ICACT20220102 Slide.20
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We summarize this research as follows.
First, We proposed a new PPM-OCDMA system that prevents the degradation of
the emission time per symbol and suppresses the interference caused by reflected light.
Second, we proposed a new generation method of optical ZCZ sequences suitable for the proposed system.
Thank you very much.
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ICACT20220102 Slide.19
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This slide shows the correlation value of the optical ZCZ sequence with
ZCZ size Z equals 2 at 4 positions and sequence length N equals 64.
The ZCZ with Z equals 2 appears at shift 0, 16, 32 and 48.
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ICACT20220102 Slide.18
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This slide shows the correlation value of the optical ZCZ sequence with
ZCZ size Z equals 1 at 4 positions and sequence length N equals 32.
The ZCZ with Z equals 1 appears at shift 0, 8, 16 and 24.
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ICACT20220102 Slide.17
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This slide shows the correlation value of the optical ZCZ sequence with
ZCZ size Z equals 1 at 2 positions and sequence length N equals 16.
The ZCZ with Z equals 1 appears at shift 0 and 8.
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ICACT20220102 Slide.16
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For example, this slide shows the correlation value of the optical ZCZ sequence with
ZCZ size Z equals 1 and sequence length N equals 8.
The left-side figure shows autocorrelation, the right-side figure shows cross-correlation values.
The ZCZ with Z equals 1 appears at shift 0.
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ICACT20220102 Slide.15
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This slide shows construction of optical ZCZ sequence set with Z equals two to the power of z at two to the power of g positions.
The bi-phase sequences with Z equals 2 at two to the power of g positions are generated by
interleaving these sequences with Z equals 1 at two to the power of g positions.
Similarly, sequences with Z equals 4 at two to the power of g positions are generated from
the sequences Z equals 2 at two to the power of g positions.
Therefore, sequences with Z equals two to the power of z at two to the power of g positions by
interleaving sequence with Z equals 1 at two to the power of g, z times repeatedly.
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ICACT20220102 Slide.14
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Finally, I explain about the optical ZCZ sequence set with ZCZ size Z equals two to the power of z at two to the power of g positions.
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ICACT20220102 Slide.13
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This slide shows construction of optical ZCZ sequence set with Z equals 1 at two to the power of g positions.
The bi-phase sequences with Z equals 1 at 2 positions are generated by interleaving these sequence with Z equals 1 at shift 0.
Similarly, sequences with Z equals 1 at 4 positions are generated from the sequences Z equals 1 at 2 positions.
Therefore, sequences with Z equals 1 at two to the power of g positions by
interleaving sequence with Z equals 1 at shift 0, g times repeatedly
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ICACT20220102 Slide.12
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Second, I explain about the optical ZCZ sequence set with ZCZ size Z equals 1 at two to the power of g positions.
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ICACT20220102 Slide.11
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This slide shows construction of optical ZCZ sequence set with Z equals 1 at shift 0.
A bi‐phase sequence of length N is given by this equation, where h sub N over two is
Sylvester‐type Hadamard sequence of length N over 2.
Similarly, a binary sequence of length N is given by this equation.
A set of pairs of bi‐phase sequences and binary sequences is an optical ZCZ sequence set
with Z equals 1, and Number of sequences M equals N over 2 minus 2.
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ICACT20220102 Slide.10
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First, I explain about the optical ZCZ sequence set with ZCZ size Z equals 1 at sfhit 0.
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ICACT20220102 Slide.09
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I will explain how to construct the optical ZCZ sequence set for the proposed PPM system.
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ICACT20220102 Slide.08
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This slide shows the optical ZCZ sequence set suitable for the proposed PPM system.
This figure shows its autocorrelation and cross‐correlation function.
In the side loves, ZCZs are evenly spaced at G positions.
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ICACT20220102 Slide.07
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This slide shows the optical ZCZ sequence set and its periodic correlation functions.
An optical ZCZ sequence set is a set of pairs of bi‐phase sequences and binary sequences.
The element of bi‐phase sequences is either 1 or ‐1.
The element of binary sequences is either 1 or 0.
A periodic correlation function between a bi‐phase sequence and a binary sequence is given by this equation.
Then, this sequence set is called an optical ZCZ sequence set.
This figure shows its autocorrelation and cross‐correlation function.
Shift 0 is a peak w of the autocorrelation function.
On the other hand, the cross‐correlation function is 0 at the shift 0.
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ICACT20220102 Slide.06
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This slide shows sequences suitable for the proposed PPM system.
The expected sequence should have two features.
First, it is expected that ZCZs exist around pulse positions for tolerance to ISI.
Second, it is expected that ZCZs are evenly spaced because the pulse position should exist evenly as well.
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ICACT20220102 Slide.05
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This slide shows Proposed PPM system.
The difference between the conventional and proposed systems is the way to change the pulse position.
In the conventional system, a spreading sequence with the same length as the slot length is used,
and is assigned to a pulse position according to bit data.
On the other hand, in the proposed system, a spreading sequence with the same length as
the symbol length is used, and the pulse position is changed by cyclic shifting
This means that the symbol does not have slots which are unassigned to a spreading sequence.
In the proposed PPM system, the unlit state becomes shorter and the illumination degradation is improved.
Moreover, it is expected that the proposed system improves the bit-error rate (BER) performance by
increasing sequence length.
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ICACT20220102 Slide.04
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This slide shows EWO and conventional PPM system.
The EWO modulation and 2-PPM can transmit only one bit per symbol.
The 4-PPM can transmit two bits per symbol.
Increasing the number of slots in the PPM-OCDMA means speed-up the communication speed.
On the other hand, the LED emission time per symbol becomes shorter,
which causes a decrease in the original illumination brightness of the optical product.
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ICACT20220102 Slide.03
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This slide shows inter-symbol interference (ISI) caused by the indoor environment.
This problem occurs when the receiver is located near the wall in a room. The reflected light from the wall causes delay distortion.
The delay distortion causes ISI, which degrades the bit error rate performance.
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ICACT20220102 Slide.02
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This slide shows introduction of this presentation.
We focused on two problems of OCDMA.
The first problem is the interference by the reflected light from the wall.
This problem occurs when the receiver is located near the wall in a room.
The reflected light from the wall causes delay distortion.
The delay distortion causes inter-symbol interference (ISI), which degrades
the bit error rate performance.
The second problem is the decrease in illumination due to the modulation method.
The major modulation methods of the OCDMA system are equal weight orthogonal (EWO)
modulation and pulse position modulation (PPM).
The EWO modulation can transmit only one bit per symbol, which becomes a problem
in terms of the speed of communication.
On the other hand, the PPM can improve the bit rate by dividing the symbol into multiple slots.
However, increasing the number of slots in the PPM-OCDMA means that
the LED emission time per symbol becomes shorter, which causes a decrease in the original
illumination brightness of the optical product.
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ICACT20220102 Slide.01
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Hello. My name is Yasuaki Ohira, I¡®m from Yamaguchi University in Japan.
I'd like to talk about Construction of Optical ZCZ Sequence Set with the
Zero-Correlation Zone two to the power of z Suitable for PPM-OCDMA System.
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