Browsing by Author "Haas, Harald"

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Citation Count: 2
Flexible LED Index Modulation for MIMO Optical Wireless Communications
(Institute of Electrical and Electronics Engineers Inc., 2020) Yeşilkaya, Anıl; Purwita, Ardimas Andi; Panayırcı, Erdal; Poor, H. Vincent; Haas, Harald
The limited bandwidth of optical wireless communication (OWC) front-end devices motivates the use of multipleinput- multiple-output (MIMO) techniques to enhance data rates. It is known that very high multiplexing gains can be achieved by spatial multiplexing (SMX) at the cost of prohibitive detection complexity. Alternatively, in spatial modulation (SM), a single light emitting diode (LED) is activated per time instance where information is carried by both the signal and the LED index. Since only one LED is active, both the transmitter (TX) and receiver (RX) complexity reduce significantly while retaining the information transmission in the spatial domain. However, this simplified TX utilization approach leads SM to suffer from significant spectral efficiency losses compared to SMX. In this paper, we propose a technique that benefits from the advantages of both systems. Accordingly, the proposed flexible LED index modulation (FLIM) technique harnesses the inactive state of the LEDs as a transmit symbol. Therefore, the number of active LEDs changes in each transmission, unlike conventional techniques. Moreover, the system complexity is reduced by employing a linear minimum mean squared error (MMSE) equalizer and an angle perturbed receiver. Numerical results show that FLIM outperforms the reference systems by at least 6 dB in the low and medium/high spectral efficiency regions.
Citation Count: 2
Generalized LED Index Modulation Optical OFDM for MIMO Visible Light Communications Systems
(IEEE, 2016) Basar, Ertuğrul; Panayırcı, Erdal; Uysal, Murat; Haas, Harald
In this paper we propose a generalized light emitting diode (LED) index modulation scheme for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) visible light communications (VLC) systems. The proposed scheme generalizes the LED index modulation concept by using the spatial multiplexing principle to transmit complex OFDM signals through VLC channels by separating these signals into their real-imaginary and positive-negative parts. The maximum a posteriori (MAP) estimator of the proposed scheme which relies on quadratic programing (QP) problem is presented for flat VLC channels. It is shown via computer simulations that the proposed scheme achieves considerably better error performance than the existing VLC-MIMO-OFDM systems due to its power efficiency and improved transceiver structure.
Citation Count: 0
Görünür Isıkla Haberlesmede Fiziksel Katman Güvenligi
(2021) Panayırcı, Erdal; Kurt, Güneş Zeynep Karabulut; Koca, Mutlu; Haas, Harald
Optik Kablosuz Haberlesme ve bunun olası bir uygulaması olan Görünür Isıkla Haberlesme (Visible Light Communications (VLC)), sahip oldugu çok yüksek bant genisligi, bilgi iletim kapasitesi, elektromanyetik girisimlere karsı yüksek bagısıklıgı, uzaysal ortamlarda yüksek oranda güvenli kapsama özelligi ve çalısma frekans spektrumunun belli regülasyonlarla düzenlenmemis olması nedeniyle, genis bir uygulama alanı içinde, çok önemli teknik ve operasyonel üstünlükler saglamakta ve radyo tabanlı kablosuz haberlesme sistemlerine bir seçenek olarak veya onların tamamlayıcı niteliginde karsımıza çıkmaktadır. Son bir kaç yıl içinde, varolan sifreleme tekniklerini güçlendirmek için ve onlara tamamlayıcı bir ek olarak, fiziksel katman güvenligi (physical layer security) diye adlandırılan umut verici yeni bir arastırma ve ilgi alanı ortaya çıkmıstır. Fiziksel katman güvenligi, haberlesme ortamındaki yetkili olmayan kisilerden bilginin saklanması amacıyla, her türlü üst katman sifrelemeden bagımsız olarak, tamamen iletisim kanal ortamının özelliklerini kullanarak, gelistirilen teknik ve yöntemlerdir. Projede, genisbant aglarda VLC fiziksel katman düzeyinde güvenligi saglamak amacıyla, geleneksel yaklasımların ötesinde hızlı ve güvenilir çözümler için, etkin kuramsal çalısmalardan baslayarak laboratuvar düzeyine kadar genis bir spektrumda özgün ve yenilikçi algoritmaların tasarımı önerilmektedir. Bu bakımdan, proje, 1003-BIT-GNBT 2018- 1 Genisbant Haberlesme Agları için Veri Isleme Teknolojileri Çagrı Metnindeki (a) ve (b) amaçları ile büyük bir uyum içinde, arastırma bileseni yüksek, yenilikçi ve özgün bir proje niteligindedir. Projede, geleneksel sistemlere göre getirilen yenilikler ve saglanan üstünlükleri su sekilde sıralanabilir: 1. Projede, fiziksel katman güvenligine sahip VLC sisteminin gerçeklenmesinde, Indis modülasyonu ve bunun bir takım varyasyonları olan uzamsal modülasyon, uzay kaydırmalı anahtarlama ve OFDM-indis modülasyonu gibi yeni modülasyon teknikleri ve çok-girisli-çok çıkıslı