A frame synchronization solution for orthogonal frequency division multiplexing system

To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox, a timing metric related to TSC scheme is put forward and examined. The specific method to select a threshold value provides more precise detection results, which can be shown by performance comparison between the two schemes through Monte Carlo simulation. Taking IEEE 802.1 la WLAN standard as an example, the proposed approach is superior to the most popular Schmidl scheme in terms of BER.

Performance of multi-band orthogonal frequency division multiplexing ultra wide-band system on IEEE UWB channels

Multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wide-band (UWB) is a novel wireless communication technology. It has many advantages and is being actively researhed. In this study, we constructed and implemented a simulation model of UWB communication systems in Simulink. We found the MB-OFDM UWB system has the best performance in distance between 4 m to 10 m without the line-of-sight requirement.

The Effect and Compensation of Phase Noise on Orthogonal Frequency Division Multiplexing (OFDM) System

Orthogonal Frequency Division Multiplexing (OFDM) is characterized by its high data rate. However, the modulation method used in the system is subject to the influence of phase noise due to the need of time synchronization. In this paper, an algorithm based on MMSE (minimum mean square error) is developed to compensate the influence of both the common phase error (CPE) and inter carrier interference (ICI), which are two aspects of phase noise, under common Gaussian white noise. The result of noise cancellation is presented in signal-to-noise ratio (SNR) and symbol error rate (SER). Like digital signal in general, SNR can reduce SER with or without phase noise compensation. The compensation of phase noise significantly reduces the SER of the decoded signal. However, the bandwidth of phase noise still determines the signal accuracy. Under high bandwidth of phase noise, increasing SNR will only slightly increase SER, which is not efficient.

Joint nonlinearity and chromatic dispersion pre-compensation for coherent optical orthogonal frequency-division multiplexing systems

This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk- off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high- dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20 × 80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold （for Q 〉 10 dB） about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/（nm.km） dispersion coefficients.

Security in Multicast Over α-μ Fading Channels with Orthogonal Frequency Division Multiplexing

The orthogonal space-frequency block coding (OSFBC) with orthogonal frequency division multiplexing (OFDM) system reduces complexity in the receiver which improves the system performance significantly. Motivated by these advantages of OSFBC-OFDM system, this paper considers a secure wireless multicasting scenario through multiple-input multiple-output (MIMO) OFDM system employing OSFBC over frequency selective α-μ fading channels. The authors are interested to protect the desired signals from eavesdropping considering the impact of the number of multicast users and eavesdroppers, and the fading parameters α and μ. A mathematical model has been developed based on the closed-form analytical expressions of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multi-casting (SOPM) to ensure the security in the presence of multiple eaves-droppers. The results show that the security in MIMO OSFBC OFDM system over α-μ fading is more sensitive to the magnitude of α and μ and this effect increases in the high signal-to-noise ratio (SNR) region of the main channel.

Implementation of Synchronization Technology in Orthogonal Frequency Division Multiplex System Based on Field Programming Gate Array

In this paper,analyzed is the symbol synchronization algorithm in orthogonal frequency division multiplex(OFDM)system,and accomplished are the hardware circuit design of coarse and elaborate synchronization algorithms.Based on the analysis of coarse and elaborate synchronization algorithms,multiplexed are,the module accumulator,division and output judgement,which can evidently save the hardware resource cost.The analysis of circuit sequence and wave form simulation of the design scheme shows that the proposed method efficiently reduce system resources and power consumption.

Performance Evaluation of Wavelength Division Multiplexing Photonic Analogue-to-Digital Converters for High-Resolution Radar Systems

The performance of the wavelength division multiplexing (WDM) photonic analogue-to-digital converter (ADC) used for digitization of high-resolution radar systems is evaluated numerically by using the peak signal-to-noise ratio (SNR) metric. Two different WDM photonic ADC architectures are considered for the digitization of radar signals with 5 GHz of bandwidth (spatial resolution of 3 cm), in order to provide a comprehensive study of the compromises present when deploying radar signals with high-resolution: 1) a four-channel architecture with each channel employing an ADC with 5 GSamples/s, and 2) an eight-channel architecture with each channel employing an ADC with 2.5 GSamples/s. For peak powers of the pulsed source between 10 and 20 dBm and a distance between the radar antenna and the sensing object of 2.4 meters, peak SNR levels between 29 and 39 dB are achieved with the eight-channel architecture, which shows higher peak SNR levels when compared with the four-channel architecture. For the eight-channel architecture and for the same peak powers of the pulsed source, peak SNR levels between 11 and 16 dB are obtained when the distance increases to 13.5 meters. With this evaluation using the peak SNR, it is possible to assess the performance limits when choosing a specific radar range, while keeping the same resolution.

Cyclic-Auto-Correlation Based Timing Estimation Algorithm for Time-Frequency Overlapping Multi-Carrier Signals

In recent years,the time-frequency overlapping multi-carrier signal has been a novel and valuable topic in blind signal processing,especially in the non-cooperative receiving field.But there is little related research in public published papers.This paper proposes two timing estimation algorithms,which are non-data-aided and based on the cyclic auto-correlation function.In order to evaluate the performance of the proposed algorithms,the theoretical bound of the timing estimation is derived.According to the analyses and simulation results,the effectiveness of the proposed algorithms has been demonstrated.It shows that MethodⅠhas better performance than MethodⅡ.However,MethodⅡdoes not need prior information,so it has a wider range of applications.

