Separation of cochannel GSM signals using an adaptive array

The Global System for Mobile communications (GSM) is a digital cellular radio network that employs time division multiple access (TDMA). In such a cellular system, frequencies are reused in different regions for spectral efficiency, and thus, the transmissions in a given cell can interfere with those in distant cells. This cochannel interference can be a major impairment to the signal of interest. In this paper, we describe a beamformer and equalizer system that is capable of separating and demodulating several cochannel GSM signals. The signal model includes intersymbol interference (ISI) induced by the Gaussian transmit filter, and the channel model incorporates multipath propagation and additive white Gaussian noise. The GSM synchronization sequences are used to compute the beamformer weights and achieve frame synchronization simultaneously. Decision-feedback equalization is employed to compensate for the transmit filter ISI and to demodulate the data     

An experimental adaptive array to suppress weak interfering signals

An experimental adaptive antenna system to suppress weak interfering signals is described. It is a sidelobe canceller with two auxiliary elements. Modified feedback loops are used to control the array weights. The received signals are simulated in hardware for parameter control. Digital processing is used for algorithm implementation and performance evaluation. The experimental results are presented. They show that interfering signals as much as 10 dB below the thermal noise level in the main channel are suppressed by 20-30 dB. Such a system has potential application in suppressing the interference encountered in direct broadcast satellite communication systems     

A systolic array realization of the adaptive decision feedback equalizer

This paper presents a systolic array architecture for the adaptive decision feedback equalizer. The design is based on an algebra developed earlier by Kung and Lin (Proceedings of the Conference of Elliptic Problem Solvers, Monterey, CA, January 1983; Research Report CMU-CS-84-100, Department of Computer Science, Carnegie-Mellon University, Pittsburgh, PA, April 1983.) and is largely made up of two basic processing cells that are computationally equivalent and simple to realize. To maintain accuracy of the algorithm, the array needs to be operated by a clock with a speed twice of that the input. The increase in clock speed can, however, be exploited to reduce the total number of adders and multipliers by about 50%.     

Robust adaptive array beamforming for cyclostationary signals undercycle frequency error

This paper deals with the problem of robust adaptive array beamforming for cyclostationary signals. By exploiting the signal cyclostationarity, the SCORE algorithms presented by Agee, Schell and Gardner (1990) have been shown to be effective in performing adaptive beamforming without requiring the direction vector of the desired signal. However, these algorithms suffer from severe performance degradation even if there is a small mismatch in the cycle frequency of the desired signal. In this paper, we first evaluate the performance of the SCORE algorithms in the presence of cycle frequency error (CFE). An analytical formula is derived to show the behavior of the performance degradation due to CFE. Based on the theoretical result, we then develop an efficient method in conjunction with the SCORE algorithms to achieve robust adaptive beamforming against the CFE. Several simulation examples for confirming the theoretical analysis and showing the effectiveness of the proposed method are also presented     

An experimental SMI adaptive antenna array simulator for weakinterfering signals

An experimental sample matrix inversion (SMI) adaptive antenna array for suppressing weak interfering signals is described. The experimental adaptive array uses a modified SMI algorithm to increase the interference suppression. In the modified SMI algorithm, the sample covariance matrix is redefined to reduce the effect of thermal noise on the weights of an adaptive array. This is accomplished by subtracting a fraction of the smallest eigenvalue of the original covariance matrix from its diagonal entries. The test results obtained using the experimental system are compared with theoretical results. The two show a good agreement     

ISI mitigation using decision feedback loop demonstrated with PMDdistorted 10 Gbit/s signals

Electrical polarisation mode dispersion (PMD) and receiver bandwidth generated intersymbol interference (ISI) mitigation using an analogue decision feedback loop for 10 Gbit/s NRZ signals is demonstrated. ISI caused by first-order (PMD) of up to 120 ps differential group delay was equalised. Error free recovery of signals with completely closed eye diagrams was achieved     

Analysis of modified SMI method for adaptive array weight control

The authors characterize the performance of the diagonally loaded sample matrix inverse (SMI) algorithm versus the number K of snapshots used in the covariance matrix estimate by providing O(1/K) statistics (bias and variance) of the array weights, output powers, and output power ratios such as signal to interference noise ratio (SINR) and INR. The approach accommodates wideband signals. Monte Carlo simulations verify the theoretical analysis     

Performance of a 2-element adaptive array by a maximum-signal/noise-ratio algorithm

The performance of a 2-element adaptive array by a maximum-signal/noise-ratio algorithm is investigated. It is shown that the cancellation of interference is a function of its correlation with the signal and of the noise both received and introduced by the array elements. It is also shown that if the interference has the same angle of incidence as the signal no interference cancellation takes place.     

Performance analysis of narrowband beamforming using fully and partial adaptive beamformers with a spherical array

This research proposes an improved narrowband partial adaptive beamformer analysis using a proposed spherical array. Comparison between the fully and the partial adaptive beamformers is given. The study is performed by investigating performance parameters like the beamformer output signal-to-noise ratio and the beamformer output signal-to-interference-plus-noise ratio both in the steady state and along adaptation. Furthermore, computational complexity and convergence speed of the proposed sensor arrangement are also analyzed and examples are given. The results demonstrate that this beamformer considerably reduces the number of complex operations and features faster convergence speed.     

