Adaptive Antenna Array Research Articles

NULL STEERING BEAMFORMER USING HYBRID ALGORITHM BASED ON HONEY BEES MATING OPTIMISATION AND TABU SEARCH IN ADAPTIVE ANTENNA ARRAY

In this article, a new hybrid algorithm based on Honey Bees Mating Optimization (HBMO) combined with the Tabu Search (TS) for null steering beamformer in adaptive antenna array is presented. The proposed method HBMO/TS is applied to a set of random cases to estimate the excitation weights of an antenna array that steer the main lobe towards a desired signal, place nulls towards several interference signals and achieve the lowest possible value of side lobe level. Moreover, the proposed algorithm is tested and compared with two other well-known approaches that are the Least Mean Squares (LMS) and Genetic Algorithm (GA). The abovementioned methods have been performed considering uniform linear antenna array and achieved by controlling only the phase of each array element. Results obtained prove the efiectiveness of our proposed approach HBMO/TS.

Phased Antenna Array With a Sidelobe Cancellation for Suppression of Jamming

A procedure of synthesis of an adaptive antenna array providing reduction of susceptibility to jamming or interference is presented. This approach is based on the sidelobe cancellation in the required direction. In this case, the form of the radiation pattern can be transformed by a modification of the system of sampling coefficients. An example of the forming of the required radiation pattern and corresponding current distribution is demonstrated .

Impact of Antenna Placement on Frequency Domain Adaptive Antenna Array in Hybrid FRF Cellular System

Frequency domain adaptive antenna array (FDAAA) is an effective method to suppress interference caused by frequency selective fading and multiple-access interference (MAI) in single-carrier (SC) transmission. However, the performance of FDAAA receiver will be affected by the antenna placement parameters such as antenna separation and spread of angle of arrival (AOA). On the other hand, hybrid frequency reuse can be adopted in cellular system to improve the cellular capacity. However, optimal frequency reuse factor (FRF) depends on the channel propagation and transceiver scheme as well. In this paper, we analyze the impact of antenna separation and AOA spread on FDAAA receiver and optimize the cellular capacity by using hybrid FRF.

Analysis of interference cancellation techniques in OFDMA systems employing adaptive antenna arrays

We analyze the problem of interference cancellation in OFDMA cellular communication systems employing adaptive antenna arrays at the receiver and operating in the channels with frequency-selective fading and interference from the neighboring base stations. This problem is very important for modern broadband cellular systems operating with a low coefficient of multiple use of frequencies. Under such conditions of the network deployment, the system efficiency is restricted by the level of intrachannel interference from the neighboring base stations transmitting in the same frequency channel. In this work, we analyze different methods for measuring the interference characteristics and using them for spatial processing of received signals. Five different methods for signal processing in an adaptive antenna array of the receiver are discussed. Each approach (reception method) has its own interference immunity and complexity degree. Comparative analysis of the interference immunity of the considered receivers has been performed for different frequency-channel loads and different numbers of interfering stations. Recommendations for using the considered receivers are given.

Unconditional, on the directions of arrival, statistics of the adaptive antenna arrays

ABSTRACTA comprehensive study on the statistics of adaptive antenna arrays is presented. The main contribution is the derivation of the probability distribution function of the cochannel interference for the uplink of mobile communications systems, unconditioned on the interferers' directions of arrival. Closed‐form results for the cumulative distribution function, moment generating function, and outage probability are also reported. Numerical verification is provided, utilizing both simulation and published data. Copyright © 2011 John Wiley & Sons, Ltd.

