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Orthogonal frequency division multiplexing (OFDM) combined with offset quadrature amplitude modulation (OQAM) have aroused wide interest for optical communication recently. With the relaxation of orthogonal condition from the complex field to the real field, optical OFDM/OQAM faced with serious intrinsic imaginary interference (IMI) brought by chromatic dispersion and polarization mode dispersion. As have been discussed in previous publications, frequency domain channel estimation methods utilizing the concept of pseudo pilot have been proved effective in combating IMI. In this paper, we discussed a novel frequency domain channel estimation method based on the using of three consecutive full loaded pilot blocks for optical OFDM/OQAM system. In this approach, the pseudo pilot was constructed with three consecutive loaded pilot blocks. The discussed method can efficiently promote the power of the pseudo-pilot and improve the system robustness against IMI effect significantly. As demonstrated in the Montel Carlo simulation results, 1.8dB advantage in require optical signaI to noise ratio (OSNR) at a BER target of $10^{-3}$ could be achieved with the using of the discussed method, compared with the IAM-C method.

This paper analyses the performance of two advanced modulation techniques for reducing the peak-to-average power ratio (PAPR) of a visible light communication (VLC) system namely, double precoded OFDM which is a variant of DFT precoded OFDM used in 4G LTE-A and optical generalized frequency division multiplexing (OGFDM) which is a variant of one of the proposed 5G waveform (GFDM). The performance of double precoded OFDM and OGFDM is compared against asymmetrically clipped optical OFDM (ACO-OFDM) on the basis of PAPR and SER. The results show that double precoded OFDM and OGFDM reduces the PAPR by 9 and 5 dB respectively, over ACO-OFDM.

International audience; In this paper, we present the orthogonal frequency division multiplexing (OFDM) technique based on discrete multitone modulation (DMT) over multimode fiber (MMF), at length up to 5Km at a bit rate of 20 Gb/s. Through numerical simulations, we investigate the optimal launching conditions of the MMF fiber. The effect of the fiber length on the performances of the system is also studied.

We clarified the regularity of the dispersion performance of an optical fractional Fourier transform circuit, realizing variable dispersion compensation in an optical OFDM system. The generic form of dispersion performance is presented.

Orthogonal frequency division multiplexing (OFDM) combined with offset quadrature amplitude modulation (OQAM) have become the hot research topic recently. OFDM/OQAM utilizes the specially designed filter bank with promising time-frequency localization (TFL) property to overcome inter-symbol-interference (lSI). However, the orthogonal condition for OFDM/OQAM only holds in the real field. Optical OFDM/OQAM systems faced with serious intrinsic imaginary interference (IMI) effect induced by chromatic dispersion (CD) and polarization mode dispersion (PMD)., which decreased the transmission performance significantly. In this paper., we proposed a pilot power optimization based channel estimation method to improve the system robustness against IMI effect for optical OFDM/OQAM systems. The general pilot design criterion has been proposed in this paper., and numerous pilot structures reported in previous publications have been compared with the proposed method. As demonstrated in the simulation results., the pseudo pilot structures satisfying the proposed structure could obtain optimal pseudo pilot power., which could improve the system robustness against IMI effect and amplified spontaneous emission (ASE) evidently.

There is no doubt that Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) is considered as an attractive modulation format. The previously mentioned term has received a great deal of attention in recent years within the long haul fiber-optic transmission community. However, the benefit of optical OFDM is concerned with indefinite quantity of eliminating Inter Symbol Interference (ISI). Such a quantity is caused due to Chromatic Dispersion (CD) and polarization-mode dispersion (PMD).

