Covariance matrix augmentation to produce adaptive array pattern troughs

Mailloux, Robert J.

doi:10.1109/aps.1995.529973

Cited by 33 publications

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“…In particular, the following refinements are introduced to improve the robustness of null broadening techniques: 1) a new constrained optimisation problem is formulated to broaden both nulls and mainlobe; 2) the optimisation problem is solved using semidefinite programming (SDP) [8], [9]; 3) nonequal number of additive sources are assigned to different users to reduce the total number of optimisation parameters, which makes the SDP solution more efficient. The proposed approach is compared with the conventional null broadening technique proposed in [6] for downlink communications from high altitude platforms (HAPs) [10]. The performance improvement due to the modified null broadening approach is significant.…”

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confidence: 99%

“…The drawback is that there is currently no reliable method to select the optimal loading factor [5]. Null broadening [6], [7] is another robust approach. In [6], a cluster of equal-strength incoherent sources are artificially distributed around each original source in order to generate a trough like pattern.…”

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confidence: 99%

“…Different from assigning a unit power to the desired user, as in the case of the MVDR beamformer [2] and the null broadening method in [6], the problem (6) sets a constraint to the total received power of a cluster of 'desired users' in order to broaden the mainlobe. The problem (6) can be described as a minimisation problem, consisting of an objective function and one equality constraint function.…”

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confidence: 99%

“…In order to produce a trough pattern in each of the interference direction, Mailloux proposed to distribute U equal-strength incoherent sources around each original interference source [6]. Fig.1 illustrates the null broadening approach in the scenario of HAP communications [10] with a vertical linear antenna array mounted on a HAP at an altitude H, providing the coverage over a circular area of radius r. In this case, the modified covariance matrix R has entries [6] …”

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confidence: 99%

“…Null broadening [6], [7] is another robust approach. In [6], a cluster of equal-strength incoherent sources are artificially distributed around each original source in order to generate a trough like pattern. However, the mainlobe is not broadened.…”

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Modified null broadening adaptive beamforming: constrained optimisation approach

Zakharov

2007

Electron. Lett.

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A constrained optimisation approach for null broadening adaptive beamforming is proposed. This approach improves the robustness of the traditional MVDR beamformer by broadening nulls for interference direction and the mainlobe for the desired direction. This optimisation is efficiently solved by semidefinite programming. The proposed approach, when applied to high altitude platform (HAP) communications using a vertical linear antenna array, provides significantly better coverage performance than a previously reported null broadening technique.Introduction: Antenna beampattern optimisation is widely used to improve the system capacity in wireless communications. Adaptive beamformers are well known for their high resolution and sidelobe suppression [1]. Among them, the Minimum Variance Distortionless Response (MVDR) beamformer [2] is one of the most traditional techniques. However, the performance of the MVDR beamformer significantly degrades if the steering information is inaccurate [3]. The most common technique to improve the robustness of the MVDR beamformer is the diagonal loading [3], [4]. The drawback is that there is currently no reliable method to select the optimal loading factor [5]. Null broadening [6], [7] is another robust approach. In [6], a cluster of equal-strength incoherent sources are artificially distributed around each original source in order to generate a trough like pattern. However, the mainlobe is not broadened. This may result in a poor coverage performance when the system is suffering high steering errors while the mainlobe of the beampattern is narrow. Furthermore, arranging equal number of additive sources for each interferer evidently limits the coverage performance.In this letter, we propose an improved null broadening method. In particular, the following refinements are introduced to improve the robustness of null broadening techniques: 1) a new constrained optimisation problem is formulated to broaden both nulls and mainlobe; 2) the optimisation problem is solved using semidefinite programming (SDP) [8], [9]; 3) nonequal number of additive sources are assigned to different users to reduce the total number of optimisation parameters, which makes the SDP solution more efficient. The proposed approach is compared with the conventional null broadening technique proposed in [6] for downlink communications from high altitude platforms (HAPs) [10]. The performance improvement due to the modified null broadening approach is significant. Null broadening techniques: MVDR adaptive beamforming places nulls in the direction of interferers whilst assigning unit power to the desired user. The N × 1 MVDR weight vectors for the mth desired user is given by [2]

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Modified null broadening adaptive beamforming: constrained optimisation approach

Zakharov

2007

Electron. Lett.

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Efficient Radio Transmission with Adaptive and Distributed Beamforming for Intelligent WiMAX

Lian

Nikookar

Ligthart

2011

Wireless Pers Commun

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In this paper, we introduce Adaptive Beamforming (AB) and Distributed Beamforming (DB) as two efficient techniques for Intelligent WiMAX (I-WiMAX). I-WiMAX is a new maritime communication system, consisting of Smart Radio (SR) principles and mobile WiMAX based on the IEEE 802.16e standard. Adopting AB, the same spectrum can accommodate more users by directing the main beam towards desired users while antenna pattern nulls towards others. To reduce the channel interferences caused by spectrum reusing, the Null Broadening (NB) method is required for downlink beamforming of I-WiMAX. A new NB method is presented in this paper with iterative weights computing for different OFDM subcarriers. Considering the spatial channel model seen at Subscriber Stations (SS) based on the von Mises distribution, the coverage range of one Base Station (BS) is dramatically enlarged by employing the NB technique. Meanwhile, assuming those SS which are within the coverage range as nodes of a relay network, the DB technique is introduced to forward signals to distant SS by forming the main beams towards them instead of deploying more BS to increase the communication range. It is proven in this paper that DB can successfully do the job. To reuse the spectrum, two DB methods are presented by directing different beams towards different required directions at the same time. With the AB and DB techniques, reliable I-WiMAX links can be established for long distances, with more optimum spectrum use and less infrastructure.

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Robust anti‐jamming method for high dynamic global positioning system receiver

Zhang

Xin-li

et al. 2016

IET signal process.

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An anti-jamming model is set up for the high dynamic global positioning system (GPS) receiver embedded in a high-speed vehicle. With a view to identify the characteristics of interferences in high dynamic condition and the shortcomings of traditional null widening methods, a novel statistical space-time null widening (SSTNW) method is proposed in this study. The SSTNW method can suppress interferences effectively in high dynamic conditions and can remove disturbance by nonideal factors, i.e. it improves the robustness of the anti-jamming algorithm of the high dynamic GPS receiver remarkably. At the same time, in view of the characteristics of space-time adaptive processing (STAP), a novel orthogonal constraint STAP is proposed to solve the distortion of the GPS signal in STAP. Simulation tests validate the feasibility and effectiveness of the proposed algorithm.

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Covariance matrix augmentation to produce adaptive array pattern troughs

Cited by 33 publications

References 1 publication

Modified null broadening adaptive beamforming: constrained optimisation approach

Modified null broadening adaptive beamforming: constrained optimisation approach

Efficient Radio Transmission with Adaptive and Distributed Beamforming for Intelligent WiMAX

Robust anti‐jamming method for high dynamic global positioning system receiver

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