Multiplex communications – Phase modulation
Reexamination Certificate
1996-11-14
2001-09-25
Vu, Huy D. (Department: 2663)
Multiplex communications
Phase modulation
C375S302000
Reexamination Certificate
active
06295273
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
The present invention relates to a phase modulation multiplexing transmission unit for multiplexing and transmitting a phase modulation signal in a spectrum spread (referred to as, SS hereinafter) transmission system.
FIG. 5
is a block diagram showing a construction of a conventional phase modulation multiplexing transmission unit.
The prior art shown in
FIG. 5
comprises a signal division unit
1
for dividing a digital input signal into two division signals I
1
(
n
) and I
2
(
n
) for outputting and spread code generators
2
a
and
2
b
for generating and outputting spread codes C
1
(
n
) and C
2
(
n
) for spectrum spreading. This prior art further comprises multiplication units
3
a
and
3
b
for outputting multiplication signals Sa and Sb obtained by multiplying the division signals I
1
(
n
) and I
2
(
n
) by the spread codes C
1
(
n
) and C
2
(
n
) output from the spread code generators
2
a
and
2
b
, respectively.
Additionally this prior art comprises an adder
5
for outputting a synthetic signal Sc(n) obtained by summing the multiplication signals Sa and Sb output from the multiplication units
3
a
and
3
b
, a modulator
6
for two-phase modulating (referred to as, BPSK hereinafter) the synthetic signal Sc(n) output from the adder
5
, a transmission amplifier
7
for amplifying and outputting the phase modulation signal output from the modulator
6
and an antenna
8
through which the amplified phase modulation signal output from the transmission amplifier
7
is transmitted.
The operation of this prior art is described hereinafter.
The signal division unit
1
divides a digital input signal into two division signals I
1
(
n
) and I
2
(
n
), each of which is input to the multiplication units
3
a
and
3
b
, respectively. The spread code generators
2
a
and
2
b
generate spread codes C
1
(
n
) and C
2
(
n
) for spectrum spreading, each of which is output to the multiplication units
3
a
and
3
b
, respectively. The multiplication unit
3
a
multiplies the division signal I
1
(
n
) input from the signal division unit
1
by the spread code C
1
(
n
) output from the spread code generator
2
a
. The resultant multiplication signal Sa is obtained from the following equation (1).
Sa=I
1
(
n
)*
C
1
(
n
) (1)
The multiplication unit
3
b
multiplies the division signal I
2
(
n
) input from the signal division unit
1
by the spread code C
2
(
n
) output from the spread code generator
2
b
. The resultant multiplication signal Sb is obtained from the following equation (2).
Sb=I
2
(
n
)*
C
2
(
n
) (2)
The adder
5
sums the multiplication signals Sa and Sb output from the multiplication units
3
a
and
3
b
, respectively for synthesizing. The resultant synthetic signal Sc(n) is obtained from the following equation (3).
Sc(
n
)=
Sa+Sb=I
1
(
n
)*
C
1
(
n
)+
I
2
(
n
)*
C
2
(
n
) (3)
The modulator
6
two-phase modulates (BPSK) the synthetic signal Sc(n), which is amplified by the transmission amplifier
7
and then transmitted through the antenna
8
. The spread codes C
1
(
n
) and C
2
(
n
) respectively generated by the spread code generators
2
a
and
2
b
have excellent self-correlation characteristics using code exhibiting good mutual correlation characteristics (close to non-correlation).
FIG. 6
shows coordinates of the synthetic signal Sc(n) output from the adder
5
.
As
FIG. 6
shows, the multiplication signals Sa and Sb respectively output from the multiplication units
3
a
and
3
b
overlap with each other at coordinates (1, 0) and (−1, 0) on the phase plane. The synthetic signal Sc(n) is defined by signal coordinates (2, 0), (−2, 0) and (0, 0) as shown in FIG.
6
. Accordingly the peak level of dualized synthetic signal Sc(n) is doubled, thus increasing the electric power by 4 times (2
2
).
FIG. 7
is a graphical representation of an input/output characteristic of the transmission amplifier
7
.
Referring to
FIG. 7
, assuming that the number of multiplexing is 2 (dual), the peak level of the BPSK input/output signal input to the transmission amplifier
7
becomes two times higher than that before multiplexing owing to a high ratio of the average power to the peak power (peak factor). In order to amplify the modulation signal output from the modulator
6
through the transmission amplifier
7
and to transmit the resultant amplified phase modulation signal at a low bias, a broad linear area is required.
Prior arts disclosed by a publication of JP-A-360434/1992 titled “Spectrum spread transmission unit and spectrum spread reception unit” and a publication of JP-A-30079/1993 titled “Spectrum spread modulation unit” have been well known as arts related to the above-described device.
In the publication of JP-A-360434/1992, each bit of parallel data is spread based on a plurality of spread codes and parallel transmitted for spectrum spread transmission at a high rate.
In the publication of JP-A-30079/1993, parallel data converted from serial data are delayed for shifting codes through spread modulation with n delay PN codes which have been phase corrected. As a result, efficient high rate data transmission is realized by preventing degradation in the spectrum spread communication characteristic.
Those conventional phase modulation multiplexing transmission units allow for high rate data transmission. However they need substantially a broad area where the transmission amplifier
7
amplifies the modulation signal output from the modulator
6
at a low bias for transmission. As a result, a large-sized transmission amplifier is necessary, resulting in increasing the cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the aforementioned problem of those prior arts.
It is another object of the present invention to provide a phase modulation multiplexing transmission unit reducing the size of a transmission amplifier for executing amplification at a low bias in relatively a narrow linear area due to decreased peak of the multiplexing signal during multiplexing and high-rate data transmission. Reducing the transmission amplifier size, therefore leads to cost reduction.
The present invention is achieved by a phase modulation multiplexing transmission unit comprising: multiplication means for outputting a plurality of multiplication signals derived from multiplying each of a plurality of division signals obtained by dividing a digital input signal by respective ones of a plurality of spread code signals; phase shifting means for shifting a phase so that all or less than all of the plurality of multiplication signals has a phase difference; addition means for outputting a multiplexing signal by summing the plurality of all multiplication signals, including those that have been phase shifted and those that have not been phase shifted; and modulation means for modulating the multiplexing signal for outputting.
Furthermore, the present invention is achieved by a phase modulation multiplexing method comprising steps of: generating a plurality of multiplication signals by multiplying each of a plurality of division signals obtained by dividing a digital input signal by respective ones of a plurality of spread code signals; shifting a phase so that all or less than all of the plurality of multiplication signals has a phase difference; generating a multiplexing signal by summing a plurality of multiplication signals including those that have been phase shifted and those that have not been phase shifted; and modulating the multiplexing signal.
In the phase modulation multiplexing transmission unit of the present invention, multiplexing (addition) is executed by shifting the phase of the phase modulation signal. As a result, the ratio of the average power to the peak power (peak factor) of the multiplexed signal for multiplexing and high rate data transmission is decreased. That is, the decreased multiplexed signal peak requires only a narrow linear area where the transmission amplifier amplifies the modulation signal for outputt
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Vu Huy D.
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