周期为4v(几乎)平衡理想二进制序列构造研究

具有理想自相关特性的序列在无线通信、雷达以及密码学中具有重要的作用.因此为了扩展更多可应用于通信系统的理想序列,该文基于2阶分圆类和中国剩余定理,提出3类新的周期为T=4v(v是奇素数)平衡或几乎平衡理想二进制序列构造方法.构造所得序列的周期自相关函数满足:当v≡3(mod4)时,序列的周期自相关函数旁瓣值取值集合为{...     

新的Ⅱ型偶长Z-互补对构造

为丰富Z-互补对(ZCP)的参数形式,研究了新的Ⅱ型ZCP的构造方法。基于迭代法,实现了Ⅱ型(2^k+2N,(2^k+2-1)N)-ZCP的构造,当N=1时,可得Z-最优Ⅱ型(2^k+2,(2^k+2-1))-ZCP。进一步,将迭代法与插值法相结合,构造了Ⅱ型(2^k+1N+2^k+1,2^k+1N+2^k+1-N/2)-ZCP;当N=2时,可得Z-最优Ⅱ型(3×2^k+1,3×2^k+1-1)-ZCP。所提方法可以生成新的偶长ZCP,实现了对现有ZCP数量的扩展。     

利用互补序列降低OFDM信号PAR

正交频分复用（OFDM）是下一代高速通信系统的一项关键技术，峰平比（PAR）过高是限制OFDM技术应用的一个关键因素。为了降低OFDM信号的峰平比，基于格雷互补序列和Reed-Muller码的关系，提出一种构造互补序列的分组编码方法。仿真结果表明，该分组编码方法可以将OFDM信号的PAR降为3.01dB．     

基于格雷互补序列的OFDM无线激光通信定时同步

正交频分复用(OFDM)是一种能够有效对抗频率选择性衰落的通信技术。因此,结 合了OFDM技术的无线激光通信技术成为对抗大气湍流影响的一种重要技术。但是OFDM技术 容易受到符号定时同步偏移的影响,导致信号的快速傅里叶变换窗口失准而严重降低通信 性能。针对基于OFDM的无线激光通信系统的定时同步问题,提出了一种新的定时同步 方案。该方案的训练符号由格雷互补序列组成,利用格雷互补序列的自相关特性,将接收 到的训练序列与本地序列做相关运算,实现精确稳定的定时同步。结合大气湍流模型,通 过实验与仿真的方式验证了本文提出的方案相比于基于伪随机序列和恒包络自相关序列的 方案有更好的定时同步性能。尤其是在0-4 dB的低信噪比时,本方 案的定时同步偏移均方 差小于1个采样点,这也使得本方案在大气弱湍流信道下,相较于对比方案有2-4 dB的性能提升。     

一类四元零相关区非周期互补序列集构造法

零相关区非周期互补序列集在多载波码分多址通信系统中有着重要应用.已有的四元零相关区非周期互补序列集构造方法都是基于二元或四元零相关区互补序列集,得到的序列集参数受到初始互补序列集参数的限制.该文给出了一种构造法,利用四元正交序列集来构造四元非周期互补序列集.本文方法得到的序列集参数达到理论界限,并且零相关区长度可以灵活设定以满足不同的应用场合.另外给出了两类基于二元正交矩阵的四元正交序列集的构造方法,得到的四元正交序列集可以用于构造四元零相关区非周期互补序列集.二元正交矩阵存在数目很多,因此本文方法可以为多载波码分多址系统提供大量四元非周期互补序列集.     

