Performance of anM-ary orthogonal communication system using stationary stochastic signals

This paper considers the performance of a communication system which transmits forTseconds the real part of a sample function of one ofMstationary complex Gaussian processes whose spectral densities are all frequency translations of the functionS_{xi (f). At the receiver white Gaussian noise of one-sided densityN_{0}is added. The center frequencies of the processes are assumed to be sufficiently separated that theMcovariance functions are orthogonal overT. Exponently tight bounds are obtained for the error probability of the maximum likelihood receiver. It is shown that the error probability approaches zero exponentially withTfor all ratesR = (ln M)/Tup toC= int_{-infty}^{infty} [S_{xi (f)/N_{0}] df - int_{- infty}^{infty} ln [1 + S_{xi}(f)/N_{0}] dfwhich is shown to be the channel capacity. Similar results are obtained for the case of stochastic signals with specular components.     

Cooperative communication system for high performance using ambient signals

This paper proposes the Internet connectivity of RF-powered devices in the backscatter system. The RF-powered devices do not use a battery and charge energy by harvesting from ambient RF signals of TV, a cellular phone and Wi-Fi devices. The Internet connectivity of the RF-powered devices in the backscatter system is very useful in Internet of things technology because the RF-powered devices which are called to a tag have a small size by the harvesting from ambient RF signals without a battery. This paper proposes a method improving the communication performance of the Wi-Fi backscatter system by applying the cooperative communication scheme.

     

Estimation of elbow-induced wrist force with EMG signals using fast orthogonal search

In many studies and applications that include direct human involvement-such as human-robot interaction, control of prosthetic arms, and human factor studies-hand force is needed for monitoring or control purposes. The use of inexpensive and easily portable active electromyogram (EMG) electrodes and position sensors would be advantageous in these applications compared to the use of force sensors, which are often very expensive and require bulky frames. Multilayer perceptron artificial neural networks (MLPANN) have been used commonly in the literature to model the relationship between surface EMG signals and muscle or limb forces for different anatomies. This paper investigates the use of fast orthogonal search (FOS), a time-domain method for rapid nonlinear system identification, for elbow-induced wrist force estimation. It further compares the forces estimated using FOS with the forces estimated by MLPANN for the same human anatomy under an ensemble of operational conditions. In this paper, the EMG signal readings from upper arm muscles involved in elbow joint movement and sensed elbow angular position and velocity are utilized as inputs. A single degree-of-freedom robotic experimental testbed has been constructed and used for data collection, training and validation.     

偏振正交法抑制双向传输系统瑞利干涉噪声

瑞利后向散射引起的干涉噪声是双向光纤传输系统的主要噪声来源。本文对单模光纤双向传输系统中瑞利后向散射的一般理论和偏振特性进行了分析,并提出了采用偏振正交法减小干涉噪声的方法。建立了10 GHz模拟RF信号单波长双向传输系统,并采用偏振旋转器件实现正、反向传输光的偏振近似正交传输。通过数值模拟,分析了本系统瑞利后向散射偏振状态与入射光偏振状态、反向光偏振旋转角的关系,进一步分析了系统干涉噪声抑制水平。模拟分析结果表明,在80°～90°范围内旋转偏振态,能够使瑞利后向散射降低至少一个数量级;系统信噪比提高了近15倍。利用偏振正交法减小双向传输系统的干涉噪声,有对偏振旋转的精度要求不高、容易操作的优点。     

Suboptimum coherent detection of orthogonal phase-modulated signals

A suboptimum scheme for coherent demodulation of orthogonal phase-modulated signals in the additive white Gaussian noise channel is proposed and analyzed in terms of bit error probability. It is analytically shown that the suboptimum scheme provides the bit error performance competitive to the conventional optimum scheme, while requiring much less implementation complexity.     

