Varghese Antony Thomas

Performance Improvement and Cost Reduction Techniques for Radio Over Fiber Communications

Advanced cost reduction and performance improvement techniques conceived for Radio Over Fiber (ROF) communications are considered. ROF techniques are expected to form the backbone of the future fifth generation of wireless networks. The achievable link performance and the associated deployment cost constitute the most salient metrics of an ROF architecture. In this paper, we commence by providing a rudimentary overview of the ROF architecture, and then we elaborate on ROF techniques designed for improving the attainable system performance. We conclude by describing the ROF techniques conceived for reducing the ROF system installation costs.

Millimeter-Wave Radio Over Fiber Optical Upconversion Techniques Relying on Link Nonlinearity

A study of advanced upconversion techniques used in radio over fiber (ROF) is provided. With the huge increase in both the number of wireless communication subscribers and the bandwidth required per customer, migrating to higher frequencies, i.e., from lower radio frequency to millimeter-wave carriers, is an essential solution. However, due to the short propagation range of millimeter waves, a large number of radio access points are required for providing reliable coverage, which would increase the infrastructure costs. Hence, the transmission of RF signals between the central (or control) points and radio access points (or remote antenna units) using optical fibers is one of the major access network solutions that have been proposed for future high-bandwidth wireless communication systems. In this paper, we introduce the basics of ROF communication, including optical modulation, the optical channel, and the optical detection techniques. Then we survey the family of advanced optical upconversion techniques that exploit the nonlinearity of the ROF link. Specifically, we describe how optical upconversion can be achieved by exploiting the Mach-Zehnder modulators nonlinearity, wavelength conversion techniques, or the photodetectors nonlinearity. The wavelength conversion techniques rely on the nonlinearities present in the fiber, in the optical amplifier, or in the electroabsorption modulator.

Baseband Radio over Fiber Aided Millimeter-Wave Distributed Antenna for Optical/Wireless Integration

A Baseband Radio Over Fiber (BROF) architecture is proposed, where upto four Radio Frequency (RF) carriers can be generated, while using the heterodyne photo-detection of only two optical signals. This proposed BROF architecture has a star-like structure and it is composed of six Radio Access Units (RAUs), where data is transmitted from the Central Unit (CU) to the Base Station (BS) and from the BS to the RAU over a distance of 20 Km and 0.3 Km, respectively, at a rate of 768 Mbps. The performance of the system supporting four carrier frequencies drops by at most 1dB, at a BER of 10-9, compared to conventional heterodyne photo-detection.

A Full-Duplex Diversity-Assisted Hybrid Analogue/Digitized Radio Over Fibre for Optical/Wireless Integration

A duplex Radio Over Fibre (ROF) ring architecture is proposed taking into account the constraints imposed by the cost of fibre laying and of the optical/electronic components, as well as the spectral efficiency and the duplex link performance. It has been shown that relying on Analogue ROF (AROF) and state-of-the-art Digitized ROF (DROF) architectures for downlink and uplink transmission, respectively, attains a high-integrity duplex performance. A sophisticated amalgam of Optical Carrier Suppression (OCS), Code Division Multiplexing (CDM), optical frequency multiplexing, Optical Carrier Reuse (OCR) and distributed antennas is conceived.

Duplex Digitized Transmission of 64-QAM Signals over a Single Fiber Using a Single Pulsed Laser Source

We demonstrate digitized duplex transmission of 64-QAM signals using pulsed optical communications. Bidirectional data transmission is achieved over a single 25 km optical fibre using a single optical pulsed source. The choice of suitable parameters for bandpass sampling technique used for the digitization of the 16 MSamples/s 64-QAM signal are discussed. It is demonstrated that using digitized transmission of RF signals, long distance transmission can be supported at a performance close to that of the back-to-back analogue benchmarker.

Error Vector Magnitude Analysis of Fading SIMO Channels Relying on MRC Reception

We analytically characterize the data-aided error vector magnitude (EVM) performance of a single-input multiple-output (SIMO) communication system relying on maximal ratio combining (MRC) having either independent or correlated branches that are nonidentically distributed. In particular, exact closed form expressions are derived for the EVM in η-μ fading and κ-μ shadowed fading channels and these expressions are validated by simulations. The derived expressions are expressed in terms of Lauricellas function of the fourth kind FD(N) (.), which can be easily computed. Furthermore, we have simplified the derived expressions for various special cases such as independent and identically distributed branches, Rayleigh fading, Nakagami-m fading, and κ-μ fading. Additionally, a parametric study of the EVM performance of the wireless system is presented.