Algorithm for Suppression of Wideband Probing in Adaptive Array with Multiple Desired Signals

The integrity of signal environment for a navigation system among other factors depends critically on the capability of the adaptive antenna array in controlling (reconfiguring) its radiation pattern for various signal scenarios. For a signal environment consisting of simultaneous multiple desired signals and probing sources, the output signal-to-noise ratio of the adaptive antenna array depends on the efficiency of the adaptive algorithm employed for weight estimation. Sufficient antenna gain is required to be maintained towards each of the desired signals, while simultaneously suppressing returns towards the sources probing from distinctly different directions. The weight estimation for the multiple desired signal environments is carried out using a novel modified version of the improved least mean square (LMS) algorithm. This modified scheme effectively suppresses the narrowband/wideband probing towards the antenna array (linear/planar). The weight estimation and the steering vector are adapted according to the multiple desired signal environments. Each spectral line of the wideband source is considered as an independent narrowband source. This is incorporated in the correlation matrix of the received signal. The simulation results demonstrate the efficacy of this novel algorithm in active cancellation of narrowband/wideband probing sources, even while the simultaneous multiple signals in desired directions are maintained. The performance of the proposed algorithm is reported to be better than that of standard LMS and recursive LMS algorithm. Defence Science Journal, 2011, 61(4), pp.325-330 , DOI:http://dx.doi.org/10.14429/dsj.61.1092

적응배열 안테나를 이용한 기상 레이다에서의 클러터 제거

기상 레이다에서 급변하는 기상 상황에 관한 신뢰성 있는 정보를 추출하기 위해서는 해당 영역에서 높은 해상도를 갖는 풍속 측정이 필요하다. 그러나 정확한 펄스 페어 추정치를 얻기 위해서는 상대적으로 강력한 고정 및 이동 클러터들을 매우 효과적으로 제거하여야만 한다. 이러한 클러터 제거상의 문제점을 해결하기 위하여 간단한 위상배열 안테나를 적용할 수 있다. 모의 구현한 클러터 및 기상신호들을 이용하여 적응배열 안테나를 이용한 기상 레이다에서의 클러터 제거 능력을 분석하였다. 또한 적응배열 기상 레이다에서 얻은 펄스 페어 추정치와 원래의 추정치 값을 비교 분석하였다. High resolution windspeed profile measurements are needed in a weather radar to provide the reliable information of rapidly changing weather conditions. However, it is necessary to remove both stationary and moving clutter to obtain the accurate pulse pair estimates. To overcome these problems, a simple adaptive array antenna may be applied to clutter removal. Using the simulated weather and clutter data, the clutter cancellation capability is analyzed for a weather radar with an adaptive antenna. The pulse pair estimates obtained from the adaptive weather radar are compared with those of the raw data.

선형 제한 조건의 최적 가중 벡터에 대한 연구

본 논문에서는 적응 배열 안테나 시스템에서 간섭 및 재밍 신호를 제거하기 위해서 최적 가중 벡터를 연구하였다. 최적 가중 벡터는 선형 제한 조건에서 최소 분산 알고리즘과 비용함수를 적용시켜 구하였고, 목표물의 신호를 정확히 추정하였다. 적응 배열 안테나 시스템은 간섭 및 재머전력을 감소시키고 신호대 잡음비를 향상시키는 시스템이다. 적응 배열 안테나 시스템은 각 안테나 배열 소자의 출력이 탭(Tap)을 거쳐 지연되고 각 탭에 복소 가중치가 곱해져서 최종적으로 하나의 복합신호를 만든다. 최적의 가중치를 구하기 위해서 본 논문에서는 입력 공분산 행렬의 최적 가중벡터를 이용하였다. 본 논문에서 제안된 알고리즘으로 모의 실험한 결과 분해능은 <TEX>$3^{\circ}$</TEX>이하로 향상되었으며 부엽은 약 10 dB 감소하였음을 입증하였다. The optimum weight vector is studied to remove interference and jamming signals in adaptive array antenna system. The optimum weight vector is calculated to apply a minimum variance algorithm and cost function in linearly constrained conditions, and accurately estimates target's signal. Adaptive array antenna system is the system which improves signal to noise ratio(SNR) and decreases interference and jammer power. Adaptive array antenna system delays at tap output of antenna array element. Each tap finally makes the complex signal of one in multiplier complex weight. In order to obtain optimum's weight calculation, optimum weight vector is used in this paper. After simulation, resolution is increased below <TEX>$3^{\circ}$</TEX>, and sidelobe is decreased about 10 dB.