Multicarrier orthogonal CDMA signals for quasi-synchronouscommunication systems

Proposes a multicarrier orthogonal CDMA signaling scheme for a multiple-access communication system, such as the reverse channel of a cellular network, as an alternative to the multi-user interference cancellation approach. The average variance of cross-correlations between sequences is used as a measure for sequence design. The authors search for sets of sequences that minimize the probability of symbol detection error, given that there is imperfect synchronization among the signals, that is, the signals are quasi-synchronous. Orthogonal sequences based on the Sylvester-type Hadamard matrices (Walsh functions) are shown to provide a significant improvement over the case where a Hadamard (orthogonal) matrix is chosen at random. Computer searches suggest that this set of codes is optimal with respect to the above measure. The issue of chip pulse shaping is investigated. Optimal pulses designed to minimize multiple-access interference in quasi-synchronous systems are obtained for various bandwidths and are shown to provide a large improvement over the raised cosine pulses. A multicarrier signaling scheme is introduced in order to reduce chip level synchronization offsets between the users     

Noncoherent multistage multiuser detection of M-ary orthogonal signals

In recent years, a great deal of research has been performed on methods of alleviating the performance degradations suffered by code division multiple access (CDMA) systems due to multiple access interference. In this paper, we consider a multistage detector for noncoherent CDMA using M-ary orthogonal signals. Using a decorrelating detector as its first stage, the detector iteratively estimates the multiple access interference affecting the desired signal, subtracts the estimated interference, and forms symbol estimates for each of K users. Through numerical examples, the bit error performance of the proposed detector is demonstrated to be superior to that of previous detectors for the same signalling scheme. This revised version was published online in June 2006 with corrections to the Cover Date.     

Envelope detection of orthogonal signals with phase noise

The authors analyze the performance of receivers that use envelope detection at an IF to detect optical signals with orthogonal modulation formats. Exact closed-form expressions for the error probability conditioned on the normalized envelope were obtained. The only information necessary for obtaining the unconditional error probability is a small set of tilted moments of the envelope. The authors then provide an approximation to this envelope which is not only accurate to the first order in phase noise strength, but also has the same range as the actual random envelope. This approximation was used to obtain the bit error performance of the three receiver models considered. A tight lower bound in closed form is given. The analysis is extended to the case of N-ary frequency-shift-keying (FSK) to provide very tight upper and lower bounds to the bit error probability     

Feedback beamforming technique for receiving multipath coherent signals

A novel feedback beamformer is proposed for receiving multipath coherent signals. First, a subtraction-based minimum variance distortionless response beamformer is utilized to obtain an estimation of the desired signal. Then its output is fed back to the original full aperture array where a minimum mean square error (MMSE) beamformer is applied. Due to multipath-matched feature of the MMSE beamformer, the novel feedback beamformer can combine multipath signals without aperture loss. Two feedback schemes are proposed and their effectiveness is verified via simulation.     

反馈电压偏置型Hopfield 网络电域盲检测相干光通信信号

为解决无线分集相干光接收机的自适应盲检测问题,提出了一种新的离散时间连续状态的网络输出反馈偏置型的复Hopfield 神经网络用以解决多值QAM 信号的盲检测问题。反馈电压偏置的引入即不脱离传统Hopfield 模型,又能有效满足多值信号检测时所需的搜索空间变大的特殊要求。全文完成多值信号盲检测的优化问题构造和能量函数的映射,给出能量函数的证明、分析和它的约束条件,给出适用该问题的激活函数的基本特征,正确盲检测信号的权矩阵的配置方法。最后,通过详细的仿真结果展示和与其他算法性能对比进一步验证算法的有效性和优越性并指出算法所存在的问题和下一步的研究方向。     

通信信号自动识别方法

通信信号的自动识别是通信信号处理的一个重要研究课题,近年来随着数字信号处理技术的发展,通信信号的调制方式增加了,对通信信号的自动识别提出了更高的要求.许多新的方法应用于该领域,本文对近年来这个领域的研究作了综合评述,讨论了其中存在的问题,并指出了今后的发展方向.     

Design of signals for analog communication

A method for the design of time-limited and effectively band-limited waveforms for analog communication systems is developed. The design problem is first formulated in theL_2 (0, T)space. Nonlinear modulation threshold effects are incorporated directly into the design by introducing constraints in the form of minimum distance between points on the locus. It is shown that all pertinent information can be expressed in terms of the inner product function generated by the locus and its cross derivative. The design is then transformed into a constrained minimization problem in a space of inner product functions. The cases of stationary locus andN-dimensional locus are further investigated.     

