The Experimental Design of Radio-over-Fibre System for 4G Long Term Evolution

The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is the potential key to meet the exponentially increasing demand of the mobile end users. The entire LTE network architecture and signal processing is carried out at the enhanced NodeB (eNB) level, hence the increased complexity and cost. Therefore, it is not efficient to deploy eNB for the purpose of extending the network coverage. As a solution, deployment of relay node (RN), with radio-over-fibre (RoF) acting as the interface between eNB and RN is proposed. Due to the high path loss and multipath fading, wireless interface would not be the ideal channel between eNB and RN. A detailed investigation is carried out by comparing the Rayleigh multipath fading channel with the optical fibre channel, where the latter achieved a ~31 dB of signal-to-noise ratio (SNR) gain. The distributed feedback laser (DFB) is selected as the direct modulated laser (DML) source, where the modulation method introduces a positive frequency chirp (PFC). The existing mathematical expression does not precisely explain on how the rate equations contribute to PFC. Therefore, an expression for PFC is proposed and derived from the carrier and photon densities of the rate equations. Focusing on theoretical development of DML based RoF system, a varying fast Fourier transform (FFT) scheme is introduced into LTE-Advanced (LTE-A) technology as an alternative design to the carrier aggregation. A range of FFT sizes are investigated with different levels of optical launch power (OLP), the optimum OLP has been defined to be within the range of ~-6 to 0 dBm, which is known as the intermixing region. It is found that FFT size-128 provides improved average system efficiency of ~54% and ~65% in comparison to FFT size-64 and FFT size-128, respectively, within the intermixing region. While fixing FFT size to 128, the investigation is diverted to the optimisation of optical modulators. The author revealed that the performance of dual electrode-Mach Zehnder modulator (DE-MZM) is superior to both DML scheme and single electrode (SE)-MZM, where DE-MZM achieved a transmission span of 88 km and 71 km for 16-quadrature amplitude modulation (QAM) and 64-QAM, respectively. At the initial experimental link design and optimisation stage, an optimum modulation region (OMR) is proposed at the optical modulation index (OMI) of 0.38, which resulted in an average error vector magnitude (EVM) of ~1.01% for a 10 km span. The EVM of ~1.01% is further improved by introducing the optimum OLP region at –2 dBm, where the observed average EVM trimmed to ~0.96%. There is no deviation found in the intermixing region by transmitting the LTE signal through a varying transmission span of 10 to 60 km, additionally, it was also revealed that the LTE RoF nonlinear threshold falls above the OLP of 6 dBm. The proposed system was further developed to accommodate 2×2 multiple-input and multiple-output (MIMO) transmission by utilising analogue frequency division multiplexing (FDM) technique. The studies procured that the resulting output quality of signal at 2 GHz and 2.6 GHz is almost identical with a twofold gain in the peak data rate and no occurrence of intermodulation (IMD). In order to emulate the complete LTE RoF solution, an experimental design of full duplex frequency division duplex (FDD) system with dense wavelength division multiplexing (DWDM) architecture is proposed. It is found that channel spacing of 50 MHz between the downlink (DL) and uplink (UL) introduces severe IMD distortion, where an adjacent channel leakage ratio (ACLR) penalty of 14.10 dB is observed. Finally, a novel nonlinear compensation technique utilising a direct modulation based frequency dithering (DMFD) scheme is proposed. The LTE RoF system average SNR gain observed at OLP of 10 dBm for the 50 km transmission span is ~5.97 dB. External modulation based frequency dithering (EMFD) exhibits ~3 dB of average SNR gain over DMFD method

Theoretical and experimental design of an alternative system to 2 x 2 MIMO for LTE over 60 km directly modulated RoF link

Relay nodes (RN) are used as an important structure to extend the coverage of the Third Generation Partnership Program’s Long Term Evolution (3GPP-LTE). The promising technology as the interface between eNodeB (eNB) and RN is radio-over-fibre (RoF), due to its longer span transmission capability. In this paper, we propose an alternative technique to 2×2 multiple-input and multiple-output (MIMO) in LTE structure for transmission over 60 km directly modulated RoF link by introducing frequency division multiplexing (FDM) for orthogonal FDM (OFDM). The system is demonstrated theoretically and experimentally. In the baseband, quadrature phase shift keying (QPSK), 16-quadrature amplitude modulation (QAM) and 64-QAM are considered as the single carrier modulations (SCM) according to the LTE standard. The system degradation pattern is identical between the theoretical and experimental system, thus proving the accuracy of the theoretical system design. The real time QPSK, 16-QAM and 64-QAM system achieved an average EVM of 5.84%, 5.90% and 5.97%, respectively for 2 GHz and 2.6 GHz bands. These resultant EVMs are below the 8% 3GPP-LTE EVM requirement

Non-rectangular perfect reconstruction pulse shaping based ICI reduction in CO-OFDM