A data clipping and normalization technique is employed to improve the performance of the overall direct detection optical orthogonal frequency division multiplexing (DCO-OFDM) system. A detailed analysis of clipping distortion introduced by digital clipping and normalization is provided. The normalization operation amplifies the clipped data signal to the maximum input amplitude of a digital-to-analog converter (DAC). Based on the analysis, a BER formula of the proposed scheme is derived over the AWGN channel and single fiber channel. Performance of an optical clipped OFDM with normalization is assessed through numerical simulations and Monte Claro simulation over the AWGN channel. Theoretical analysis and simulation results both show that the clipping and normalization scheme can greatly improve the BER of an optical OFDM. In particular, BER performance of the proposed transmission scheme was measured in a practical OFDM transmission platform. The measured experimental results show that the clipped and amplified OFDM signal exhibits superior performance in comparison with the conventional OFDM signal. The received sensitivity at a BER of 10−3 for a 4 Gsamples/s (2.6667 Gbits/s) clipped and normalized OFDM signal with clipping ratio of 4 after 100 km standard single-mode fiber (SMF) transmission was improved by 4.3 dB when compared with the conventional OFDM system. The measured results also showed that the clipped OFDM signal exhibits superior performance in comparison with the conventional OFDM signal. Therefore, a clipping and normalization at the transmitter is most effective, and a substantial performance improvement can be obtained by a simple normalization after clipping.

This paper proposes an iterative soft interference canceller with the assistance of LDPC code for mitigating beat interference in a pilot-assisted optical-OFDM. The LDPC code is analytically optimized by EXIT chart based on Turbo principle.

In this paper, a novel data-aided linear fitting-based (DALF-based) blind phase estimation method for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) is proposed. Similar to our previous work done in the pilot-based blind phase estimation method, the pilot subcarriers are used to transmit unknown amplitude modulation signals in order to improve spectral efficiency. But the so-called pilot subcarriers can be reduced to only two in the DALF-based method, while the conventional pilot-aided-based (PA-based) method requires almost four real pilot subcarriers. A performance comparison of the conventional PA-based and DALF-based phase estimation methods has been demonstrated through a 16-QAM CO-OFDM simulation. The results show that the performance of the proposed DALF-based method is better than the conventional one with higher SE and has the potential in the large capacity CO-OFDM systems.

Because the partial transmit sequence (PTS) peak-to-average power ratio (PAPR) reduction technology for optical orthogonal frequency division multiplexing (O-OFDM) systems has higher computational complexity, a novel two-stage enhanced-iterative-algorithm PTS (TS-EIA-PTS) PAPR reduction algorithm with lower computational complexity is proposed in this paper. The simulation results show that the proposed TS-EIA-PTS PAPR reduction algorithm can reduce the computational complexity by 18.47% in the condition of the original signal sequence partitioned into 4 sub-blocks at the remaining stage of n-d=5. Furthermore, it has almost the same PAPR reduction performance and the same bit error rate (BER) performance as the EIA-PTS algorithm, and with the increase of the subcarrier number, the computational complexity can be further reduced. As a result, the proposed TS-EIA-PTS PAPR reduction algorithm is more suitable for the practical O-OFDM systems.

The pilot-assisted peak-to-average power ratio (PAPR) reduction technique proposed for optical orthogonal frequency division multiplexing (OFDM) communication systems is evaluated empirically and theoretically in this letter. The PAPR reduction is achieved by rotating the phase of data symbols with $P$ iterations of randomly generated pilot symbol sequence. The results of our hardware implementation and analysis show a close agreement to that of computer simulations. In comparison with basic OFDM, where no PAPR reduction technique is implemented, experimental PAPR reduction gain of pilot-assisted OFDM at a complementary cumulative distribution function of $10^{-3}$ with $P=5$ is $\sim 2$ dB. This gain is $\sim 0.2$ dB less than that of analytical results. The experimental results also show that the pilot-assisted technique does not cause any significant deterioration of the bit error performance.

The performance of theory analysis on DD-OFDM system for ROF links has been investigated. The theoretical model of DD Optical OFDM transmission system has been discussed. It consists of fundamentals and mathematical analysis of a typical DD-OFDM system. A typical low-cost DD-OFDM system has been simulated. The results show that the simple structure and low-cost of the DD-OFDM system is attractive for the future cost-effective broadband access networks.

In this paper, we propose and demonstrate effective laser phase noise compensation for coherent optical orthogonal frequency-division multiplexing (OFDM) systems that have long OFDM symbols. The phase noise compensation is achieved via hybrid modulated multiband optical OFDM, aided by the digital filter bank technique. For this, one of the multiple subbands is modulated as discrete Fourier transform spread OFDM. Our experimental results show that laser phase noise up to 1 MHz can be compensated for 114.8-Gb/s 16-QAM signals with 480-km standard single mode fiber transmission.