Anti-scanning research for MPWFRFT communication signals

Due to the importance of weighted fractional Fourier transform (WFRFT) applications, it has become an important technology in the fields of OFDM and CDMA. Although the single parameter weighted fractional Fourier transform (SPWFRFT) is the most widely used method at present, the multiple-parameter weighted fractional Fourier transform (MPWFRFT) has received increasing attention in order to further improve the anti-scanning performance of the system. Thus, considering the characteristics of digital communications signals with the MPWFRFT, the anti-scanning method is investigated herein. By studying the process of the SPWFRFT, we establish the influence factors and calculate the weighted coefficients. Then, the influence factor is spread, and multiple parameters are added, which allow MPWFRFT processing to be studied in-depth. Based on this research, we carry out anti-scanning research under different conditions. By studying the relationship between the parameters M and V, the optimal parameter setting rules are given. Further, the bit error rate is discussed emphatically, and the minimum scanning interval of all parameters is given. In addition, we discuss the complexity and how to easily decode the useful signals at the receiver, and then the anti-scanning performance of MPWFRFT communication systems is proved.

     

跳频正交网台信号分选算法研究

跳频正交网台信号的分选是跳频通信侦察领域亟待解决的关键问题,在简要叙述 2种典型跳频组网方式基本特征的基础上,从侦察和反侦察相结合的角度出发,进一步深入分 析了2种组网方式的组网机理和不同跳频网之间信号特征的差异性,并找出了可用于分选的 特征参数;重点讨论了2种网台信号的分选问题,分别给出了1种分选算法。     

信道预测联合收发分集的正交信号误码性能

为解决采用最小均方误差(MMSE)信道预测的发射天线选择(TASP)/接收天线最大比合并(MRC)的无线通信系统设计问题,利用抛物柱面函数以及高斯Q函数的近似表达式和矩生成函数(MGF)法,分别推导了瑞利块衰落信道上采用TASP/MRC天线分集的相干检测M进制正交和双正交信号的平均误符号率(ASER)精确表达式以及正交信号ASER的近似表达式.数值计算和仿真结果验证了采用TASP/MRC和相干检测的正交/双正交ASER精确表达式的正确性以及正交信号ASER近似表达式的准确性.上述M进制正交/双正交信号ASER精确或近似表达式,可用于设计采用相干检测M进制正交和双正交信号的TASP/MRC天线分集系统,并能够快速地确定收发天线数和信道预测器级数等参数,避免耗时的计算机仿真.     

Differentially en/decoded orthogonal space-time block codes withAPSK signals

In this letter, we propose a differential en/decoding scheme for Alamouti's orthogonal space-time code using amplitude/phase-shift keying (STC-APSK) signals and two transmit antennas. It is compared with the differential en/decoding scheme using 16APSK and single transmit antenna. It is also compared with the differential en/decoding scheme for Alamouti's orthogonal space-time code using 16PSK (STC-16PSK) signals and two transmit antennas. We find that the performance of the differentially en/decoded STC-APSK with 4.5 b/s/Hz is significantly better than that of the differentially en/decoded 16APSK with 4 b/s/Hz, and is almost the same as that of the STC-16PSK with 4 b/s/Hz over Rayleigh flat fading channels     

Generalized multinomial detectors for data communication signals

A detector with multinomial input (MN) previously derived for on-off communication systems is generalized to include binary antipodal signals with arbitrary shapes. The proposed detector is distinguished by its simpler implementation. No multiplications are needed and it has a relatively good performance. Results of numerical examples are obtained under Gaussian and non-Gaussian noise environments for different numbers of quantization levels. Solutions for M-ary signaling are also discussed     

A transparent repeater for digital communication signals

A method is presented for retransmitting a digital communication signal over channels with different signal-to-noise ratios (SNRs), without complete demodulation and remodulation (Demod/Remod). The method, which we call signal code modulation (SCM), converts samples of the incoming signal into digital and analog symbols whose characteristics are designed to match the channel. The SCM method trades bandwidth for SNR in the classical manner and achieves a performance close to that of conventional Demod/Remod methods. However, it does so by performing relatively simple operations on the sampled input signal and does not require detailed knowledge of its fine structure (framing, coding, etc.).     

在用广电信号与火炬传递信号的干扰分析

石家庄市是北京2008奥运会火炬传递城市之一,“祥云”火炬将从革命圣地西柏坡传递到市内主会场。虽然火炬传递时间短,但前期无线电安全保障工作涉及面广、任务重、难度大、要求高。在奥运火炬传递这项庞大的系统工程中．无线电安全保障和优质服务起着关键作用．其协调、管控水平是体现北京奥运会“科技奥运”理念的一个重要方面。