In this paper, we propose to increase residual carrier frequency offset tolerance based on short perfect reconstruction pulse shaping for coherent optical-orthogonal frequency division multiplexing. The proposed method suppresses the residual carrier frequency offset induced penalty at the receiver, without requiring any additional overhead and exhaustive signal processing. The Q-factor improvement contributed by the proposed method is 1.6 dB and 1.8 dB for time-frequency localization maximization and out-of-band energy minimization pulse shapes, respectively. Finally, the transmission span gain under the influence of residual carrier frequency offset is ̃62% with out-of-band energy minimization pulse shape

A model of extended technology acceptance for behavioral intention toward EVs with gender as a moderator

Technology has contributed significantly to the adoption of EVs (EVs) in the era of industry 4. 0. However, consumer intentions for EVs have been elusive, and the pace of adoption has been confined. Therefore, this study aims to investigate the influence of external factors in promoting customer behavioral intention for EVs. The study also investigates the mediating role of perceived ease of use (PEU) and perceived usefulness (PU) between external factors and consumer intentions for EVs. It also examined the moderating role of gender on the study variables. A study approach based on the expanded version of the technology acceptance model (TAM) was utilized to analyse data from 203 customers in China. The model was tested using structural equation model (SEM) and multigroup analysis (MGA) techniques. The results indicated that two external factors have a positive relationship with TAM constructs. The results also indicate that PEU and PU have a serial mediating relationship between external factors and behavioral intention. Finally, the study revealed gender-related differences in TAM for EVs. The study's findings help managers to design successful strategies by knowing the external factors impacting customer EV intentions and gender differences. Finally, this is a ground-breaking research that applies TAM to the automobile sector. As a result, examining both new and current factors and evaluating them in a new setting adds to the body of the literature on the adoption of technology

FFT size optimization for LTE RoF in nonlinear fibre propagation

This papers investigates the performance of the fast Fourier transform (FFT) sizes- 64, 128, 256, 512 and 1024 for the orthogonal frequency division multiplexing (OFDM) scheme in 3 rd generation partnership program (3GPP)-long term evolution (LTE) and LTE-Advanced (LTE-A). This paper aims to optimize the FFT sizes with respect to quadrature phase shift keying (QPSK), 16, 64 and 256-quadrature amplitude modulation (QAM). This optimization is for the transmission of LTE signals between eNodeB (eNB) and relay node (RN) to extend the mobile coverage employing radio-over-fibre (RoF). This paper will take into account the positive frequency chirp (PFC) induced by distributed feedback laser (DFB) through direct modulation with chromatic dispersion (CD) and self phase modulation (SPM) impairments into consideration. We present the optimum optical launch power (OLP) region termed as the intermixing region between linear and nonlinear optical fibre propagation. The optimum OLP in this investigation takes place at -4 dBm which falls within the intermixing region. At the transmission rate of 200, 400, 600 and 800 Mb/s of QPSK, 16, 64 and 256-QAM, the FFT size-128 provides the optimum power penalty with average system efficiency with respect to FFT size-64 is 54% and FFT size-256 is 65%

Experimental realization of multi-service RoF system using OCS-PolMux techniques

Optical Carrier Suppression has been proven as an efficient way of generating high frequency optical carrier for Radio over Fiber (RoF) systems. However, previous studies show that OCS with the combination of RF and optical components can only transmit a single service in RoF system. This paper shows that two different services can be transmitted using a single wavelength through RoF system with the use of Polarization Multiplexing (PolMux) method. The combination of these two techniques enables multiservice RoF such as LTE and WiFi services to be transmitted simultaneously to the customers

Experimental demonstration of data-dependent pilot-aided phase noise estimation for CO-OFDM

We demonstrate a novel phase noise estimation scheme for CO-OFDM, in which pilot subcarriers are deliberately correlated to the data subcarriers. This technique reduces the overhead by a factor of 2

Exceeding the nonlinear-shannon limit using Raman laser based amplification and optical phase conjugation

We demonstrate that a combination of Raman laser based amplification and optical phase conjugation enables transmission beyond the nonlinear-Shannon limit. We show nonlinear compensation of 7x114Gbit/s DP-QPSK channels, increasing system reach by 30%

Investigation of Optical Modulators in Optimized Nonlinear Compensated LTE RoF System

In this paper, we investigate a nonlinear compensation technique with two different architectures using direct modulation (DM) and external modulation (EM) techniques, termed as DM based frequency dithering (DMFD) and EM based frequency dithering (EMFD). We show that DMFD and EMFD methods operate substantially different in radio-over-fiber (RoF) system by optimizing the dithering technique relative to the LTE technology. The proposed techniques is only applicable if the condition of {fL < fd < fRF} is met, where fL represents the dithering boundary limit of 14 MHz, fd is DMFD signal frequency and fRF is the RoF carrier frequency. Analysis of the optical launch power for DMFD and EMFD methods reveal that the stimulated Brillouin scattering (SBS) threshold is above ~6 dBm for the LTE-RoF system. In addition, we also unveil that DMFD and EMFD methods do not introduce additional distortion for the linear and optimum optical launch power regions, which are frequency chirp driven regions. If the given condition is met, the proposed method improves the LTE-RoF system without any shortcoming. Finally, at 10 dBm launch power, DMFD and EMFD methods exhibits an average signal-to-noise ratio (SNR) gain of ~5.95 dB and ~7.71 dB, respectively