基于PSWFs的非正弦通信系统正交多址接入技术研究

针对椭圆球面波函数(PSWFs)非正弦通信系统多个用户如何共享时频资源进行通信的问题,展开基于PSWFs的非正弦通信系统正交多址接入技术研究。首先,基于PSWFs的信号特性,提出了PSWFs非正弦通信系统频分多址(PSWFs-FDMA)、时分多址(PSWFs-TDMA)和阶分多址接入(PSWFs-ODMA)方法。其次,与循环前缀正交频分复用(CP-OFDM)对比分析了调制信号的能量聚集性、频谱效率和相邻子波带间的干扰,证明所提正交多址技术的可行性。最后,在双选择信道下,将PSWFs-TDMA/FDMA、PSWFs-ODMA与CP-OFDM对比分析了系统吞吐量,与正交频分多址接入(OFDMA)对比了不同接入方式的误码性能。理论与仿真分析表明,PSWFs非正弦通信系统正交多址能够比CP-OFDM通信系统提高约1.4倍的系统吞吐量。在多径信道下,PSWFs-ODMA增加时宽情况下的误码性能最好;在双选择信道,多普勒频移较小的中低速场景下,PSWFs-TDMA/FDMA的误码性能比OFDMA要好。     

广义频分复用系统及峰均功率比研究

利用循环前缀的正交频分复用技术仍然存在循环前缀导致的频谱利用率较低,对移动台高速运动引入的多普勒频移敏感等问题。该文主要讨论基于波形设计的广义频分复用系统,即通过设计合适的发送波形,能够有效地抑制无线通信信道中多径干扰和多普勒频移等问题。本文还讨论了基于波形设计的广义频分复用系统的峰值平均功率比问题,并且给出了广义频分复用系统在非线性高功率放大器模型下的性能。     

OFDMA蜂窝通信系统子载波分配技术分析

介绍了正交频分复用多址接入方案(OFDMA),并分析、比较了瑞利衰落下系统采 用不同子载波分配方案的性能。结果表明:OFDMA系统中,若不使用自适应子载波分配时,采 取间隔扩展分配方式的系统性能要优于分组分配方式;若使用自适应分配时,系统性能可以得 到很大提高,但增加了实现复杂度。     

异步多址正交频分复用信号解码算法研究

提出了异步情况下基于独立分量分析的正交频分复用多址(Orthogonal Frequency Division Multiple Access, OFDMA)接入信号解码算法.该算法可以在传输延迟及载波频偏未知情况下, 对多用户OFDMA信号进行盲分离和解码, 不需要去除循环前缀, 增加了接收信号能量, 提高了解码性能.理论分析和仿真表明:在平稳信道环境下, 相比于传统的基于快速傅里叶变换的OFDMA信号解码算法, 该算法具有更好的性能.     

一种基于递归最小二乘的OFDM系统自适应均衡算法

当循环保护前缀(CP)长度小于信道冲激响应长度时,正交频分复用(OFDM)通信系统的子载波间正交性遭到破坏,接收信号存在符号间干扰(ISI)和子载波间干扰(ICI),普通的频域单抽头均衡器不再适用.为解决这个问题,研究一种基于递归最小二乘(RLS)算法的频域自适应均衡器.理论分析和仿真结果表明,该均衡器能有效消除由于循环前缀不足引起的符号问干扰和子载波间干扰,较好地恢复传输信号.     

OFDM/OQAM系统中联合迭代信道估计和信号检测

与基于复数域空间正交条件的传统正交频分复用系统(OFDM with Cyclic Prefix, CP-OFDM)有所不同,基于交错正交调制的正交频分复用系统(OFDM/Offset QAM, OFDM/OQAM)满足实数域空间严格正交条件。因此在多径衰落信道条件下,CP-OFDM系统中的信道估计方法会导致OFDM/OQAM系统严重的字符间干扰和载波间干扰。该文结合OFDM/OQAM系统结构特点,提出了一种基于迭代信道估计和信号检测算法。该算法通过信道估计器和接收到的信号互相交换信息,消除导频序列中的字符间干扰和载波间干扰,提高信道估计和信号检测的准确度。仿真分析结果表明,经过一定次数迭代处理后,OFDM/OQAM迭代信道估计性能趋近于理想信道估计性能。     

