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Volkan Kumbasar Ouz Kucur A. Arif Ergin Ertan
ztürk 《Wireless Communications and Mobile Computing》2009,9(9):1243-1250
Using genetic algorithm (GA), optimal wavelets are obtained to reduce ISI and ICI powers of a wavelet‐based orthogonal frequency division multiplexing (OFDM) system over a practical two path low‐voltage powerline channel or two path fading channel by relaxing the perfect quadrate mirror filter (QMF) orthogonality. Optimum wavelet‐based OFDM system experiences less interference compared to conventional and Daubechies (Db) wavelet‐based OFDM systems. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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多用户OFDM系统上行链路的粗频偏及定时估计 总被引:1,自引:0,他引:1
上行链路中的粗频偏及定时估计是多用户 OFDM系统的关键技术之一。如果粗频偏估计不准 ,将带来严重的子载波间干扰 ( ICI) ,而定时估计引入的符号间干扰 ( ISI)虽然可以通过加入保护间隔予以消除 ,但是如果定时估计不稳定将影响整频偏移的估计及均衡的效果。本文提出了一种基于 PN序列的粗频偏及定时估计 ,仿真结果表明该方法具有良好的性能 相似文献
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基于Radix-22 SDF(single-path delay feedback)的蝶形运算结构设计了一个级数在64、256、1024、2048之间可选的可伸缩FFT(Scaleable FFT)处理器,以较少的硬件规模满足了宽带自适应正交频分复用(OFDM)传输系统子载波数目可变、数据流量高、低处理延迟、设置灵活的处理要求.文中还针对输入OFDM信号的波形分布特性,仿真分析了该FFT处理器在采用不同的中间处理字长和旋转因子量化字长时其输出信噪比和所占用逻辑单元数目的变化,并据此合理选择了实现参数,在性能提高的同时有效减少了其硬件规模. 相似文献
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FFT算法在OFDM中的应用研究与设计 总被引:4,自引:0,他引:4
针对当前高速数据传输技术中多径效应,符号间干扰的缺陷,提出了正交频分复用(OFDM)系统的设计方案。该方案利用快速傅里叶变换FFT实现调制和解调。这里以Quartus Ⅱ为平台用VHDL语言编程实现各模块,设计了FFT处理器。通过综合仿真和时序分析与MATLAB仿真结果比较验证其正确可行。该系统可以解决高速信息流在信道中的传输问题,可以有效地对抗多径效应,消除符号间干扰,实现数据的高速传输。 相似文献
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针对正交频分复用系统中接收信号因受传输环境的大、小尺度衰落、多普勒衰落影响,使接收信号均值变化较大而导致ADC过载和解调器溢出的问题,提出了一种基于双环设计理念的数字AGC设计算法;该算法通过在解调器的设计中,引入前、后环反馈的双环AGC,使接收系统解调时动态地调节信号均值,防止均值发生过大跳变;实验仿真结果显示,接收信号时,该方法可以降低系统的均方差,有效地防止ADC过载和OFDM解调器溢出;当信号经历信道为动态信道,调节效果更佳。 相似文献
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叶奕亮 《南京邮电学院学报(自然科学版)》2009,(5):69-71
提出了OFDM(正交频分复用)利用FFT(傅里叶变换)实时同步方式的方案,在多径环境下具有有良好的特性。研究了OFDM的原理后,采用防卫间隙相关处理等技术对接收信号进行FFT、检波,进而求得传递函数,并对此传递函数进行IFFT(快速傅里叶逆变换),求得时间轴延迟信号,实现高精度实时处理。 相似文献
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OFDM系统中高速FFT处理器的FPGA实现 总被引:1,自引:0,他引:1
针对OFDM系统中FFT处理器的设计要求,选择并具体分析FFT基4-DIF算法流程,并利用现场可编程设计开发了高速FFT信号处理器。本设计采用Verilog HDL语言进行描述,并通过了仿真和验证。 相似文献
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Confidentiality of information must be maintained when it is required to be transmitted over a communication channel or when it is stored in a computer for further information access. Establishing a highly reliable and secure means of wireless communication for the transfer of digital data (text, images, audio, and video) from source to destination is becoming a prime requirement in present‐day wireless communications. Security can be achieved at the network level as well as at the data level. Data‐level security is made through cryptographic techniques. This paper emphasizes data‐level security aspects in a wireless communication system for the secure transmission of images over an AWGN channel condition. Here, a crypto orthogonal frequency division multiplexing system (crypto‐OFDM system) is designed using Rubik's cube encryption algorithm scheme for secured transmission of images under the MATLAB environment. The quality of the image transmission is analyzed using peak signal to noise ratio (PSNR) and BER at different SNR conditions. The quality of the encryption algorithm was also tested with statistical metrics, which are the histogram, NPCR, UACI, entropy, correlation coefficient analysis, etc. The numerical results reveal that a DCT‐based crypto‐OFDM system with Rubik's cube algorithm show a better performance over earlier cryptosystems and also perform superior to the original/basic OFDM system. The statistical analysis tests prove that Rubik's cube algorithm is one of the most robust algorithms for security point of view and is easy to implement, as Rubik's cube algorithm makes use of natural characteristics of pixel values, which form the basis for designing the secret key . 相似文献
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基于改进FFT算法的OFDM调制/解调模块设计 总被引:4,自引:4,他引:0
文章对传统FFT算法进行了改进,改进后的算法将N点DFT分解成二维√N点DFT的组合,在结构上更适合于用流水线方式实现FFT.文章首先对算法进行了推导,然后基于该算法设计了一个64点、32位字长的定点IFFT/FFT模块,用于802.11a中OFDM的调制/解调.与传统的流水线FFT比较,该模块中的复数乘法运算全部采用移位相加操作完成,因而消除了乘法器及旋转因子ROM的使用,降低了功耗.最后,对该模块进行了验证仿真.结果表明,在流水线饱和的情况下,该模块完成一个64点的FFT运算只需要8个时钟周期,在20MHZ时钟频率下,该模块的功耗为0.26W,完全能满足移动通信中对于高速度、低功耗的要求. 相似文献
