结合天线选择和索引组合映射调制的MIMO系统研究

空间调制是一种高数据速率、低复杂度的多输入多输出无线传输技术,因其发射天线被信息序列随机激活,若被激活的信道状态不佳将导致系统误码性能下降.于是,提出一种结合天线选择和索引组合映射调制的传输方案.该方案将传统空间调制的激活天线索引比特和星座符号索引比特组合映射为一个新的调制符号,结合天线选择算法确定最佳发射天线子集,将新的调制符号通过最佳信道进行传输.在算法实现过程中采用了奇异值分解和硬限制检测等方法降低计算复杂度.实验分别仿真了两种天线选择算法下的系统性能.结果表明,提出的方案比传统的空间调制系统具有更好的误比特率特性.     

放大转发中的最优功率分配与最佳中继选择

用最优功率分配与最佳中继选择相结合的方法实现了放大转发系统的误比特率最小化。为了使单中继非协作放大转发系统的误比特率最小,通过分析媒体接入控制(MAC)层的请求发送/允许发送(RTS/CTS)信息,获得候选中继前向信道和后向信道的增益,以信道增益为变量,得到最佳功率分配的闭合表达式。同时,以误比特率作为中继选择准则,实现分布式最佳中继选择。仿真结果表明,与同类算法相比,该功率分配与中继选择策略使系统的误比特率达到最小。     

参数规划最优值函数的B-预不变凸凹性

本文利用点到集映射图的概念,提出了一种新的不变凸(凹)点到集映射的概念,讨论了参数规划问题最优值函数的B-预不变凸凹性,研究了最优值函数的B-预不变凹性与其最优解集映射的不变凸性之间的关系,得到了若干新的结论,所得结果包含并推广了已有文献中的相关研究结果。     

基于深度学习的OFDM半相干水声通信方法

针对正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)水声通信中常用的相干和非相干通信分别面临的对多普勒敏感和频谱效率低的问题,提出一种高阶幅度键控调制的半相干通信技术,将OFDM符号时频帧结构中全部频点采用高阶幅度键控调制方式,并利用信号幅度信息完成半相干信道估计。通过两种基于深度学习的算法优化半相干信道估计这一非线性过程,较非相干通信有效提高了频谱效率,较一定信噪比下的相干通信提高了鲁棒性,降低了误比特率和系统复杂度,并利用元学习算法降低深度学习算法对训练数据的依赖。最后,提取海试信道数据,完成OFDM半相干水声通信系统仿真,验证了所提方法在频谱效率和系统误比特率性能方面较非相干和相干通信的优势,当信道长度改变时,基于元学习的算法依然可以获得较好的性能。     

无线网络中基于MPSK的物理层网络编码

提出了一种新的物理层网络编码方法,将无线网络中物理层网络编码采用的调制方法推广到八进制相移键控(8PSK)以及多进制相移键控(MPSK).该方法在中继节点采用星座映射,将MPSK和信号星座映射到MPSK信号星座.接收节点收到MPSK信号后进行解调,借助已有信息进行译码(异或)操作,得到对方节点信息,完成信息交换.仿真验证了该方法的有效性,与已有的物理层网络编码方法相比,该方法在中继节点节约了50%的能量消耗,进一步提高了信息传输速率.     

求解一类非线性双层规划问题的混合遗传算法

本文研究下层目标函数为拟凹函数的非线性双层规划问题。利用下层目标的最优值能在可行域极点上达到的性质,将求极点的方法引入遗传算法,提出了一种混合遗传算法。为了提高该算法的效率,结合种群最优个体,给出了有利于产生高质量后代的杂交和变异算子。对于下层问题存在多个最优解的情况,证明了其最优解可表示为极点最优解的凸组合,并利用这一结论修正了算法,使得该算法也能求解下层多解的情形。数值结果表明本文提出的算法是有效的。     

数字集群系统业务信道编解码性能研究

讨论了数字集群系统业务信道编解码的实现过程,指出了RCPC编码在数字集群中的重要作用。通过计算机仿真研究了RCPC解码步长对于系统误比特率性能的影响,给出了选择解码步长的数据,为系统的实现提出了理论依据。     

专用污水接纳船罐舱设计与模糊评判

首先产生一组包含最优解的罐舱设计方案，然后运用模糊评价方法，优选了罐舱设计方案。     

卫星星座自主时间同步算法的研究

主要研究了空间卫星间时间同步的方法.在分析了卫星星座的特点和空间时间同步的要求后,提出了一种新的卡尔曼滤波方法来实现星座内卫星间的时间同步,并得到整个星座的系统时间.该方法通过伪距测量得到各卫星间的伪距,用卡尔曼滤波器得到卫星间的钟差和频率差,再对这些钟差和频率差进行加权统计平均,得到星座的系统时间,并以此结果修正卡尔曼滤波器参数,循环渐进优化预测结果,使整个星座内的卫星钟同步于星座的系统时间.对该方法进行仿真后,结果表明具有良好的收敛性和准确的预测值.     