LED (light emitting diode) yapıları ile, dikgen olmayan çoklu erisimin birlikte çalısan MIMO-NOMA teknigi önerilmektedir. Elde edilecek yeni ve özgün algoritmalar geleneksel sistemlere göre hesaplama karmasıklıgı düsük, güç randımanı yüksek ve çok kullanıcılı senaryolar için de çalısabilme yetenegine sahip olacaktır. Özellikle, sadece bu modülasyon tekniklerine özgü, yapay karıstırma (artifical jammig) sinyal üretme özelligi, bu tekniklerin fiziksel güvenligin saglanmasında geleneksel yaklasımlara kıyasla en önemli üstünlügünü olusturmaktadır. Ayrıca, gelistirilecek algoritmalara iliskin ?erisilebilecek maksimum gizlilik kapasitesi? ve ?gizlilik oranları?nın analitik yollardan belirlenmesi için izlenecek kuramsal yaklasımlar, sistem mimarilerinin farklı olmasından dolayı, geleneksel sistemlerde izlenen yollardan çok daha farklı olacaktır. 2. LED?lerin ve ısıgın neden oldugu kısıtlar sonucu, radyo frekanslı kabosuz haberlesmedeki geleneksel kanal kestirim tekniklerinin uygulanamaması nedeniyle, Masif MIMO yapıdaki görünür ısık kanalların optimal ve hızlı kestiriminde yeni kanal kestirim algoritmalarının tasarımı önerilmektedir. Ayrıca, kestirim hataları ve kanal bilgilerin vericiye iletilmesindeki gecikmelerin, sistemin bit hata basarımına etkilerininin kuramsal ve bilgisyar benzetimleriyle incelenmesi hedeflenmektedir. 3. Projede son olarak, fizisel katman güvenligine sahip VLC sistemlerin laboratuvar ortamında donanımsal olarak geçeklestirilmesi ve gerçek-zamanda çalısmasının test edilmesi önerilmektedir. Literatürde bir karıstırma sinyali üreterek gizliligi saglayan geleneksel sistemlerle, algoritmanın gerek hesaplama karmasıklıgı ve hızı, gerekse hata basarımı ve erisilebilecek enbüyük gizlilik oranları farklı sinyal-gürültü düzeylerinde karsılastırılarak üstünlügü kanıtlanacaktır.
Citation Count: 0
A Novel Transmit Array Structure for Optical Spatial Modulation
(IEEE, 2019) Çoğalan, Tezcan; Haas, Harald; Panayırcı, Erdal
The performance of multiple input single output (MISO) and multiple input multiple output (MIMO) systems is limited by spatial channel correlation. This limitation becomes particularly severe in light lidelity (LiFi) systems, which use intensity modulation/direct detection (IM/DD) for data transmission, because light emitting diodes (LEDs) can only emit incoherent light. This paper proposes a novel transmitter structure that provides spatially separated channels and enables optical MISO/MIMO spatial modulation (SM) transmission without the need for a power allocation algorithm or a transmit precoding technique. A single LED array, which consists of multiple LEDs with different characteristics, is considered in an indoor environment. Different numbers of transmit LEDs are chosen for SM transmission based on the relation between channel correlation and bit error probability. It is shown that the proposed structure provides reliable SM transmission when the modulation order for M-ary pulse amplitude modulation (PAM) is considered as 2 and 4. Computer simulations also show that higher modulation order, e.g., 8-PAM, can be supported but at a slightly degraded bit error ratio (BER) performance.
Citation Count: 92
Optical MIMO-OFDM With Generalized LED Index Modulation
(IEEE-INST Electrical Electronics Engineers Inc, 2017) Yeşilkaya, Anıl; Basar, Ertugrul; Miramirkhani, Farshad; Panayırcı, Erdal; Uysal, Murat; Haas, Harald
Visible light communications (VLC) is a promising and uncharted new technology for the next generation of wireless communication systems. This paper proposes a novel generalized light emitting diode (LED) index modulation method for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)-based VLC systems. The proposed scheme avoids the typical spectrum efficiency losses incurred by time- and frequency-domain shaping in OFDM signals. This is achieved by exploiting spatial multiplexing along with LED index modulation. Accordingly real and imaginary components of the complex time-domain OFDM signals are separated first then resulting bipolar signals are transmitted over a VLC channel by encoding sign information in LED indexes. As a benchmark we demonstrate the performance analysis of our proposed system for both analytical and physical channel models. Furthermore two novel receiver designs are proposed. Each one is suitable for frequency-flat or selective channel scenarios. It has been shown via extensive computer simulations that the proposed scheme achieves considerably better bit error ratio versus signal-to-noise-ratio performance than the existing VLC-MIMO-OFDM systems that use the same number of transmit and receive units [LEDs and photo diodes (PDs)]. Compared with the single-input single-output (SISO) DC biased optical (DCO)-OFDM system both spectral efficiency and DC bias can be doubled and removed respectively simply by exploiting a MIMO configuration.
