Browsing by Author "Turan, B."

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Broadcasting brake lights with MIMO-OFDM based vehicular VLC
(IEEE, 2016) Turan, B.; Narmanlıoğlu, Ömer; Coleri Ergen, S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
Inter-vehicular connectivity to enhance road safety and enable highly autonomous driving is increasingly becoming popular. Despite the prevalent works on radio-frequency (RF) based vehicular communication schemes, visible light communication (VLC) is considered to be a promising candidate for vehicular communications due to its low complexity and RF interference-free nature. This paper investigates applicability of VLC to enhance road safety based on real world measurements. Deployment of multiple light emitting diodes (LEDs) enables multiple-input multiple-output (MIMO) transmission in the context of vehicular VLC. We consider direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) based MIMO transmission scheme and evaluate the performances of different MIMO modes including repetition code (RC) and spatial multiplexing (SM), different modulation orders and different transmitter-receiver selection. The results reveal that selection of the closest transmitters to the receivers, provide better performance due to high signal-to-noise-ratio (SNR) requirements for RC mode. However, usage of all possible transmitters does not always yield better performance due to power division at the transmitter side. Moreover, SM suffers from channel correlation whereas the performance of RC shows more degradation on higher-order modulations that are required to yield the same throughput with SM.
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Cooperative MIMO-OFDM based inter-vehicular visible light communication using brake lights
(Elsevier, 2018-05) Narmanlıoğlu, Ömer; Turan, B.; Ergen, S. C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
Inter-vehicular connectivity to enhance road safety and support highly autonomous driving is increasingly becoming popular. Despite the prevalent works on radio-frequency (RF) based vehicular communication schemes, visible light communication (VLC) is considered to be a promising candidate for vehicular communications due to its low complexity and RF interference-free nature. Deployment of multiple light emitting diodes (LEDs) enables multiple-input multiple-output (MIMO) transmission in the context of vehicular VLC. This paper investigates applicability of both point-to-point (direct) vehicular VLC and decode-and-forward relaying based cooperative vehicular VLC including relay terminals between source and destination terminals to enhance road safety based on real world measurements. We consider direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) based MIMO transmission scheme and evaluate the performances of different MIMO modes including repetition code (RC) and spatial multiplexing (SM), different modulation orders with different transmitter–receiver selection mechanisms to support line-of-sight (LoS) and beyond LoS multi-hop vehicular VLC. The results reveal that the selection of the closest transmitters to the receivers provides better performance due to high signal-to-noise-ratio requirements for RC mode whereas SM suffers from channel correlation. Usage of all possible transmitters does not always yield better performance due to the power division at the transmitter side. On the other hand, the performance of RC shows more degradation on higher-order modulations that are required to yield the same throughput with SM. Therefore, considering the higher order modulation requirement for RC based VLC, SM is concluded to be a favorable MIMO scheme for cooperative vehicular VLC. We further demonstrate the benefits of multi-hop transmission over direct transmission with respect to different number of relay vehicles as a consequence of varying inter-vehicular distances between source and destination vehicles.
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IEEE 802.15.13-compliant visible light communications in vehicular networks
(Taylor & Francis, 2018-01) Turan, B.; Narmanlıoğlu, Ömer; Uysal, Murat; Electrical & Electronics Engineering; Hu, F.; UYSAL, Murat; Narmanlıoğlu, Ömer
Current research activities and standardization efforts in intelligent transportation systems (ITS) have mainly focused around the deployment of radio frequency (RF)-based communication techniques for vehicular networking. Considering the wide deployment of light emitting diodes (LEDs) both in automotive lighting and roadside infrastructure, visible light communication (VLC) has emerged as a potential complementary technology for both vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications. VLC is based on the principle of modulating LEDs at very high frequencies that are not noticeable by the human eye. Recognizing the economic potential of VLC technology, the IEEE 802.15.13 Task Group has been preparing a new standard on VLC. In this chapter, we explore the potential usage of the IEEE 802.15.13 standard for vehicular networks and evaluate its performance for V2V communications through Monte Carlo simulations under the consideration of channel model obtained by experimental results.
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Measurement based non-line-of-sight vehicular visible light communication channel characterization
(IEEE, 2022-09) Turan, B.; Narmanlıoğlu, Ömer; Koc, O. N.; Kar, E.; Coleri, S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
Vehicular visible light communication (V-VLC) aims to provide secure complementary vehicle-to-everything-communications (V2X) to increase road safety and traffic efficiency. V-VLC provides directional transmissions, mainly enabling line-of-sight (LoS) communications. However, reflections due to nearby objects enable non-line-of-sight (NLoS) transmissions, extending the usage scenarios beyond LoS. In this paper, we propose wide-band measurement based NLoS channel characterization, and evaluate the performance of direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) V-VLC scheme for NLoS channel. We propose a distance based NLoS V-VLC channel path loss model considering reflection surface characteristics and NLoS V-VLC channel impulse response (CIR) incorporating the temporal broadening effect due to vehicle reflections through weighted double gamma function. The proposed path loss model yields higher accuracy up to 14 dB when compared to single order reflection model whereas CIR model estimates the full width at half maximum up to 2 ns accuracy. We further demonstrate that the target bit-error-rate of $10^{-3}$ can be achieved up to 7.86 m, 9.79 m, and 17.62 m distances for black, orange and white vehicle reflection induced measured NLoS V-VLC channels for DCO-OFDM transmissions.