SIGNAL CONSTELLATIONS DESIGN FOR DIFFERENTIAL UNITARY SPACE-TIME IN MIMO-OFDM SYSTEM OVER FREQUENCY-SELECTIVE FADING CHANNELS

In this paper, the design of signal constellations parameters is studied for Differential Unitary Space-Time Modulation (DUSTM) based on the design criterion of maximizing the diversity product. Further, noninteger searching method for the signal constellation parameters design is proposed in order to get better codes. Experimental results show that under the different Doppler spread and data transmission rate, the proposed design performs better than the previous design using integer parameters in Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system over frequency-selective fading channels.

A High Spectral Efficient Frequency-Domain Channel-Estimation Method for the Polarization-Division-Multiplexed CO-OFDM-OQAM System

Contrary to the other multi-carrier modulation systems, the coherent optical orthogonal frequency division multiplexing communication system with an offset quadrature amplitude modulation (CO-OFDM-OQAM) possesses inherent imaginary interference (IMI). This has an important impact on the channel estimation process. Currently, a variety of frequency-domain channel estimation methods have been proposed. However, there are various problems that still exist. For instance, in order to reduce the influence of IMI, it is necessary to insert more guard intervals between the training sequence and the payload, leading to the occupation of excessive spectrum resources. In order to address this problem, this work designs a high spectral efficient frequency-domain channel estimation method for the polarization-division-multiplexing CO-OFDM-OQAM systems. First, the working principle of the proposed method is described in detail. Then, its spectral efficiency, power peak-to-average ratio, and channel estimation performance are studied based on simulations. The simulation results show that the proposed method improves the spectral efficiency without worsening the power peak-to-average ratio. The channel estimation capability of this method is verified in three scenarios of long-distance transmissions, including back-to-back, 100 km, and 200 km transmissions. .

Coarse-fine joint target parameter estimation method based on AN-RSC in OFDM passive radar

In this paper,we study the accuracy of delay-Doppler parameter estimation of targets in a passive radar using orthogonal frequency division multiplexing(OFDM)signal.A coarse-fine joint estimation method is proposed to achieve better estimation accuracy of target parameters without excessive computational burden.Firstly,the modulation symbol domain(MSD)method is used to roughly estimate the delay and Doppler of targets.Then,to obtain high-precision Doppler estimation,the atomic norm(AN)based on the multiple measurement vectors(MMV)model(MMV-AN)is used to manifest the signal sparsity in the continuous Doppler domain.At the same time,a reference signal compensation(RSC)method is presented to obtain highprecision delay estimation.Simulation results based on the OFDM signal show that the coarse-fine joint estimation method based on AN-RSC can obtain a more accurate estimation of target parameters compared with other algorithms.In addition,the proposed method also possesses computational advantages compared with the joint parameter estimation.

Adaptive channel estimation based on pilot signals and transform-domain processing in SISO/MIMO OFDM systems

Based on the transform-domain characteristics of pilot signals,a band suppression filter is used as a transform-domain filter to restrain the interference of noise in channel estimation.The performance effect on channel estimation for an orthogonal frequency division multiplex （OFDM） system by different energy coefficients in the transform domain and the energy coefficient under the different signal-to-noise ratios （SNR） are also analyzed.A new energy coefficient expression is deduced.It is theoretically proven that dynamically selecting an energy coefficient can significantly improve the performance of channel estimation.Simulation results show that the proposed algorithm can achieve better performance close to the theoretic bounds of perfect channel estimation. The algorithm is adapted to single-input single-output （SISO） OFDM and multi-input multi-output （MIMO） OFDM systems.

基于三维正交频分复用的可见光通信系统研究

为解决调制带宽受限和频率选择性衰落问题,提出了一种基于三维正交频分复用(3D-OFDM)的可见光通信系统,通过三维星座映射,该系统增加了相邻星座点间的最小欧式距离(MED),从而降低了系统的误码率。针对接收机的硬判决易受到可见光信道非线性效应和采样频偏干扰的问题,提出了一种基于K均值聚类解调的三维星座解映射方法。结果表明,在误码率为3.8e-3时,与采用16QAM和8QAM调制的2D-OFDM系统相比,所提出的16ary与8ary的3D-OFDM,分别能够实现3 dB和5 dB的信噪比增益;此外,所提出的3D-OFDM系统在峰均功率比(PAPR)方面也有优势,分别降低了0.3 dB和0.4 dB。所提出的3D-OFDM可见光通信系统具有更优的误码性能。

Design of integrated radar and communication system based on MIMO-OFDM waveform

Orthogonal frequency division multiplexing (OFDM) waveform enables radar and communication functions simultaneously, which encounters low angle resolution and poor data rate for traditional single input single output (SISO) systems. To solve these problems, an integrated radar and communication system (IRCS) with multiple input multiple output (MIMO) OFDM waveform is proposed. The different limitations of radar and communication in designing such a system are investigated. Then, an optimization problem is devised to obtain suitable system parameters, including the number of subcarriers, subcarrier spacing, number of symbols, pulse repetition frequency (PRF) and length of cyclic prefix (CP). Finally, to satisfy the requirements of both radar and communication, the IRCS parameters are derived in three typical cases. Several numerical results are presented to illustrate the demands of radar and communication, inconsistent or consistent, for the IRCS parameters and the superiority of the proposed system.

