Fiber-optic sensor array based on Sagnac interferometer with stablephase bias

We propose and experimentally demonstrate a novel fiber sensor array based on a Sagnac interferometer with very simple electronic signal processing. A stable quadrature phase bias was obtained using a phase modulator, and the polarization-induced signal fading was suppressed by using a depolarizer and a broad-band source. A phase sensitivity of about 4.0 μrad_rms/√Hz at 5 kHz was obtained using a two-sensor array     

Space-diversity reception for v.h.f. mobile radio

Work on aerial diversity reception to combat multipath fading is described. A 3-channel adaptive array has been built around a conventional v.h.f.?a.m. receiver, and been modified to measure signal amplitudes and relative phases. Experimental results show the effects of typical multipath environments, and the improvement obtained with an adaptive array.     

BER performance of linear STBC from orthogonal designs over MIMO correlated Nakagami-m fading channels

This paper presents the evaluation of the average bit error rate (BER) performance of linear space-time block codes (STBC) from orthogonal designs over correlated identically distributed Nakagami-m fading channels. Starting from the moment-generating function (MGF) of the multipath component signals at the antenna array elements, analytical expressions of the BER performance for both integral and nonintegral Nakagami-m fading parameters are derived. Closed-form expressions of the spatial cross-correlation function for mobile nonfrequency selective Nakagami-m fading multiple-input-multiple-output (MIMO) channels are obtained, which are valid for small angle-of-arrival (AOA) spread. In this expressions, various parameters of interest, such as the mean AOA of the signal, AOA spread, and array configurations, are all taken into account. The effects of antenna array configuration and the operating environment (mean AOA, AOA spread, Nakagami fading parameter) on the BER performance of the system are illustrated by several numerical examples.     

使用分集技术的信号调制类型识别

针对衰落环境下的调制识别,该文基于决策理论和多天线接收分集技术提出了一种解决方法。根据对未知信道和信号参数的不同处理方式,推导了用于识别的似然函数,并构造了分类器。采用多天线分集技术提高正确识别率,并考虑了天线空间位置对分集合并的影响,提出了解决办法。计算机仿真结果表明该文所述方法的有效性和正确性。     

On antenna array receiver principles for space-time-selectiveRayleigh fading channels

Optimum (in the sense of minimum-error probability) single-symbol diversity detection for fading, noisy channels is too complex for practical implementation. A simplified, near-optimum array receiver is proposed, which is based on the statistics (i.e., the covariance-function matrix) of the fading channel. This detector is then analyzed by calculating the exact error probability. When there is a spread of the direction of arrival of the incident radio waves, the proposed detector significantly gains over an adaptive antenna array (which forms a weighted sum of the received antenna signals). Also, for this adaptive array, a fundamental difference between maximum-likelihood weights and least-mean-square weights is observed     

Experiment on coherent adaptive antenna array for wideband DS-CDMAmobile radio

A four-element pilot symbol-assisted coherent adaptive antenna array diversity receiver for 4.096 Mchip/s wideband direct sequence code division multiple access mobile radio is implemented and its performance in a multipath fading environment is evaluated by a laboratory experiment using hardware fading simulators. The receiver comprises an adaptive antenna array using the normalised least mean square algorithm and Rake combiner. It is demonstrated that, for the three-user case, the required average signal-to-interference ratio obtaining average BER of 10^-3 can be reduced by ~8 dB compared to four-branch antenna diversity     

Polarization-induced fading in fiber-optic sensor arrays

The statistics of polarization-induced visibility fading is studied for fiber-optic interferometric (Michelson or Mach-Zehnder) sensor arrays made of either regular single-mode fibers or polarization-maintaining fibers. Performance is measured in terms of the probability to observe visibilities, all of which exceed a given value, for all members of the array. Very poor performance is obtained for arrays made of nonpolarization maintaining fibers, unless the input state of polarization is dynamically controlled to optimize the visibility of the worst sensor of the array. While the use of the more costly polarization-maintaining fibers could, in principle, solve this polarization-related fading problem, finite extinction ratios of couplers and splices make the performance of such arrays comparable to that of nonpolarization maintaining arrays with optimally controlled input-polarization     

