Antimultipath communication by injecting tone into null in signal spectrum

• US 4,675,880 A
• Filed: 05/02/1985
• Issued: 06/23/1987
• Est. Priority Date: 05/02/1985
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Davarian, Faramaz
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Huseman, M.
• Application Number:
  US06/729,719
• Time in Patent Office: 782 Days
• Field of Search: 375/38, 375/39, 375/54, 375/55, 375/87, 375/102, 375/101, 360/42, 329/120, 329/124, 332/23 A, 455/35, 455/65
• US Class Current: 375/261
• CPC Class Codes: H04B 7/005 Control of transmission; Equalising

Abstract

A transmitter for digital radio communication creates a null by balanced encoding of data modulated on an RF carrier, and inserts a calibration tone within the null. By having the calibration tone coincide in phase and frequency with the transmitted radio frequency output for coherent demodulation of data at the receiver where the tone calibration signal is extracted and used for multipath fading compensation.

Claims

1. A method of radio communication comprised of the steps of transmitting a radio frequency signal so modulated with digital data as to produce a null in its radio frequency spectrum, and injecting in the modulated radio carrier signal a calibration tone within said null for use by receivers for compensation of multipath fading distortions, including the steps at a receiver of base band filtering the received signal, dividing the base band filtered signal into inphase and quadrature base band signals, low pass filtering said inphase and quadrature base band signals for detection of said tone calibration signal and signal match filtering said inphase and quadrature base band signals, mixing the detected calibration tone and match filtered signals of the inphase base band signal and separately of the quadrature phase signal, and summing the resulting signals of said separate mixing steps to combine them into a signal suitable for sampling and data detection.

2. Apparatus for radio communication of digital data with multipath fading compensation comprised of

a transmitter having means for splitting said digital data into inphase and quadrature signals, means for applying balanced encoding of data for each signal to create a null at the center of a radio carrier frequency output spectrum, means for signal band limiting each of said balanced encoded signals, means for quadrature modulation of each signal with a calibration tone, and means for summing the resultant signals with said calibration tone, thereby inserting said calibration tone at said null of the balanced data encoded radio frequency spectrum, and

a receiver of said radio frequency output of said transmitter having means for extracting the signal received by band pass filtering and means for band pass filtering said calibration tone from the band pass filtered signal received, means for mixing the band pass filtered calibration tone with itself, means for low pass filtering the output of said mixing means to produce a base band signal, means for threshold comparison of said base signal with a test level, and means for algebraically dividing said band pass filtered calibration tone by the output of said threshold comparison means, and means for mixing said calibration tone with said extracted signal received, thereby compensating for multipath fading, wherein said calibration tone at said transmitter coincides in phase and frequency with the transmitted radio carrier frequency signal for coherent demodulation of data at the receiver.

3. Apparatus for radio communication of digital data with multipath fading compensation comprised of

a transmitter having means for splitting digital data into inphase and quadrature signals, means for applying balanced encoding of data for each signal to create a null at the center of a data modulated radio frequency output spectrum, means for signal band limiting each of said balanced encoded signals, means for quadrature modulation of the two signals, and means for summing said signals with a calibration tone, thereby inserting said calibration tone at said null of the radio frequency output spectrum, and

a base band receiver of said data modulated radio frequency carrier of said transmitter with said calibration tone, said receiver having means for dividing a received signal into inphase and quadrature base band signals, separate means for each of said inphase and quadrature base band signals for calibration tone detection and signal match filtering, means for mixing the detected calibration tone and match filtered signals of the inphase base band signal and separately of the quadrature phase signal, and means for summing the outputs of said separate mixing means to combine them into a signal suitable for sampling and data detection.

4. Apparatus as defined in claim 3 including a predetection band pass filter of the signal received before dividing into inphase and quadrature base band signals for noise band limiting.