High resolution range profile analysis based on multicarrier phase-coded waveforms of OFDM radar

Orthogonal frequency division multiplexing（OFDM） radar with multicarrier phase-coded waveforms has been recently introduced to achieve high range resolution.The conventional method for obtaining the high resolution range profile（HRRP） is based on matched filters.A method of synthesizing HRRP based on the fast Fourier transform（FFT） and decoding is proposed.The mathematical expressions of HRRP are derived by assuming an elementary scenario of point-scattering targets.Based on the characteristic of OFDM multicarrier signals,it mainly analyzes the influence on HRRP exerted by several factors,such as velocity compensation errors,the sampling frequency offset,and so on.The conclusions are significant for the design of the OFDM imaging radar.Finally,the simulation results demonstrate the validity of the conclusions.

Frequency Diversity for OFDM Mobile Communication via Underwater Acoustic Channels

The major constraint on the performance of orthogonal frequency division multiplexing （OFDM） based underwater acoustic （UWA） communication is to keep subcarriers orthogonal. In this paper, Doppler estimation and the respective compensation technique along with various diversity techniques were deliberated for OFDM-based systems best suited for underwater wireless information exchange. In practice, for mobile communication, adjustment and tuning of transducers in order to get spatial diversity is extremely difficult. Considering the relatively low coherence bandwidth in UWA, the frequency diversity design with the Doppler compensation function was elaborated here. The outfield experiments of mobile underwater acoustic communication （UWAC） based on OFDM were carried out with 0.17 bit/（s-Hz） spectral efficiency. The validity and the dependability of the scheme were also analyzed.

Joint frequency offset tracking and PAPR reduction algorithm in OFDM systems

This paper presents an algorithm that aims to reduce the peak-to-average power ratio（PAPR） of orthogonal frequency division multiplexing（OFDM） communication systems while maintaining frequency tracking.The algorithm achieves PAPR reduction by applying the complex conjugates of the data symbol obtained from the frequency domain to cancel the phase of the data symbol.A likelihood estimator is used to obtain the sub-carrier phase error due to the residual carrier frequency offset（RCFO） using the same complex conjugates as a pilot signal.Furthermore,a joint time and frequency domain multicarrier phase locked loop（MPLL） is developed to compensate additional frequency offset.Simulation results show that this algorithm is capable of reducing PAPR without impacting the frequency tracking performance.

Blind channel estimation for multiple antenna OFDM system subject to unknown carrier frequency offset

The problem of channel estimation for multiple an- tenna orthogonal frequency division multiplexing （OFDM） systems subject to unknown carrier frequency offset （CFO） is addressed. Multiple signal classification （MUSIC）-Iike algorithm, which generally has been used for direction estimation or frequency estimation, is used for channel estimation in multiple antenna OFDM systems. A reduced dimensional （RD）-MUSIC based algorithm for channel estimation is proposed in multiple antenna OFDM systems with unknown CFO. The Cramer-Rao bound （CRB） of channel estimation in multiple antenna OFDM systems with unknown CFO is derived. The proposed algorithm has a superior performance of channel estimation compared with the Capon method and the least squares method.

Joint timing synchronization and frequency offset acquisition algorithm for MIMO OFDM systems

For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform （FRFT） is proposed. The linear frequency modulation signals superimposed on the data signals are used as the training signals. By performing FRFT on the received signals and searching the peak value of the FRFT results, the receiver can realize timing synchronization and frequency offset acquisition simultaneously. Compared with the existing methods, the proposed algorithm can provide better timing synchronization performance and larger frequency offset acquisition range even under multi-path channels with low signal to noise ratio. Theoretical analysis and simulation results prove this point.

Pseudo-noise preamble based joint frame and frequency synchronization algorithm in OFDM communication systems

Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window, and the carrier frequency offset （CFO） due to Doppler frequency shift or the frequency mismatch between the transmitter and receiver oscil ators, can bring severe inter-symbol interference （ISI） and inter-carrier interference （ICI） for the OFDM system. Relying on the relatively good correlation charac-teristic of the pseudo-noise （PN） sequence, a joint frame offset and normalized CFO estimation algorithm based on PN preamble in time domain is developed to realize the frame and frequency synchronization in the OFDM system. By comparison, the perfor-mances of the traditional algorithm and the improved algorithm are simulated under different conditions. The results indicate that the PN preamble based algorithm both in frame offset estimation and CFO estimation is more accurate, resource-saving and robust even under poor channel condition, such as low signal-to-noise ratio （SNR） and large normalized CFO.