Name: Roziane Schneider Guimarães
Type: MSc dissertation
Publication date: 20/12/2017
Advisor:

Namesort descending Role
Jair Adriano Lima Silva Advisor *
Marcelo Eduardo Vieira Segatto Co-advisor *

Examining board:

Namesort descending Role
Helder Roberto de Oliveira Rocha Internal Examiner *
Jair Adriano Lima Silva Advisor *
Marcelo Eduardo Vieira Segatto Co advisor *
Reginaldo Barbosa Nunes External Examiner *

Summary: This Master’s thesis aims to study the design and to evaluate the performance of a visible
light communication (VLC) system using discrete multitone (DMT) that transmit multicar-
rier signals with and without constant-envelope. Based on electrical phase modulation, the
CE-OFDM (constant-envelope orthogonal frequency division multiplexing), that reduces
the peak-to-average power ratio of conventional DMT signals to only 3 dB, is for the first
time proposed to reduce the harmful effects to the health of a Human being exposed in an
environment with a VLC communication system.
It is known that intense variations of amplitude over a time interval of more than 5 ms,
which corresponds to frequencies lower than 200 Hz, are detrimental to the health of a
Human being. Normally called flicker, this feature is inherent in systems employing DMT
modulation due to their high PAPR values (typically above 11 dB). Thus, techniques such
as CE-OFDM that reduce PAPR are extremelly important, specially those that doesnt
introduce substantial modifications in the transceiver structure.
The performance evaluation was performed using numerical simulation of a DMT and a
CE-OFDM system, designed and implemented from impulsive responses obtained from
VLC channel models for communication in a single-input single-output (SISO) scenario
using a central light-emitting diode (LED) as transmitter and a photodiode as receiver, and
another in a multiple-input and single-output (MISO) configuration with four transmitter
LEDs and a photodetector.
In the simulation performed with the DMT modulation, it was observed that for 4, 16
and 32-QAM subcarrier mapping, in both scenarios, the performance were satisfactory,
with bit rates equals to 200, 400 and 500 Mbps, respectively. However, in both, for a
higher-level mapping like 64-QAM (600 Mbps), the performance was compromised by
the appearance of a plateau in curves of bit-error-rate around 10 −3 , for a total system
bandwidth of 200 MHz.
However, for the CE-OFDM system, it was observed that an excessive increase in the phase
modulation index (most important parameter in the system perfromance) degrades the
performance due to the non-linear nature of this transformation technique. The optimum
modulation index for the simulated SISO and MISO systems was 0.5 and 0.2 respectively.
The proposed CE-OFDM outperforms the convetional DMT only in the MISO scenario, for
bit rates around 55.1, 110 and 165 Mbps, with 4-QAM, 16-QAM and 64-QAM subcarrier
mapping respectively, considering a total bandwidth of 200 MHz.
Keywords:Visible light communication, DMT and OFDM modulation/multiplexing tech-
niques, constant-envelope OFDM, PAPR and flicker.

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