一种改进的无边带信息PTS-OFDM系统

部分传输序列(PTS)技术是减小OFDM信号峰均比的一种有效技术,具有无失真,性能优越的特点,但存在计算复杂度高以及需要传输边带信息(SI)的缺点,会增加系统开销,降低有效数据传输率.本文提出了一种无需单独传输SI信息的PTS优化方案,给出了实现方案及系统控制策略,并对该系统的峰平比和误码率性能进行了Matlab仿真和分析.结果表明,提出的PTS方案在不降低系统数据率的情况下可以有效改善OFDM信号的峰均比特性以及系统BER性能,且不受调制方式影响.     

OFDM中峰平比降低方法的比较研究

本文首先介绍了OFDM调制中存在的峰平比过高的问题 ,接着给出了峰平比的定义及峰平比分布函数的推导 ,着重讨论了几种主要的降低峰平比的方法 ,并对它们进行了比较分析。     

降低峰平比对MASK-OFDM系统性能的改善

OFDM系统由于其优越的性能，在高速无线通信以及高速用户环路HDSL和非对称数字用户线ADSL中得到了广泛应用，但该信号较大的峰平比是使用中的一大障碍。本文首先分析OFDM信号的峰平比，在此基础上提出降低峰平比的方法，运用仿真姑果分析了降低峰平比对OFDM—MASK系统误码性能和频谱的改善。     

降低PAPR的PTS算法比较

正交频分复用（OFDM）是一种有效降低符号间干扰的高速数据调制技术。在技术实现过程中若峰均比（PAPR）过高,发射机和接收机内部放大器线性要求就会很高,从而限制了OFDM调制技术的实际应用。部分传输序列（PTS）算法可以有效地降低峰均比。在此通过介绍几种改进型的部分传输序列方法,并且在峰均比降低性能、计算复杂度和其他性能指标几个方面做出了分类对比,这对今后降低PAPR的研究有一定的指导意义。     

用多幅值CPM减小OFDM信号的PAPR

正交频分复用(OFDM)是一种多载波调制(MCM)技术,其具有良好的抗多径衰落的能力和非常高的信道利用率.但是OFDM有一个固有缺点就是存在较高的峰平功率比(PAPR),本文提出将多幅值的连续相位调制信号与部分响应序列相结合的方法来减少OFDM信号的PAPR.     

基于频域导频PTS-OFDM系统峰平比降低技术

对于无线通信系统而言,OFDM是一种非常有吸引力的传输技术,但是OFDM信号具有较高的峰平比特性.为了减小信号峰平比,本文利用部分传输序列PTS技术,提出了一种适用于基于频域导频OFDM系统的峰平比降低实现方案,给出了其实现算法及系统控制策略;并利用计算机仿真对该系统的峰平比和误码率性能进行了分析,仿真结果表明:PTS技术可以有效地改善OFDM信号的高峰平比特性.本方案采用FPGA实现其相应的硬件电路,经过实际的OFDM系统样机传输测试,证明了所提方法的实用性及其良好的性能.     

一种降低PTS复杂度的新方法

正交频分复用(OFDM)的主要缺点是峰平比(PAPR)过高,由于OFDM发射端功率放大器的非线性,高的峰平比会导致信号的频谱扩展,同时降低了放大器的工作效率.提出了一种基于部分传输序列(PTS)改善正交频分复用信号峰平比(PAPR)的优化算法.仿真结果表明,优化算法大大降低了系统的复杂性,实现更容易,在性能和计算复杂度之间取得了较好的折衷.     

Turbo码综合性能分析与Turbo编码调制

对 Ｔｕｒｂｏ码的 ＲＳＣ分量码、交织器、调制方式、信道以及迭代译码算法进行了综合研究与性能分析，并给出了一种基于逐比特ＭＡＰ算法的Ｔｕｒｂｏ编码与多元调制相结合的编码调制方式。仿真结果表明，该方案将Ｔｕｒｂｏ码的高编码增益与多元调制的高频谱利用率有效地结合在一起，是一种功率和频谱高效的编码调制方式，比传统的ＴＣＭ方式有更好的性能。     