Digital coherent superposition (DCS) for optical orthogonal frequency-division multiplexing (OFDM) subcarrier pairs with Hermitian symmetry can simultaneously reduce the inter-carrier interference (ICI) from laser phase noise and cancel the fiber nonlinearity to the first order. In this paper, we study an interesting scenario, where we upgrade the conventional OFDM with 4-quadrature amplitude modulation (QAM) to DCS-OFDM with 16-QAM, which have equal spectrum efficiency and require no change on hardware. We conduct a simulation to compare the tolerance to the laser phase noise and fiber nonlinearity, which are the main concerns for such an upgrading. First, the 16-QAM DCS-OFDM relaxes the laser linewidth requirement and performs better with a smaller fast Fourier transform size. Second, the nonlinear tolerance of 16-QAM DCS-OFDM is better when the nonlinear effects appear. The nonlinear tolerance of DCS-OFDM depends on the dispersion compensation scheme. The maximum SNR improvement is 3.4 dB with full post-dispersion compensation, and it can increase to 6.6 dB with symmetrical dispersion compensation at the launch power of 4 dBm. Finally, we verify that the maximum SNR improvement of 16-QAM DCS-OFDM with full post-dispersion compensation is 3.7 dB at the launch power of 6.2 dBm in the experiment.

A comprehensive theoretical model of direct detection (DD) optical orthogonal frequency division multiplexing (OOFDM) system is described in general. The principle of OOFDM is introduced in detail. Several key technologies in DD-OOFDM system have been discussed. The advantages and methods for optical single sideband (OSSB) and channel estimation are analyzed completely. Other key technologies are introduced briefly.

This paper investigates the effects of zero padding and cyclic prefixing in channel equalization for coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. Two equalization-based algorithms, namely zero forcing (ZF) and minimum mean square error (MMSE) based equalizers are employed for the system The computer simulation results show that the zero padded (ZP)-CO-OFDM system outperforms its counterpart, the CP-CO-OFDM system. These results indicate that the ZP-CO-OFDM system can mitigate effects of the fiber link such as chromatic dispersion and polarization mode dispersion better than the CP-CO-OFDM system. The results also show that the MMSE based equalizer only slightly outperforms the ZF-based equalizer, that has associated low computational complexity, in the ZP-CO-OFDM system.

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) system has become attractive for use in the long haul optical transmission in the recent years. This paper extends the linear constellation precoding to the CO-OFDM system to form LCP-CO-OFDM system in order to combat the problem of large peak-to-average power ratio (PAPR) associated with the OFDM transmission scheme. In addition, three equalization-based algorithms, minimum mean square error (MMSE), zero forcing (ZF) and maximum likelihood (ML) algorithms are employed for the LCP-CO-OFDM system. The simulation results obtained suggest that the LCP-CO-OFDM system demonstrates superiority to the uncoded CO-OFDM system. The ML-based equalizer also shows the best performance in comparison with the two other equalizers, while ZF-based equalizer shows the worst performance in comparison with the LCP-CO-OFDM system.

Visible light communications (VLC) has attracted increasing attention recently from both the industry and academic fields due to its untamed free bandwidth, which can be used to provide ultra-high speed wireless communications. However, high peak to average power ratio (PAPR) is a major issue in VLC system that is based on orthogonal frequency division multiplexing (OFDM) technology. PAPR causes nonlinearities in the transmitted signal and increases the complexity in retrieving the original signal at the receiver. In this paper, a new and hybrid PAPR reduction scheme is proposed for the OFDM-based VLC system using combined signal clipping techniques and partial transmit sequence (PTS). For this proposed hybrid scheme, the signal clipping method is combined with a modified PTS method that is suitable for VLC transmission in order to further reduce the PAPR as well as the bit error rate (BER) of the OFDM-based VLC system. Evaluation of the proposed hybrid scheme has been conducted for different modulation orders and the results has been compared to the clipping methods as well as conventional PTS techniques. The simulation results obtained show that the proposed hybrid scheme provides more than 3 dB PAPR reduction gain as compared to the basic VLC-OFDM signal at a CCDF of 10−1. In comparison with the signal clipping and conventional PTS method, the proposed method obtained PAPR reduction gain of approximately 0.4 dB and 2 dB, respectively. Moreover, the proposed scheme also outperforms the other methods in terms of BER performance for all scenarios.