Calibrating adaptive antenna arrays for high-integrity GPS

A major challenge in using GPS guidance for aircraft final approach and landing is to reject interference that can jam reception of the GPS signals. Antenna arrays, which use space---time adaptive processing (STAP), significantly improve the signal to interference plus noise ratio, but at the possible expense of distorting the received signals, leading to timing biases that may degrade navigation performance. Rather than a sophisticated calibration approach to remove biases introduced by STAP, this paper demonstrates that a relatively compact calibration strategy can substantially reduce navigation biases, even under elevated interference conditions. Consequently, this paper develops an antenna bias calibration strategy for two classes of adaptive array algorithm and validates this method using both simulated and experimental data with operational hardware in the loop. A proof-of-concept system and an operational prototype are described, which implement the adaptive antenna algorithms and deterministic corrections. This investigation demonstrates that systems with adaptive antenna arrays can approach the accuracy and integrity requirements for automatic aircraft landing, and in particular for sea-based landing on board aircraft carriers, while simultaneously providing significant attenuation of interference. Evidence suggests that achieving these goals is possible with minimal restrictions on system hardware configuration--specifically, limitations on the permissible level of antenna anisotropy and the use of sufficient analog-to-digital converter resolution.

A New Blind Beamforming and Hop-Timing Detection for FH Communications

Hop-timing detection is of extreme importance for the reception of frequency hopping (FH) signals. Any error in the hop-timing detection has a deleterious effect on the performance of the receiver in frequency hopping (FH) communication systems. However, it is not easy to detect the hop-timing under low signal to noise power ratio (SNR) environments. Adaptive array antennas (AAA) have been expected to improve the performance of FH communication systems by beamforming for the direction of arrival of the desired signal. Since the conventional AAA exploits at least the coarse synchronization for dehopping of FH signals before achieving the beamforming, any fault in the hop-timing detection causes the deterioration of the performance of AAA. Using AAA based on the constant modulus algorithm (CMA), this paper proposes a new method for blind beamforming and hop-timing detection for FH signals. The proposed method exploits both the spatial and temporal characteristics of the received signal to accomplish the beamforming and detect the hop-timing without knowing any a priori information such as fine/coarse time synchronization and training signal. The performance verifications of the proposed method based on pertinent simulations are presented.

Adaptive Array Antenna Using On-Off and CMA Algorithms for Microwave RFID Readers

This paper proposes an adaptive antenna using a combination of on-off and CMA algorithms. With the proposed technique, the on-off algorithm is first employed to search for a desired signal direction in which maximum received power is achieved. Then, interference is suppressed by performing CMA. Simulations are conducted according to the potential application of the proposed adaptive antenna. The simulation results show the SINR improvement implying that the proposed adaptive antenna can be applied to microwave RFID systems in order to resolve reader collision. Furthermore, the proposed adaptive antenna is implemented and then experimented. The experimental results verify that the proposed adaptive antenna can reduce interference resulting in the collision problem.

Simulation and Evaluation of a Simple Adaptive Antenna Array for a WCDMA Mobile Communication

This paper presents a uniform Linear Array model of a simple adaptive antenna array based on signal-to-interference and noise ratio (SINR) maximization. The SINR using the adaptive antenna array was investigated for a conventional narrowband beam former by varying the number of antenna array elements and number of interfering signals or users. The results obtained were compared with that of omni-directional antenna. The graph obtained from the results showed significant improvement in SINR as the number of antenna elements increases in the presence of large interferers for odd numbered array.