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Po‐Hao Chang Shiann‐Shiun Jeng Jia‐Ming Chen 《International Journal of Communication Systems》2010,23(4):447-461
One major defect in orthogonal frequency division multiplexing systems is the high peak‐to‐average power ratio (PAPR) at the transmitter. The linear nonsymmetrical transform (LNST) technique, one of the companding transform (CT) techniques for PAPR reduction, offers excellent performance, but requires additional side information. In this paper, a new ‘root CT’ technique without additional side information is proposed, and it can reach a good trade‐off between the PAPR reduction and the bit error rate (BER). The theoretical analysis of the proposed root technique is also derived. The simulation results show that the proposed root CT technique can achieve more efficient PAPR reduction and better power spectrum density than those of the LNST technique. The BER of the proposed CT technique without additional side information is close to that of the LNST technique with additional side information when the AWGN or multipath fading channels are considered. Furthermore, the simulation results also demonstrate that the proposed technique offers better performance than that of the µ‐law technique over the AWGN and multipath fading channels. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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在基于正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)的无线系统中,快速傅里叶变换(Fast Fourier Transform,FFT)作为关键模块,消耗着大量的硬件资源。为此,针对于IEEE802. 11a标准的无线局域网基带技术,提出了一种低硬件开销、低功耗的基-24算法流水线架构FFT处理器设计方案。在硬件实现上,采用单路延迟负反馈(Single-path Delay Feedback,SDF)流水线架构;为了降低硬件资源消耗,基于新型的改良蝶形架构利用正则有符号数(Canonical Signed Digit,CSD)常数乘法器替代布斯乘法器完成所有的复数乘法运算。设计采用QUARTUS PRIME工具进行开发,搭配Cyclone 10 LP系列器件,编译结果显示该方案与其他已存在的方案相比,至少节约硬件成本25%,降低功耗18%。 相似文献
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Cognitive radio is a novel technology to address the problem of spectrum under-utilization, by allowing the secondary users to dynamically use the spectrum of the primary users. OFDM is a potential candidate for the physical layer of cognitive radio, due to its inherent features of spectrum shaping, spectrum analysis and robustness to multipath. OFDM based cognitive radio, however suffers from out-of-band radiation (OOBR). In cognitive radio, suppression of OOBR is much more important as the interference to the primary users needs to be kept to the minimum possible level. In the literature, time and frequency characteristics of the transmitted signal have been exploited to minimize the OOBR. In this paper, we investigate the possibility of combining merits of the constellation expansion (CE) technique and the active interference cancellation (AIC) technique for suppression of OOBR. We show through simulations that the joint technique based on CE and AIC achieves much better OOBR reduction, with a slight degradation in error performance. 相似文献
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基于OFDM信号的循环平稳特性,提出一种在射频干扰环境下OFDM系统的盲信号干扰噪声比估计方法。通过分析发送信号,射频干扰信号以及高斯白噪声的周期自相关函数能量分布规律,选取合适的延时变量和循环频率在功率谱域能有效分离信号功率和干扰加噪声功率分量,从而估计出信号干扰噪声比值。计算机仿真结果表明,和经典的二阶四阶矩(M2M4, second-order and fourth-order moments)盲信号干扰噪声比估计方法相比,新方法不仅能够有效估计射频干扰环境下OFDM系统的信号干扰噪声比值,而且无论是估计性能还是复杂度都优于M2M4方法;同时在快衰落Rayleigh信道下,新方法也能有效的估计出信号干扰噪声比值。进一步,所提方法具有对射频干扰信号密度不敏感的优点。 相似文献
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Shiann‐Shiun Jeng Jia‐Ming Chen Po‐Hao Chang 《International Journal of Communication Systems》2011,24(11):1467-1479
Orthogonal Frequency Division Multiplexing (OFDM) systems have become the most promising wireless communication systems in the recent years. For OFDM systems, there is one major drawback, which is the high peak‐to‐average power ratio (PAPR). Companding techniques have been frequently proposed to reduce PAPR. Exponential companding technique offers efficient PAPR reduction with a low bit error rate (BER). However, the exponential companding technique is difficult to implement. This paper utilizes the Padé approximation to simplify the exponential companding technique. The simulation results demonstrate that the proposed companding technique offers the same performance results as those of the exponential companding technique, while Additive White Gaussian Noise (AWGN) or multipath fading channel is considered. Further, the hardware implementation results show that the complexity of the proposed companding technique is less than that of the exponential companding technique. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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