Spectrum spread transmission method and apparatus

• US 6,038,249 A
• Filed: 03/18/1997
• Issued: 03/14/2000
• Est. Priority Date: 03/19/1996
• Status: Expired due to Fees

• Current Assignee: Hitachi Denshi Kabushiki Kaisha
• Original Assignee: Hitachi Denshi Kabushiki Kaisha
• Inventors: Akiyama, Toshiyuki
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): Corrielus, Jean B
• Application Number:
  US08/819,088
• Time in Patent Office: 1,092 Days
• Field of Search: 375/200, 375/206, 375/208, 375/282, 375/281, 375/333, 375/261, 375/279-280, 370/342, 370/335, 380/34, 329/304, 332/103
• US Class Current: 375/143
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04L 25/03828 Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties partial response systems H04L25/497

Abstract

Transmission method and apparatus allow two channel simultaneous transmission of information codes having a transmission rate of 1.5 Mbps necessary for the transmission of motion pictures or semi-motion pictures through a 2.4 GHz small power communication band (ISM band). Carrier frequencies f_fa and f_hb of the two channels are set to different values from each other, QPSK modulation is demodulated in a receiver and then inverse-spread of the spectrum spread is conducted, and a low pass filter having a root roll-off characteristic is inserted to a succeeding stage of a spectrum spread circuit of a transmitter and a preceding stage of the spectrum inverse-spread circuit of the receiver.

Claims

1. A spectrum spread system transmission apparatus using a binary phase shift keying (BPSK) system or a quadrature phase shift keying (QPSK) system and a spectrum spread system by direct spread modulation, wherein two or more channels are provided by using a spread code having the number of repetition bits (chip length) smaller than a longest channel code permitted by a predetermined transmission band and a predetermined transmission rate, and carrier frequencies of the channels are set to different values from each other, said transmission apparatus comprising:

(a) a receiver including;

a receiving antenna,

a BPSK or QPSK demodulator for each channel, connected to said receiving antenna, and

a spectrum inverse-spread circuit for each channel, receiving a base band signal from said BPSK or QPSK demodulator;

(b) a transmitter including;

a spectrum spread circuit for each channel, receiving an information code,

a BPSK or QPSK modulator for each channel, receiving said spread code signal of the base band from said spectrum spread circuit, and

a transmitting antenna connected to said BPSK or QPSK modulator; and

(c) a frequency characteristic control circuit inserted at a point between said spectrum spread circuit for each channel of said transmitter and said transmitting antenna and a point between said receiving antenna and said spectrum inverse-spread circuit for each channel of said receiver, for limiting bands of frequency characteristics of corresponding channels to ranges narrower than a main robe band determined by chip rates of the spread code of the corresponding channels,

wherein said frequency characteristic control circuit inserted between said spectrum spread circuit for each channel and said transmitting antenna of said transmitter is a root roll-off filter, and said frequency characteristic control circuit inserted between said receiving antenna and said spectrum inverse-spread circuit for each channel of said receiver comprises a first filter having two taps for summing the demodulated base band signal and a signal delayed from the base band signal by one half period of a pulse period of the spread signal, and a second filter for eliminating frequency components having frequencies higher than the frequency of the spread signal in the base band signal.

2. A spectrum spread system transmission apparatus according to claim 1, wherein a 2.4 GHz small power communication band is used for the transmission band used for the transmission, and the transmission rate of information code transmitted on at least one channel of said two or more channels transmitted through the predetermined transmission band is set to not less than 1 Mbps.

3. In a spectrum spread system transmission apparatus using a binary phase shift keying (BPSK) system or a quadrature phase shift keying (OPSK) system and a spectrum spread system by direct spread modulation, wherein two or more channels are provided and carrier frequencies of the channels are set to different values from each other, a spectrum spread system transmission method used for the transmission apparatus comprising the steps of:

(a) in a transmitter during a transmission mode;

spectrum-spread-modulating an information code by a spectrum spread circuit for each channel to generate a spread code signal of a base band,

modulating the spread code signal of the base band for each channel by a BPSK or OPSK modulator, and

transmitting an output of the BPSK or OPSK modulator from a transmitting antenna;

(b) in a receiver during a receive mode;

demodulating the signal received by a received by a receiving antenna for each channel by a BPSK or OPSK demodulator to generate a base band signal, and

demodulating the base band signal for each channel by a spectrum inverse-spread circuit to produce the information code; and

(c) limiting bands of frequency characteristics of the corresponding channels to ranges narrower than a main robe band determined by chip rates of spread codes of corresponding channels by a frequency characteristic control circuit inserted at a point between said spectrum spread circuit for each channel of said transmitter and said transmitting antenna and a point between said receiving antenna and said spectrum inverse-spread circuit for each channel of said receiver,

wherein said frequency characteristic control circuit inserted between said spectrum spread circuit for each channel and said transmitting antenna of said transmitter is a root roll-off filter, and said frequency characteristic control circuit inserted between said receiving antenna and said spectrum inverse-spread circuit for each channel of said receiver comprises a first filter having two taps for summing the demodulated base band signal and a signal delayed from the base band signal by one half period of a pulse period of the spread code signal, and a second filter for eliminating frequency components having frequencies higher than the frequency of the spread signal in the base band signal.