单载波频域均衡在地空高速数据链的应用

地空数据链的信道属于低仰角的多径信道,存在较严重的符号间干扰。正交频分复用(OFDM)是得到认可的有效抗多径方案,单载波频域均衡(SC-FDE)采用与OFDM相似的频域均衡方式,具有与OFDM相近的性能和复杂度,并克服了OFDM的一些不足。在比较SC-FDE和OFDM相似性、分析SC-FDE的信道估计与均衡基础上,提出了采用SC-FDE的地空高速数据链解调器结构,该结构在保留单载波处理的优点条件下实现高效的频域均衡。     

多载波与单载波频域均衡系统的仿真与测量

我国数字电视地面广播传输标准GB20600-2006(以下简称国标)兼容多载波正交频分复用(OFDM)和单载波频域均衡(SC-FDE)2种块传输技术.为了在国标框架下对2种传输技术的抗频率选择性衰落性能进行比较,根据国标的系统参数对采用低密度奇偶校验码(LDPC)的OFDM和SC-FDE传输系统进行了仿真,并对国标实际系统进行了测量.仿真和实测结果均表明:在LDPC编码系统中,OFDM的抗频率选择性衰落性能好于SC-FDE系统,且随着信道频率选择性衰落的恶化和调制级别的提高,这种优势会更加明显.此仿真和实测结果可以为国标系统的实现与优化提供参考.     

子载波FH—OFDM系统仿真

文章结合OFDM与FHN者的特点,分析了两种FH—OFDM通信系统模型,并给出了子载波FH—OFDM系统的公式。在此基础上,利用Matlab对子载波FH—OFDM进行了仿真,并对仿真结果进行了分析,结果表明子载波FH—OFDM具有更好的误码性能和更强的抗多径干扰能力。     

单载波频域均衡(SC-FDE)技术浅析

均衡技术是克服多径变参信道衰落的一种有效手段,也是宽带无线通信中对抗多径的一种重要方法。从设计原理出发,进行了单载波频域均衡(SC-FDE)的设计,分析了单载波均衡的技术特点,并与多载波OFDM技术在通信容量、PAPR等方面进行了比较,最后在莱斯信道进行了仿真分析,给出仿真结果,表明单载波频域均衡系统能够获得较好的性能,降低误码率。对系统工程设计有一定的借鉴意义。     

可见光通信中多载波调制技术比较分析

介绍了可见光通信系统的工作原理,论述了正交频分复用(OFDM)和离散多音频调制(DMT)2种常用多载波调制解调技术的原理特点。针对可见光通信系统调制带宽有限的情况,提出了将多载波调制技术应用于可见光通信系统的技术方案。仿真验证了OFDM和DMT调制解调技术应用于可见光通信系统时的性能,比较分析了2种多载波调制解调技术在不同信噪比条件下的传输速率和误码率。仿真结果表明,DMT技术相对于传统的OFDM技术更适用于可见光通信系统。     

单载波频域均衡技术的研究

介绍了单载波频域均衡技术的原理,在理论上对SC-FDE系统和OFDM系统的峰值平均功率比及对载波频偏和相位噪声的敏感度进行了比较.最后对SC-FDE系统和OFDM系统的性能进行了计算机仿真.     

基于小波脊线的OFDM与单载波信号识别

正交频分复用(OFDM,Orthogonal Frequency Division Multiplexing)与单载波信号广泛应用于短波通信领域。针对低信噪比和多径环境下OFDM与单载波信号识别效率低的问题,本文提出了基于小波脊线的信号识别算法。本文推导了常用信号对应的小波脊线幅度和脊点位置,并分析了小波脊线幅度和脊点形态。通过理论推导和仿真测试证明了OFDM与单载波信号对应小波脊线具有不同特征,对小波脊线差分、中值滤波、并利用其熵作为特征值能够有效的进行OFDM信号与单载波信号的识别。仿真结果证明该算法对输入信号点数要求低,在低信噪比和短波中等信道下识别效果具有稳健性和有效性。      

载波频偏对编码OFDM系统性能的影响

OFDM系统具有抗多径干扰和频带利用率高的优点,信道编码可以有效地提高传输系统的可靠性,但载波频率偏移会降低OFDM系统的性能。通过研究在有频率偏移和无频率偏移两种条件下OFDM系统中卷积编码和Turbo编码的传输性能,并进行了对比。根据仿真结果表明,Turbo编码的性能优于卷积码且编码效率越高,误比特率越小。在小信噪比情况下,信噪比对系统性能的影响大于频率偏移所产生的影响。而在大信噪比情况下,频率偏移的影响远远大于信噪比的影响。     

最优中继选择的子载波选择算法性能分析

将协作分集技术与正交频分复用(OFDM)技术相结合的协作通信系统,研究了一种OFDM协作通信最优中继选择算法和在此基础上与最优中继选择算法结合后子载波选择算法,并对它的性能进行详细分析.同时利用仿真分析了中继转发子载波信道容量和信噪比关系的协作通信性能,以及最优中继选择算法和基于最优中继选择算法的子载波选择算法的误码率.仿真结果显示,基于协作通信系统误码率性能得到了更大的提高.可见,协作分集技术与OFDM技术结合的协作通信系统大大提高了无线通信系统的性能,降低了误码率,增强了无线通信的鲁棒性.     

