Recovery of missing samples in Orthogonal Frequency Division Multiplexing signals with optimisation using data carriers

A definition of least cyclostationary order (LCO) is proposed based on the inner cyclic period of single carrier and orthogonal frequency division multiplexing (OFDM) signals. The LCOs of single carrier and OFDM signals are derived. Since the LCO has a relationship with the carrier frequency offset (CFO), a blind CFO estimation scheme for single carrier and OFDM signals can be proposed. The novel scheme is entirely blind without any priori information and is proved to be the same as cumulants estimation when the LCO is known. However, the new scheme is superior to the estimation based on cumulant when the LCO is unknown. The mean-square error of M-phase shift keying signals approaches the Cramer–Rao bound in additive white Gaussian noise (AWGN) channel. Simulation results are given to verify the effectiveness of the proposed blind estimation scheme in Rician fading channel and in AWGN channel.

We investigate a novel dispersion compensating technique in double sideband (DSB) modulated and directed-detected (DD) passive optical network (PON) systems using super-Nyquist image induced aliasing. We show that diversity is introduced to the higher frequency components by deliberate aliasing using the super-Nyquist images. We then propose to use fractional sampling and per-subcarrier maximum ratio combining (MRC) to harvest this diversity. We evaluate the performance of conventional orthogonal frequency division multiplexing (OFDM) signals along with discrete Fourier transform spread (DFT-S) OFDM and code-division multiplexing OFDM (CDM-OFDM) signals using the proposed scheme. The results show that the DFT-S OFDM signal has the best performance due to spectrum spreading and its superior peak-to-average power ratio (PAPR). By using the proposed scheme, the reach of a 10-GHz bandwidth QPSK modulated OFDM-PON can be extended to around 90 km. We also experimentally show that the achievable data rate of the OFDM signals can be effectively increased using the proposed scheme when adaptive bit loading is applied, depending on the transmission distance. A 10.5% and 5.2% increase in the achievable bit rate can be obtained for DSB modulated OFDM-PONs in 48.3-km and 83.2-km standard single mode fiber (SSMF) transmission cases, respectively, without any modification on the transmitter. A 40-Gb/s OFDM transmission over 83.2-km SSMF is successfully demonstrated.

Integration system of photon-assisted W-band millimeter wave wireless communication and free space optical communication based on OFDM signal transmission

Orthogonal frequency division multiplexing (OFDM) signals have a generic problem of high peak to average power ratio (PAPR) which is defined as the ratio of the peak power to the average power of the OFDM signal. The drawback of the high PAPR is that the dynamic range of the power amplifiers (PA) & digital-to-analog (D/A) converters required during the transmission and reception of the signal is higher. As a result, the total cost of the transceiver increases, with reduced efficiency. This paper includes an idea of the PAPR constraint, along with the implementation and analysis of some specific algorithms for PAPR reduction of the OFDM signals. All the PAPR reduction algorithms are implemented and tested in the OFDM transceiver designed using Matlab. Analyzing some specific algorithms, we propose a novel algorithm by combining the subcarrier phase adjustment and linear combination of the time domain OFDM signals. Simulation results for a OFDM system employing Quadrature Amplitude Shift Keying (QASK) symbols and Quadrature Amplitude Modulation (QAM) can achieve a PAPR reduction of 5 dB.

Recently many researchers have turned their interests to Orthogonal Frequency Division Multiplexing (OFDM) signal since its promising features in radar. This paper concerns a novel Synthetic Aperture Radar (SAR) system which employs this OFDM signal. Though the OFDM will bring lots of advantages, the performance may be changed since the signal of SAR is different from conventional ones. To evaluate the change, this paper will give a theoretical analysis and the corresponding simulation results from the viewpoint of ambiguity function. This ambiguity function is equivalent to the role of Point Spread Function (PSF) which is often used in SAR for evaluating resolutions. Comparing to the conventional SAR with LFM signal, it is proved that the resolution of SAR based on OFDM is equivalent to the conventional one or even better. This ambiguity function also provides a principle for selecting various OFDM signals as the transmit signal of SAR.

We have investigated and demonstrated a novel scheme to generate orthogonal frequency division multiplexing (OFDM) signals for Radio Over Fiber (ROF) systems using a direct-modulation laser (DML). We employ the Fiber Bragg Grating (FBG) because the bandwidth of the optical modulator is largely reduced and the architecture of the ROF system is simpler. The 40 GHz optical mm-wave signal was generated by a DML driven by the 2.5Gb/s electrical OFDM signals carried by only 20 GHz RF signals. This novel scheme employs a low-cost DML to generate mm-wave signal to carry OFDM signals which is a practical scheme to be applied for the future broadband access networks.

