Browsing by Author "Ardakani, Maryam Haghighi"

Now showing 1 - 6 of 6

Metadata only
Diversity techniques for ultraviolet communications
(2016-08) Ardakani, Maryam Haghighi; Uysal, Murat; Uysal, Murat; Demiroğlu, Cenk; Kurt, G. K.; Department of Electrical and Electronics Engineering; Ardakani, Maryam Haghighi
Strong molecular and aerosol scattering in ultraviolet (UV) wavelengths enable mechanisms where transmitter can communicate with the receiver in the absence of line of sight (LOS) link. Recent advances in solid state technologies have enabled the production of efficient semiconductor ultraviolet (UV) LED sources and detectors which led to a renewed interest in UV communication. Non-line-of-sight (NLOS) communication is particularly desirable to relax or eliminate pointing, acquisition and tracking requirements‎. ‎This thesis investigates spatial diversity techniques for NLOS UV communication systems‎. ‎Particularly‎, ‎we explore cooperative diversity in the form of relaying and multi-input multi-output (MIMO) communications to extract spatial diversity advantages.‎ ‎In the first chapter‎, ‎we provide an overview of NLOS UV communication discussing its advantages and applications and present a literature survey‎. ‎In the second chapter‎, ‎we present the NLOS UV channel model used in this thesis‎. ‎In third chapter‎, ‎we consider a cooperative UV system with orthogonal cooperation protocol and use DC biased optical orthogonal frequency division multiplexing (DCO-OFDM) as the underlying physical layer‎. ‎Under the assumption that turbulence can be ignored‎, ‎we study both amplify-and-forward (AF) and detect-and-forward (DF) relaying‎. ‎We analyze BER performance of the cooperative OFDM UV system under consideration and optimize the performance through optimal power allocation‎. ‎We also consider a variable-rate cooperative OFDM UV system and investigate bit loading (i.e.‎, ‎use of different modulation orders per subcarrier) in an effort to maximize the throughput.‎ ‎In the fourth chapter‎, ‎we further consider the effects of turbulence and investigate the performance of a multi-hop UV system with DF relaying‎. ‎Based on the asymptotic outage expressions‎, ‎we present a diversity gain analysis and obtain the diversity order as a function of link distance and system parameters‎. ‎In fifth chapter‎, ‎the performance of MIMO UV systems over turbulence channels is studied‎. ‎We derive BER expressions for MIMO UV systems over NLOS log-normal turbulence channels‎. ‎We also investigate the performance of single-input multiple-output (SIMO) and multiple-input single output (MISO) as special cases.‎
Metadata only
Non-line-of-sight ultraviolet communications over atmospheric turbulence channels
(IEEE, 2015) Ardakani, Maryam Haghighi; Heidarpour, Ali Reza; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Ardakani, Maryam Haghighi; Heidarpour, Ali Reza
Ultraviolet (UV) communication enables non-line-of sight (NLOS) outdoor wireless connectivity and is particularly desirable to relax or eliminate pointing and tracking requirements of infrared links. In the current literature, atmospheric turbulence effects are typically ignored under the assumption of short link distances and clear weather conditions. In this paper, we address the statistical modeling of turbulence experienced in NLOS UV links. We assume that the NLOS link consists of two line-of-sight (LOS) paths each of which experiences log-normal distributed fading. We obtain a closed-form expression for the probability density function of turbulence induced fading. Based on the derived expression, we investigate bit error rate performance for different system configurations. Numerical simulations are further presented to confirm the accuracy of our derivation.
Metadata only
Performance analysis of MIMO NLOS UV communications over atmospheric turbulence channels
(IEEE, 2016) Ardakani, Maryam Haghighi; Heidarpour, Ali Reza; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Ardakani, Maryam Haghighi; Heidarpour, Ali Reza
Strong molecular and aerosol scattering in ultraviolet (UV) wavelengths enable the non-line-of-sight (NLOS) outdoor wireless connectivity which is attractive in many applications due to covertness and security. In the current literature, atmospheric turbulence effects are typically ignored under the assumption of short link distances and clear weather conditions. In this paper, we investigate the performance of multiple-input multiple-output (MIMO) UV systems over turbulence channels. Specifically, we derive bit error rate (BER) expressions over an NLOS UV channel which is modeled as an overlap of two log-normal LOS links. Our results demonstrate that fading variance is scaled by the number of transmitters and receivers and MIMO deployment with proper configurations results in significant BER improvements. Simulation results are further provided to confirm the analytical findings.
Metadata only
Performance analysis of MIMO NLOS UV communications over atmospheric turbulence channels
(IEEE, 2016) Ardakani, Maryam Haghighi; Heidarpour, Ali Reza; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Ardakani, Maryam Haghighi; Heidarpour, Ali Reza
Strong molecular and aerosol scattering in ultraviolet (UV) wavelengths enable the non-line-of-sight (NLOS) outdoor wireless connectivity which is attractive in many applications due to covertness and security. In the current literature, atmospheric turbulence effects are typically ignored under the assumption of short link distances and clear weather conditions. In this paper, we investigate the performance of multiple-input multiple-output (MIMO) UV systems over turbulence channels. Specifically, we derive bit error rate (BER) expressions over an NLOS UV channel which is modeled as an overlap of two log-normal LOS links. Our results demonstrate that fading variance is scaled by the number of transmitters and receivers and MIMO deployment with proper configurations results in significant BER improvements. Simulation results are further provided to confirm the analytical findings.
Metadata only
Relay-assisted OFDM for NLOS ultraviolet communication
(2015) Ardakani, Maryam Haghighi; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Ardakani, Maryam Haghighi
Ultraviolet (UV) communication enables non-line-of-sight (NLOS) outdoor wireless connectivity and is particularly desirable to relax or eliminate pointing and tracking requirements of infrared links. The main two degrading factors in UV links are high path loss and intersymbol interference resulting from the frequency selectivity nature of the channel. In this paper, we propose the powerful combination of relay-assisted (cooperative) transmission and multicarrier architecture based on orthogonal frequency division multiplexing (OFDM) for a superior performance over UV channels. Specifically, we consider a cooperative diversity system with orthogonal cooperation protocol and use DC-biased optical OFDM as the underlying physical layer. We investigate the error rate performance of the proposed relay-assisted OFDM UV system and demonstrate significant performance gains over point-to-point OFDM UV systems.
Metadata only
Relay-assisted OFDM for ultraviolet communications: performance analysis and optimization
(IEEE, 2017) Ardakani, Maryam Haghighi; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Ardakani, Maryam Haghighi
Ultraviolet (UV) communication enables non-line-of-sight (NLOS) outdoor wireless connectivity and is particularly desirable to relax or eliminate pointing and tracking requirements of infrared links. In comparison to infrared counterparts, UV links are subject to relatively higher path loss as well as intersymbol interference resulting from frequency selective nature of the channel. In this paper, we propose the powerful combination of relay-assisted transmission and multi-carrier architecture based on orthogonal frequency division multiplexing (OFDM). Specifically, we consider a cooperative diversity system with orthogonal cooperation protocol and use DC-biased optical OFDM as the underlying physical layer. We consider both amplify-and-forward (AF) and detect-and-forward (DF) relaying. We investigate the error rate performance of the proposed relay-assisted OFDM UV system under consideration and demonstrate performance gains over point-to-point OFDM UV systems. We further determine optimal power allocation schemes to improve the performance. We also propose a variable-rate UV OFDM system and improve system throughput via bit loading.