低采样率高分辨率压缩功率谱估计方法的仿真研究

低采样率的宽带功率谱估计在很多领域具有应用价值.采用压缩多核采样结构得到信号的压缩测量值, 然后建立测量值相关函数与信号相关函数之间的关系, 用最小二乘法实现相关函数估计, 最后实现功率谱的估计.该压缩采样方法的等效采样率为M/N·f_s, 可在没有任何对时域或频域稀疏性的假设条件下降低采样率.仿真分析表明, 该方法的系统噪声与加性噪声性能比周期图法略有降低, 但只要系统设计合理, 对于一定信噪比的信号, 系统噪声与加性噪声基本可以忽略, 并给出了对应的理论分析.估计分辨率与周期图法相比, 等效长度相同时略有提高; 由于本文方法降低了测量值的数目, 对于一定长度的数据来说, 估计分辨率得到了极大的提高.本文方法适用于低信噪比信号的低采样率高分辨率功率谱估计.     

Outage mutual information of space-time MIMO channels

We derive analytical expressions for the probability density function (pdf) of the random mutual information between transmitted and received vector signals of a random space-time independent and identically distributed (i.i.d.) multiple-input multiple-output (MIMO) channel, assuming that the transmitted signals from the multiple antennas are Gaussian i.i.d.. We show that this pdf can be well approximated by a Gaussian distribution, and such a Gaussian approximation is based on expressions for the given pdfs mean and variance that we derive. We prove that at high signal-to-noise ratio (SNR), every factor of 2 increase in SNR leads to an increase in outage rate in the amount of min(M,N) bits, where M and N denote the number of transmit and receive antennas, respectively. A simple expression for the moment generating function (MGF) of the mutual information pdf is also provided, based on which we establish normality of the pdf, when both M and N are large, and the SNR is large.     

Futher Results on Rate 1/N Convolutional Code Constructions with Minimum Required SNR Criterion

New good(K, 1/N)convolutional codes for8 leq K leq 13and2 leq N leq 8were found and tabulated which require minimum signal-to-noise ratio (SNR) for given desired bit error rates (BER) with Viterbi decoding. The transfer function bound was used for the BER evaluations.     

高斯白噪声背景下的LFM信号的分数阶Fourier域信噪比分析

目标大机动运动使雷达回波表现为频率和调频率参数均未知的LFM信号。未知参数LFM信号的检测和估计采用分数阶Fourier变换来实现受到越来越多的关注,为此本文着重分析其分数阶Fourier变换的信噪比。首先推导出时限线性调频信号的分数阶Fourier变换模平方,给出了在分数阶Fourier域的峰值点与未知参数的关系,然后研究了附加白噪声LFM信号在分数阶Fourier域的统计特性,确定了其信噪比,并与理想情况(即参数频率和调频率参数已知)下线性相位匹配滤波器的输出信噪比进行了比较。     

Selection diversity combining with multiple antennas for MM-waveindoor wireless channels

Presents predetection and postdetection combining schemes for selection diversity reception with multiple antennas for MM-wave indoor radio channels. For those combining schemes, a reduction in complexity is achieved by limiting the number of combined signals to small values and by increasing the number of received signals. Bit error rate (BER) performance of binary phase shift keying (BPSK) with predetection combining of selected signals (CSS) and BER performance of differential BPSK with postdetection CSS are analyzed for slow fading and Rayleigh-distributed envelope statistics. Predetection maximal ratio combining of signals that comes from a single group or several groups of diversity channels as well as postdetection combining of received signals for groups of channels are considered. In comparing predetection combining with groups (PCG) and predetection combining of the best signals (PCB), we observe that the required SNR for achieving a certain BER is approximatively the same (with PCG having a slight advantage of 0.5 dB) for a given number, N, of diversity channels and L combined signals. Furthermore. PCG is equivalent to PCB for L=N since both techniques then correspond to conventional predetection maximal ratio combining (MRC), PCG and PCB are also equivalent when L=1 as both schemes then correspond to conventional selection combining. A small degradation of approximately 2 dB in the required SNR is observed when postdetection diversity reception with groups (PDG) is used instead of PCG. For L=N, PDG reduces to post detection MRC. The PDG technique is considered more suitable than PCB or PCG for MM-indoor wireless systems     

利用脉间跳频和信号增强技术实现低信噪比下雷达距离超分辨

针对大时带积(TB)线性/非线性调频(LFM/NLFM)脉压信号,本文研究了低信噪比(SNR)下获得雷达距离维超分辨性能的技术和方法。首先提出了一种有效的信号增强算法,并通过脉间跳频的设计获得了不同目标回波非相关性,进而提出了一系列进一步降低超分辨处理的SNR门限的有效方法。计算机模拟表明:同样条件下本文方法较直接频域处理使超分辨估计所需的SNR门限改善了10dB以上,较好地解决了低SNR环境下雷达距离域的多目标超分辨问题。     

A matrix-based algorithm for estimating multiple coherence of a periodic signal and its application to the multichannel EEG during sensory stimulation