Citation Count: 22
Physical Layer Security for Multi-User MIMO Visible Light Communication Systems with Generalized Space Shift Keying
(Institute of Electrical and Electronics Engineers Inc., 2021) Su, Nugman; Panayırcı, Erdal; Koca, Mutlu; Yeşilkaya, Anıl; Poor, Harold Vincent; Haas, Harald
We consider the physical layer security (PLS) of multi-user (MU) multiple-input-multiple-output visible light communication (VLC) systems with an eavesdropper (Eve) and propose a novel spatial constellation design technique based on generalized space shift keying (MU-GSSK-SCD). The received signals of the legitimate users are optimized jointly, such that their bit error ratios (BERs) are minimized and Eve's BER is significantly degraded. The emission power of randomly selected light-emitting diodes is adjusted, by exploiting users' channel state information at the transmitter. Our strategy ensures that legitimate users receive confidential messages fully in an undistorted fashion, while any meaningful leakage to Eve is strongly prohibited, without any artificial noise addition. Every user can decode only its information, hence inter-user security is also guaranteed. The PLS improvements are presented in terms of both BERs and achievable secrecy rates in practical VLC scenarios. For various user configurations, it is shown that MU-GSSK-SCD increases the BER at Eve to the 0.5 level, while providing minimized BERs to the legitimate users. The achievable secrecy rate region is derived for MU-GSSK-SCD and it is shown that full secrecy can be achieved at 0 dB signal-to-noise ratio (SNR) level with a user separation as small as 90 cm.
Citation Count: 18
Physical-layer security in visible light communications
(Institute of Electrical and Electronics Engineers Inc., 2020) Şadi, Yalçın; Erküçük, Serhat; Erküçük, Serhat; Şadi, Yalçın; Panayırcı, Erdal; Haas, Harald; Poor, Harold Vincent
Optical wireless communications (OWC) and its potential to solve physical layer security (PLS) issues are becoming important research areas in 6G communications systems. In this paper, an overview of PLS in visible light communications (VLC), is presented. Then, two new PLS techniques based on generalized space shift keying (GSSK) modulation with spatial constellation design (SCD) and non-orthogonal multiple access (NOMA) cooperative relaying are introduced. In the first technique, the PLS of the system is enhanced by the appropriate selection of a precoding matrix for randomly activated light emitting diodes (LEDs). With the aid of a legitimate user's (Bob's) channel state information (CSI) at the transmitter (CSIT), the bit error ratio (BER) of Bob is minimized while the BER performance of the potential eavesdroppers (Eves) is significantly degraded. In the second technique, superposition coding with uniform signaling is used at the transmitter and relays. The design of secure beamforming vectors at the relay nodes along with NOMA techniques is used to enhance PLS in a VLC system. Insights gained from the improved security levels of the proposed techniques are used to discuss how PLS can be further improved in future generation communication systems by using VLC.
Citation Count: 27
Physical-Layer Security With Optical Generalized Space Shift Keying
(Ieee-Inst Electrıcal Electronıcs Engıneers Inc, 2020) Panayırcı, Erdal; Yeşilkaya, Anıl; Çoğalan, Tezcan; Poor, H. Vincent; Haas, Harald
Spatial modulation (SM) is a promising technique that reduces inter-channel interference while providing high power efficiency and detection simplicity. In order to ensure the secrecy of SM, precoding and friendly jamming are widely adopted in the literature. However, neither of those methods can take advantage of SM. In this paper, a novel spatial constellation design (SCD) technique is proposed to enhance the physical layer security (PLS) of optical generalized space shift keying (GSSK), which can retain some benefits of SM. Due to the lack of small-scale fading, the quasi-static characteristics of the optical channel is used to tailor the received signal at the legitimate user's (Bob's) side. The PLS of the system is guaranteed by the appropriate selection of the power allocation coefficients for randomly activated light emitting diodes (LEDs). With the aid of Bob's channel state information at the transmitter, the bit error ratio (BER) of Bob is minimized while the BER performance of the potential eavesdroppers (Eves) is significantly degraded. Monte-Carlo simulation results show that the proposed SCD-zero forcing precoding (ZFP) forces Eve to experience a BER of around 0.5 by outperforming both the conventional and ZFP based GSSK for all practical signal-to-noise-ratio regimes and Bob-Eve separations.
