Coarse-Fine Joint Target Parameter Estimation Method Based on AN-RSC in OFDM Passive Radar

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.

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.

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.

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.

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

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.

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

Multicarrier modulation technique also known as Orthogonal Frequency Division Multiplexing (OFDM) is considered to be the most rapidly growing technique for 4th Generation wireless communication system. Due to its high speed data rate and its ability of multipath fading channel robustness. OFDM becomes an attractive technique and it is widely adopted in many wireless communications system. OFDM signal carries its major drawback of high Peak to Average Power Ratio (PAPR) problem. Out of band radiation and in band distortion produced due to its high PAPR. Mobile phone communication suffer severe drawback during its amplification. When OFDM employed a non linear Power Amplifier (PA), it produces the fluctuation in amplitude of OFDM signal. This paper discusses the method to overcome PAPR in terms of its performance by using improved clipping technique for PAPR reduction. This method is easy to implement and reduces the amount of PAPR by clipping the peak of the maximum power signal. We present an improved method for PARR reduction for reducing peak magnitude of OFDM signal. This scheme simultaneously minimizes the peak magnitude of PAPR in OFDM signal.

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.

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.

Orthogonal frequency division multiplexing (OFDM) is an attractive and effective technique for wireless communications. However, an OFDM signal has a large peak-to-average power ratio (PAPR), which will cause serious nonlinear distortion especially when the signal passes through a nonlinear system. Adaptive symbol selection scheme (ASSS) is used to reduce the unwanted PAPR by selecting the adaptive OFDM signal with the smallest PAPR before transmitting. Because of the side information needed in ASSS, the effective data rate finally got in the receiver decreases. We develop a new modulation method using ASSS and channel estimation together, which can transmit the needed side information in the pilot tones made by channel estimation during the signal transmission. Our simulation results show that the method we proposed is a promising and valuable technique for reducing PAPR in OFDM signals.

Real-time data transmission with high data rate and low bit error rate is realized by underwater multi-carrier acoustic communication system, which plays an important role in AUV. OFDM (orthogonal frequency division multiplexing) is an attractive multi-carrier communication method around the world. According to the requirements of OFDM signal transmission in underwater multi-carrier acoustic communication, the OFDM signal transmitter with FPGA (field programmable gate array) and DSPs (digital signal processor, ADSP-TS101) is designed and implemented. And the methods of interrupts of DMA (direct memory access) and half-full are used to realize data transmission between DSP and FIFO (first in first out) with high speed. And the signal synthesis method, DDWS (direct digital wave synthesis), is adopted to realize producing OFDM signal. From the results, we can see that the transmitter has good steady and can complete the signal transmission in real time.