Evaluation of the Interference and Noise Suppression Capability of Uniform Linear Array Adaptive Beamforming Antenna

This paper evaluates the interference and noise suppression capability of uniform linear array adaptive beamforming antenna, at base stations of WCDMA mobile communication system. The signal-to-interference and noise ratio (SINR) was the performance index used for the evaluation and analysis. SINR was investigated for a conventional narrow band beam former by varying the number of antenna array elements, the inter-element spacing and number of interfering signals or users. The results were compared with that of omni-directional antenna. The graph obtained showed significant improvement in SINR as the number of antenna elements increases in the presence of large interferers for odd numbered array. the most common of all the array geometries employed in cellular and personal communication systems (PCS) (2), and it is the simplest to be used in investigating SINR improvement. In this paper, we provide a detailed presentation of SINR improvement ability of a ULA. In particular, we consider the effect of varying the number of antenna elements, number of interfering users and the inter-element spacing on the SINR improvement with the exclusion of mutual coupling. The performance of omni-directional antenna and adaptive antenna array were compared based on SINR maximization.

Mitigation of Adaptive Antenna Induced Bias Errors in GNSS Receivers

Antenna arrays equipped with adaptive filtering allow global navigation satellite system (GNSS) receivers to operate in environments with harsh, sustained interference. However since these antennas utilize spatial and temporal filters, they have the potential to introduce significant bias errors into the code and carrier phase measurements made by GNSS receivers. For precision navigation applications, these biases must be mitigated. A novel bias estimation and correction technique is described in which additional logic is added to the receiver in order to provide runtime compensation for these antenna-induced biases. The technique is general in the sense that it can be applied to a wide variety of adaptive antenna and receiver implementations. It utilizes a computationally efficient bias estimation equation that incorporates stored antenna data, the adaptive filter weights, and the receiver discriminator function. After estimating the bias, the receiver can compensate for the bias errors either in the navigation processor or in the tracking loop of the GNSS receiver. Simulations demonstrate centimeter-level bias correction accuracy for a variety of signals using an adaptive antenna array in an environment with interference.

A New On-Line/Off-Line Adaptive Antenna Array Beamformer for Tracking the Mobile Targets

An adaptive antenna array system adjusts the main lobe of radiation pattern in the direction of desired signal and points the nulls in the direction of undesired signals or interferers. The essential goal of beamforming is to reduce the complexity of weighting process and to decrease the time needed for adjusting the antenna radiation pattern. In this article a new adaptive weighting algorithm is proposed for both least mean squares (LMS) and constant modulus (CM) algorithms. It is appropriate and applicable for antenna array systems with moving targets and also mobile applications as well as sensor networks. By predicting the relative velocity of source, the next location of the source will be estimated and the array weights will be determined using LMS or CM algorithm before arriving to the new point. For the next time associated to the new sampling point, evaluated weights will be used. Furthermore, by updating these weights between two consecutive times the effects of error propagation will be eliminated. Therefore, in addition to reduction in computational complexity at the time of weight allocation, relatively accurate weight allocation can be obtained. Simulation results of this investigation show that the angular error related to both LMS-based and CM-based algorithms is less than the conventional LMS and CM algorithms at different signal to noise ratios (SNRs). On the other hand, due to considering off-line process, online computational complexity of new algorithms is slightly low with respect to previous ones.

ROBUST MVDR BEAMFORMER FOR NULLING LEVEL CONTROL VIA MULTI-PARAMETRIC QUADRATIC PROGRAMMING

MVDR beamformer is one of the well-known adaptive beamforming techniques that offers the ability to resolve signals that are separated by a fraction of an antenna beamwidth. In an ideal scenario, the MVDR beamformer can not only minimize the array output power but also maintain a distortionless mainlobe response toward the desired signal. Unfortunately, the MVDR beamformer may have unacceptably low nulling level, which may lead to significant performance degradation in the case of unexpected interfering signals. A new robust MVDR beamforming is presented to control the nulling level of adaptive antenna array. In this proposed approach, the beamforming optimization problem is formulated as a multi-parametric quadratic programming (mp-QP) problem such that the optimal weight vector can be easily obtained by real-valued computation. The presented method can guarantee that the nulling level are strictly below the prescribed threshold. Simulation results are presented to verify the efficiency of the proposed method. Received 25 February 2011, Accepted 21 March 2011, Scheduled 25 March 2011 Corresponding author: Fu Lai Liu (fulailiu@126.com). † F. L. Liu is also with School of Automation, Southeast University, Nanjing, China.

