincident with another Fourier coefficient and having added Fourier coefficients spaced symmetrically within the frequency range of the very low frequency block IF signal.

3. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, the method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels, as claimed in claim 1:

comprising the further steps of;

determining first moments of Fourier transform power spectra associated with each individual frequency defined channel,

identifying individual spectra distorted by noise and interference and

repeating the determination of first moments to generate an improved reduced noise content power spectra associated with individual frequency defined channels.

4. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, the method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels, as claimed in claim 1:

comprising the further step of;

limiting determination of the instantaneous frequencies of each FM carrier in each individual frequency defined channel to a FM frequency range known to have been transmitted.

5. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, a method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels;

comprising the steps of;

receiving a block of receive channels as a plurality of analog RF signals to be processed;

converting the plurality of analog RF signals into a very low frequency block IF signal by heterodyning techniques and further converting the block IF signal into a digitized time series;

windowing the digitized time series into a plurality of defined frequency ranges equal to the number of defined channels;

including;

defining a window time span having a time duration less than a time duration of 1/4 cycle of a present baseband modulating frequency, and

restricting frequency domain sidelobes produced by windowing to a value less than a minimum acceptable post detection signal to noise ratio,

generating Fourier coefficients with fast Fourier transforms in response to the windowing in order to identify the information signals of the individual channels of the digitized time series by recovering from the Fourier coefficients instantaneous frequencies from each FM carrier in each individual frequency defined channel;

including;

performing a plurality of passes of first moment calculation that incorporate power spectra offset from a channel center frequency by an amount at least equal to a sum of a peak frequency deviation of FM modulation and a highest value of a modulating frequency to calculate an estimate of instantaneous frequency, and

limiting the calculated estimate of instantaneous frequency to a maximum value known to have been transmitted;

comparing a number of passes of first moment calculation to a required number of passes of first moment calculation;

calculating a local mean power value for spectra nearest the calculated estimate of instantaneous frequency;

computing a sum mask and threshold values relative to the spectra and identifying spectra values that are acceptable;

recovering the individual voice channels from the instantaneous frequencies of each FM carrier.

6. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, a method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels, as claimed in claim 5;

comprising the further step of;

converting the block of RF signals into a very low frequency block IF signal by heterodyning techniques such that its low end frequency is coincident in frequency with a selected Fourier coefficient and its high end frequency is coincident with another Fourier coefficient above the selected Fourier coefficient and having added Fourier coefficients spaced symmetrically within the frequency range of the very low frequency block IF signal.

7. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, a method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels;

comprising the steps of;

receiving a block of receive channels as a plurality of analog RF signals to be processed;

converting the plurality of RF signals into a very low frequency block IF signal and further converting the block IF signal into a digitized time series;

windowing the digitized time series into a plurality of defined frequency ranges equal to the number of defined channels;

including;

defining a window time span having a time duration less than a time duration of 1/4 cycle of a present baseband modulating frequency, and

restricting frequency domain sidelobes produced by windowing to a value less than a minimum acceptable post detection signal to noise ratio,

generating Fourier coefficients with fast Fourier transforms in response, to the windowing in order to identify the information signals of the individual channels of the digitized time series by recovering from the Fourier coefficients instantaneous frequencies from each FM carrier in each individual frequency defined channel;

including;

relating the Fourier coefficients to the channel frequencies such that its low end frequency is coincident in frequency with a selected Fourier coefficient and its high end frequency is coincident with another Fourier coefficient higher than the selected Fourier coefficient and having added Fourier coefficients spaced symmetrically within the frequency range of the very low frequency block IF signal;

performing a first moment calculation that incorporates power spectra offset from a channel center frequency by an amount at least equal to a sum of a peak frequency deviation of FM modulation and a highest value of a modulating frequency, and

excluding from the first moment calculation power spectra offset from a channel center frequency by an amount that exceeds a sum of a peak frequency deviation of FM modulation and a highest value of a modulating frequency,

recovering the individual voice channels from the instantaneous frequencies of each FM carrier with FM detection techniques.

8. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, a method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels;

comprising the steps of;

receiving a block of receive channels as a plurality of analog RF signals to be processed;

converting the plurality of analog RF signals into a very low frequency block IF signal and further converting the block IF signal into a digitized time series;

windowing the digitized time series into a plurality of defined frequency ranges equal to the number of defined channels;

including;

defining a window time span having a time duration less than a time duration of 1/4 cycle of a present baseband modulating frequency, and

restricting frequency domain sidelobes produced by windowing to a value less than a minimum acceptable post detection signal to noise ratio,

generating Fourier coefficients with fast Fourier transforms in response to the windowing in order to identify the information signals of the individual channels of the digitized time series by recovering from the Fourier coefficients instantaneous frequencies from each FM carrier in each individual frequency defined channel;

including;

performing a first moment calculation that incorporates power spectra offset from a channel center frequency by an amount at least equal to a sum of a peak frequency deviation of FM modulation and a highest value of a modulating frequency to calculate an estimate of instantaneous frequency, and

limiting the calculated estimate of instantaneous frequency to a maximum value known to have been transmitted;

recovering the individual voice channels from the instantaneous frequencies of each FM carrier.

9. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, a method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels with a high degree of linearity;

comprising the steps of;

receiving a block of receive channels as a plurality of analog RF signals to be processed;

converting the plurality of analog RF signals into a very low frequency block IF signal and converting the block IF signal into a digitized time series;

windowing the digitized time series into a plurality of defined frequency ranges equal to the number of defined channels;

including;

defining a window time span having a time duration less than a time duration of 1/4 cycle of a present baseband modulating frequency, and

restricting frequency domain sidelobes produced by windowing to a value less than a minimum acceptable post detection signal to noise ratio,

generating Fourier coefficients with fast Fourier transforms in response to the windowing in order to identify the information signals of the individual channels of the digitized time series by recovering from the Fourier coefficients instantaneous frequencies from each FM carrier in each individual frequency defined channel;

including;

performing at least a first moment calculation that incorporates power spectra offset from a channel center frequency by an amount at least equal to a sum of a peak frequency deviation of FM modulation and a highest value of a modulating frequency, and

recovering the individual voice channels from the instantaneous frequencies of each FM carrier.

10. In a Frequency Division Multiple Access (FDMA) wireless radiotelephone system using FM modulated signals, a method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels with a high degree of sensitivity;

comprising the steps of;

receiving a block of receive channels as a plurality of analog RF signals to be processed;

converting the plurality of analog RF signals into a very low frequency block IF signal and further converting the block IF signal into a digitized time series;

windowing the digitized time series into a plurality of defined frequency ranges equal to the number of defined channels;

including;

generating Fourier coefficients with fast Fourier transforms in response to the windowing in order to identity the information signals of the individual channels of the digitized time series by recovering from the Fourier coefficients instantaneous frequencies from each FM carrier in each individual frequency defined channel;

including;

performing at least a first moment calculation that incorporates power spectra offset from a channel center frequency by an amount at least equal to a sum of a peak frequency deviation of FM modulation and a highest value of a modulating frequency, and

excluding from the first moment calculation power spectra offset from a channel center frequency by an amount that exceeds a sum of a peak frequency deviation of FM modulation and a highest value of a modulating frequency,

recovering the individual voice channels from the instantaneous frequencies of each FM carrier.

11. A method of processing FM signals in a Frequency Division Multiple Access (FDMA) radiotelephone system;

having a plurality of analog radio signals in substantially adjacent frequency defined channels;

comprising the steps of;

intercepting the plurality of analog radio signals with an antenna;

receiving the plurality of radio signals as a unitary block radio signal;

converting the block radio signal to an analog IF signal;

converting the IF signal into a digitized time series by sampling the analog IF signal;

windowing the digitized time series to improve selectivity between channels;

generating Fourier coefficients with fast Fourier transforms in response to the windowing in order to identify the information signals of the individual frequency defined channels of the digitized time series by recovering from the Fourier coefficients instantaneous frequency signals from each FM carrier in each individual frequency defined channel;

selecting a high quality diversity path based on carrier-to-noise ratio and expanding the instantaneous frequency signals;

detecting a baseband modulating information signal;

shaping the baseband modulating information signal by de-emphasis to remove noise;

formatting the baseband modulating information signal for transmission to a control location;

transmitting the signal formatted to a land telephone network.

