Digital synthesized wideband noise-like waveform

• US 5,848,160 A
• Filed: 02/20/1996
• Issued: 12/08/1998
• Est. Priority Date: 02/20/1996
• Status: Expired due to Term

• Current Assignee: Microelectronics Technology Inc (MTI Laboratory Inc)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: O'Connor, Roger J., Cai, Khiem V.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): White, Carmen D.
• Application Number:
  US08/603,673
• Time in Patent Office: 1,022 Days
• Field of Search: 380/44, 380/46, 380/47, 364/717
• US Class Current: 380/44
• CPC Class Codes: H04B 1/707 using direct sequence modulation

Abstract

Apparatus and a method for generating a digital synthesized Gaussian noise-like waveform that may be used to modulate and demodulate communication data. The present invention uses a seed input that addresses a read only memory look-up table, for example, containing digital samples having Gaussian statistics. A sequence generator generates a pair of pseudo-random sequences in response to the seed input that address the read only memory to look up and output a pair of pseudo-random Gaussian samples that are used to generate the Gaussian noise-like waveform. A processor converts the pair of pseudo-random Gaussian samples into corresponding analog I and Q signals, and a modulator 33 modulates the analog I and Q signals to generate a modulated output signal having the Gaussian noise-like waveform.

Claims

1. Apparatus for generating a digitally synthesized noise-like waveform that may be used to modulate and demodulate communication data, said apparatus comprising:

a seed generator for generating a predetermined random seed input;

a read only memory look-up table comprising pseudo-random digital samples having predetermined statistics;

a sequence generator coupled between the seed generator and the read only memory look-up table for generating a pair of pseudo-random sequences in response to the predetermined seed input that address the read only memory look-up table and output a pair of pseudo-random samples;

processing means coupled to the read only memory look-up table for combining the pair of pseudo-random samples with communication data to generate a spread spectrum waveform; and

modulation means coupled to the processing means for processing the spread spectrum waveform to generate a modulated output signal having a digitally synthesized noise-like waveform.

2. The apparatus of claim 1 wherein the processing means comprises:

first and second processing channels that respectively comprise;

a mixer;

an m-bit digital-to-analog converter; and

an analog low pass filter.

4. The apparatus of claim 2 wherein the seed generator comprises means for generating a cryptographic key.

5. The apparatus of claim 1 further comprising:

a quadrature modulator and a local oscillator for quadrature modulating the spread spectrum waveform to generate the modulated output signal having the digitally synthesized noise-like waveform.

3. The apparatus of claime 2 wherein the first and second processing channels each further comprise a low pass filter.

6. A method for generating a digitally synthesized noise-like waveform, said method comprising the steps of:

storing pseudo-random digital samples having predetermined statistics;

generating a predetermined random seed input;

generating a pair of pseudo-random sequences in response to the predetermined random seed input;

outputting a pair of pseudo-random samples in response to the pair of pseudo-random sequences;

combining the pair of pseudo-random samples with communication data to generate a spread spectrum waveform;

modulating the spread spectrum waveform to generate a modulated output signal having a digitally synthesized noise-like waveform.

7. The method of claim 6 wherein the step of generating a predetermined seed input comprises generating a cryptographic key.