Pulse or digital communications – Spread spectrum
Reexamination Certificate
2000-02-17
2004-08-10
Corrielus, Jean B. (Department: 2631)
Pulse or digital communications
Spread spectrum
C455S013400, C455S574000, C455S127500
Reexamination Certificate
active
06775317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for spread spectrum communications and to a transmitter and receiver thereof, and more particularly to a method for spread spectrum communications between a base station and a mobile station and to a transmitter of the base station and a receiver of the mobile station.
2. Description of the Related Art
FIG. 1
is a block diagram of a conventional transmitter used for spread spectrum communications. In this diagram, reference numeral
8
-
1
denotes a transmitting baseband processing part,
8
-
2
a baseband modulating part,
8
-
3
a spread modulating part,
8
-
4
a power amplifying part,
8
-
5
a local-transmitting-frequency generating part and
8
-
6
a spread-code generating part.
FIG. 2
illustrates respective circuits of these functional parts of FIG.
1
.
The transmitting baseband processing part
8
-
1
functions to adapt an analog voice signal to a modulation method of the baseband modulating part
8
-
2
. In a case of performing a narrowband frequency modulation, as shown by (a) of
FIG. 2
, the transmitting baseband processing part
8
-
1
outputs a voice input signal by passing the voice input signal through a differential circuit
9
a
-
1
, an amplitude limiter
9
a
-
2
and a low-pass filter
9
a
-
3
. In the frequency modulation, the differential circuit
9
a
-
1
functions to improve talk articulation and the amplitude limiter
9
a
-
2
functions to limit frequency shifts.
In a case in which the baseband modulating part
8
-
2
performs a digital modulation, the transmitting baseband processing part
8
-
1
converts an analog input signal of, for example, voice or the like, into a digital signal, and then outputs the digital signal to the baseband modulating part
8
-
2
.
The baseband modulating part
8
-
2
performs a carrier modulation according to a communication information signal of the voice, low-spead data or the like which is outputted from the transmitting baseband processing part
8
-
1
. In a case in which the signal to be transmitted is a digital signal from the beginning like an individual connection control signal of each mobile station, the digital signal is directly inputted from a logic circuit portion (not shown) into the baseband modulating part
8
-
2
. The baseband modulating part
8
-
2
modulates the inputted signal and then outputs the modulated signal to the spread modulating part
8
-
3
.
Additionally, in a case of outputting, for example, an FM (i.e., frequency modulation) signal of 150 MHz, in the baseband modulating part
8
-
2
, as shown by (b) of
FIG. 2
, a frequency modulator
9
b
-
1
generates an FM wave of several MHz to several tens of MHz by the input information signal of the voice, data or the like. Then a frequency converter
9
b
-
2
uses the FM wave of several MHz to several tens of MHz and a signal of a local transmitting frequency of 140 MHz to output a narrowband FM signal of 150 MHz.
In a case of performing a digital modulation such as FSK or the like, the baseband modulating part
8
-
2
shifts a transmitting frequency to a plus direction or a minus direction according to the digital input signal of the voice, data, or the like.
The spread modulating part
8
-
3
spreads the signal (for example, the FM wave of 150 MHz, or the like) which has been modulated by a spread code. Hence, the modulation performed in the spread modulating part
8
-
3
is not a modulation by the information signal.
In the spread modulating part
8
-
3
, as shown by (c) of
FIG. 2
, a ring modulator
9
c
-
1
spreads and modulates an input signal by the spread code consisting of a string of binary code (1, 0), and outputs a spread wave of 150 MHz via a bandpass filter
9
c
-
2
.
The power amplifying part
8
-
4
amplifies the signal outputted from the spread modulating part
8
-
3
by a power amplifier thereof consisting of one stage or a plurality of stages, and then supplies an power-amplified radio-frequency signal to a transmitting antenna
8
-
7
.
The local-transmitting-frequency generating part
8
-
5
, as shown by (d) of
FIG. 2
, is a PLL synthesizer which consists of a reference oscillator
9
d
-
1
, a phase detector
9
d
-
2
, a low-pass filter
9
d
-
3
, a voltage-controlled oscillator
9
d
-
4
and a variable frequency divider
9
d
-
5
. The local-transmitting-frequency generating part
8
-
5
generates a local-transmitting-frequency signal corresponding to an inputted local-transmitting-frequency designation signal as a frequency division of the PLL synthesizer, and sends the local-transmitting-frequency signal to the frequency converter
9
b
-
2
of the baseband modulating part
8
-
2
.
In the local-transmitting-frequency generating part
8
-
5
, the phase detector
9
d
-
2
detects a phase difference between a signal from the reference oscillator
9
d
-
1
and a signal from the variable frequency divider
9
d
-
5
, and, via the low-pass filter
9
d
-
3
, inputs the two signals into the voltage-controlled oscillator
9
d
-
4
.
A signal outputted from the voltage-controlled oscillator
9
d
-
4
is inputted into the variable frequency divider
9
d
-
5
, in which a frequency of the output signal is divided according to a frequency division designated by the local-transmitting-frequency designation signal and then is transmitted to the phase detector
9
d
-
2
.
The spread-code generating part
8
-
6
generates the spread code designated by a spread-code designation signal and outputs the spread code to the spread modulating part
8
-
3
. The spread code is, for example, a string of binary code (1, 0) of 3 Mbs, and is distributed into each of mobile stations so as to identify each mobile station and spread a transmitting signal sent thereto. The length of the code string is related to an identification code and the length of a bit is related to a width of the spread.
The baseband modulating part
8
-
2
modulates the communication information signal of the voice, data or the like at a low speed. The spread modulating part
8
-
3
spreads the transmitting signal according to the identification code of each of the mobile stations and performs a modulation at a middle/high speed.
FIG. 3
is a block diagram illustrating a conventional receiver used for spread spectrum communications. In this diagram, reference numeral
10
-
1
denotes a receiving baseband processing part,
10
-
2
a baseband demodulating part,
10
-
3
a despread modulating part,
10
-
4
a high-frequency amplifying part,
10
-
5
a local-receiving-frequency generating part and
10
-
6
a despread-code generating part.
FIG. 4
illustrates respective circuits of these functional parts of FIG.
3
.
An antenna
10
-
7
receives a radio signal and inputs the radio signal into the high-frequency amplifying part
10
-
4
in which, as shown by (a) of
FIG. 4
, the inputted radio signal is amplified by passing through a bandpass filter
11
a
-
1
, an amplifier
11
a
-
2
and a bandpass filter
11
a
-
3
and then is outputted to the despread modulating part
10
-
3
. The amplifier
11
a
-
2
is formed by a stage of an amplifying circuit or by a plurality of stages of the amplifying circuit.
The despread modulating part
10
-
3
despreads a spread wave outputted from the high-frequency amplifying part
10
-
4
so as to shrink the spread wave back to its original signal prior to spreading. In the despread modulating part
10
-
3
, as shown in (b) of
FIG. 4
, a ring modulator
11
b
-
1
despreads the spread wave of, for example, 3 Mbps, by a despread code formed by a string of binary code (1, 0) so as to converge the spread wave to become a narrowband FM wave of 150 MHz (i.e., in a case in which the narrowband FM has been used).
The baseband demodulating part
10
-
2
demodulates a basic modulation wave outputted from the despread modulating part
10
-
3
to produce a baseband signal and outputs this communication information signal of the voice, data or the like to the receiving baseband processing part
10
-
1
. In a case in which the signal to be received by the receiving baseban
Corrielus Jean B.
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Tran Khanh Cong
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