The \"Rap\" on ROF: Radio over Fiber Using Radio Access Point for High Data Rate Wireless Personal Area Networks

A wireless personal area network (WPAN) allows the wireless devices in a users personal workspace to be connected to the network. Due to the huge increase in both the number of wireless communication subscribers and the bandwidth required per customer with the proliferation of smart devices, the low-frequency radio spectrum is becoming overcrowded. A natural solution for future WPANs is to migrate to higher radio frequency (RF) carriers [1]. High data-rate WPANs may be implemented based on the Federal Communications Commission (FCC) compliant ultrawideband (UWB) standard [2] or on the IEEE 802.15.3c standard [3]. The UWB signal was defined by the FCC as a signal having a bandwidth larger than 20% of the carrier frequency or a bandwidth of at least 500 MHz in the 3.1-10.6-GHz band; IEEE 802.15.3c relies on a carrier frequency in the 60-GHz license-free industrial, scientific, and medical (ISM) band. The implementation of both the UWB standard and the IEEE 802.15.3c standard faces certain challenges, which may be tackled with the aid of radio over fiber (ROF) techniques that employ optical generation of the wireless signal. ROF networking solutions have been proposed for future high-bandwidth wireless communication systems that rely on the transmission of RF signals between the base station (BS) and remote antennas [1], [4]-[8].

Simultaneous Optical Phase and Intensity Modulation Transmits Independent Signals in Radio Over Fiber Communication

We propose and mathematically characterize a novel Radio Over Fiber (ROF) architecture, which uses a single MZM for simultaneously modulating the intensity and phase of an optical carrier with either two different RF signals or a RF signal and a baseband signal. The detection of these two independent signals is conceived along with possible applications of the proposed architecture. The operation and performance of the proposed system is shown through simulations.

Throughput and Delay Analysis of Cognitive Go-Back-N Hybrid Automatic Repeat reQuest Using Discrete-Time Markov Modelling

Cognitive radio (CR) techniques have been proposed for improving the spectral efficiency by exploiting the temporarily unoccupied segments of the licensed spectrum, provided that the transmission of primary users (PUs) is not hampered. In this paper, we propose a cognitive Go-Back-N Hybrid Automatic Repeat reQuest (CGBN-HARQ) scheme that enables the cognitive user (CU) to opportunistically transmit data over a primary radio (PR) channel. Based on the sensing decisions by the CU, it decides about the availability of the PU’s channel for its own transmission using the proposed CGBN-HARQ scheme. In addition, it enables the CR transmitter to receive feedback concerning the success/failure of its prior transmissions during the sensing and transmission phases of the time-slot (TS). A discrete time Markov chain model is invoked for the theoretical analysis of the proposed system, where we conceive an algorithm to generate all possible states of the CR transmitter. Both the throughput and delay of the CGBN-HARQ scheme is analyzed by deriving a range of closed-form formulas, which are validated by simulation results. The occupation of the channel by the PU and the reliability of the CU’s channel significantly affect both the achievable throughput and the delay of the CGBN-HARQ scheme. Finally, our studies show that the number of packets transmitted within a TS should be adapted according to the communication channel for attaining the maximum throughput and the lowest average transmission delay.

Single ODSB Radio-Over-Fiber Signal Supports STBC at Each RAP

We propose and mathematically characterize a novel radio-over-fiber (ROF) downlink, where a radio access point (RAP) benefits from the transmit diversity gain of space-time block coding (STBC). Significantly, this transmit diversity is achieved using a single optical modulator in the base station (BS). In the proposed architecture, each RAP is fed with a single optical double-sideband signal, where each sideband transmits one of the two STBC-encoded signals. This optical signal is generated in the BS by performing the simultaneous optical upconversion of the baseband STBC signals using a single Mach-Zehnder modulator. The proposed optical backhaul is designed and simulated to impose negligible degradation to that imposed by the dominant wireless link, thereby enabling a designer to exploit the advantages offered by a wireless link having a diversity gain.