一种构造最佳四元二维互补阵列的新方法

该文利用最佳四元二维互补阵列和准最佳四元二维互补阵列的性质,给出了一种构造最佳四元二维互补阵列的新方法。使用这种方法,可以将一个二维的st 阶的最佳四元二维互补阵列和一个2st 阶的准最佳四元二维互补阵列,构造成新的一类二维4st 阶和2s2t 阶的最佳四元二维互补阵列。     

四元零相关区周期互补序列集构造法

该文分别基于二元零相关区周期互补序列集和二元周期互补序列集做为初始序列,利用逆Gray映射构造了四元零相关区周期互补序列集。如果选取的初始序列集参数可以达到理论界限,得到的四元零相关区周期互补序列集接近甚至达到理论界限。零相关区互补序列集相比传统互补序列集具有更多的序列数目,应用到通信系统中可以支持更多的通信用户。     

基于非理想信道状态信息对DCO-OFDM-IM系统建模与分析

针对传统DCO-OFDM-IM系统进行信道估计时没有考虑信道误差影响,导致获得非理想信道状态信息（CSI）而造成信道估计有效性降低等问题,利用最小均方误差信道估计（MMSE）算法并基于非理想信道状态信息建立了DCO-OFDM-IM系统模型,推导了其理论误码率闭合表达式。同时考虑到DCO-OFDM-IM系统中采用最大似然检测算法（ML）当调制阶数增大时存在检测复杂度高,系统传输速率低等问题,而利用对数似然检测算法（LLR）降低检测复杂度,最后采用蒙特卡罗方法进行系统仿真性能的仿真对比。结果表明：当调制阶数和索引组合相同,误码率为10^-3时,LLR检测算法比ML所需信噪比平均改善约2 dB;在能量比为1∶8时,采用MMSE估计比LS信道估计算法系统性能改善约4 dB;当系统信道估计误差越小时,越可能获得理想CSI,提升了信道估计有效性。     

分析第四代移动通信技术(4G)的关键技术

以第四代移动通信技术作为切入点,分别介绍了OFDM正交频分复用技术、无线定位技术、以及IPv6协议技术的基本概念、特点、以及应用价值,指出了以上技术在第四代移动通信领域中的应用价值。     

第四代移动通信的核心技术——OFDM及SC-FDE

首先简要介绍了正交频分复用(OFDM)技术的产生背景,然后重点介绍了OFDM的基本原理实现框图,并对中频信号做了相应的理论推导。最后对OFDM的性能做了详细的描述,其中主要介绍了OFDM的优点和缺点及SC-FDE。     

基于802.16e的OFDM调制解调技术的研究

随着正交频分复用技术（OFDM）的日益成熟,它在现实生活中的应用的范围也越来越广泛了。OFDM技术现在不仅广泛的应用在数字广播、数字电视中,而且由于其具有抗多径衰落,频谱利用率高,传输速度快的优点,被普偏认为是第四代移动通信物理层的关键技术之一,它能够同时为多个用户提供高数据速率的视频和语音服务。主要是针对基于802.16e标准的OFDM的不同调制解调方式在不同信道中传输的优缺点进行研究比较。     

Robust and fast frequency offset estimation for OFDM based satellite communication

A pilot-aided Orthogonal Frequency Division Multiplexing (OFDM) frequency offset estimator designed for satellite communication system is proposed in the paper. The estimator focuses on the acquisition of the integer part of carrier frequency offset and the acquisition range is as large as the whole signal bandwidth. Making full use of the phase difference between received pilot and local referential pilot, a fast estimation is obtained. Compared with existing method, our method can also work well even in SNR as low as 0dB. Simulations verify the good performance of our method.     

PILOT－BASED FREQUENCY OFFSET DETECTION SCHEME IN OFDM SYSTEM

The frequency offset information is extracted from local pilot amplitude characteristics, which suffer much less distortion in frequency-selective fading channels than those utilizing frequency domain correlation techniques. Simulation shows that the performance of this scheme has better performance than the existing frequency domain pilot-based frequency offset detection scheme.     

Reducing the Peak-to-Average Power Ratio of OFDM system with low complexity

This paper proposes a companding scheme, where small signals are enlarged and large signals are reduced, to reduce the Peak-to-Average Power Ratio（PAPR）. Computer simulation results show that the proposed technique has two advantages at least when compared with the conventional methods such as partial transmit sequence, selective mapping and the previous companding. First, it gets better PAPR performances with a lower complexity. Second, the scheme achieves greater performances gain with hardly any damnification of OFDM signals in some degree.     