一种基于OFDM-chirp的雷达通信一体化波形设计与处理方法

雷达通信一体化波形设计是近年来的研究热点。有学者提出利用正交频分复用(OFDM)信号的奇偶载波分别调制雷达与通信功能来实现一体化。但OFDM通信系统一般采用循环前缀(CP)来避免多径效应带来的载波间干扰(ICI)和符号间干扰(ISI),这会降低能量利用率,并会形成虚假目标,影响雷达性能;此外,传统的OFDM一体化信号对多普勒比较敏感,微小的多普勒频偏也会带来正交性能的严重下降。该文在此基础上提出了一种新的波形设计和处理方法。该方法利用空白保护间隔替代循环前缀,可以在对抗多径效应的同时避免出现由于循环前缀引入的虚假目标,有效防止载波间干扰和符号间干扰。在信号处理方法上,该文提出利用雷达发射信号的先验信息进行信道估计与补偿多普勒频偏的方法。与传统方法相比,该文方法降低了系统在导频与训练序列等资源上的开销,提升了能量利用率和频谱效率,并且改善了峰值旁瓣比(PSLR)、积分旁瓣比(ISLR)和通信误码率(BER)等指标。仿真实验验证了该文方法的有效性。      

OFDMA技术及其在IEEE802.16a中的应用

正交频分多址(OFDMA)是以正交频分复用(OFDM)调制为基础的新一代多址技术,具有很高的带宽利用率。首先结合OFDMA在有线电视网络中的应用介绍了它的基本原理,然后简单介绍了它在宽带无线接入IEEE802.16a中的应用,主要是关于子信道划分的问题。     

正交频分多址联接及其关键技术

正交频分多址(OFDMA)是一种基于正交频分复用(OFDM)原理的多址技术,具有很高的带宽利用率,同时汇集了OFDM、跳频及时分多址(TDMA)技术的诸多优点,在无需使用均衡器的情况下,可有效地克服码间干扰。与传统的直扩CDMA(DS-CDMA)或多址CDMA(MC-CDMA)相比,OFDMA提供的容量更大。     

LTE中的OFDMA技术

LTE多址技术与WCDMA中的多址技术不同。在LTE系统中,下行链路多址技术建立在正交频分复用多址（OFDMA）的基础上,而上行链路多址技术则是基于单载波频分多址（SC-FDMA）技术的。文章分析了OFDMA实现过程,描述了OFDMA发射机和接收机结构与原理,讨论了OFDMA的优势与挑战。     

A Joint Use of Both PAPR Reduction and Neural Network Predistortion Approaches to Compensate the HPA Non-Linearity Impact on FBMC/OQAM Signals

Filter Bank Multi-carrier Modulations with Offset Quadrature Amplitude Modulations (FBMC/OQAM) is an appropriate alternative to Orthogonal Frequency Division Multiplexing (OFDM) for the fifth generation radio access technology. Being a multi-carrier modulation scheme (MCM), FBMC/OQAM suffers from high Peak to Average Power Ratio (PAPR) and thus exhibits significant distortion in the presence of a non-linear high power amplifier (HPA). To date, no research has considered the idea of combining both linearization and PAPR reduction approaches for the FBMC/OQAM system to cope with this problem. In this paper we jointly used the Tone Reservation (TR) PAPR reduction scheme and the Neural Networks Predistortion (NNPD) as a linearization scheme for both the FBMC/OQAM and the OFDM systems. We suggest a serial combination of the TR and the NNPD schemes. Numerical results showed that the proposed combination of the TR and the NNPD schemes provided better performances than when used separately for both OFDM and FBMC/OQAM systems.     

A Novel Channel Estimation Scheme for OFDM/OQAM‐IOTA System

An OFDM/offset QAM (OQAM)‐IOTA system uses the isotropic orthogonal transform algorithm (IOTA) function, which has good localization properties in the time and frequency domains. This is employed instead of the guard interval used in a conventional OFDM/QAM system in order to be robust for multi‐path channels. However, the conventional channel estimation scheme is not valid for an OFDM/OQAM‐IOTA system due to the intrinsic inter‐symbol interference of the IOTA function. In this paper, a condition is derived to reduce the intrinsic interference of the IOTA function. This condition is obtained with the proposed pilot structure used for perfect channel estimation. We also derive the preamble structure appropriate for practical channel estimation of the OFDM/OQAM‐IOTA system. Simulation results show that the OFDM/OQAM‐IOTA system with the proposed preamble structure performs better than the conventional OFDM system, and it has the additional advantage of an increased data transmission rate which corresponds to the guard interval retrieval.     