一种基于调制m序列的直接序列扩频信号调制方法

为提高直接序列扩频通信系统的频谱利用率,该文提出在m序列周期等于信息比特位宽整数倍情况下的直接序列扩频信号——调制m序列的信号调制与解调方法(m-DSSS)。首先结合调制m序列相关性数值仿真结果验证m-DSSS信号捕获可行性,然后根据信息比特的排列组合情况,设计一种基于多通道的m-DSSS信号调制和解调方法,并对m-DSSS信号通过加性高斯白噪声信道后的抗干扰能力建立数学模型。最后在相同频谱利用率条件下,与码移键控(CSK)调制方式进行了仿真对比试验。仿真结果表明,m-DSSS信号不仅比CSK信号具有更低的副峰,且当载波采用BPSK调制时,m-DSSS还可通过判断极性来辅助信号捕获,在误码率优于1e-3条件下,m-DSSS信号比CSK信号有2 dB以上优势,验证了m-DSSS调制用于直扩系统的可行性。     

网格编码调制结合低密度校验码的应用方案设计及性能分析

提出一种利用网格编码调制将低密度校验码与高阶数字调制相结合的应用方法，其中在网格编码调制中采用递归系统卷积码进行编码用以实现基于对数似然比的软译码方法，构造了低密度校验码和网格编码调制相结合的编译码系统。仿真结果表明，该方案将低密度校验码的高编码增益与多元调制的高频谱利用率有效结合在一起，是一种功率和频谱高效的编码调制方式，比传统的网格编码方式有更好的性能。     

Performance analysis of peak power and band-limited OFDM system with linear scaling

The performance of the orthogonal frequency-division-multiplexing (OFDM) system over the strictly peak power and band-limited channel is analyzed in terms of the required input back-off, bit-error rate (BER), and channel capacity on the assumption that the power amplifier is perfectly linearized. The peak-power limitation is implemented by linearly scaling the band-limited OFDM signal such that the maximum peak power of each OFDM symbol is always below the saturation level of the amplifier. The theoretical performance analysis requires the knowledge of the distribution of the peak power normalized by the symbol-wise (local) average power, referred to as symbol-wise peak-to-average power ratio (PAR) in the paper, and we also develop a method to numerically calculate its statistical distribution. The analysis of BER performance suggests that the linear scaling causes practically negligible degradation. Furthermore, the benefit of additional application of simple PAR reduction schemes, such as symbol selection and deliberate clipping and filtering, is also examined.     

Analysis of peak-to-average power ratio for IS-95 and thirdgeneration CDMA forward link waveforms

The peak-to-average power ratio (PAR) of IS-95-type code division multiple-access (CDMA) forward link waveforms is an important parameter which directly relates to system capacity performance. In this paper, analytical expressions are derived for the PAR. The probability that the instantaneous-to-average power ratio (IAR) exceeds a given value is also derived. The analysis is carried out parametric in 1) the number of active traffic channels; 2) the fractions of power allocated to different forward link channels; and 3) other parameters related to the forward link power budget. An analysis is also given for the distribution of the IAR for the forward link modulation planned for third generation (3G) versions of the IS-95 system and a simple modification to present and future IS-95 modulation schemes is shown that reduces the forward link PAR by up to 3 dB     

Peak-to-average power ratio in MIMO-OFDM systems using selective mapping

This letter evaluates the peak-to-average power ratio (PAR) performance in a space-time block coded (STBC) multi-input multi-output orthogonal frequency-division multiplexing (MIMO-OFDM) system using the selective mapping (SLM) approach. The investigated SLM-based MIMO-OFDM system selects the transmitted sequence with the lowest average PAR over all transmit antennas and retrieves the side information very accurately at the expense of only 0.5-dB degradation of the PAR, which can improve the overall detection performance of the MIMO-OFDM system with erroneous side information, compared to the individual SLM approach.     

An active-set approach for OFDM PAR reduction via tone reservation

Common to all orthogonal frequency division multiplexing (OFDM) systems is a large peak-to-average-power ratio (PAR), which can lead to low power efficiency and nonlinear distortion at the transmit power amplifier. Tone reservation uses other unused or reserved tones to design a peak-cancelling signal that lowers the PAR of a transmit OFDM block. In contrast to previous methods, the new active-set method proposed here converges very quickly toward a minimum-PAR solution at a lower computational cost. An efficient real-baseband algorithm is well suited for discrete multitone (DMT) modulation over twisted-pair copper wiring, where some subchannels may have an insufficient SNR to reliably send data. The real PAR problem occurs in the analog signal before the power amplifier, and results focus on this figure of merit. The performance of oversampling before applying PAR reduction is analyzed, and results show that this is necessary to sufficiently handle the analog PAR problem. An extension of the real-baseband technique can be applied to complex-baseband signals to help reduce PAR in wireless and broadcast systems. By sacrificing 11 out of 256 OFDM tones (4.3%) for tone reservation, over 3 dB of analog PAR reduction can be obtained for a wireless system.     