Performance analysis of modified flux-locked-loop additionalpositive feedback SQUID

An analysis of the additional positive feedback (APF) effect on SQUID performance in terms of frequency response is presented. The effect of negative feedback with an external flux-locked-loop amplifier on overall performance in terms of immunity to electromagnetic interference (EMI) is discussed. Disadvantages and limitations of APF are pointed out. An improved APF circuit with local negative feedback at high frequencies which improves the SQUID's overall EMI robustness is introduced. A 1/f noise reduction technique which can be used with APF while improving EMI rejection is also introduced. Simulations and a comparison between the two alternative designs are performed     

偏振模色散补偿的2种反馈控制信号特性比较

为了研究光纤通信系统中存在高阶偏振模色散时,采用偏振度和电带宽作反馈信号,偏振模色散的补偿效果,采用数值模拟方法比较了两种常用的反馈控制信号对偏振模色散性能的影响,由模拟结果可知,从性能上讲,两种反馈信号都随1阶偏振模色散变化而具有线性变化,当系统中有高阶偏振模色散时,二者均不具有线性的变化,但偏振度的性能要优于电带宽信号。结果表明,这对偏振模色散补偿具有一定的指导意义。     

Performance analysis of an adaptive broadband beamformer based on a two-element linear array with sensor delay-line processing

The performance of a two-element broadband beamforming structure with sensor delay-lines (SDLs) attached is studied for two adaptive implementations, in terms of the direction of the interfering signals, the inter-spacing between delay-line sensors and the length of the SDLs. Compared with the conventional broadband beamformers with tapped delay-lines (TDLs), the SDL based structure has a better performance in two aspects: its output signal to interference plus noise ratio (SINR) drops less as the inter-delay within delay-lines increases; with the same number of delays and weights it can achieve a better performance than the TDL one.     

Performance of adaptive array antenna with arbitrary geometry in the presence of mutual coupling

The effect of the mutual coupling between the array elements on the performance of the adaptive array antennas (AAA) is investigated when the actual received voltages which include the mutual coupling are directly used to estimate the weight vector based on the adaptive algorithm. The output signal-to-interference-noise ratio (SINR), the convergence of the adaptive algorithm and the synthesized pattern are evaluated to study the effect due to the existence of the mutual coupling. It is found that the mutual coupling affects the antenna adaptive gain, but does not affect the adaptive processing. It is also found that the mutual coupling does not always degrade the iterative convergence of the adaptive algorithm. It is proved that any invertible matrix for compensating the mutual coupling cannot improve the output SINR. It is also indicated that the radiation pattern can be correctly synthesized in the presence of the mutual coupling by introducing the universal steering vector (USV) whose element corresponds to the array element pattern.     

Eigenspace-based adaptive array beamforming with robustcapabilities

This paper deals with adaptive array beamforming based on eigenspace-based (ESB) techniques with robust capabilities. It has been shown that ESB adaptive beamformers demonstrate the advantages of fast convergence speed and less sensitivity to steering angle error over conventional beamformers. In conjunction with a signal subspace construction method, we present an efficient technique to achieve the advantages of ESB adaptive beamforming with less computing cost and more robust capabilities over existing ESB techniques. Several computer simulation examples are provided for illustrating the effectiveness of the proposed technique     

Iterative equalization with adaptive soft feedback

In this letter, a novel equalization algorithm applying soft-decision feedback and designed for binary transmission is introduced. In contrast to conventional decision-feedback equalization (DFE), iterations are necessary, because a simple matched filter serves as feedforward filter, which collects signal energy, but creates noncausal intersymbol interference. The rule for generating soft decisions is adapted continuously to the current state of the algorithm. In most cases, standard DFE methods are clearly outperformed. For a class of certain channel impulse responses, performance of maximum-likelihood sequence estimation is attained, in principle. The high performance of the scheme is explained using results from neural network theory     

不完美反馈自适应多天线跨层系统的性能分析

为提高网络无线通信的频谱利用率,提出一种自适应闭环多输入多输出(MIMO)跨层设计方案。该方案是融合物理层的自适应调制技术(AM)和数据链路层的自动重传技术(ARQ);发射端利用反馈信息,自适应选择调制模式和发射权矢量,并自动重传数据,形成三重反馈的闭环MIMO跨层系统。推导了不完美反馈下的系统频谱效率和中断概率闭合表达式,分析了时延对跨层系统性能的影响。仿真结果表明:对比单发/单收(SISO)跨层系统以及开环MIMO跨层系统,自适应闭环MIMO跨层系统的性能有明显提高。     

Multiple-access channels with different generalized feedback signals

This paper is concerned with a communication channel with two senders and one receiver, in which each sender observes a private feedback signal. The two feedback signals are not necessarily equivalent to or derived from the signal observed by the receiver. An achievable rate region is demonstrated for this multiple-access channel by means of a new superposition coding scheme. In particular it is shown that a rate region, previously obtained for the multiple-access channel with "perfect" feedback to both senders, remains achievable when the feedback connection to one of the senders is eliminated.     

The performance of a defocused adaptive array with afinite-distance signal source

An approximate expression for the output signal-to-noise ratio (SNR) is obtained as a function of the steering distance and the steering angle. From that expression, a rule of thumb is drawn to determine both the steering angle and the steering distance which result in a given loss. The simulations show that the introduction of a single interferer does not affect the performance because of the interference nulling ability of the array for nonmain beam interferers. For the purpose of comparison with a conventional beamforming array, the range beamwidth and 3-dB degradation steering angle of an Applebaum adaptive array was derived. It is shown that the parameters for the conventional beamforming array cannot be directly applied to an Applebaum-type adaptive array