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Papers by Muhammad Rahman

Research paper thumbnail of An efficient modulation technique to mitigate nonlinearities in optical OFDM

2014 Australasian Telecommunication Networks and Applications Conference (ATNAC), 2014

The optical OFDM (O-OFDM) system is a growing technology for next generation high-speed optical c... more The optical OFDM (O-OFDM) system is a growing technology for next generation high-speed optical communication. Two types of O-OFDM; CO-OFDM (Coherent-Optical OFDM) and Direct-current-based optical OFDM (DC-OFDM) are discussed. Mach-Zehnder modulators (MZMs) are used in up-converter part of CO-OFDM system to convert the RF signal to optical signal when the light cannot directly modulate for higher speed. The MZM has a cosine behavior with high nonlinear characteristic that affects the system performance. This paper aims to investigate an efficient pulse modulation technique for mitigating nonlinearity effect in the Mach-Zehnder modulator of CO-OFDM system. It also highlights the proposed method, an efficient CO-OFDM system to solve the existing nonlinearity issue. This technique influences positively on OSNR to reduce non linearity over different distances of optical channel and improve the system performance in terms of power consumption and bandwidth efficiency.

Research paper thumbnail of Comparing Optical Properties of GaN/InGaN Based LEDs Using Different MQWs and SO 2 Nano Lenses

INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY

We investigate the optical properties of polarized InGaN/GaN-based multiple quantum well (MQW) li... more We investigate the optical properties of polarized InGaN/GaN-based multiple quantum well (MQW) light emitting diodes (LEDs) coupled with and without nanolens on the top layer of LED structure. We suggested the CWDM-VLC concept for the first time, and to execute it, we have designed a narrow spectrum high bandwidth LED. MQW or Nano-lens have been used together in this work to examine the performance in terms of Purcell factor (Fp), effects of MQWs, 3dB bandwidth of the LED and far field divergence, using finite-difference timedomain (FDTD) technique. A parabolic nano-lens array mounted to the top layer of the LED narrows the spectrum and boosts LED bandwidth by reducing far-field divergence. With this simulated LED, the lowest recombination time of 0.94ns was obtained, which helped to raise the data rate up to 7.85 GHz. These findings could allow the development of efficient light sources and high bandwidth LEDs for applications such as smart lighting and visible-light communication (VLC).

Research paper thumbnail of Analysis of FSO and Optical Fiber Based Hybrid Network Using High Speed WDM Transmission

INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, 2022

Free Space Optics (FSO) is one of the most effective solutions for high-speed wireless communicat... more Free Space Optics (FSO) is one of the most effective solutions for high-speed wireless communication under air turbulence or environmental hazard, while radio over fiber (RoF) shows better performance for long-distance communication. Wavelength division multiplexing (WDM) is the most effective method for multichannel fiber to the home (FTTH) networks. The main objective of this study is to integrate the system performance with RoF and FSO links in order to improve network flexibility and expand the wireless network's coverage in the presence of weather hazards. The signal is generated by an array of optical lasers in the simulation and propagates through a maximum 3 km WDM-FSO link and a long fiber optic backhaul. As a result, each WDM channel can transmit 2.5 Gb/s data, getting a total data rate of 40 Gb/s using 16 WDM channels with a channel spacing of 100 GHz (0.8 nm). Finally, in order to improve the system performance, different optical amplifiers such as EDFA, SOA, and Raman are used in this hybrid WDM network.

Research paper thumbnail of Cross-Layer Optimization of OFDM Systems for 4G Wireless Communications

Proceedings of the 9th International OFDM–Workshop, Dresden, Germany, Sep 1, 2004

Abstract—In this paper we advocate cross–layer optimiza-tion over the whole ISO/OSI protocol stac... more Abstract—In this paper we advocate cross–layer optimiza-tion over the whole ISO/OSI protocol stack. As an example we refer to a system using multiple description coding at application layer combined with orthogonal frequency division multiplexing at the link level to provide robustness against hostile wireless channels. In the proposed optimization design negotiation between application, data link control and physical layer is exploited to increase user quality of service in terms of picture signal to noise ratio and bandwidth efficiency. By ...

Research paper thumbnail of Humidity sensor based on microfiber resonator with reduced graphene oxide

A simple relative humidity (RH) sensor based on a tapered single mode fiber loop resonator (MLR) ... more A simple relative humidity (RH) sensor based on a tapered single mode fiber loop resonator (MLR) is proposed and experimentally verified. The refractive index of the microfiber in the MLR was modified by environmental humidity, and its emission wavelength changed with RH level. Reduced graphene oxide (rGO) material was used for this device due to its inherent characteristics of high water permeability and high sensitivity whereby long response and recovery times are reduced. Moreover, humidity sensors have been widely used in different fields and are used in the solutions of numerous problems. The performance of tapered fiber was measured with and without rGO and at fiber diameter of 4.04 m. The spectrum was observed to shift with the wavelength as relative humidity increased, and measured sensitivity with rGO was 0.0537 nm/%RH and without rGO was 0.0316 nm/%RH in the range of 30 to 50% relative humidity.