Error probability performance for W-CDMA systems with multiple transmit and receive antennas in correlated Nakagami fading channels

The bit error rate (BER) performance of a two-dimensional (2-D) RAKE receiver, in combination with transmit diversity on the downlink of a wide-band CDMA (W-CDMA) system, is presented. The analyses assume correlated fading between receive antenna array elements, and an arbitrary number of independent but nonidentical resolvable multipaths combined by the RAKE receiver in the general Nakagami-m (1960) fading channel framework. The impact of the array configuration (e.g., the number of transmit antennas and receive antennas, the antenna element separation) and the operating environment parameters (such as the fading severity, angular spread and path delay profile) on the overall space-path diversity gain can be directly evaluated. In addition, the exact pairwise error probability of a convolutional coded system is obtained, and the coding gain of a space-path diversity receiver is quantified.     

干涉型光纤传感器阵列消PIF技术的研究

针对低双折射光纤双光束干涉型传感器两臂偏振态随机变化引起的信号衰落,提出了一种新型消偏振方式,它可以在可见度略有下降的情况下,较好地消除偏振态变化引起的信号可见度的随机变化。该方案是通过相互正交的两个偏振态来补偿由于其中一个偏振态变化导致的干涉信号衰落。通过自动增益控制电路可以使传感信号稳定,能够在信噪比有所下降的情况下消除偏振衰落的影响,实现了干涉型光纤传感器的消偏振衰落。     

DS-CDMA system with joint channel estimation and MAP detection intime-selective fading channels

In this paper, maximum a posteriori (MAP) detection is applied to a direct-sequence code-division multiple-access (DS-CDMA) system jointly with identification and estimation of time-selective fading channels. By sampling the outputs of the matched filter and combining antenna array elements, strong and time-varying multiple-access interference (MAI) is characterized and suppressed instantaneously. The decision statistics for MAP detection are obtained from the conditional probability density function of the prediction error. The prediction is accomplished by approximating the fading channel with a constrained nonlinear state model. Unknown parameters such as auto-regressive (AR) process coefficients, noise covariance matrices, and the antenna array vector are estimated based on received sample vectors only. Also, differential modulation is applied to eliminate the need for pilot insertion. Through computer simulations, near-optimum bit error rates (BERs) are found     

Tradeoff between diversity gain and interference suppression in a MIMO MC-CDMA system

In this paper, the uplink of an asynchronous multi-carrier direct-sequence code-division multiple-access (MC-DS-CDMA) system with multiple antennas at both the transmitter and the receiver is considered. We analyze the system performance over a spatially correlated Rayleigh fading channel with multiple-access interference (MAI), and evaluate the antenna array performance with joint fading reduction and MAI suppression. Assuming perfect channel knowledge available at the transmitter, maximal ratio transmission is employed to weight the transmitted signal optimally in terms of combating signal fading. At the receiver, adaptive beamforming reception is adopted to both suppress MAI and combat the fading. Note that while correlations among the fades of the antennas in the receive array reduce the diversity gain against fading, the array still has the capability for interference suppression. We examine the effect of varying the number of transmit and receive antennas on both the diversity gain and the interference suppression.     

Analysis of Phase-Conjugating Arrays in Multipath Environments

The ability of a phase-conjugating array (PCA) to reduce fading in single-reflector, dual-reflector, and blocked-line-of-sight multipath environments is presented. Compared to a reference four-element antenna array, the PCA improves worst case signal fading by as much as 39 dB. Agreement between the experimental results and a ray-tracing model is observed, verifying the model as a viable method for characterizing array performance in multipath environments.      

A New, Low-Cost, Switched Beam and Fully Adaptive Antenna Array for 2.4 GHz ISM Applications

A new, low-cost, switched-beam and fully adaptive antenna array suitable for 2.4 GHz ISM applications is proposed in this paper. The array comprises of four elements, equal in number receiving RF and IF components, as well as a microcontroller based unit which is responsible for the control of the array. The array is designed with the aid of a custom genetic algorithm, while measurements results are presented indicating consistency between design and implementation. In addition, multipath fading mitigation capability of the array is demonstrated via channel measurements results.     