Wave Arrival Direction Estimation Adaptive Antenna Array with Music Algorithms

Passive radar based on GSM is a hot research field of new illuminators passive radars, and the wave arrival direction estimation is the key problem for detecting target. This paper designed adaptive antenna array for the GSM passive radar system, and give the complete Matlab simulation to verify the execution of the schedule, meanwhile, the result shows that the MUSIC algorithms is high accurate in the wave arrival direction compared with the Capon. All of this made a useful contribution to the research and application of the GSM-based passive radar.

A New Combination of RAKE Receiver and Adaptive Antenna Array Beamformer for Multiuser Detection in WCDMA Systems

The aim of this paper is to combine smart antenna beamforming and RAKE receiver in wideband code division multiple access (WCDMA). The proposed method combines spatial diversity as well as temporal diversity to improve the performance and overcome both interferences and multipath fading. This investigation has focused on one of the new proposed blind beamforming algorithms. It is based on constrained constant modulus (CCM) algorithm which is used for deriving a recursive-least-squares (RLS-) type optimization algorithm. We illustrate the comparison of bit error rate (BER) of the proposed receiver with simple correlator and also 1D-RAKE receiver in multiuser detection (MUD) WCDMA. The simulation results show that the proposed 2D-RAKE receiver offers lower BER rather than conventional ones, that is, it is an effective solution for decreasing the effect of interference and increasing the capacity, in a joint state.

Frequency Domain Adaptive Antenna Array for Broadband Single-Carrier Uplink Transmission

In this paper, a frequency domain adaptive antenna array (FDAAA) algorithm is proposed for broadband single-carrier uplink transmissions in a cellular system. By employing AAA weight control in the frequency domain, the FDAAA receiver is able to suppress the multi-user interference (MUI) and the co-channel interference (CCI). In addition, the channel frequency selectivity can be exploited to suppress the inter-symbol interference (ISI) and to obtain frequency diversity (or the multi-path diversity). Another advantage of the FDAAA algorithm is that its performance is not affected by the spread of angles of arrival (AOA) of the received multi-path signal. In this study the structure of FDAAA receiver is discussed and the frequency domain signal-to-interference-plus-noise-ratio (SINR) after weight control is investigated. The performance of the FDAAA algorithm is confirmed by simulation results. It is shown that, the optimal FDAAA weight to obtain the best BER performance is that which fully cancels the interference when single-cell system is considered; On the other hand, when multi-cell cellular system is considered, the optimal FDAAA weight depends on both the cellular structure and the target signal to noise ratio (SNR) of transmit power control (TPC).

LSCMA Blind Adaptive Algorithm with Comparison of Optimization Capabilities for Smart Antenna Systems

In the present paper convergence characteristics of blind beam-forming algorithm Least Square Constant Modulus Algorithm (LSCMA) are analyzed. This algorithm is used with Smart antenna systems (SAS) for improving the performance of wireless communication system by optimizing the radiation pattern according to the signal environment. This can increase the coverage and capacity of a system in multipath channels by overcoming the interference and noise. The data rate can be enhanced by mitigating fading due to cancellation of multipath components. In this paper optimization capabilities of LSCMA are considered by changing of parameters. The results reveal improvement in gain and reduction in side-lobe level. The reference signal is basically a training sequence used to train the adaptive antenna array or a desired signal based upon an a priori knowledge of nature of the arriving signals. In case where a reference signal is not available one must opt to a group of optimization techniques that are blind to the exact content of the incoming signals. In this paper the comparison of optimization capabilities of LSCMA blind adaptive BFA with reference to number of antenna elements and their spacing is presented. Section II presents functioning of ABFA and the mathematical description of LSCMA. In section III simulation results using MATLAB 7.0 with reference to number of antenna elements, inter-element distance and angle of arrival (AOA) are obtained to find the optimized values. The array factor plots and LSCMA output for the same values of above parameters are presented.