The coherence between the stimulation signal and the electroencephalogram (EEG) has been used in the detection of evoked responses. The detector's performance, however, depends on both the signal-to-noise ratio (SNR) of the responses and the number of data segments (M) used in coherence estimation. In practical situations, when a given SNR occurs, detection can only be improved by increasing M and hence the total data length. This is particularly relevant when monitoring is the objective. In the present study, we propose a matrix-based algorithm for estimating the multiple coherence of the stimulation signal taking into account a set of N EEG channels as a way of increasing the detection rate for a fixed value of M. Monte Carlo simulations suggest that thresholds for such multivariate detector are the same as those for multiple coherence of Gaussian signals and that using more than six signals is not advisable for improving the detection rate with M = 10. The results with EEG from 12 normal subjects during photic stimulation at 10 Hz showed a maximum detection for N greater than 2 in 58% of the subjects with M = 10, and hence suggest that the proposed multivariate detector is valuable in evoked responses applications.     

A Multidigit Adaptive Delta Modulation (ADM) System

A multidigit adaptive delta modulation (ADM) system has been proposed where the error signal, between the input and the approximated signal produced by ADM coder, is coded in an auxiliary encoder. The error in the auxiliary coder is processed by another ADM and so on. The bit rate of each of these coders isf_{r}/Nwhere fris the overall transmission rate andNis the number of coders used. The bit streams are interleaved for transmission and at the receiver they are separated and decoded, and these signals are added and filtered. It is shown that for a given transmission rate, each coder operates at a basic sampling rate of frBsuch thatN_{opt} = f_{r}/f_{rB}gives the optimum number of coders to be used for maximum signal-to-noise ratio (SNR). A bound is derived for the maximum SNR of such a system and is compared with the bounds derived for other predictive coders. The experimental results of a two-digit ADM are presented. An average SNR of 30 dB is obtained with a dynamic range of 32 dB at fr= 32 kbits/s for band-limited noise signals. The SNR increases with the sampling rate at 15 dB/octave, as against 9 dB for a single-digit ADM. The frequency response is good and the variation of SNR with the message frequency of the delta coding system has been improved. The effect of channel errors has also been studied and the performance of the system is found satisfactory.     

低信噪比下线性/非线性调频信号距离超分辨

本文研究了应用高分辨阵列处理算法实现雷达距离超分辨问题。利用我们提出的针对线性／非线性调频（ＬＦ ／ＮＬＦＭ）信号的降噪算法,提高了回波信号的有效信噪比（ＳＮＲ）。通过将ＭＯＤＥ算法拓展到色噪声环境中,基于频域处理解决了不同目标速度接近时造成的目标回波强相关甚至相干给超分辨处理带来的困难。计算机模拟表明,本文方法可在低ＳＮＲ下实现多目标的距离超分辨估计,并克服了现有方法在ＳＮＲ门限、回波相干性、计算量等方面的限制。     

New Short Constraint Length, Rate 1/N Convolutional Codes Which Minimize the Required SNR for Given Desired Bit Error Rates

New, good (K, 1/N) convolutional codes are tabulated for3 leq K leq 7and2 leq N leq 8, which were selected based on the criterion of minimizing the required signal-to-noise ratio (SNR) for given desired bit error rates (BER). A transfer function upper bound was used to find the BER performance. Partial searches were performed using the idea that "good codes generate good lower rate codes." The new codes save signal energy up to 0.4 dB compared to previously reported codes of the same parameters.     

基于矩阵二值化的频率捷变雷达信号分选

针对频率捷变雷达信号的分选,提出了一种基于时频矩阵二值化的频率捷变雷达信号分选新方法。该方法首先对信号进行时频变换,得到时频矩阵;然后对时频矩阵二值化处理,提取信号在时频域能量分布归一化值作为信号的相参特征;最后采用支持向量机分类器实现信号分选。文中对频率捷变雷达信号进行仿真实验,结果表明,该方法在较低信噪比下仍能获得较为满意的分选准确率,当信噪比为6dB时,信号分选准确率达到96.17%,验证了所提出方法的有效性。     

Performance of M-ary PSK signals in slow Rayleigh fading channels

The error rate performance of M-ary coherent phase shift keyed signals and M-ary differential phase shift keyed signals in slow Rayleigh fading channels is analysed. Closed-form expressions for the symbol error rate are presented. The coherent PSK signals are 3 dB stronger than the differential PSK signals at high SNR for given M in a Rayleigh fading environment.<>     

Time-variant distortions in OFDM

We analyze the degradation of orthogonal frequency division multiplexing (OFDM) signals from time-variant distortions like carrier and sampling frequency offset, Doppler spread and oscillator phase noise. We propose a novel analytical framework in the discrete-time domain based on the FFT demodulation of a single OFDM symbol and unify previous methods with some new results. Exact definitions of the signal-to-subcarrier-interference ratio (SIR) and the effective signal-to-noise ratio (SNR) are given and evaluated for a HIPERLAN/2 system     

On ternary phase-shift keyed signaling (Corresp.)