具有相位误差敏感性的CM阵波束形成器

本文针对短波衰落信道的特点,通过提出一种具有相位误差敏感性的CM阵波束形成器,实现了CM阵对衰落信号的捕获和自动跟踪,并通过计算机模拟证明该波束形成器在衰落信道条件下具有良好的收敛性能。     

A two-element adaptive antenna array for IS-136 PCS base stations

We describe computer simulation and laboratory performance results of a real-time two-element adaptive antenna array testbed for the uplink of a 1.9-GHz IS-136 PCS base station. Our simulations and real-time experimental results with a channel emulator show less than a 1-dB implementation loss as compared to theoretical results for the noise-only case. With interference, at low fading rates the implementation loss to is only a few decibels. However, the performance degrades with increasing fading rate, such that the adaptive array performance is similar to maximal ratio combining at 60-m/h fading rates (179 Hz at 1.9 GHz)     

Performance of an array receiver with a Kalman channel predictorfor fast Rayleigh flat fading environments

We develop an approach for using an antenna array for tracking fast Rayleigh flat fading channels and suppressing cochannel interference. The fast flat fading process is assumed to be a general autoregressive (AR) process in order to characterize temporal variation of channels and evaluate its effect on the receiver structure and performance. The optimal array receiver structure that minimizes the probability of error for BPSK signals is derived, which includes a Kalman filter to predict the fading channels. A simple integral expression for the probability of error is also derived for the optimal receiver. In particular, we analyze the case with identical shaping filters. An irreducible probability of error is shown to exist due to the prediction error of multiple channels. Another interesting observation from the study is that the diversity gain with m antenna elements in the presence of k interferences is usually greater than (m-k), even in the presence of channel prediction error. Simulations are carried out to verify the theoretical analysis     

复合衰落信道建模及模拟方法研究

针对传统信道模拟器仅考虑多径衰落的问题,建立了包含路径损耗、阴影衰落和多径衰落的复合衰落信道模型,提出了一种基于高斯变量分解和谐波叠加原理的硬件模拟方法,推导了该方法输出衰落幅值理论分布与仿真参数的内在联系,并详细分析了可编程逻辑器件定点化模型输出周期性及位宽选择等问题。针对原型化模拟器的实测结果表明,该模拟方法输出信道衰落的统计特性与理论值吻合,可用于实验室中无线通信系统的性能测试和验证。      

Multibeam antennas with polarization and angle diversity

A 10-GHz discrete cylindrical lens array with multiple beams is designed and characterized as a receiving angle-diversity array for wireless communications in a multipath environment. The array also has dual-orthogonal polarization and therefore built-in polarization diversity. The array is designed for wide-angle scanning between -45° and 45° and measured scanning patterns are presented. The polarization isolation between the two channels is about 30 dB at boresite and about 10 dB for a 30° scan angle. The addition of the lens array at the very front end of a link shows significant reduction of multipath fading peak-to-null ratio     

频率选择性衰落信道下长扩频序列CDMA 系统的盲波束成形

本文提出一种适用于频率选择性衰落信道下长扩频序列CDMA系统，基于DMMSE准则的盲波束成形方案。该方案反频率选择性衰落信道分解成若干个非频率选择性衰落子信道，不需要训练符号开销，回避跟踪衰落信道参数，以所需用户的扩频序列作为永久性训练序列。仿真结果验证了其抵抗远近效应、抑制多址干扰的能力。     

Spatial fading correlation function of circular antenna arrays withLaplacian energy distribution

We derive an analytical formula for the fading correlation function of a uniform circular array (UCA) when the angular energy follows a Laplacian distribution. The fading correlation for a UCA is a function of antenna spacing, array geometry, as well as the distribution of the received energy in terms of the angle-of-arrival (AOA). Computer simulations are carried out to verify the analytical results