Visible light communications (VLCs) have received extensive attention in the research community thanks to their advantages of high bandwidth, low cost, robustness to electromagnetic interference, operation in an unregulated spectrum, and high degree of spatial confinement in indoor scenarios. One of the main limitations for high data-rate transmission in VLC systems is the limited modulation bandwidth of commercial light emitting diodes. To circumvent this limitation, spectrally efficient modulation schemes should be used. Optical orthogonal frequency-division multiplexing (O-OFDM)-based schemes have become very popular and several proofs of concept have shown their ability to attain over gigabits per second transmission rates. We consider here the use of pulse amplitude modulation and carrier-less amplitude and phase modulation schemes together with frequency-domain equalization (FDE) at the receiver as interesting alternatives to O-OFDM. We show the advantages of the former schemes in terms of the peak-to-average-power ratio, and demonstrate through numerical results the merits of FDE-based signaling in attaining high data rates.

Traditional OFDM techniques in VLC suffer from high PAPR and serious clipping distortion. In this paper, we propose a Precoded-DC-Biased Optical OFDM technique for VLC system. Numerical simulations are presented, proving substantial benefits in terms of PAPR and BER.

One major drawback of coherent optical OFDM (CO-OFDM) is its vulnerability to nonlinear fiber effects due to its high peak-to-average power ratio. Fiber nonlinearities can be mitigated using machine learning algorithms that are a nonlinear decision classifier. In this study, C-ELM based nonlinear equalizer is proposed for a MQAM CO-OFDM. MQAM CO-OFDM systems are simulated by designing a Monte Carlo simulation. In this simulation, the effect of fiber nonlinearities on received signals is demonstrated with constellation diagrams and results are given in form of BER-Fiber Length variations.

In this paper, we propose a block decision-aided (BL-DA) laser phase noise (LPN) estimation algorithm for coherent optical OFDM (CO-OFDM) systems. The OFDM symbols are divided into several blocks and the LPN estimation and compensation procedure is performed based on the decisions between these blocks. The proposed BL-DA algorithm can be applied for higher LPN estimation while at the same time ensuring a better estimation performance. Simulations are carried out in a 70.6 Gbit/s 16-QAM CO-OFDM system to verify the feasibility and efficiency of the BL-DA algorithm.

60-Ghls Optical OFDM transmissions over 100m OM1 MMF IMDD system are experimentally demonstrated utilizing 10-GHz EML intensity modulators at single 1550nm wavelength. Adaptive subcarrier bit and power loading schemes are also employed to defeat channel fading in a simple and straightforward center launching configuration. Experimental results show a good feasibility in short reach data center interconnections.

We propose a novel common phase error estimation method based on projection histogram (PH). Experimental results show that the proposed method can effectively compensate the common phase error. Compared to BPS, similar performances are obtained with much lower complexity.

A computationally efficient IFFT implementation for asymmetrically clipped optical OFDM transmitter is proposed and implemented in a Field-Programmable Gate Array. The overall computational complexity is reduced by 68% in a real-time transmitter.

