Modulation and demodulation system for spread spectrum transmission

• US 5,170,411 A
• Filed: 09/19/1991
• Issued: 12/08/1992
• Est. Priority Date: 09/21/1990
• Status: Expired due to Fees

• Current Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation)
• Original Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation)
• Inventors: Ishigaki, Yukinobu
• Primary Examiner(s): CANGIALOSI, SALVATORE A
• Application Number:
  US07/762,885
• Time in Patent Office: 446 Days
• Field of Search: 375/1
• US Class Current: 375/147
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H
• CPC Class Codes: H04K 3/228 Elimination in the received signal of jamming or of data corrupted by jamming interference suppression in receivers H04B1/10

Abstract

A modulation and demodulation system for spread spectrum transmission comprises modulation and demodulation sections. The modulation section spreads/modulates an input information signal by multiplying by a PN code to provide a spread spectrum signal. The demodulation section despreads/demodulates the spread spectrum signal including interference mixed therein by substantially using the same spread code. In the demodulation section, a first multiplier despreads the received signal by multiplying by the PN code to provide a despread demodulation signal, a high-pass filter extracts a first spread interference signal from the despread demodulation signal, a second multiplier multiplies the spread interference signal by a high-frequency range emphasized PN code, a low-pass filter attenuates high-frequency range components of the output signal of the second multiplier, a third multiplier multiplies the output signal of the low-pass filter by a high-frequency range attenuated PN code, an emphasizing circuit emphasizes low-frequency range components of the output signal of the third multiplier to provide a second spread interference signal, and a subtracter obtains the difference between the second spread interference signal and the despread demodulation signal to provide the interference-free demodulated information signal.

Claims

1. A modulation and demodulation system for spread spectrum transmission comprising a modulation section including a first pseudo noise (PN) code generating circuit, and a demodulation section including a second PN code generating circuit, wherein said first and second PN code generating circuits generate substantially identical PN codes, said modulation section includes spreading means for spreading and modulating an input information signal by multiplying by a first PN code from said first PN code generating circuit to provide a spread spectrum signal, and said demodulation section includes a despreading means for receiving said spread spectrum signal from said spreading means through one of a transmission means or a recording medium and despreading and demodulating said spread spectrum signal by a second PN code from said second PN code generating circuit, wherein said despreading means comprises;

first emphasizing means (F2) for emphasizing high-frequency components of said second PN code higher than a predetermined frequency to produce a high-frequency range emphasized PN code,

attenuating means (F4) for attenuating high-frequency components of said second PN code higher than said predetermined frequency to produce a high-frequency range attenuated PN code,

a first multiplier (3) for receiving said spread spectrum signal with interference unintentionally mixed therein through said one of said transmission means or said recording medium, and despreading said spread spectrum signal and said interference mixed therein by multiplying by said second PN code to provide a despread demodulation signal,

a high-pass filter (F₁) for producing a first spread interference signal from said despread demodulation signal by blocking a demodulated information signal and demodulated interference components both included in said despread demodulation signal, said interference components lying in a frequency band of said demodulated information signal,

a second multiplier (4) for multiplying said first spread interference signal by said high-frequency range emphasized PN code to provide a first multiplied output signal,

a low-pass filter (F₃) for attenuating components of said first multiplied output signal, which lie above said predetermined frequency,

a third multiplier (5) for multiplying an output signal of said low-pass filter by said high-frequency range attenuated PN code to provide a second multiplied output signal,

second emphasizing means (F₅) for emphasizing components of said second multiplied output signal in a low-frequency range which corresponds to a frequency range blocked by said high-pass filter (F₁), to provide a second spread interference signal equivalent to said first spread interference signal included in said despread demodulation signal, and

a subtracter of obtaining a difference between said second spread interference signal and said despread demodulation signal to provide said demodulated information signal including substantially no interference components.