单载波频域均衡信道估计分析

针对高速率信息传输系统中多径衰落对单载波频域均衡(SC-FDE)信道估计造成的影响,在SC-FDE原理基础上,将无线通信中信噪比估计和SC-FDE中信道估计结合起来,对现有信噪比估计算法进行优化。分析和仿真结果表明,此方法能有效地改善多径衰落信道中信道估计的有效性,提高了频域均衡的效果,从而改善了SC-FDE系统的误码率(BER)性能。     

基于SC-FDE和Turbo码的图像传输技术

分析了单载波频域均衡技术和Turbo编译码技术,研究了基于这两种技术的无线图像传输方案,并对联合SC-FDE和Turbo码图像传输方案进行了数值仿真研究。仿真结果表明,把SC-FDE技术和Turbo码技术结合应用到无线图像传输中可以明显提高接收图像质量,改善信噪比性能。相比较传统无SC-FDE的图像传输方案,在误码率为10-5时有约1.5dB的增益。从而表明,联合SC-FDE和Turbo码可以实现图像的更加可靠的传输,是实现图像的高速传输和高频谱利用率的有效方法。     

Maximum diversity in single-carrier frequency-domain equalization

In broadband wireless communications, multipath propagation often results in an overall channel with a long impulse response that could span tens or even hundreds of symbol intervals. To equalize such long channels, conventional single-carrier time-domain equalization becomes infeasible due to high computational complexity. Relying on the use of fast Fourier transform, single-carrier frequency-domain equalization (SC-FDE) offers low-complexity equalization as well as other desirable features. In this correspondence, we prove that SC-FDE is also capable of collecting full multipath diversity even without channel coding. As far as we are aware, this is the first analytical proof of the diversity gain of SC-FDE. This conclusion justifies those existing simulation results regarding the performance comparison between SC-FDE and orthogonal frequency-division multiplexing (OFDM), and offers important guidelines for further improving SC-FDE and OFDM     

Performance analysis of concatenated BCH and convolutional coded OFDM system

ABSTRACT

Orthogonal Frequency Division Multiplexing (OFDM) is a widely used technique for wireless communications. But uncoded OFDM is not sufficient by itself, that is why channel coding is included to increase the system performance. In this study, concatenated Bose Chaudhuri Hocquenghem (BCH) and Convolutional Coded (CC) OFDM system is investigated for multipath fading channel with Additive White Gaussian Noise (AWGN). The simulation results show that the proposed concatenated code needs lower Signal-to-Noise Ratio (SNR) when compared with single BCH code, single convolutional code and even with other concatenated systems. Throughout the simulations BCH coding is performed with 128, 256, 512 Fast Fourier Transform (FFT) lengths; whereas convolutional coding is performed with 1/2, 1/3 coding rates. Furthermore, interleavers are added to the system to prevent the burst errors that occur over the channel. With the proposed system, the best result is obtained by using BCH(511,340) and CC(3,1,7) concatenation which is 8.2 dB SNR value for 10^?3 Bit Error Rate (BER). This result is very close to ideal AWGN channel value, which is 8 dB for 10^?3 BER.     

自适应OFDM系统的仿真研究

OFDM（正交频分复用）是一种无线环境下的高速传输技术,适合在多径传播和多普勒频移的无线移动信道中传输高速数据.他能有效对抗多径效应,消除符号间干扰,对抗频率选择性衰落,而且信道利用率高.本文介绍了OFDM技术特点,讨论了自适应OFDM系统,并运用Matlab/Simulnk软件,对自适应OFDM系统进行了仿真.通过仿真结果的对比得出结论,在相同的信道信噪比（SNR）下,自适应的OFDM系统比传统的OFDM系统有更低的误比特率（BER）.     

