The major drawback in Orthogonal Frequency Division Multiplexing (OFDM) system is due to the high Peak-to-Average Power Ratio (PAPR), so the performance of the system is significantly degraded by the nonlinearity of a...The major drawback in Orthogonal Frequency Division Multiplexing (OFDM) system is due to the high Peak-to-Average Power Ratio (PAPR), so the performance of the system is significantly degraded by the nonlinearity of a High Power Amplifier (HPA) in the transmitter.In order to mitigate distortion, a block coding scheme for reducing PAPR in OFDM systems with large number of subcarriers based on complementary sequences and predistortion is proposed,which is capable of both error correction and PAPR reduction. Computer simulation results show that the proposed scheme significantly improves Bit Error Rate(BER) performance as compared to an uncoded system when an HPA is employed or a coded system without predistortion.展开更多
Most satellite digital radio （SDR） systems use orthogonal frequency-division multiplexing （OFDM） transmission, which means that variable envelope signals are distorted by the RF power amplifier （PA）. It is custo...Most satellite digital radio （SDR） systems use orthogonal frequency-division multiplexing （OFDM） transmission, which means that variable envelope signals are distorted by the RF power amplifier （PA）. It is customary to back off the input power to the PA to avoid the PA nonlinear region of operation. In this way, linearity can be achieved at the cost of power efficiency. Another attractive option is to use a linearizer, which compensates for the nonlinear effects of the PA. In this paper, an OFDM transmitter conforming to European Telecommunications Standard Institute SDR Technical Specifications 2007-2008 was designed and implemented on a low-cost field-programmable gate array （FPGA） platform. A weakly nonlinear PA, operating in the L-band SDR frequency, was used for signal transmission. An adaptive linearizer was designed and implemented on the same FPGA device using digital predistortion to correct the undesired effects of the PA on the transmitted signal. Test results show that spectral distortion can be suppressed between 6-9 dB using the designed linearizer when the PA is driven close to its saturation region.展开更多
Efficient nonlinear companding transform (NCT) scheme for reducing peak-to-average power (PAPR) of orthogonal frequency division multiplexing (OFDM) signals is proposed. This scheme transforms the Gaussian-distributed...Efficient nonlinear companding transform (NCT) scheme for reducing peak-to-average power (PAPR) of orthogonal frequency division multiplexing (OFDM) signals is proposed. This scheme transforms the Gaussian-distributed signals into the specified statistics form defined as a piecewise function. By adjusting the transform parameters, it enables more design flexibility in companding form so that a favorable trade-off between PAPR and bit error rate (BER) can be offered. Compared to existing techniques, the scheme can achieve an effective reduction in PAPR as well as an improved BER performance simultaneously.展开更多
本文针对高功率放大器(HPA)的非线性失真导致OFDM(Orthogonal Frequency Division Multiplexing)系统传输性能下降问题,采用两个类似结构的单输入单输出BP神经网络串联后级联HPA实现其预失真,前一网络是HPA的AM-AM特性的逆模型,用来实现...本文针对高功率放大器(HPA)的非线性失真导致OFDM(Orthogonal Frequency Division Multiplexing)系统传输性能下降问题,采用两个类似结构的单输入单输出BP神经网络串联后级联HPA实现其预失真,前一网络是HPA的AM-AM特性的逆模型,用来实现HPA的幅度预失真,后一网络是HPA的AM-PM特性模型,回避了其逆模型的建立,实现了HPA更高精度的相位预失真,提高了整体预失真效果。仿真结果显示了即使输入回退只有2.93dB,带外谱增长仍能降低约10dB,表明该方案能够方便高效地实现OFDM系统中HPA的自适应预失真,大大提高OFDM系统的传输性能。展开更多
针对强记忆功放的非线性问题,提出一种基于自适应扩展卡尔曼滤波与神经网络的高功放(High power amplifier,HPA)预失真算法.采用实数固定延时神经网络(Real-valued focused time-delay neural network,RVFTDNN)对间接学习结构预失真系...针对强记忆功放的非线性问题,提出一种基于自适应扩展卡尔曼滤波与神经网络的高功放(High power amplifier,HPA)预失真算法.采用实数固定延时神经网络(Real-valued focused time-delay neural network,RVFTDNN)对间接学习结构预失真系统中的预失真器和逆估计器进行建模,扩展卡尔曼滤波(Extended Kalman filter,EKF)算法训练神经网络,从理论上指出Levenberg-Marquardt(LM)算法是EKF算法的特殊情况,并用李亚普诺夫稳定性理论分析EKF算法的稳定收敛条件,推导出测量误差矩阵的自适应迭代公式.结果表明:自适应EKF算法的训练误差和泛化误差均比LM算法更低,预失真后的邻道功率比(Adjacent channel power ratio,ACPR)比LM算法改善了2 d B.展开更多
本文针对幅度预矫正技术在降低OFDM系统PAPR(peak-to-average power ratio)的同时增加了系统平均功率的缺点,采用对部分输入符号进行两个相反方向的放大和缩小,以达到进一步降低系统PAPR,并且降低系统平均功率的目的。分析及仿真结果表...本文针对幅度预矫正技术在降低OFDM系统PAPR(peak-to-average power ratio)的同时增加了系统平均功率的缺点,采用对部分输入符号进行两个相反方向的放大和缩小,以达到进一步降低系统PAPR,并且降低系统平均功率的目的。分析及仿真结果表明,在保证系统在AWGN信道中的误比特率性能的前提下,在概率为10^(-4)处,改进后的方法比原方法PAPR降低了0.6dB,系统平均功率也有明显降低。本文方法具有算法简单、不产生失真,不发送边带信息及灵活性高,且易于与其他降低PAPR技术结合使用等特点,具有较好的实用价值。展开更多
基金Supported in part by the National 863 program of China(No.2001AA123014)
文摘The major drawback in Orthogonal Frequency Division Multiplexing (OFDM) system is due to the high Peak-to-Average Power Ratio (PAPR), so the performance of the system is significantly degraded by the nonlinearity of a High Power Amplifier (HPA) in the transmitter.In order to mitigate distortion, a block coding scheme for reducing PAPR in OFDM systems with large number of subcarriers based on complementary sequences and predistortion is proposed,which is capable of both error correction and PAPR reduction. Computer simulation results show that the proposed scheme significantly improves Bit Error Rate(BER) performance as compared to an uncoded system when an HPA is employed or a coded system without predistortion.