A SYNCHRONIZATION ALGORITHM FOR HF （HIGH FREQUENCY） BROADBAND OFDM SYSTEM

In this letter, a kind of associated synchronization algorithm which is suitable for HF （High Frequency） broadband OFDM （Orthogonal Frequency Division Multiplexing） system is presented based on describing and constructing the GMW （Gorden, Mills and Welch） sequence. The algorithm is based on the Schmidl and Minn＇s symbol timing principle, the constructed GMW sequence is transmitted and disposed, and the synchronization is adjudicated using the correlation of GMW sequence. The simulation result indicates that this algorithm has high performance synchronization ability under the low SNR （Signal to Noise Ratio） at two different kinds of channel models.     

A fast bit-loading algorithm for high speed power line communications

Adaptive bit-loading is a key technology in high speed power line communications with the Orthogonal Frequency Division Multiplexing (OFDM) modulation technology. According to the real situation of the transmitting power spectrum limited in high speed power line communications, this paper explored the adaptive bit loading algorithm to maximize transmission bit number when transmitting power spectral density and bit error rate are not exceed upper limit. With the characteristics of the power line channel, first of all, it obtains the optimal bit loading algorithm, and then provides the improved algorithm to reduce the computational complexity. Based on the analysis and simulation, it offers a non-iterative bit allocation algorithm, and finally the simulation shows that this new algorithm can greatly reduce the computational complexity, and the actual bit allocation results close to optimal.     

一种新的OFDM帧同步检测法

文章在研究T．Schmidl＆D．Cox算法和H．Minn算法的基础上．提出一种OFDM系统的帧同步检测方法．利用特殊训练符号的互相关信息来完成帧同步检测，提高了帧同步的精度。计算机仿真表明．文中提出的算法具有更强的适应性和抗多径能力。     

OFDMA系统跨层资源分配算法

OFDM具有高频谱利用率和抗多径衰落的优点,已被公认为第三代移动通信系统长期演进标准以及第四代移动通信系统的核心技术。OFDMA是基于OFDM的一种多用户接入技术,在OFDMA系统中,各用户在不同的子载波上同时传输数据。主要研究了OFDMA系统中的跨层资源分配算法。详细分析了保证速率比例公平的非实时业务跨层资源分配算法,仿真结果说明该算法能够较好地保证用户之间的公平性,并能够获得较大的系统吞吐量和较小的业务延时。     

采用基于互补序列分组编码的OFDM系统性能分析与仿真

为了减小正交频分复用（OFDM）信号的峰值-平均值功率之比（PAPR），本文利用互补序列和Reed-Muller码的关系，详细提出了一种构造互补序列的分组编码方法的具体实现方案。分析了其在AWGN和选频衰落信道中的性能，并做了相应的仿真。仿真结果表明，编码后每个OFDM信号的最大PAPR不超过3dB；采用该编码方法的OFDM在AWGN中当信噪比不到11dB时就可以实现BER为10^-6，在衰落信道中如果采用软判决译码，则当信噪比达到20dB左右时可以实现BER为10^-3。     

A novel estimation method of timing offset for OFDM based WLAN systems

The conventional timing synchronization methods based on time domain correlation have the problems of timing metric plateau in Additive White Gaussian Noise(AWGN) channel and estimation error in multipath fading channel. To resolve the problems, this paper proposes a novel timing metric using the characteristics of long training symbols in IEEE802.11a and a new timing recovery method based on the new timing metric for Orthogonal Frequency Division Multiplexing(OFDM)-based WLAN systems. The proposed timing metric is defined as a sum of absolute values of the imaginary parts of all the subcarrier samples. It exhibits a unique characteristic that is very sensitive to the true synchronization point since it has minimum value at the true synchronization point and maximum around the true synchronization point. The simulation results show that the performance of timing synchronization is significantly improved, as a result, the probability of error estimation is lower than 10^-4 when Signal-to-Noise Ratio(SNR) is more than 10dB.