SELECTIVE FADING TRANSFORMER

• US 3,605,019 A
• Filed: 01/15/1969
• Issued: 09/14/1971
• Est. Priority Date: 01/15/1969
• Status: Expired due to Term

• Current Assignee: Don G. Freeman, Gordon R. Schwarz, John M. Davis, Joseph T. Cutter, Richard Vanblerkom
• Original Assignee: Don G. Freeman, Gordon R. Schwarz, John M. Davis, Joseph T. Cutter, Richard Vanblerkom
• Inventors: Cutter, Joseph T., Davies, John M., Schwarz, Gordon R., Vanblerkom, Richard, Freeman, Don G.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Pecori, P. M.
• Application Number:
  US04/791,415
• Time in Patent Office: 972 Days
• Field of Search: 179/1AS,15.55 324/77 325/41,65
• US Class Current: 370/210
• CPC Class Codes: H04B 7/04 using two or more spaced independent antennas

Abstract

The invention is a communication system which causes errors introduced by selective frequency fading channels to be time localized. It does this by transmitting the Fourier transform of the baseband signal. The preferred embodiment consists of a frequency division multiplexor multiplexing a plurality of channels and a Fourier transformer taking the Fourier transform of the digital representation of the resultant waveform. The Fourier transform is reconverted into an analog representation by a D-A converter and transmitted by means of an A-D converter. The receiver reconverts the analog representation of the Fourier transform into a digital signal, a Fourier transformer takes the inverse transform, as a D-A converter, reconverts the digital representation back into an analog waveform and then an FDM demodulator demultiplexes the analog waveform resulting in a signal representative of the input to the transmitter with errors introduced by the channels appearing as burst errors (time localized).

Claims

1. A communications system time localizing errors of signals sent through a selective frequency fading channel including:

a transmitter including;

frequency division multiplexing means converting a plurality of binary data sources into a single analog waveform;

first analog-to-digital converter means taking the output of said frequency division multiplexing means and producing a digital representation of its input;

a first real time digital Fourier analyzer means taking the output of said analog-to-digital converter means and producing its Fourier transform representation; and

a first digital-to-analog converter means converting the output of said real time digital Fourier analyzer into an analog waveform; and

transmitting means transmitting the output of said digital-toanalog converter over a selected frequency fading channel;

a receiver including;

receiving means receiving said analog waveform transmitted by said transmitting means;

second analog-to-digital converter means converting the output of said receiving means into its digital representation;

second real time digital Fourier analyzer means taking the inverse transform of the output of said second analog-todigital converter means;

second digital-to-analog converter means converting the output of said real time digital Fourier analyzer into its analog representation; and

frequency division demultiplexing means converting the output of said second digital-to-analog converter means into a plurality of waveforms representative of the input to said transmitter.

2. A device as in claim 1 including:

error correcting means associated with said frequency division multiplexing means encoding the input to said frequency division multiplexing means so as to correct for burst errors.

3. A device as in claim 2 wherein said first real time digital Fourier analyzer includes:

preprocessor means transforming the input to said real time digital Fourier analyzer into a complex function, the real part of which is even and the iMaginary part of which is odd; and

a Fourier transformer taking the Fourier transform of said complex function by means of the Cooley-Tukey algorithm.

4. A communications system for time localizing errors caused by selected fading frequency communications channels, comprising:

a transmitter comprising;

freequency division multiplexing means for converting a plurality of data sources into a single waveform;

a first real time digital Fourier transformer responsive to the output of said frequency division multiplexing means for producing a Fourier transform representation of said outputs;

transmitting means for transmitting the output of said Fourier transformer including time localized errors over a communications channel subject to selective frequency fading;

a receiver, comprising;

receiving means for receiving said waveform transmitted by said transmitting means;

a second real time Fourier transformer for taking the inverse transform of the output of said receiving means; and

frequency division demultiplexing means for converting the output of said second Fourier transformer into a plurality of waveforms representative of the input to said transmitter.

5. A device as in claim 4, further comprising:

error code generating means associated with said frequency division multiplexing means for encoding the input to said frequency division multiplexing means; and

error code decoding means connected to the outputs of said frequency division demultiplexing means for correcting burst errors.