基于并行干扰抵消的OFDM/OQAM系统中的信号检测方法

在多径衰落信道中,基于交错正交幅度调制的正交频分复用(OFDM with Offset QAM,OFDM/OQAM)系统使用迫零均衡器进行信号检测时,不能完全消除信道复数特性和滤波器实数正交特性引入的时域符号间干扰和频域子载波间干扰,及信道估计误差导致的误码率性能损失。该文利用对数据初始判决并重构相邻载波及符号间干扰的思想,通过分析采用迫零均衡信号检测时的残余干扰与信道估计误差干扰,提出了一种基于并行干扰抵消和迫零均衡器结合的OFDM/OQAM信号检测方法,并在IEEE 802.22技术标准的两种典型多径衰落信道中进行了计算机仿真与比较研究。仿真结果表明,与基于迫零均衡的检测方法相比,基于并行干扰抵消的迭代信号检测方法在误码率为1%时,可获得1 dB至2 dB的性能提升。     

Novel Peak‐to‐Average Power Ratio Reduction Methods for OFDM/OQAM Systems

The tone reservation method is one of the most effective pre‐distortion methods for peak‐to‐average power ratio reduction in orthogonal frequency division multiplexing (OFDM) systems. Its direct application to OFDM systems with offset quadrature amplitude modulation (OQAM) is, however, not effective. In this paper, two novel TR‐based methods are proposed, specifically designed for OFDM/OQAM systems by taking into consideration the overlapping nature of OQAM signals. These two methods have different approaches to the generation of the peak‐cancelling signal. The first one (overlapped scaling tone reservation) generates the peak‐cancelling signal using a least squares approximation algorithm with possible adjacent symbol overlap; the second one (multi‐kernel tone reservation) generates the peak‐cancelling signal by using multiple impulse‐like time domain kernels. It is shown by simulation that, when used in OFDM/OQAM systems, the proposed methods can provide better performance than the direct application of the existing controlled clipping tone reservation method, and even outperform the multi‐block tone reservation method.     

OQAM/OFDM信号二阶循环平稳性分析

OQAM/OFDM是一种基于正交滤波器组的多载波调制信号,其特殊的生成机制决定了循环谱结构的复杂性。该文从OQAM/OFDM系统的连续时间基带模型出发,证明了OQAM信号具有的二阶循环平稳性,推导了谱相关函数表达式,并分析了OQAM信号的各种谱相关特征,以及多径衰落信道对其的影响。仿真实验表明了理论分析的正确性。     

A Simplified Power Adaptation Scheme for Wireless Orthogonal Frequency Division Multiple Access

Recently, orthogonal frequency division multiplexing (OFDM) has been received more and more attention because of its ability to eliminate large ISI, multipath delay and high spectral efficiency. The principle of OFDM is to divide the frequency selective multipath wireless channels into a set of orthogonal flat fading subchannels, so that a high-speed data stream is split into a set of lower rate streams. OFDMA is a kind of air interface access based on OFDM. In OFDMA, the carriers ar…     

基于OFDM-MSFH系统的全部载波接入方法的研究

本文根据MB-OFDM-UWB系统的特点,提出了将OFDM技术和MSFH(多级跳频)技术结合的全部载波多址接入方案.该多址方案有二级构成,其中前一级使用OFDM,设计时参考了Multi-band OFDM Physical Proposal for IEEE 802.15 TaskGroup3a中的物理层建议,后一级采用跳频模块,并将基于余数域的多级跳频图案应用到该多址方案中,不仅大大减小了多用户碰撞的概率,而且有利于超宽带信号的生成.理论分析和仿真结果表明,基于OFDM和多级跳频结构的全部载波多址接入方案在系统容量、误比特率性能、抗干扰等方面具有诸多的优势.在8用户情况下,当系统误比特率为10~(-2)时,基于该结构的全载波方案比TH-PPM多址方案改善信噪比5dB左右.     

一种改进的OFDM/OQAM系统信道估计算法

基于块状导频的信道估计方法可以克服OFDM/OQAM(OFDM/Offset QAM)系统所固有的符号间和载波间干扰,从而成为该类系统通用的信道估计方法。该文基于块状导频结构和OFDM/OQAM的系统特点,分析了系统相邻子载波之间的相关性,并在此基础上提出一种改进的信道估计算法,通过计算相邻子载波的相关系数,在频域进行有效的加权运算来降低干扰和噪声对信道估计的影响。分析和仿真结果表明,该算法能够有效地提高传统算法的信道估计精度和系统性能。     

Robust channel estimation for OFDM/OQAM

When orthogonal frequency division multiplexing offset-QAM (OFDM/OQAM), termed OQAM in short, was revealed to possess several advantages compared to OFDM, the channel estimation (CE) technique became a crucial issue for OQAM to make a practical sense. Based on the previous proposal on CE of OQAM, this letter addresses the study of a decisive factor that directly determines the CE performance. The idea is to relax the orthogonality constraint of the prototype filter used for transmitting the preamble. This provides a larger degree of freedom for finding a good balance between its time and frequency localization (TL and FL). Two prototype filter design algorithms are proposed and show that the proposed preamble-based CE method can almost attain the perfect CE.