Visible light communication (VLC) has become a promising complement to its radio-frequency (RF) counterpart. In VLC systems, orthogonal frequency division multiplexing (OFDM) has drawn much attention due to its high data rate, simple equalization and robustness to the inter-symbol interference (ISI). In this paper, we present a comparative performance evaluation of several classical optical OFDM schemes, including DC-biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), pulse-amplitude-modulated discrete multitone (PAM-DMT), unipolar OFDM (U-OFDM) and Flip OFDM. Since DCO-OFDM suffers from energy efficiency loss due to addition of DC-bias, whilst ACO-OFDM, PAM-DMT and U-OFDM/Flip OFDM are spectrally inefficient due to their unique frame structures, the state-of-the-art energy- and spectrum- efficient optical OFDM schemes are investigated, including asymmetrically clipped DC-biased optical OFDM (ADO-OFDM), hybrid ACO-OFDM (HACO-OFDM), asymmetrically clipped absolute value optical OFDM (AAO-OFDM), the spectral and energy efficient OFDM (SEE-OFDM), layered ACO-OFDM (LACO-OFDM), enhanced U-OFDM (eU-OFDM), optical OFDM with index modulation (O-OFDM-IM) and optical dual-mode index modulation aided OFDM (DM-OFDM). In this paper, their principles are firstly illustrated, then performance comparisons are conducted for those optical OFDM schemes in terms of spectral efficiency, energy efficiency and computational complexity. Since light emitting diodes (LEDs) need to support both the illumination and communication simultaneously, dimming control should be considered in VLC systems. Therefore, dimmable optical OFDM for practical VLC systems incorporating illumination is also addressed.

This paper presents a novel theoretical characterization of the pilot-assisted (PA) technique proposed for peak-to-average-power-ratio (PAPR) reduction in optical orthogonal frequency division multiplexing (O-OFDM). The two systems considered are direct-current biased O-OFDM (DCO-OFDM) and asymmetrically clipped O-OFDM (ACO-OFDM) in optical wireless communications. The DCO-OFDM and ACO-OFDM time-domain signals approach Gaussian and half-Gaussian distributions, respectively. The PA technique uses $P$ iterations of a pilot sequence to rotate the phase of $U$ data symbols within a PA O-OFDM frame and select the frame with the least PAPR. Thus, we utilize order statistics to characterize the PAPR distributions of the PA DCO-OFDM and ACO-OFDM system. The PA technique results in higher reduction in PAPR for high $P$ but at the expense of increased complexity. In the theoretical framework developed, we are able to determine $P$ that gives reasonable PAPR reduction gain. The theoretical analysis of PAPR reduction effects on the average optical and electrical signal power is studied. Results show that the PA technique is capable of reducing the optical energy per bit to noise power spectral density $E_{\mathrm {b({opt})}}/N_{0}$ ratio required to meet target bit-error-rate in an additive white Gaussian noise channel. Comparisons of the analytical results of PA O-OFDM signal with that of computer simulations show very good agreement.

In this article, we demonstrate the use of Symbol-Spaced, Fractionally-Spaced Decision Feedback Equalizers(SS-DFE, FS-DFE) using Least Mean Square(LMS) algorithm and Maximum Likelihood Sequence Estimator for the compensation of accumulated Chromatic Dispersion and Polarization Mode Dispersion over a maximum distance of 5000 km in a 100 Gbps Direct Detecction Orthogonal Frequency Division Multiplexing(DD-OFDM) system. BER is 10e −4 at 8.5 dBm for MLSE and 10e-3 at 7dBm for SS-TDE DFE equalization, 10e-3 at 7dBm for FS-TDE DFE equalization and 10e-1 at 4dBm without equalization for a distance of 5000km.

A cost-effective and energy-efficient self-homodyne downstream scheme is proposed for WDM-PON with inserted pilot sub-samples and interferometer-based detection. A 10-Gbps self-homodyne OFDM downstream transmission is experimentally demonstrated over 20-km SSMF with error-free operations.

We demonstrate high-bitrate coherent optical OFDM transmission utilizing low-noise Kerr frequency comb as multi-channel laser source. 4QAM-OFDM data with total bitrate of 136.0 Gb/s are successfully transmitted over a 100 km fiber link.

A simple and low-cost scheme is proposed for reducing the distortions in the coherent optical orthogonal frequency-division multiplexing (CO-OFDM) system. The total wireless channel noise and the distortions in the receiver can be considered as an additive white Gaussian noise model and all distortions can be reduced using maximum likelihood sequence estimation (MLSE) equalizers. The performance of the CO-OFDM is analyzed for different fiber lengths and laser powers. Results show that the MLSE-equalized system can outperform with a higher

We propose an efficient blind carrier frequency offset estimation algorithm for CO-OFDM systems, which utilizes only one OFDM symbol without exhaustive search computations.