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Neural network based digital pre-distorter design for DCO-OFDM visible light communications
(IEEE, 2022) Narmanlıoğlu, Ömer; Turan, B.; Coleri, S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
Direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) is an appealing modulation scheme for reliable, high-speed optical transmissions and foreseen to be used in the upcoming IEEE 802.11bb visible light communication (VLC) standard. However, non-linear characteristics of light emitting diodes (LEDs) as VLC transmitters degrade the bit error rate (BER) performance of DCO-OFDM due to its high peak-to-average-power ratio. In this paper, we propose neural network based digital pre-distorter (DPD) to mitigate non-linear LED response for DCO-OFDM transmission. The proposed scheme extends the reliable transmission range by 1.75 m and 1.8 cm for non-compensated LED response and Memory Polynomial based DPD, respectively.
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On the performance of MIMO OFDM-based intra-vehicular VLC networks
(IEEE, 2016) Turan, B.; Narmanlıoğlu, Ömer; Coleri Ergen, S.; Uysal, Murat; Electrical & Electronics Engineering; NARMANLIOĞLU, Ömer; UYSAL, Murat; Narmanlıoğlu, Ömer
Vehicular hotspots for on-board Internet access using Long Term Evolution (LTE) as the backhaul network has recently gained popularity. Currently, Wi-Fi is the most common technology to provide in-vehicle access, where data has been relayed through on board LTE receiver. Despite its wide acceptance, coexistence and contention based data rate limitations with Wi-Fi necessitates alternatives for in-vehicle data access schemes. This paper investigates the performance of hybrid LTE and visible light communication (VLC) networks using LTE as the backhaul and VLC as the on-board access network.Under the consideration of vehicle interior unique channel characteristics and light emitting diode (LED) deployment flexibility, best transmitter configuration using repetition coding (RC) and spatial multiplexing (SM) multiple input multiple output (MIMO)modes is determined. Proposed configurations based on direct current biased optical orthogonal frequency-division multiplexing(DCO-OFDM) are compared with respect to their bit-error-rate (BER) performances. Furthermore, the performance of intravehicular VLC networks for single and multi-user scenarios is investigated.
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Physical layer implementation of standard compliant vehicular VLC
(IEEE, 2017) Turan, B.; Narmanlioglu, Omer; Coleri Ergen, S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlioglu, Omer
Visible light communication (VLC) has recently gained popularity as a complementary technology to radio frequency (RF) based alternatives for vehicular communications as a low-cost, secure and RF interference free technology. In this paper, we propose IEEE 802.15.7 standard-compliant physical layer (PHY) implementation and experimental evaluation, using commercial off-the-shelf (COTS) automotive light emitting diode (LED) fog light for the purpose of low-latency safety message dissemination. We first show that the standard is applicable to line of sight (LoS) vehicle-to-vehicle (V2V) VLC. We then demonstrate that the proper selection of modulation coding schemes (MCS) plays an important role in order to minimize bit-error- rate (BER) for the reliable transmission with varying inter-vehicle distances. We also addressed the angular limitations of COTS automotive LED light for viable vehicular VLC.
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Pilot-aided channel estimation on SC-PAM based visible light communications
(IEEE, 2018-07-02) Narmanlıoğlu, Ömer; Turan, B.; Kizilirmak, R. Ç.; Ergen, S. C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
Estimation of the time-varying optical wireless channel response is crucial in order to decode received signals coherently. In this work, we investigate symbol-error-rate and mean absolute error performance of different interpolation techniques including linear, nearest, spline, and piece-wise cubic Hermite interpolating polynomial (pchip), which are used in pilot-aided channel estimation process for visible light communication. The performance of interpolators is evaluated in realistic time-varying channel model, generated on Zemax software and compared with each other under the consideration of different modulation orders, different pilot symbol periods, and different user equipment (UE) speeds through Monte Carlo simulations. The results reveal that spline and pchip techniques are more robust to low pilot symbol transmission rate and fast time-varying channel conditions as a consequence of high UE speeds. However, low complex linear interpolation technique can be chosen for highly rated pilot signal transmission cases or when optical channel varies slowly over the time.
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Poster: on-board camera video transmission over vehicular VLC
(IEEE, 2017) Narmanlioglu, Omer; Turan, B.; Kebapci, Burak; Coleri Ergen, S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlioglu, Omer; Kebapci, Burak
Vehicular connectivity is envisaged to extend vehicle on-board camera videos to the nearby vehicles in order to increase drivers' road awareness. This paper demonstrates the possibilities of video transmission captured by vehicle on-board forward-looking camera via visible light communications (VLC) using taillights to provide see-beyond the front vehicle assistance. Line of sight (LoS) inter-vehicular video transmission using direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) based VLC with the data rate of 6.42 Mbps and lower latency than 32 msec is validated through experiments.
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SC-FDE based MIMO uplink transmission over infrared communication channels
(IEEE, 2018-07-02) Narmanlıoğlu, Ömer; Turan, B.; Kızılırmak, R. Ç.; Ergen, S. C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
In this paper, we propose a multiple-input multiple-output (MIMO) uplink transmission scheme for optical wireless communication applications. The transmission is based on optical single-carrier frequency domain equalization (SC-FDE) due to its low complexity where the signal is transmitted over infrared communication channels. Based on non-sequential ray tracing, we first obtained realistic infrared MIMO channel impulse responses including low-pass filter effect of infrared light-emitting-diodes. We then investigate the performance of bit-error-rate (BER) and peak to average power ratio (PAPR) with respect to different modulation orders using spatial multiplexing.