Research paper thumbnail of MEASURING OSNR IN WDM SYSTEMS—EFFECTS OF RESOLUTION BANDWIDTH AND OPTICAL REJECTION RATIO

In the last few years, we have witnessed the extensive deployment of wavelength-division multiple... more In the last few years, we have witnessed the extensive deployment of wavelength-division multiplexed (WDM) networks. These systems are configured to allow multiple channels at different wavelengths i to share the same optical fiber, increasing the effective transmission rate on that fiber. But with this new technology arose a new challenge: the parameters providing direct information on system performance (such as the bit error rate (BER) and BER estimation techniques like Q-factor or eye analysis) cannot be measured directly on a multichannel system. These key parameters require spectral demultiplexing prior to making an individual evaluation of the BER performance on each demultiplexed channel. Alternatively, optical signalto-noise ratio (OSNR) can be derived, for each individual channel, from an optical spectrum measurement to obtain indirect information about the performance of these channels and hence of the system.

Conference Presentations by Muhammad Rahman

Research paper thumbnail of Analysis of the effects of multiple reflection paths on high speed VLC system performance

IEEE, 2018

In the recent past, research in visible light communication (VLC) has gained a lot interest due t... more In the recent past, research in visible light communication (VLC) has gained a lot interest due to its distinct characteristics in supporting high-speed optical wireless communication and illumination simultaneously. To implement a reliable VLC system, few parameters have to be considered for communication channels such as distance between transmitter and receiver, data rate, line of sight (LOS) and non-line of sight (NLOS) communication paths, signal power and delay of the channel. In this paper, we designed and simulated a LOS and NLOS multipath VLC model using single and multiple LEDs. Basic on-off keying (OOK) modulation scheme and available conventional LED configuration have been considered to analyze the effects of field of view (FOV) and the reflection of the light signal on received power level. Moreover, BER and quality of transmission were measured for single and multipath transmissions considering distance, incident and irradiance angles.

Research paper thumbnail of An efficient modulation technique to mitigate nonlinearities in optical OFDM

2014 Australasian Telecommunication Networks and Applications Conference (ATNAC), 2014

The optical OFDM (O-OFDM) system is a growing technology for next generation high-speed optical c... more The optical OFDM (O-OFDM) system is a growing technology for next generation high-speed optical communication. Two types of O-OFDM; CO-OFDM (Coherent-Optical OFDM) and Direct-current-based optical OFDM (DC-OFDM) are discussed. Mach-Zehnder modulators (MZMs) are used in up-converter part of CO-OFDM system to convert the RF signal to optical signal when the light cannot directly modulate for higher speed. The MZM has a cosine behavior with high nonlinear characteristic that affects the system performance. This paper aims to investigate an efficient pulse modulation technique for mitigating nonlinearity effect in the Mach-Zehnder modulator of CO-OFDM system. It also highlights the proposed method, an efficient CO-OFDM system to solve the existing nonlinearity issue. This technique influences positively on OSNR to reduce non linearity over different distances of optical channel and improve the system performance in terms of power consumption and bandwidth efficiency.

Research paper thumbnail of Comparing Optical Properties of GaN/InGaN Based LEDs Using Different MQWs and SO 2 Nano Lenses

INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY

We investigate the optical properties of polarized InGaN/GaN-based multiple quantum well (MQW) li... more We investigate the optical properties of polarized InGaN/GaN-based multiple quantum well (MQW) light emitting diodes (LEDs) coupled with and without nanolens on the top layer of LED structure. We suggested the CWDM-VLC concept for the first time, and to execute it, we have designed a narrow spectrum high bandwidth LED. MQW or Nano-lens have been used together in this work to examine the performance in terms of Purcell factor (Fp), effects of MQWs, 3dB bandwidth of the LED and far field divergence, using finite-difference timedomain (FDTD) technique. A parabolic nano-lens array mounted to the top layer of the LED narrows the spectrum and boosts LED bandwidth by reducing far-field divergence. With this simulated LED, the lowest recombination time of 0.94ns was obtained, which helped to raise the data rate up to 7.85 GHz. These findings could allow the development of efficient light sources and high bandwidth LEDs for applications such as smart lighting and visible-light communication (VLC).

