Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-06-23
2002-08-20
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C375S142000
Reexamination Certificate
active
06438118
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a code-multiplexing communication apparatus capable of removing an autocorrelated distortion with use of a simple circuit structure.
2. Description of the Related Art
There has proposed a code-multiplexing communication apparatus for realizing a large scale communication with transmission of multiplexing spread spectrum code.
In such code-multiplexing communicating apparatus,
FIG. 7A
shows a transmission unit of the communication apparatus, while
FIG. 7B
shows a reception unit thereof, noting that the number of code multiplex is 2 (or N=2) in this case.
Referring to
FIG. 7A
, the transmission unit has: a splitter
701
for splitting incoming transmitted data into two data signals; a spread code generator
702
for generating a spread code; spreaders
703
and
704
for carrying out a spreading for data signals split by the splitter
702
; an adder
705
for adding signals from the spreaders
703
and
704
; and modulator
706
for modulating signal from the adder
705
to output a transmitting signal.
Referring also to
FIG. 7B
, the reception unit has a de-spread code generator
711
for generating a spread code used for a de-spreading; a correlator
712
for carrying out a correlated calculation of an incoming received signal and the spread code; an equalizer
713
for equalizing an output signal from the correlator
712
; and a coupler
714
for reproducing receiving data from an output signal of the equalizer
713
.
With the constitution described above, the transmitted data is inputted to the splitter
701
that splits the data into two data signals. As a result, a half symbol rate of the transmitted data is inputted to each of the spreaders
703
and
704
.
In addition, the spread code generator
702
generates a code used for the spreading in which such code is of the 11-bit Barker code, for example. The code supplied to the spreaders
703
and
704
also have a phase displacement corresponding to a displacement between two chips or two integrated circuits.
The spreaders
703
and
704
perform the spreading for the data signals split by the splitter
701
with use of the spread code supplied from the spread code generator
702
. The adder
705
adds both the spread spectrum signals generated in the spreaders
703
and
704
to output a multiplexed signal.
The modulator
706
converts the multiplexed signal from the adder
705
into a radio wave to be able to transmit a transmitting signal as wireless.
In the case of reception unit as shown in
FIG. 7B
, the de-spreading code generator
711
generates a spread code used for a de-spreading and supplies it to the correlator
712
.
The correlator
712
carries out a correlated calculation of an incoming received signal and the spread code from the de-spread code generator
711
to perform the de-spreading. A code-multiplexed signal is split into two signals that correspond to the two chips.
In the case of practical data transmission, a multi-path distortion is contained in the received signal on the transmission. Assuming that one of two codes to be multiplexed has a waveform caused by a multi-path distortion as shown in
FIG. 8A
(one pulse is expanded) and the other code to be multiplexed also has a waveform caused by the multi-path distortion as shown in
FIG. 8B
, for example, the waveforms of those codes being multiplexed interfere in each other, therefore, the waveform becomes a state as shown in FIG.
8
C. Thus, the two codes may not be split under this state without arising error. To this end, the equalizer
713
removes such multi-path distortion and outputs a waveform as shown in FIG.
8
D.
The equalizer
713
may be used a decision feedback equalizer shown in FIG.
9
. In the case where a signal shown in
FIG. 8A
is supplied to the equalizer shown in
FIG. 9
, a decider
901
receives a first data “1.0” through an adder
903
to output data “+1” which is supplied to a delay element
902
. Subsequently, data “0.7” is inputted to the adder
903
, but the data “0.7” is inputted to the adder
903
from a multiplier
904
received data “+1” from the delay element
902
, therefore, the output of adder
903
becomes “0”. Because of this, the decider
901
outputs “0” to the delay element
902
. At the subsequent timing, data “0.3” is inputted to the adder
903
. At this time, the output of adder
903
becomes “0” since data “−0.3” is inputted to the adder
903
from a multiplier
906
which receives data “+1” from a delay element
905
. That is, the output of multiplier
904
is “0” since the output of delay element
902
is “0”. As a result, the decider
901
outputs “0”. As described above, the equalizer
713
outputs a signal from which a multi-path distortion is removed. In the case where the multiplexed signal shown in
FIG. 8C
is inputted to the equalizer
713
, the multi-path distortion is also removed, obtaining the output signal shown in FIG.
8
D. It is noted that the coefficient of multiplication for the multipliers
904
and
906
may be determined by transmitting a preamble signal having predetermined information prior to the data transmission.
Accordingly, the signal being removed the multi-path distortion is supplied to the coupler
714
which converts the received signal into a signal form similar to the transmitted data to thereby output received data.
Japanese patent laid-open gazette 9-102758 discloses such code-multiplexing communication apparatus similar to that described above.
For the purpose of manufacturing more reliable apparatus, there would be some significant points, as follows. The code-multiplexing communication apparatus should be considered an autocorrelated distortion, that is, in the case of increasing the multi-path distortion, removal of the distortion may not be sufficiently carried out by the equalizer due to the affection of autocorrelated distortion.
For example, in the case of performing the correlated calculation with use of the 11-bit Barker code, an autocorrelated distortion represents a waveform as shown in FIG.
10
A. That is, when coinciding the phase of waveforms, a value becomes “+1”, however, when displacing these phases, the value does not sufficiently become “0”, causing a distortion alternately indicated values “0” and “−1/11” as distortion value. Assuming that a multi-path distortion is present in the transmission path as shown in
FIG. 10B
, not only an amplitude where the phase is matched changes, but also a distortion where the phase is displaced changes increasingly, with reference to the output of correlator
712
shown in FIG.
10
C.
Under such condition of the large multi-path distortion, as the code multiplex is performed, the self-correlated distortion is accumulated, causing deterioration of the signal deciding performance.
It is possible to remove the autocorrelated distortion with use of the equalizer, however, in order of removing the distortion expanded to 21 chips, the constitution of equalizer becomes enormous size so that the tap coefficient of equalizer is required to make longer.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a code-multiplexing communication apparatus capable of removing an autocorrelated distortion with use of a simple circuit structure, preventing transmitting signal from reducing a signal deciding performance, increasing the number of code multiplex and enhancing transmission efficiency.
According to a first aspect of the present invention, there is provided a code-multiplexing communication apparatus including: a splitting unit for splitting incoming serial transmitted data into N number of signal sequences; N number of spread units for performing out a spreading for each of the N number of signal sequences with use of a spread code; an adding unit adding the N number of signal sequences with the spreading processed by the N number of spread units to output code-multiplexed signal; and a modulating unit for modulating the code-multiplexed signal, in whic
NEC Corporation
Nguyen Chau
Trinh D.
Whitman, Curtis & Christofferson P.C.
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