Directed selected mapping for peak-to-average power ratio reduction in MIMO OFDM

Peak-to-average power ratio (PAR) reduction in OFDM using antenna arrays (MIMO OFDM) is considered. In particular, a generalisation of selected mapping (SLM), called directed SLM (dSLM), is introduced. It is shown that, in contrast to schemes proposed in the literature, dSLM utilises the potential offered by MIMO transmission. As a result, the complementary distribution function of the PAR exhibits a steeper decay, increased by a factor equal to the number of transmit antennas. This effect is similar to the diversity gain in error performance when using MIMO transmission     

低峰值平均功率比的多载波CDMA

多载波CDMA技术是CDMA和正交频分复用(OFDM)技术的综合,具有抗干扰能力强、频谱效率高、数据传输速率高等优点,在未来个人通信业务(PCS)和第三代移动通信中具有良好的发展前景。但是,多载波CDMA信号峰平比比较高,影响到功放的功率效率,这已成为目前多载波CDMA系统实用化的一大障碍。本文利用格雷互补序列的特性有效降低多载波CDMA信号的峰平比,对于任意载波数的多载波CDMA信号,其峰平比上限为6dB。     

PTS-OFDM的一种新的子块分割方法

正交频分复用(OFDM)的一个主要缺点是信号的峰值功率与平均功率比(PAR)很高,部分传输序列(PTS)是一种有效降低OFDM信号PAR的方法。在PTS方法中,采用不同的分割方法可以改善PAR性能。文章提出一种新的子块分割方法——联合分割方法来降低任意子载波数目OFDM系统的PAR。仿真结果表明,联合分割方法既降低了系统的运算复杂度,又降低了系统的PAR。     

Peak-to-average power ratio and power efficiency considerations in MIMO-OFDM systems

Peak-to-average power ratio (PAR) reduction is a powerful tool that can increase power efficiency and reduce distortion noise in MIMO-OFDM systems. Various PAR metrics have been used in the MIMO-OFDM literature without justifications regarding the physical mechanisms that support those PAR definitions. In this paper, we show that in order to deliver high power efficiency, two MIMO-OFDM linear-scaling schemes are possible: one that scales all MIMO branches with the same factor and another that uses a different scaling factor for each branch. For each system, we derive a meaningful PAR metric that should be used.     

Comparing Selected Mapping and Partial Transmit Sequence for PAR Reduction

Selected mapping (SLM) and partial transmit sequence (PTS) are two existing distortionless peak-to-average power ratio (PAR) reduction schemes that have been proposed for orthogonal frequency division multiplexing (OFDM). Previously, it was argued that SLM and PTS have comparable PAR reduction performance but that the latter has lower computational complexity because it uses fewer IFFTs. In this paper, we show that the overall computational complexity of PTS is only lower than that of SLM in certain cases, and that SLM always has better PAR reduction performance. We compare the two schemes using three different performance metrics by assuming a given amount of computational complexity that can be afforded. Using the metrics, we show that SLM outperforms PTS for a given amount of complexity.     

On Trellis Shaping for PAR Reduction in OFDM Systems

The application of trellis shaping was proposed to reduce the peak-to-average power ratio (PAR) of orthogonal frequency division multiplexing (OFDM) signals. In this letter, we review the trellis-shaping schemes presented in the literature, and we introduce modifications such as a new decoding metric and the use of sequential decoding. We conduct comprehensive complexity and performance comparisons for the different schemes, and one interesting result of this work is that, in terms of PAR-reduction capability, trellis shaping with time-domain metrics is generally superior to trellis shaping with frequency-domain metrics. Furthermore, the proposed modifications enable trellis shaping for PAR reduction with a flexible performance-complexity tradeoff.