12. A block receiver signal processing method applicable to an analog FM frequency domain multiple access (FDMA) wireless cellular radio telephone system using one FM carrier per channel and conveying a plurality of information signals occurring in substantially adjacent channels;

comprising the steps of;

receiving a block of receive channels as a plurality of analog RF signals to be processed,

converting the block of analog RF signals into a block of IF signals by means of analog amplification, filtering and heterodyning methods,

converting the block analog IF signal into a digitized time series by means of a high speed, high precision analog to digital converter,

applying a window function to the digitized time series to produce acceptable levels of selectively, dynamic range, linearity and amplitude flatness,

applying the windowed time series to a fast Fourier transform (FFT) processor to isolate, in frequency, individual channels in the block,

detecting the FM signals based on a multi-pass first moment method using the FFT derived power spectra associated with each channel of interest.

applying an expansion step of a companding process and de-emphasis low pass filtering for recovery of voice signals, identifying specific supervisory audio tones (SAT) that may be present, identifying a presence of signaling tone ST and decoding Manchester encoded data messages,

formatting the digitized voice, and the information content of decoded data messages, SAT and ST for transmission by means of a digital data link,

transmitting the channel information by means of digital data links to a central location, and

interfacing the channel information with the digital bus structure at the control site.

13. The block receiver signal processing method as claimed in claim 12,

wherein the step of detecting the FM signals is based on a multi-pass detection process,

comprises the further steps of:

generating estimates of the FM instantaneous frequency by means of a first moment calculation based on power spectra associated with the carrier frequency,

using a power mask to reject power spectra, for the purpose of subsequent first moment calculations, that are excessively corrupted by noise and interference,

limiting the estimates of instantaneous frequency to the maximum deviation known to have been transmitted.

14. In a wireless radio telephone system, apparatus connected for receiving voice and data signals in block form from a group of individual radio signals each incorporating a single FM carrier that is distinct in frequency;

comprising

a receiver assembly connected for processing the group of individual radio signals in the block form and converting the radio signals to an IF frequency;

an analog-to-digital converter connected for converting the radio signal in the block form into a digital time series format;

a window function processor connected for applying a window function to the digital time series;

a fast Fourier transform processor operative and connected for isolating in frequency multiple spectra associated with each individual FM carrier in the block form;

an FM detector connected for estimating an instantaneous frequency of individual FM carrier based on the first moment of power spectra associated with the individual FM carrier and recovering voice and signal information of each FM carrier;

a detection circuit connected for recovering voice and data signals, SAT (supervisory audio tones) and manchester encoded data;

a data link interface connected for formatting the voice and data signals for digital transmission to a control and processing location.

15. In a wireless radio telephone system, as claimed in claim 14:

wherein the fast Fourier transform processor is a discrete Fourier transform processor.

16. In a wireless radio telephone system, as claimed in claim 14:

further including;

the FM detector including apparatus for identifying Fourier spectra excessively corrupted by noise by subsequent recalculations of the first moment.

17. In the wireless radio telephone system, as claimed in claim 14:

further including;

the FM detector including apparatus for exploiting a correlation between errors in estimating the instantaneous frequency of the FM carrier and a magnitude of estimated frequency to compensate for the error.

18. A signal processing arrangement for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels;

comprising;

an analog processor for accepting a block composite signal containing the plurality of FM information signals from an antenna;

an analog-to-digital processor to convert the single block of RF signals into a digitized time series;

conversion circuitry for converting the block of RF signals into a very low frequency block IF signal having its low end frequency coincident in frequency with Fourier coefficient and its high end frequency coincident with another Fourier coefficient and having added Fourier coefficients spaced symmetrically within the frequency range of the very low frequency block IF signal;

digital signal processing apparatus including stored program instructions for windowing the digitized time series and generating Fourier coefficients with fast Fourier transforms to identify the individual channels of the digitized time series by recovering instantaneous frequencies from each FM carrier in each individual frequency defined channel; and

the stored instructions in digital signal processing apparatus operative to determine first moments of Fourier transform power spectra associated with each individual frequency defined channel and for identifying individual spectra distorted by noise and interference and repeating the determination of first moments to generate an improved reduced noise content associated with individual frequency defined channels;

FM detection circuitry for recovering the individual voice channels from the instantaneous frequencies of each FM carrier.

