Article

Optimization of Optical Modulator for LTE RoF in Nonlinear Fiber Propagation

IEEE Photonics Technology Letters (Impact Factor: 2.11). 04/2012; 24(7):617-619. DOI: 10.1109/LPT.2012.2185927

ABSTRACT

This letter proposes an optimized launch power for the direct detection of optical orthogonal frequency-division multiplexing (DD-OOFDM) for radio-over-flber (RoF). The aim is to optimize the physical layer connectivity for the third generation partnership program-long-term evolution employing RoF technologies. We also analytically derive an expression for the distributed-feedback laser, laser-induced positive frequency chirping, incorporating the phenomena that induce phase distortion at the receiver, and explicitly explain the transient chirp of DD-OOFDM. Results show that transmission at the optimized launch power of -4 dBm improves the system power efficiency of 16-quadrature amplitude modulation (QAM) DD-OOFDM by ~20% and ~37%, 64-QAM DD-OOFDM by ~21% and ~35% compared to launch powers in the linear and nonlinear regions, respectively.

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    • "Optical mmwaves can be generated in a number of ways including (i) direct modulation of a laser, which is the simplest method for data rates below several Gb/s with a transmission span <100 km. However, laser chirping degrades the quality of transmitted signal particularly in long haul transmission spans [9] [10]; (ii) harmonic generation, which uses frequency modulation – intensity modulation (FM-IM) to generate a wide range of optical mm-wave frequencies [11]. However, the latter scheme is rather complex to implement requiring several electro-optic devices and modulators [11]; (iii) the optical heterodyne method, which is mostly used with wavelength division multiplexing (WDM) with a wavelength spacing equivalent to the optical mm-wave frequency and requiring two lasers with identical linewidths [12]. "

    Full-text · Article · Apr 2015
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    • "It is shown in [21] that the joint distortion between positive frequency chirp and chromatic dispersion introduces an average power penalty of ∼3 dB. But since we are maintaining the optical launch power (OLP) within the optimum region [5], the effect of positive frequency chirp will be minimized. "
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    ABSTRACT: In this paper, we experimentally demonstrate the seamless integration of full duplex system frequency division duplex (FDD) long-term evolution (LTE) technology with radio over fiber (RoF) for eNodeB (eNB) coverage extension. LTE is composed of quadrature phase-shift keying (QPSK), 16-quadrature amplitude modulation (16-QAM) and 64-QAM, modulated onto orthogonal frequency division multiplexing (OFDM) and single-carrier-frequency division multiplexing for downlink (DL) and uplink (UL) transmissions, respectively. The RoF system is composed of dedicated directly modulated lasers for DL and UL with dense wavelength division multiplexing (DWDM) for instantaneous connections and for Rayleigh backscattering and nonlinear interference mitigation. DL and UL signals have varying carrier frequencies and are categorized as broad frequency spacing (BFS), intermediate frequency spacing (IFS), and narrow frequency spacing (NFS). The adjacent channel leakage ratio (ACLR) for DL and UL with 64-QAM are similar for all frequency spacings while cross talk is observed for NFS. For the best case scenario for DL and UL transmissions we achieve error vector magnitude (EVM) values of ~2.30%, ~2.33%, and ~2.39% for QPSK, 16-QAM, and 64-QAM, respectively, while for the worst case scenario with a NFS EVM is increased by 0.40% for all schemes.
    Full-text · Article · Jan 2014 · Journal of Optical Communications and Networking
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    • "The DMFD method is primarily introduced to compensate the severe distortion in the nonlinear region. In addition to the nonlinear region, we have also introduced two different propagating regions for LTE-RoF in [3] [4] [5], namely linear, and optimum OLP. The linear region is positive frequency chirp (PFC) and chromatic dispersion (CD) dependent. "
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    ABSTRACT: This paper reveals that nonlinear propagation is a critical problem for the long term evolution (LTE) technology based on the radio-over-fibre (RoF) system. Therefore, a direct modulation based frequency dithering (DMFD) method is proposed for nonlinear propagation compensation, namely the self phase modulation (SPM) and stimulated brillouin scattering (SBS). We found that DMFD method operates substantially different in RoF systems. The major difference is that DMFD signal frequency fd has to be much smaller than the RoF carrier frequency fRF; thus the condition of {fd << fRF} has to be stringently obeyed. Analysis of the optical launch power (OLP) with DMFD method reveals that the SBS threshold is above ~6 dBm for LTE-RoF system. In addition, we also unfold that DMFD method does not induce an additional distortion for the linear and optimum OLP regions, which are frequency chirp dependent. Hence the proposed method improves the LTE-RoF system without any shortcoming. Finally, at OLP values of 8 dBm and 10 dBm, LTE-RoF system exhibits an average error vector magnitude (EVM) improvement of ~4.32% and ~6.18%, respectively, for the 50 km transmission span.
    Full-text · Conference Paper · Jun 2013
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