Multiplex communications – Generalized orthogonal or special mathematical techniques – Quadrature carriers
Reexamination Certificate
1997-01-30
2001-11-20
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Generalized orthogonal or special mathematical techniques
Quadrature carriers
C370S342000, C375S130000, C375S280000
Reexamination Certificate
active
06320842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spread spectrum communication apparatus and method for multiplex communication using a plurality of codes.
2. Description of the Related Art
A spread spectrum communication apparatus using quadrature modulation is disclosed in U.S. Pat. No. 08/233,244 (filed on Apr. 26, 1994). In this prior art, a multiplexing method using a plurality of spread codes is described.
FIG. 17
shows a transmitter, and
FIG. 18
shows a receiver. In
FIG. 17
, transmission data is converted into parallel data #I
1
to #In and #Q
1
to #Qn for two channels, i.e., an in-phase channel (Ich) and a quadrature channel (Qch). Transmission data #I
1
and #Q
1
are spread-modulated in accordance with a common spread code PN
1
which is output from a code generator
84
, and then subjected to quadrature modulation. These data are converted into desired frequencies and transmitted. Similarly, transmission data #I
2
to #In and #Q
2
to #Qn are spread-modulated in accordance with common spread codes PN
2
to PN
n
, respectively, and then subjected to quadrature modulation.
Referring to
FIG. 18
, on the reception side, the received signal is separated into the channels Ich and Qch by using a carrier which is reproduced by a carrier reproduction circuit
91
, and correlations between the received signals and the spread codes PN
1
to PN
n
which are the same as those on the transmission side are calculated by correlators
907
-
1
to
907
-n and
908
-
1
to
908
-n, thereby performing spread demodulation. Thereafter, a determiner
909
demodulates the data.
In the above prior art, however, the in-phase channel (Ich) data and the quadrature channel (Qch) data are spread-modulated using the common spread codes. For this reason, as in normal QPSK, a shift between quadrature axes or a phase/frequency shift in a reproduced carrier poses a serious problem. Since a highly precise quadrature and reproduced carrier are required, the apparatus can hardly be made compact, and expensive parts are necessary. Furthermore, to increase the phase/frequency precision of the reproduced carrier, the time required for carrier reproduction is prolonged. Particularly, in packet communication, the overhead becomes large, resulting in a decrease in throughput.
In the above prior art, a plurality of signals which have undergone spread modulation are linearly added and then modulated using carriers. For this reason, the amplitude variation is large, resulting in a large increase in maximum peak power with respect to the average power. In, e.g., octet-multiplexing, the maximum peak power is eight times larger (9 dB) than the average power. Therefore, the average output and communication distance become small. To ensure a predetermined communication distance, a high-power amplifier is needed, resulting in an increase in power consumption.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve the reliability of spread spectrum communication.
It is another object of the present invention to realize high-speed spread spectrum communication.
It is still another object of the present invention to achieve size reduction of an apparatus for performing high-speed data transmission by spread spectrum communication.
It is a further object of the present invention to decrease the cost of an apparatus for performing high-speed data communication by spread spectrum communication.
It is an additional object of the present invention to reduce the power consumption in high-speed data communication by spread spectrum communication.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
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Yu, M. et al., An Improved pi/4—DQPSK Compatible Feher's “pi/4—FQPSK” Nonlinearly Amplified Modulation, Vehicular Technology Conference, 1995 IEEE 45th, Jul. 28, 1998.*
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Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hsu Alpus H.
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