具分布观测的年龄相关的种群扩散系统生育率控制的非线性问题

本文讨论了具分布观测的年龄相关的种群扩散系统最优生育率控制的非线性问题,证明了系统解的存在唯一性和最优生育率控制的存在性,得到了控制为最优的一阶必要条件及其由偏微分方程组和变分不等式组成的最优性组,并进而建立了最优生育率控制的反馈表达式。这些结果可为种群扩散系统中的最优控制问题的实际研究提供理论基础。     

A hybrid multiuser detector for DS-UWB systems with matched filter and error-bit recognizer

In this article, we propose a hybrid algorithm of multiuser detection (MUD) for direct sequence ultra-wideband (UWB) communication systems, based on matched filters (MF) and error-bit recognizers (ER). The ER embraces three steps: bit mapping, K-means clustering, and sign judgment. In this detector, we construct a mapping function and map the output base-band bits from MFs into a one-dimensional feature space to get the amplitude information. After that, we set an initial value and classify the bits into right bits and wrong ones by K-means clustering. Finally, we make the sign judgment to prevent some right bits being picked out as wrong bits and correct the wrong bits to reduce the bit error rate (BER) of the system. Compared to a conventional detector based on MFs and minimum mean square error detector, to a large extent, our detector can improve the BER performance of a system because of high recognition probability of the wrong bits in K-means clustering. What is more, the simulation results show that the proposed hybrid MUD is not sensitive to the number of users. It can achieve a good BER performance and low computational complexity when there are 20 UWB transmitters in the channel.     

Robust consideration of importance sampling in digital communication system

Abstract

This paper proposes using a mixed biasing distribution in Importance Sampling for estimating the bit error rate (BER) via Monte Carlo simulation. The proposed mixed biasing distribution is more robust than the commonly used Gaussian tail distribution when the signal or the threshold setting is disturbed by a uniformly distributed random noise. In this paper the robustness is quantified by the mean squared error.     

一种改进LS信道估计算法在稀疏多径水声信道中的应用

为了消除水声正交频分复用调制(Orthogonal Frequency Division Multiplexing,OFDM)系统中噪声对稀疏多径信道估计的影响,提出了一种改进的最小二乘(Least-Square,LS)信道估计算法。该方法在传统基于离散傅里叶变换(Discrete Fourier Transform,DFT)插值的信道估计结构上进行了改进,得到了基于阈值探测的DFT插值信道估计方法,该方法将小于阈值的时域信道响应置零,探测最有效信道抽头,有效消除噪声干扰的影响。仿真结果验证了DFT插值在稀疏多径水声信道估计中的实用性;得到了当循环前缀长度与信道长度越接近时信道估计性能(Bit Error Rate,BER)越好的结论;确定了在两种调制方式下算法的阈值系数范围;且该新算法与已有算法所需的信噪比可低约2 d B,解决了用循环前缀长度来近似信道真实长度的实际问题。     

Modified sum-product algorithms for decoding low-density parity-check codes

The authors deal with the sum-product algorithm (SPA) based on the hyperbolic tangent (tanh) rule when it is applied for decoding low-density parity-check (LDPC) codes. Motivated by the finding that, because of the large number of multiplications required by the algorithm, an overflow in the decoder may occur, two novel modifications of the tanh function (and its inverse) are proposed. By means of computer simulations, both methods are evaluated using random-based LDPC codes with binary phase shift keying (BPSK) signals transmitted over the additive white Gaussian noise (AWGN) channel. It is shown that the proposed modifications improve the bit error rate (BER) performance up to 1 dB with respect to the conventional SPA. These results have also shown that the error floor is removed at BER lower than 10^-6. Furthermore, two novel approximations are presented to reduce the computational complexity of the tanh function (and its inverse), based on either a piecewise linear function or a quantisation table. It is shown that the proposed approximations can slightly improve the BER performance (up to 0.13 dB) in the former case, whereas small BER performance degradation is observed (<0.25 dB) in the latter case. In both cases, however, the decoding complexity is reduced significantly     

Ant colony optimisation-based multiuser detection for direct-sequence CDMA systems with diversity reception

An ant colony optimisation (ACO)-based multiuser detector assisted by spatial diversity reception using direct-sequence CDMA is proposed. By taking advantage of heuristic values and the collective intelligence of ACO, the proposed detector offers almost the same bit error rate (BER) performance as the full-search-based optimum multiuser detector does, while greatly reducing the computational complexity. The near-far resistance of the ACO-based multiuser detector is also examined. The BER performance for a ten-user system deteriorates scarcely when the interfering users' energy is 12 dB higher than that of the desired user.     