Citation Count: 7
Power Control-Based Multi-User Li-Fi Using A Compound Eye Transmitter
(IEEE, 2015) Çoğalan, Tezcan; Haas, Harald; Panayırcı, Erdal
In visible light communications (VLC) the transmitted signal is non-negative and real valued and these characteristics constrain the signal space and provide new challenges for waveform design in a multi-user system. In Light Fidelity (Li-Fi) a VLC technology and similar to radio frequency (RF) systems precoder designs can be used to serve multiple users. However a signal shaping algorithm is required to address the non-negativity of the transmitted signal in Li-Fi. In this study a power allocation algorithm is proposed to achieve a multi-user Li-Fi system. A compound eye transmitter consisting of several LEDs pointing in different directions is used. This means that the process of the obtaining the inverse of the channel matrix in precoder design is not required. Results show that when a 30 degrees semi-angle is used at the transmitter and the system has 4 users the proposed transmission model can achieve 10(-5) average bit error rate (BER) performance at 1 dBm average transmission power.
Citation Count: 4
Precoded single-cell multi-user MISO visible light communications
(Institute of Electrical and Electronics Engineers Inc., 2015) Panayırcı, Erdal; Haas, Harald; Panayırcı, Erdal
This study investigates the effects of transmitter and receiver parameters on the performance of a precoded singlecell (SC) multi-user (MU) multi-input-single-output (MISO) visible light communication (VLC) system. A zero-forcing (ZF) precoding technique is used within the constraints of optical transmission power and non-negativity of an intensity modulated (IM) transmitted signal. The simulation results show that the physical features of the light emitting diode (LED) and photodiode (PD) have a significant effect on the bit error rate (BER) and total spectral efficiency (SE) performance of the VLC system. The deployment with 8 users and 45o receiver field-of-view (FOV) achieves both the targeted BER and approximately 50 bits/s/Hz total SE when the transmitter semi-angles are 30o and 60o. © VDE Verlag GMBH Berlin Offenbach Germany.
Citation Count: 2
Spatial Modulation Aided Physical Layer Security for NOMA-VLC Systems
(IEEE-Inst Electrical Electronics Engineers Inc, 2023) Panayırcı, Erdal; Koca, Mutlu; Haas, Harald; Poor, H. Vincent
We consider the physical layer security (PLS) problem in multi-user non-orthogonal multiple access (NOMA) enabled multiple-input multiple-output (MIMO) visible light communication systems intercepted by a passive eavesdropper (Eve). We propose a novel transmit precoding scheme based on receive spatial modulation (RSM) to degrade the signal-to-interference-noise ratio (SINR) of Eve by exploiting only the slow-fading characteristics of the visible light channel of the legitimate users (Bobs). The proposed PLS precoder is reinforced with secret parameter exchange with Bobs and a CSI acquisition model is proposed to reduce the PLS algorithm's computational load substantially at the transmitter. The closed-form expressions for the achievable secrecy rates and their upper and lower bounds are derived. Via Monte Carlo simulations, we confirm that Bobs can successfully decode their information in various user configurations while Eve's received SINR is significantly worsened by the jamming signal induced by the proposed precoder with secret key exchange. It is also shown that Eve's bit error rate (BER) is increased to the 0.5-level for almost any position in the considered indoor environment. Finally, we corroborate the derived secrecy expressions by computer simulations and show that the proposed scheme provides PLS for Bobs.
Citation Count: 2
Spatial Modulation Aided Physical Layer Security for NOMA-VLC Systems
(Ieee-inst Electrical Electronics Engineers inc, 2023) Panayırcı, Erdal; Koca, Mutlu; Haas, Harald; Poor, H. Vincent
We consider the physical layer security (PLS) problem in multi-user non-orthogonal multiple access (NOMA) enabled multiple-input multiple-output (MIMO) visible light communication systems intercepted by a passive eavesdropper (Eve). We propose a novel transmit precoding scheme based on receive spatial modulation (RSM) to degrade the signal-to-interference-noise ratio (SINR) of Eve by exploiting only the slow-fading characteristics of the visible light channel of the legitimate users (Bobs). The proposed PLS precoder is reinforced with secret parameter exchange with Bobs and a CSI acquisition model is proposed to reduce the PLS algorithm's computational load substantially at the transmitter. The closed-form expressions for the achievable secrecy rates and their upper and lower bounds are derived. Via Monte Carlo simulations, we confirm that Bobs can successfully decode their information in various user configurations while Eve's received SINR is significantly worsened by the jamming signal induced by the proposed precoder with secret key exchange. It is also shown that Eve's bit error rate (BER) is increased to the 0.5-level for almost any position in the considered indoor environment. Finally, we corroborate the derived secrecy expressions by computer simulations and show that the proposed scheme provides PLS for Bobs.