Radiocommunication apparatus, and radiocommunication system

Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...

Reexamination Certificate

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Details

C370S441000, C370S342000

Reexamination Certificate

active

06198731

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a radiocommunication apparatus and a radiocommunication system employing a direct spread CDMA (Code Division Multiple Access) communication scheme.
(2) Description of the Related Art
In recent years, a code division multiple access scheme employing spread spectrum communication—which is a multiple access scheme having a superior utilization efficiency of frequencies—has received attention as a transmission scheme for use in radiocommunication. This CDMA scheme is a leading candidate for the next-generation mobile communication system employed for radiocommunication between the base station and a plurality of mobile stations.
More specifically, the CDMA communication scheme is one in which multiple access is effected by spreading radio waves from each station through use of a high speed code inherent to the station. A transmitting-station transmits signals, while changing a spread code for each communication channel, at the same time over the same frequency band, and a receiving station reconstitutes only the information signal received over a communication channel assigned to the receiving station through use of its own spread code. A direct spread CDMA communication scheme is commonly employed, wherein the spectrum spreading is effected by modulating a carrier wave through use of a series of codes for spreading.
In a downward communication (communication from the base station to the mobile stations) of the direct spread CDMA communication scheme, signals are spread through use of different spread codes, and the thus-spread signals are transmitted to the mobile stations from the base station. The mobile station generally carries out despread processing for the received signal through integrate-and-damp process (or by correlation processing) of a code assigned to the mobile station (a spread code) and the received signal, whereby it obtains a desired wave.
FIG. 13
illustrates a radiocommunication system to which a common direct spread CDMA communication scheme is applied. A radiocommunication system
10
illustrated in
FIG. 13
is comprised of a transmitter
7
connected to an antenna
7
A, a receiver
8
connected to an antenna
8
A, and a radio circuit
9
through which the transmitter
7
and the receiver
8
are connected together.
The transmitter
7
is comprised of a serial/parallel converter (S/P)
70
, mixer circuits
71
a
and
71
b
, a control section
72
, a spread code generator
73
, transmission filters (TX filters)
74
a
and
74
b
, digital/analog converters (D/A)
75
a
and
75
b
, mixer circuits
76
a
and
76
b
, a voltage-controlled oscillator (a local oscillator)
77
, a 90-degree phase shifter
78
, an adder
79
, and an amplifier (a low-noise amplifier)
17
.
The mixer circuits
71
a
and
71
b
, the control section
72
, and the spread code generator
73
function as a spectrum spreading section
52
, whereas the mixer circuits
76
a
and
76
b
, the voltage-controlled oscillator
77
, and the 90-degree phase shifter
78
function as a frequency converter (an up-converter: U/C)
53
.
The receiver
8
is comprised of a hybrid device (H)
80
, mixer circuits
81
a
and
81
b
, a voltage-controlled oscillator (a local oscillator)
82
, a 90-degree phase shifter
83
, receiving filters (RX filters)
84
a
and
84
b
, analog/digital converters (A/D)
85
a
and
85
b
, correlators
86
a
and
86
b
, a code generator
87
, and a control section
88
.
The mixer circuits
81
a
and
81
b
, the voltage-controlled oscillator
82
, and the 90-degree phase shifter
83
function as a frequency converter (a down-converter; D/C)
62
. Further, the correlators
86
a
and
86
b
, the code generator
87
, and the control section
88
function as a spread demodulation section
89
.
In the radiocommunication system
10
illustrated in
FIG. 13
that has the previously-described circuit configuration, when a signal is transmitted from the transmitter
7
to the receiver
8
, the serial/parallel converter
70
converts information data (serial data) into parallel data and divides the thus-converted parallel data into two signals. The mixer circuits
71
a
and
71
b
carry out spectrum spread processing for the parallel data. That is, the two thus-converted parallel data signals are subjected to spread spectrum processing through use of a signal which is generated by the control section
72
according to a spread code received from the spread code generator
73
.
The signals having their spectra spread are then limited to a desired band by the transmission filters
74
a
and
74
b
. The signals are then converted into analog signals by the digital/analog converters
75
a
and
75
b
, and the frequencies of the thus-converted analog signals are converted by the frequency converter
53
. More specifically, the frequency of a signal output from the digital/analog converter
75
a
is converted by the mixer circuit
76
a
through use of a signal (i.e., a local signal) which has a frequency corresponding to a signal received from the voltage-controlled oscillator
77
. On the other hand, the frequency of a signal output from the digital/analog converter
75
b
is converted by the mixer circuit
76
b
through use of a signal from the 90-degree phase shifter
78
, which shifts the phase of the signal from the voltage-controlled oscillator
77
through an angle of 90 degrees. These two signals having their frequencies converted are added by the adder
79
, and a resultant signal is amplified by the amplifier
17
. Then, the thus-amplified signal is transmitted from the antenna
7
A in the form of radio waves.
In contrast, in the receiver
8
, the signal received by the antenna
8
A is divided into two signals by the hybrid device
80
. The frequencies of the signals are converted by the frequency converter
62
. At this time, the frequency of one of the two signals is converted by the mixer circuit
81
a
through use of a signal received from the voltage-controlled oscillator
82
. The frequency of the other signal is converted through use of a signal from the 90-degree phase shifter
83
, which shifts the phase of the signal from the voltage-controlled oscillator
82
through an angle of 90 degrees.
Subsequently, these signals are limited to a desired band by the receiving filters
84
a
and
84
b
, and they are converted into digital signals by the analog/digital converters
85
a
and
85
b
. The thus-digitally converted signals are subjected to despread processing performed by the spread demodulation section
89
.
More specifically, the control section
88
of the spread demodulation section
89
performs determination of code timing and code selection through use of a spread code of the receiver itself generated by the code generator
87
. The correlators
86
a
and
86
b
carry out despread processing based on the output from the control section
88
so as to output the despread information.
In the previously-described radiocommunication system
10
, the transmitter
7
and the receiver
8
can be used; for example, as the base station (a master station) and the mobile station, respectively. Specifically, audio or data information is transmitted between one master station and a plurality of mobile stations. For example, as illustrated in
FIG. 14
, if information is transmitted to three mobile stations (MS)
8
a
,
8
b
, and
8
c
from the base station (BS)
7
a
, because signals can be multiplexed through use of codes according to the CDMA scheme, signals can be sent to all the mobile stations,
8
a
,
8
b
, and
8
c
, at the same time over the same frequency.
Further, the signals to be sent to the mobile stations
8
a
,
8
b
, and
8
c
are respectively comprised of an information portion (see arrow D in
FIG. 14
) and a common signal portion (see arrow E in FIG.
14
). Contents which change according to the respective mobile station,
8
a
,
8
b
, or
8
c
(information to be sent to the mobile station
8
a
, information to be sent to the mobile station
8
b
, and information to be sent to

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