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| Impulse autocorrelation function communications system |
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| Pickup device for disc player |
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| Spread spectrum receiving device |
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| Mobile radio communications system |
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| Audio scrambling system for scrambling and descrambling audio signals |
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| Radio communication systems |
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| Multi-user acquisition procedure for multipoint-to-point synchronous CDMA systems |
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Spectrum spread transmission method and apparatus
| Details |
Inventors: Akiyama, Toshiyuki;
Assignee: Hitachi Denshi Kabushiki Kaisha (Tokyo, JP)
Primary Examiner: Pham; Chi H.
Assistant Examiner: Corrielus; Jean B
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus, LLP
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.sub.fa and f.sub.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. |
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DETAILED DESCRIPTION It is an object of the present invention to provide spectrum spread system transmission method and apparatus which allow simultaneous reception of motion pictures or semi-motion pictures at a center to meet the second demand.
In order to achieve the above object, a spectrum spread system transmission apparatus in a binary phase shift keying (BPSK) system or a quadrature phase shift keying (QPSK) system and a spectrum spread system by direct spread modulation, in accordance with a first feature of the present invention: (1) uses a spread code (PN code) having a chip length less than a maximum length of channel code permitted by a bandwidth of a predetermined transmission band and a predetermined transmission rate, (2) two or more channels are provided, and (3) carrier frequencies f.
sub.
ha, f.
sub.
hb, .
.
.
of the respective channels are set to different values from each other.
Preferably, a spread code having a chip length L which meets 2.
sup.
kmax -1>L where kmax is a maximum number which meets (B/2)/D>2.
sup.
k -1, B is the predetermined transmission band and D is the predetermined transmission rate, is used in the BPSK system as the spread code having the chip length smaller than the longest channel code.
Preferably, a spread code having a chip length L which meets 2.
sup.
kmax -1>L where kmax is a maximum number which meets (B/2)/(D/2)>2.
sup.
k -1, B is the predetermined transmission band and D is the predetermined transmission rate, is used in the QPSK system as the spread code having the chip length smaller than the longest channel code.
For example, for the two-channel transmission of 1.
5 Mbps, the channel code of the longest chip length of 15 chips (the chip rate at this time is denoted as f.
sub.
pn) is changed to the PN code of shorter, 10-chip length (the chip rate at this time is denoted as f'.
sub.
pna which is shorter than f.
sub.
pn).
Namely, the bandwidth of the main robe is set to 1.
5 Mbps.
times.
10 chips/2 phases.
times.
2=15 MHz<26 MHz which is shorter than the bandwidth of 22
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Multiplexer-related 