基于宽带突发单载波频域均衡传输的时域精细信道估计方法

单载波频域均衡(SC-FDE)是宽带无线通信系统中一种具有竞争力的解决方案,获得了广泛的关注和研究。SC-FDE方案不仅抗多径能力出色、复杂度低,且具有比正交频分复用(OFDM)信号更低的峰均比值。在突发SC- FDE系统中,接收机需要利用训练序列快速获取信道的特征信息,以避免解调性能损失。传统的基于训练序列的信道估计方法并不适合宽带猝发SC-FDE系统,难以兼顾估计准确性和复杂度。该文提出一种基于时域训练序列的精细信道估计方法。该方法利用时域PN序列得到信道参数的最大似然估计值,并利用信道稀疏的特征,根据信道噪声强度对信道估计值进行噪声抑制处理。仿真表明:与传统信道估计方法相比,该信道估计方法能取得更高的估计精度,且具有较低的实现复杂度。     

Performance Evaluation of Different PSK Schemes in an OFDM System Using a Real Time Image

Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation scheme that combines a large number of low data rate carriers into a composite high data communication system. Unlike in many other modulation techniques, the addition of cyclic prefix to the OFDM symbols combats the intersymbol interference and the orthogonality of the carriers allows it to combat Intercarrier interference in the OFDM modulation technique. Acknowledging these advantages, OFDM is the most preferred modulation technique in most of the next-generation wireless communication networks for transmitting many forms of digital data with higher efficiency. To evaluate the functionality and overall performance of an OFDM system, a digital data corresponding to a two-dimensional gray-scale image is used as a test signal. This paper aims at evaluating the performance of various phase shift keying (PSK) techniques taking a real time image as a test sample, which is converted into a form suitable for OFDM transmission, then transmitting the converted OFDM signal over the additive white Gaussian noise channel over various signal to noise ratio values. The performance is evaluated by comparing the clarity of the received image after demodulation with the original image, bit error rate (BER) Vs SNR, transmission and reception times of various PSK schemes (BPSK, QPSK,16-PSK and 256-PSK). The BER offered by BPSK is the least while transmission times offered by 256-PSK is the least. Along with these, different PSK schemes are compared by changing the clipping amplitude that is done to combat nonlinearities due to high peak to average power ratio.

     

BER minimized OFDM systems with channel independent precoders

We consider the minimization of uncoded bit error rate (BER) for the orthogonal frequency division multiplexing (OFDM) system with an orthogonal precoder. We analyze the BER performance of precoded OFDM systems with zero forcing and minimum mean squared error (MMSE) receivers. In the case of MMSE receivers, we show that for quadrature phase shift keying (QPSK), there exists a class of optimal precoders that are channel independent. Examples of this class include the discrete Fourier transform (DFT) matrix and the Hadamard matrix. When the precoder is the DFT matrix, the resulting optimal transceiver becomes the single carrier system with cyclic prefix (SC-CP) system. We also show that the worst solution corresponds to the conventional OFDM system; the conventional OFDM system has the largest BER. In the case of zero forcing receivers, the design of optimal transceiver depends on the signal-to-noise ratio (SNR). For higher SNR, solutions of optimal precoders are the same as those of MMSE receivers.     

BER assessment of FFT-OFDM against WHT-OFDM over different fading channel

Wavelets are brought into the wireless communication field as an orthogonal base of multi-carrier modulation and are now considered as a significant measure. Also, wavelets do contain the capability to improve bandwidth efficiency even more along with lower inter-symbol interference and inter-carrier interference. Appropriately, a BER versus SNR analysis is done for fast Fourier transform (FFT) based OFDM framework and wavelet haar transform (WHT) based OFDM framework in this work. The evaluationis demonstrated over Rayleigh and Rician fading channel utilizing dissimilar M-PSK modulation levels intended for FFT-OFDM and WHT-OFDM. The performance of the simulated test-bed is investigated via BER assessment as a function of SNR. The imitation outcome reports a significant improvement in BER of the simulated system using WHT-OFDM in comparison to FFT-OFDM for both Rayleigh and Rician fading channel. Also, the BER performance of both FFT-OFDM and WHT-OFDM is superior in Rician fading channel in comparison to Rayleigh fading channel.     

Development of MIMO–OFDM system and forward error correction techniques since 2000s

The multi-input multi-output–orthogonal frequency division multiplexing (MIMO–OFDM) system serves as one of the most promising techniques that support high data rate and high performance in diverse fading channel conditions. The paper presents an overview of MIMO–OFDM wireless technology, covering advances in physical-layer design, various space–time codes, space–frequency codes and efficient concatenated forward error correction techniques, along with interleaving to yield reduced bit error rate performance (BER). Further, the paper presents the evolution of various performance metrics that are reported since the 2000s in the literature. The evolution outcome is examined using a quadratic nonlinear fitting function to assess the interesting performance metrics. Since BER versus SNR analysis is found as the interesting performance study of the MIMO–OFDM system, the current status of the achieved BER under varying SNR is reviewed and presented.