Scintillation index and bit error rate of hollow Gaussian beams in atmospheric turbulence

Based on the Huygens–Fresnel principle and Rytov method, the on-axis scintillation index is derived for hollow Gaussian beams (HGBs) in weak turbulence. The relationship between bit error rate (BER) and scintillation index is found by only considering the effect of atmosphere turbulence based on the probability distribution of intensity fluctuation, and the expression of the BER is obtained. Furthermore, the scintillation and the BER properties of HGBs in turbulence are discussed in detail. The results show that the scintillation index and BER of HGBs depend on the propagation length, the structure constant of the refractive index fluctuations of turbulence, the wavelength, the beam order and the waist width of the fundamental Gaussian beam. The scintillation index, increasing with the propagation length in turbulence, for the HGB with higher beam order increases more slowly. The BER of the HGBs increases rapidly against the propagation length in turbulence. For propagating the same distance, the BER of the fundamental Gaussian beam is the greatest, and that of the HGB with higher order is smaller.     

Channel estimation for time-hopping pulse position modulation ultra-wideband communication systems

Ultra-wideband (UWB) communication systems are used in indoor environments with dense multi-path characteristics. Therefore channel estimation has an important role in the receiver of these systems. A new approach for data-aided (DA) and non-data-aided (NDA) channel estimation is proposed, which is called the pulse compression (PC) method. This method is useful for UWB systems employing time-hopping pulse position modulation. The PC method requires only some basic operations such as sampling, overlap-add and finite impulse response filtering. The PC method, in both DA and NDA scenarios, in spite of its low complexity, outperforms the maximum-likelihood (ML) method in channel parameters estimation. The bit error rate (BER) of the DA method, in single-user scenario, performs as well as the ML method, and in multi-user scenario, in the worst case, there is only 0.5 dB loss compared with the ML method. In the case of NDA scenario, the proposed method outperforms the NDA-ML method, that is, in the single-user scenario about 4 dB gain at the BER of 1023 is observed. In multi-user scenario, it outperforms significantly the NDA-ML method, and its performance loss in comparison with the perfect channel knowledge scenario is about 3 dB at the BER of 1023.     

Improvement of bit error rate and page alignment in the holographic data storage system by using the structural similarity method

Although widely recognized as a promising candidate for the next generation of data storage devices, holographic data storage systems (HDSS) incur adverse effects such as noise, misalignment, and aberration. Therefore, based on the structural similarity (SSIM) concept, this work presents a more accurate locating approach than the gray level weighting method (GLWM). Three case studies demonstrate the effectiveness of the proposed approach. Case 1 focuses on achieving a high performance of a Fourier lens in HDSS, Cases 2 and 3 replace the Fourier lens with a normal lens to decrease the quality of the HDSS, and Case 3 demonstrates the feasibility of a defocus system in the worst-case scenario. Moreover, the bit error rate (BER) is evaluated in several average matrices extended from the located position. Experimental results demonstrate that the proposed SSIM method renders a more accurate centering and a lower BER, lower BER of 2 dB than those of the GLWM in Cases 1 and 2, and BER of 1.5 dB in Case 3.     

Performance of a QAM/FSO communication system employing spatial diversity in weak and saturation turbulence channels

In this paper, the bit error rate (BER) performance and outage probability of quadrature amplitude modulation free space optical (QAM/FSO) communications with spatial diversity in turbulent environments are investigated. The equal-gain combining (EGC) and selection combining (SelC) diversity techniques are considered to mitigate turbulence-induced signal fading in the proposed system. The average BER and outage probability expressions are derived for EGC diversity in weak and saturation turbulence channels. The results indicate that using EGC diversity can significantly improve the system performance compared to employing the SelC diversity or single monolithic aperture schemes. Specifically, approximately 4 and 9?dB lower signal-to-noise power ratios are required for the 1?×?4 EGC diversity system than for the 1?×?4 SelC and non-diversity systems at a BER of 10^?10. In addition, the use of diversity techniques also significantly decreases the outage probability. The proposed scheme can be helpful for establishing a spatial diversity FSO system with a low error rate and high transmission rate.     

拖线阵声纳数字式水下数据高速传输的设计

通过拓扑结构的分析,提出了一种针对拖线阵声纳的数字式水下数据高速传输的方案;介绍了水下数据传输节点的总体设计,并详细地介绍了HOTLink发送接收控制器的设计;然后设计了基于伪随机序列码的误码分析仪,并用其测试了水下数据高速传输节点的误码率。误码测试结果和性能比较结果表明该方案切实可行,并能够方便地实现小型化。