In agreement with a recent paper by Pierce, it is shown that ternary, phase-shift keyed (PSK) signals attain the lowest bit error rate at high signal-to-noise ratio (SNR) if more than4/3binary digits can be mapped to a symbol. This point is further demonstrated by using a 3B-2T Code which maps 1.5 bits to a symbol. The spectrum and bit error rate are evaluated for the 3B-2T coded Ternary. PSK signal and compared with those of quaternary phase-shift keyed (QPSK) signal.     

On the Distortion SNR Exponent of Some Layered Transmission Schemes

We consider the problem of joint source-channel coding for transmitting K samples of a complex Gaussian source overT bK uses of a block-fading multiple-input multiple-output (MIMO) channel with M transmit and N receive antennas. We consider the case when we are allowed to code over L blocks. The channel gain is assumed to be constant over a block and channel gains for different blocks are assumed to be independent. The performance measure of interest is the rate of decay of the expected mean-squared error with the signal-to-noise ratio (SNR), called the distortion SNR exponent. We first show that using a broadcast strategy similar to that of Gunduz and Erkip, but with a different power and rate allocation policy, the optimal distortion SNR exponent can be achieved for 0 les b les (|N - M| + 1)/ min(M,N) and for b > MNL₂. This is the first time the optimal exponent is characterized for 1/min(M, N) < b < (|N - M| + 1)/min(M, N). Then, we propose a digital layered transmission scheme that uses both time layering and superposition. The new scheme is at least as good as currently known schemes for the entire range of bandwidth expansion factors b, whereas at least for some M, N, and b, it is strictly better than the currently known schemes.     

时频域重叠多信号智能检测方法研究

针对现有基于深度学习理论的信号智能检测方法大多只能对单信号或时频域不重叠的信号进行检测,本文提出了一种基于掩膜区域卷积神经网络(Mask R-CNN)与Criminisi算法的时频重叠多信号智能检测新方法.首先将一维时域信号通过时频变换得到二维时频图像.然后针对时频图中多信号重叠部分像素位置信息缺失这一问题,提出了利用...     

Information-Bearing Noncoherently Modulated Pilots for MIMO Training

In this correspondence, we deal with noncoherent communications over multiple-input-multiple-output (MIMO) wireless links. For a Rayleigh flat block-fading channel with M transmit- and N receive-antennas and a channel coherence interval of length T, it is well known that for TGtM, or, at high signal-to-noise-ratio (SNR) rhoGt1 and Mlesmin{N,lfloorT/2rfloor}, unitary space-time modulation (USTM) is capacity-achieving, but incurs exponential demodulation complexity in T. On the other hand, conventional training-based schemes that rely on known pilot symbols for channel estimation simplify the receiver design, but they induce certain SNR loss. To achieve desirable tradeoffs between performance and complexity, we propose a novel training approach where USTM symbols over a short length T_tau(tau is a small fraction of T, and recovers part of the SNR loss experienced by the conventional training-based schemes. When rhorarrinfin and TgesT_tau ges2M=2Nrarrinfin, but the ratios alpha=M/T, alpha₁ =T_tau/T are fixed, we obtain analytical expressions of the asymptotic SNR loss for both the conventional and new training-based approaches, serving as a guideline for practical designs     

基于数据辅助的MPSK信号频域信噪比估计

为在载波频率精确恢复前提高多进制数字相位调制（MPSK）信号在低信噪比下的估计精度,提出了一种数据辅助的MPSK信号频域信噪比估计算法。算法在符号定时恢复和帧同步后提取同步段符号,相关运算后在频域进行信噪比估计。仿真结果表明,算法估计均值无偏,不受载波频率误差的影响,在符号长度为512、信噪比为-10 dB时,均方误差与克拉美罗界只有0.15 dB的偏差,特别适合于接收信号包含载波频率误差且要求低信噪比下具有较高信噪比估计性能的应用。     

多重信号广义似然接收机的设计及性能分析

提出并设计了一类通用的多重信号广义似然接收机.设计时只要求各重信号中高斯噪声是独立和零均值的,而允许是有色的或者非平稳的.推导结果表明,针对各重未知信号的最好情况(高信噪比,且各重信号幅度相等)、最不利情况(信噪比很低,且各重信号幅度独立)和适中情况(信噪比不太高也不太低,且各重信号幅度独立),所设计的接收机结构都是一致的,只是某些具体参数和模块不同. 本文还针对此接收机给出了性能分析的一个比较通用的方法.仿真结果与推导的理论性能相当吻合.     

Approximate BER performance of generalized selection combining inNakagami-m fading

The error performance of generalized selection combining (GSC), which optimally combines the K highest signal-to-noise ratio (SNR) signals out of L total diversity signals, in Nakagami-m fading was recently evaluated using moment generating function (MGF) of the GSC output SNR. However, no single closed-form expression for the MGF exists for arbitrary K and L. In fact, a closed-form expression for the MGF is possible only for an individual combination of K and L. In this letter, a single closed-form expression for approximating the MGF is, therefore, derived and employed in evaluating the approximate error performance. Although the approximation is only applicable for GSC with K being a factor of L, it nonetheless achieves a high degree of accuracy