We propose, for the first time, set-partition (SP) format based optical OFDM and experimentally show that SP-64QAM/SP-128QAM intensity-modulation direct-detection OFDM exhibits greatly improved performance over conventional 16QAM and 8QAM OFDM.

We experimentally evaluate the impact of realistic phase noise on single side-band optical OFDM systems, directly detected after uncompensated propagation. Measures obtained with sources typical of short-medium reach applications are compared to a semi-analytical model.

In this paper, we experimentally demonstrate the reduction of clipping noise for an OFDM-based underwater optical wireless communication (UOWC) system using decision-aided reconstruction (DAR). 2 dB SNR gain is successfully achieved for optical OFDM M-QAM signals.

As a promising modulation technology for optical communication, Orthogonal Frequency Division Multiplexing (OFDM) is now increasingly used and a lot of ways of improving the optical efficiency of Intensity Modulated/ Direct Detection (IM/DD) systems have been proposed. And real and non-negative OFDM signals are required in this kind of system. Asymmetrically clipped DC biased Optical OFDM (DCO-OFDM), Asymmetrically Clipped Optical OFDM (ACO-OFDM) and Asymmetrically clipped DC biased Optical OFDM (ADO-OFDM) can satisfy this requirement. In this paper, we analysis the properties and performance orderly of the above three systems and simultaneously compare their performance. The simulation results show that DCO-OFDM is efficient in terms of bandwidth while the ACO-OFDM is efficient in terms of optical power. More importantly, ADO-OFDM is both power-efficient and bandwidth-efficient. At the same time, a developmentally proposal for the future OFDM in IM/DD systems is put forward.

Orthogonal Frequency Division Multiplexing (OFDM) has gained great attention in the next generation Long-Reach Passive Optical Network (LR-PON) due to its high spectrum efficiency, flexible resource allocation and natural compatibility with Digital Signal Processing (DSP)-based implementation. In this paper, we propose and demonstrate a 40Gbit/s direct-detection long reach OFDM-PON system for downstream transmission over 100km standard signal mode fiber (SSMF). By using a simple Least Square (LS) method for the channel estimation, our proposed system achieves high bit rate without the need for chromatic dispersion compensation.

An adaptively modulated optical orthogonal frequency division multiplexing (OOFDM) based system has been simulated in present research. Performance analysis in terms of bit error rate (BER) and signal to noise ratio (SNR) has been carried over the system using fixed modulation for different M-array quadrature amplitude modulation (M-QAM). An adaptive modulation over OOFDM has been analyzed over three different algorithmic schemes. Impact of adaptive modulation on spectral efficiency has also been investigated for OOFDM. Simulation results show the enhancement in terms of spectral efficiency and capacity for adaptively modulated OOFDM system.

For the real-time measurement of transmission performance in the real-time optical OFDM transmission system, realization of BER test with an optimum method by utilizing FPGA, which means to complete the calculation of BER inside transceiver, become essential and efficient. An experiment setup demonstrate the dramatic real-time property and effectiveness in testing the optical OFDM transmission system.

In this paper, in order to improve the security of optical OFDM system, we propose a new method to generate the pilot sequence of channel estimation using chaotic sequence. Firstly, we assign initial values to chaotic system, and calculate a chaotic sequence through an iteration method, then converting it into a binary sequence as the pilot of a DFT-based channel estimation algorithm. When the receiving end doesn’t know the chaotic-sequence-based pilot, the system will have very high BER, and can not restore the original data, which indicate that the new method provides a certain degree of security for optical OFDM systems without increasing the system complexity.

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10−3, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.

This paper studies the frequency offset correction technique which can be applied in optical OFDM systems. Through theoretical analysis and computer simulations, we can observe that our proposed scheme named pilot self-coding (PSC) has a distinct influence for rectifying the frequency offset, which could mitigate the OFDM performance deterioration because of inter-carrier interference and common phase error. The main approach is to assign a pilot subcarrier before data subcarriers and copy this subcarrier sequence to the symmetric side. The simulation results verify that our proposed PSC is indeed effective against the high degree of frequency offset.

In this paper, we have presented analysis of 10 Gbit/s optical OFDM-RoF transmissions links with distance of 50 km and reported the improved performance by usage of a square root module (SQRT).