19. The signal processing arrangement for processing a plurality of FM information signals as claimed in claim 18;

wherein;

the stored program instructions in the digital signal processing apparatus being operative to limit determination of the instantaneous frequencies of each FM carrier in each individual frequency defined channel known to have been transmitted.

20. In a wireless radio telephone system, signal processing apparatus for recovering individual signal channels from a group of telecommunication channels each incorporating a single FM modulated carrier per individual channel;

comprising;

an analog processor for accepting a block composite signal containing the plurality of FM information signals from an antenna;

conversion circuitry for reducing the frequency of the block RF signal to a block IF signal;

an Analog-to-Digital converter for converting the block IF signal to a digitized time series;

window processing circuitry for applying a window function to the digitized time series;

a transform processor for determining Fourier coefficients in response to the signal output of the window processing circuitry in order to frequency define individual FM modulated carriers of the block IF signal and including a stored program control including instructions for determining first moments of Fourier transform power spectra associated with each individual FM modulated carrier and for identifying individual spectra distorted by noise and interference and repeating the determination of first moments to generate an improved reduced noise content power spectra associated with individual FM modulated carriers; and

demodulation circuitry for recovering the FM information signals.

21. In the wireless radio telephone system, signal processing apparatus as claimed in claim 20;

wherein;

the conversion circuitry being operative for converting the block of RF signals into a very low frequency block IF signal having its low end frequency coincident in frequency with a Fourier coefficient and its high end frequency coincident with another Fourier coefficient and having added Fourier coefficients spaced symmetrically within the frequency range of the very low frequency block IF signal.

22. A method for processing a plurality of FM information signals occurring in substantially adjacent frequency defined channels;

comprising the steps of;

receiving a radio signal input as a single block of a plurality of RF information signals to be processed;

converting the single block of analog RF signals into a digitized time series;

converting the single block of RF signals into a very low frequency block IF signal by heterodyning techniques such that its low end frequency is coincident in frequency with Fourier coefficient and its high end frequency is coincident with a another Fourier coefficient and having added Fourier coefficients spaced symmetrically within the frequency range of the very low frequency block IF signal;

windowing the digitized time series into a plurality of defined frequency ranges equal to the number of defined channels;

generating Fourier coefficients with fast Fourier transforms in response to the windowing in order to identity the information signals of the individual channels of the digitized time series by recovering from the Fourier coefficients instantaneous frequencies from each FM carrier in each individual frequency defined channel; and

recovering individual voice channels from the instantaneous frequencies of each FM carrier;

comprising the further steps of;

determining first moments of Fourier transform power spectra associated with each individual frequency defined channel;

identifying individual spectra distorted by noise and interference; and

repeating the determination of first moments generate an improved reduced noise content power spectra associated with individual frequency defined channels.

23. In a wireless radio telephone system, a method of signal processing for recovering individual signal channels from a group of telecommunication channels each incorporating a single FM modulated carrier per individual channel;

comprising the steps of;

receiving a radio signal input as a single block of receive channels comprised of a plurality of analog RF signals to be processed;

reducing frequency of the plurality of RF signals and and converting to a block IF signal;

converting the block IF signal to a digitized time series;

applying a window function to the digitized time series and deriving a window for each channel of the IF block signal;

applying fast Fourier transform (FFT) processing to the digitized time series for determining Fourier coefficients for each individual window in order to define an instantaneous frequency for individual FM modulated carriers of the block IF signal;

recovering the individual signal channels from the Fourier coefficients by;

determining first moments of Fourier transform power spectra associated with each individual FM modulated carrier;

identifying individual spectra distorted by noise and interference; and

repeating the determination of first moments to generate an improved reduced noise content power spectra associated with individual FM modulated carriers.