Research paper thumbnail of Analysis of FSO and Optical Fiber Based Hybrid Network Using High Speed WDM Transmission

INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, 2022

Free Space Optics (FSO) is one of the most effective solutions for high-speed wireless communicat... more Free Space Optics (FSO) is one of the most effective solutions for high-speed wireless communication under air turbulence or environmental hazard, while radio over fiber (RoF) shows better performance for long-distance communication. Wavelength division multiplexing (WDM) is the most effective method for multichannel fiber to the home (FTTH) networks. The main objective of this study is to integrate the system performance with RoF and FSO links in order to improve network flexibility and expand the wireless network's coverage in the presence of weather hazards. The signal is generated by an array of optical lasers in the simulation and propagates through a maximum 3 km WDM-FSO link and a long fiber optic backhaul. As a result, each WDM channel can transmit 2.5 Gb/s data, getting a total data rate of 40 Gb/s using 16 WDM channels with a channel spacing of 100 GHz (0.8 nm). Finally, in order to improve the system performance, different optical amplifiers such as EDFA, SOA, and Raman are used in this hybrid WDM network.

Research paper thumbnail of Cross-Layer Optimization of OFDM Systems for 4G Wireless Communications

Proceedings of the 9th International OFDM–Workshop, Dresden, Germany, Sep 1, 2004

Abstract—In this paper we advocate cross–layer optimiza-tion over the whole ISO/OSI protocol stac... more Abstract—In this paper we advocate cross–layer optimiza-tion over the whole ISO/OSI protocol stack. As an example we refer to a system using multiple description coding at application layer combined with orthogonal frequency division multiplexing at the link level to provide robustness against hostile wireless channels. In the proposed optimization design negotiation between application, data link control and physical layer is exploited to increase user quality of service in terms of picture signal to noise ratio and bandwidth efficiency. By ...

Research paper thumbnail of Humidity sensor based on microfiber resonator with reduced graphene oxide

A simple relative humidity (RH) sensor based on a tapered single mode fiber loop resonator (MLR) ... more A simple relative humidity (RH) sensor based on a tapered single mode fiber loop resonator (MLR) is proposed and experimentally verified. The refractive index of the microfiber in the MLR was modified by environmental humidity, and its emission wavelength changed with RH level. Reduced graphene oxide (rGO) material was used for this device due to its inherent characteristics of high water permeability and high sensitivity whereby long response and recovery times are reduced. Moreover, humidity sensors have been widely used in different fields and are used in the solutions of numerous problems. The performance of tapered fiber was measured with and without rGO and at fiber diameter of 4.04 m. The spectrum was observed to shift with the wavelength as relative humidity increased, and measured sensitivity with rGO was 0.0537 nm/%RH and without rGO was 0.0316 nm/%RH in the range of 30 to 50% relative humidity.

Research paper thumbnail of MEASURING OSNR IN WDM SYSTEMS—EFFECTS OF RESOLUTION BANDWIDTH AND OPTICAL REJECTION RATIO

In the last few years, we have witnessed the extensive deployment of wavelength-division multiple... more In the last few years, we have witnessed the extensive deployment of wavelength-division multiplexed (WDM) networks. These systems are configured to allow multiple channels at different wavelengths i to share the same optical fiber, increasing the effective transmission rate on that fiber. But with this new technology arose a new challenge: the parameters providing direct information on system performance (such as the bit error rate (BER) and BER estimation techniques like Q-factor or eye analysis) cannot be measured directly on a multichannel system. These key parameters require spectral demultiplexing prior to making an individual evaluation of the BER performance on each demultiplexed channel. Alternatively, optical signalto-noise ratio (OSNR) can be derived, for each individual channel, from an optical spectrum measurement to obtain indirect information about the performance of these channels and hence of the system.

Research paper thumbnail of Analysis of the effects of multiple reflection paths on high speed VLC system performance

IEEE, 2018

In the recent past, research in visible light communication (VLC) has gained a lot interest due t... more In the recent past, research in visible light communication (VLC) has gained a lot interest due to its distinct characteristics in supporting high-speed optical wireless communication and illumination simultaneously. To implement a reliable VLC system, few parameters have to be considered for communication channels such as distance between transmitter and receiver, data rate, line of sight (LOS) and non-line of sight (NLOS) communication paths, signal power and delay of the channel. In this paper, we designed and simulated a LOS and NLOS multipath VLC model using single and multiple LEDs. Basic on-off keying (OOK) modulation scheme and available conventional LED configuration have been considered to analyze the effects of field of view (FOV) and the reflection of the light signal on received power level. Moreover, BER and quality of transmission were measured for single and multipath transmissions considering distance, incident and irradiance angles.