文摘Most satellite digital radio （SDR） systems use orthogonal frequency-division multiplexing （OFDM） transmission, which means that variable envelope signals are distorted by the RF power amplifier （PA）. It is customary to back off the input power to the PA to avoid the PA nonlinear region of operation. In this way, linearity can be achieved at the cost of power efficiency. Another attractive option is to use a linearizer, which compensates for the nonlinear effects of the PA. In this paper, an OFDM transmitter conforming to European Telecommunications Standard Institute SDR Technical Specifications 2007-2008 was designed and implemented on a low-cost field-programmable gate array （FPGA） platform. A weakly nonlinear PA, operating in the L-band SDR frequency, was used for signal transmission. An adaptive linearizer was designed and implemented on the same FPGA device using digital predistortion to correct the undesired effects of the PA on the transmitted signal. Test results show that spectral distortion can be suppressed between 6-9 dB using the designed linearizer when the PA is driven close to its saturation region.
文摘Efficient nonlinear companding transform (NCT) scheme for reducing peak-to-average power (PAPR) of orthogonal frequency division multiplexing (OFDM) signals is proposed. This scheme transforms the Gaussian-distributed signals into the specified statistics form defined as a piecewise function. By adjusting the transform parameters, it enables more design flexibility in companding form so that a favorable trade-off between PAPR and bit error rate (BER) can be offered. Compared to existing techniques, the scheme can achieve an effective reduction in PAPR as well as an improved BER performance simultaneously.
文摘本文针对高功率放大器(HPA)的非线性失真导致OFDM(Orthogonal Frequency Division Multiplexing)系统传输性能下降问题,采用两个类似结构的单输入单输出BP神经网络串联后级联HPA实现其预失真,前一网络是HPA的AM-AM特性的逆模型,用来实现HPA的幅度预失真,后一网络是HPA的AM-PM特性模型,回避了其逆模型的建立,实现了HPA更高精度的相位预失真,提高了整体预失真效果。仿真结果显示了即使输入回退只有2.93dB,带外谱增长仍能降低约10dB,表明该方案能够方便高效地实现OFDM系统中HPA的自适应预失真,大大提高OFDM系统的传输性能。
文摘针对强记忆功放的非线性问题,提出一种基于自适应扩展卡尔曼滤波与神经网络的高功放(High power amplifier,HPA)预失真算法.采用实数固定延时神经网络(Real-valued focused time-delay neural network,RVFTDNN)对间接学习结构预失真系统中的预失真器和逆估计器进行建模,扩展卡尔曼滤波(Extended Kalman filter,EKF)算法训练神经网络,从理论上指出Levenberg-Marquardt(LM)算法是EKF算法的特殊情况,并用李亚普诺夫稳定性理论分析EKF算法的稳定收敛条件,推导出测量误差矩阵的自适应迭代公式.结果表明:自适应EKF算法的训练误差和泛化误差均比LM算法更低,预失真后的邻道功率比(Adjacent channel power ratio,ACPR)比LM算法改善了2 d B.
文摘本文针对幅度预矫正技术在降低OFDM系统PAPR(peak-to-average power ratio)的同时增加了系统平均功率的缺点,采用对部分输入符号进行两个相反方向的放大和缩小,以达到进一步降低系统PAPR,并且降低系统平均功率的目的。分析及仿真结果表明,在保证系统在AWGN信道中的误比特率性能的前提下,在概率为10^(-4)处,改进后的方法比原方法PAPR降低了0.6dB,系统平均功率也有明显降低。本文方法具有算法简单、不产生失真,不发送边带信息及灵活性高,且易于与其他降低PAPR技术结合使用等特点,具有较好的实用价值。