We investigate the applicability of spin-controlled vertical-cavity surface-emitting lasers (spin-VCSELs) for optical transmitters in analog radio-over-fiber systems by using spin-flip rate equations. In addition to the current modulation for generating orthogonal frequency division multiplexing (OFDM) signals, we use the spin polarization modulation to excite a high-frequency polarization oscillation corresponding to a millimeter-wave carrier frequency. The polarization oscillation is converted to intensity modulation by using a polarizer, and the millimeter-wave carrier and the OFDM signals can be combined. Our results indicate that OFDM signals with millimeter-wave carrier can be generated by using the spin- VCSEL, and bandwidth of the current modulation in the spin-VCSEL limits data rate of the OFDM signals.

We have proposed a novel spatial filtering technique named Virtual Subcarrier Assignment (VISA) for orthogonal frequency division multiplexing (OFDM) signals, which enables the transceiver equipped with an adaptive array antenna (AAA) to selectively receive or reject OFDM signals through coloring them with different virtual subcarrier positions in their frequency spectra. In this paper, we develop the VISA to use multiple virtual subcarrier assignment, which assigns a different combination of multiple virtual subcarrier positions in the frequency spectrum to each OFDM signal. Furthermore, we present two kinds of recursive least square (RLS)-based array weight control methods to support the VISA with multiple subcarrier puncturing in an IEEE802.1 la-based system and evaluate the link-level performance in typical indoor wireless environments by computer simulations.

The authors propose a computationally efficient spectrum sensing solution for an orthogonal frequency division multiplexing (OFDM) signal in a frequency-selective fading channel with additive white Gaussian noise (AWGN). The authors' assumption is that the data symbols, channel coefficients and the noise variance are all unknown. The nature of the problem leads them to find an invariant detector. The optimum one is uniformly most powerful invariant (UMPI); their effort shows that this test does not exist, as the final decision statistic depends on some unknown parameters; although, they derive the most powerful invariant (MPI) detector, implanting these parameters, to provide an upper bound for invariant detectors. Instead, the authors develop the generalised likelihood ratio test (GLRT), substituting the unknown parameters by their maximum likelihood (ML) estimates in the Neyman–Pearson likelihood ratio. Furthermore, they propose a computationally efficient implementation of the resulting detector. Simulation results show a slight decrease in efficiency against gaining so much computational complexity (CC) improvement. For more comparisons they also derive the conventional energy detector, namely, generalised energy detector (GED) for a binary phase shift keying (BPSK) signal, to show the adequacy of the GLR detector performance which would be demonstrated by simulation results.

This paper presents an analysis of amplitude distortions happening in an orthogonal frequency division multiplexing (OFDM) signal at communication receivers. It is shown in this paper that the amplitude distortion causes inter-carrier interference (ICI) in an OFDM system. Simple but efficient solutions are proposed for combating different amplitude distortions and subsequent ICI cancellation. Simulation results in typical urban channel and Gaussian channel show that extra gains are obtained by introducing these techniques into an existing OFDM receiver system.

This paper studies different coarse positioning techniques for wireless networks using orthogonal frequency division multiplexing (OFDM) signals. The methods under study are based on timing synchronization algorithms and various preambles embedded in the OFDM signal. Also correlation-based approaches and Multiple Signal Classification (MUSIC) approaches are investigated. The performance of the studied estimation algorithms is analyzed in terms of root mean square error (RMSE), obtained from computer simulation results and the aim is to provide a detailed comparison of various OFDM preamble-based timing estimators.

This paper presents a novel method of symbol duration estimation for orthogonal frequency division multiplexing (OFDM) signals. This method exploits the cyclostationarity of OFDM signals and estimates the symbol duration by maximizing a sum of modulus squares of cyclic correlation estimates in the cyclic domain. The computer simulation has been carried out and good performance has been obtained when the SNR is above 4 dB

We propose a power-efficient method for transmitting multiple frequency-division multiplexed (FDM) orthogonal frequency-division multiplexing (OFDM) signals in intensity-modulation direct-detection (IM-DD) optical systems. This method is based on quadratic soft clipping in combination with odd-only channel mapping. We show, both analytically and experimentally, that the proposed approach is capable of improving the power efficiency by about 3 dB as compared to conventional FDM OFDM signals under practical bias conditions, making it a viable solution in applications such as optical fiber-wireless integrated systems where both IM-DD optical transmission and OFDM signaling are important.

Cyclostationarity is an important characteristic of signals. The orthogonal frequency-division multiplexing (OFDM) signal is cyclostationary. Explicit formulas for the spectral correlation density (SCD) for OFDM signal are derived. To illustrate the spectral correlation characteristics of OFDM signal, the magnitudes of the spectral correlation functions are graphed in graphical terms as the heights of surfaces above a bi-frequency plane. The accurate analytic expression of the SCD function is very helpful for blind signal processing.

Probabilistically shaped 64QAM OFDM signal transmission in a heterodyne coherent detection system