Results 1 - 10 of 222

Optimal Downlink Beamforming Using Semidefinite Optimization

by Mats Bengtsson, Björn Ottersten , 1999
"... When using antenna arrays at the base station of a cellular system, one critical aspect is the transmission strategy. An optimal choice of beamformers for simultaneous transmission to several co-channel users must be solved jointly for all users and base stations in an area. We formulate an optimal ..."
Abstract - Cited by 58 (5 self) - Add to MetaCart
When using antenna arrays at the base station of a cellular system, one critical aspect is the transmission strategy. An optimal choice of beamformers for simultaneous transmission to several co-channel users must be solved jointly for all users and base stations in an area. We formulate an optimal transmit strategy and show how the solution can be calculated efficiently using interior point methods for semidefinite optimization. The algorithm minimizes the total transmitted power under certain constraints to guarantee a specific quality of service. The method provides large flexibility in the choice of constraints and can be extended to be robust to channel perturbations.

Adaptive minimum bit-Error rate beamforming

by S. Chen, L. Hanzo, N. N. Ahmad - IEEE Trans. on Wireless Comm , 2005
"... A novel adaptive beamforming technique is proposed for wireless communication application based on the minimum bit error rate (MBER) criterion. It is shown that the MBER approach provides significant performance gain in terms of smaller bit error rate (BER) over the standard minimum mean square erro ..."
Abstract - Cited by 53 (35 self) - Add to MetaCart
A novel adaptive beamforming technique is proposed for wireless communication application based on the minimum bit error rate (MBER) criterion. It is shown that the MBER approach provides significant performance gain in terms of smaller bit error rate (BER) over the standard minimum mean square error (MMSE) approach. Using the classi-cal Parzen window estimate of probability density function (p.d.f.), both the block-data and sample-by-sample adaptive implementations of the MBER solution are developed. 1.

Great expectations: The value of spatial diversity in wireless networks

by Suhas N. Diggavi, Naofal Al-Dhahir, A. Stamoulis, A. R. Calderbank - PROCEEDINGS OF THE IEEE , 2004
"... In this paper, the effect of spatial diversity on the throughput and reliability of wireless networks is examined. Spatial diversity is realized through multiple independently fading transmit/receive antenna paths in single-user communication and through independently fading links in multiuser commu ..."
Abstract - Cited by 45 (8 self) - Add to MetaCart
In this paper, the effect of spatial diversity on the throughput and reliability of wireless networks is examined. Spatial diversity is realized through multiple independently fading transmit/receive antenna paths in single-user communication and through independently fading links in multiuser communication. Adopting spatial diversity as a central theme, we start by studying its information-theoretic foundations, then we illustrate its benefits across the physical (signal transmission/coding and receiver signal processing) and networking (resource allocation, routing, and applications) layers. Throughout the paper, we discuss engineering intuition and tradeoffs, emphasizing the strong interactions between the various network functionalities.
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A simple gradient sign algorithm for transmit antenna weight adaptation with feedback

by Brian C. Banister, James R. Zeidler - IEEE Trans. Signal Processing , 2003
"... Abstract—In this paper, a simple algorithm for adaptation of the complex baseband weights of a transmit antenna array using feedback from the receiver is proposed and analyzed. The system utilizes stochastic gradient adaptation to maximize the power delivered to the receiver for a constrained transm ..."
Abstract - Cited by 26 (3 self) - Add to MetaCart
Abstract—In this paper, a simple algorithm for adaptation of the complex baseband weights of a transmit antenna array using feedback from the receiver is proposed and analyzed. The system utilizes stochastic gradient adaptation to maximize the power delivered to the receiver for a constrained transmission power, which provides both fading diversity and beam steering gain. Dual perturbed transmission weight vectors are time multiplexed onto the pilot signal, and the receiver generates feedback selecting the perturbed weight vector which delivers greater power. This feedback is used to provide weight adaptation at the transmitter, and this adaptation is shown to be an update by a coarse estimate of the gradient of the delivered power. The performance of the algorithm is analyzed in terms of convergence and tracking of an AR1 fading channel, with simulations confirming the analysis. Bit error rate (BER) simulations in a dynamic fading channel show that the algorithm outperforms previously proposed vector selection feedback, and in slower fading, the algorithm substantially outperforms diversity space time coding. Index Terms—Adaptive beamforming, antenna array, stochastic gradient algorithms, transmit beamforming. I.
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Joint space-time auxiliaryvector filtering for DS/CDMA systems with antenna arrays

by Dimitris A. Pados, Stella N. Batalama - IEEE Trans. on Communications , 1999
"... Abstract — Direct-sequence/code-division multiple-access (DS/CDMA) communication systems equipped with adaptive antenna arrays offer the opportunity for jointly effective spatial and temporal (code) multiple-access interference (MAI) and channel noise suppression. This work focuses on the developmen ..."
Abstract - Cited by 25 (5 self) - Add to MetaCart
Abstract — Direct-sequence/code-division multiple-access (DS/CDMA) communication systems equipped with adaptive antenna arrays offer the opportunity for jointly effective spatial and temporal (code) multiple-access interference (MAI) and channel noise suppression. This work focuses on the development of fast joint space–time (S–T) adaptive optimization procedures that may keep up with the fluctuation rates of multipath fading channels. Along these lines, the familiar S–T RAKE processor is equipped with a single orthogonal S–T auxiliary vector (AV) selected under a maximum magnitude cross-correlation criterion. Then, blind joint spatial/temporal MAI and noise suppression with one complex S–T degree of freedom can be performed. This approach is readily extended to cover blind processing with multiple AV’s and any desired number of complex degrees of freedom below the S–T product. A sequential procedure for conditional AV weight optimization is shown to lead to superior bit-error-rate (BER) performance when rapid system adaptation with limited input data is sought. Numerical studies for adaptive antenna array reception of multiuser multipath Rayleigh-faded DS/CDMA signals illustrate these theoretical developments. The studies show that the induced BER can be improved by orders of magnitude, while at the same time significantly lower computational optimization complexity is required in comparison with joint S–T minimum-variance distortionless response or equivalent minimum mean-square-error conventional filtering means. Index Terms — Adaptive equalizers, antenna arrays, code-division multiple access, fading channels, interference suppression, multipath channels, spread-spectrum communication. I.
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Adaptive minimum symbol error rate beamforming assisted receiver for quadrature amplitude modulation systems

by S. Chen, H. -q. Du, L. Hanzo - in Proc. VTC2006-Spring
"... Abstract An adaptive beamforming assisted receiver is proposed for multiple antenna aided multiuser systems that employ bandwidth efficient quadrature amplitude modulation (QAM). A novel minimum symbol error rate (MSER) design is proposed for the beamforming assisted receiver, where the system’s sym ..."
Abstract - Cited by 24 (20 self) - Add to MetaCart
Abstract An adaptive beamforming assisted receiver is proposed for multiple antenna aided multiuser systems that employ bandwidth efficient quadrature amplitude modulation (QAM). A novel minimum symbol error rate (MSER) design is proposed for the beamforming assisted receiver, where the system’s symbol error rate is directly optimized. Hence the MSER approach provides a significant symbol error ratio performance enhancement over the classic minimum mean square error design. A sample-by-sample adaptive algorithm, referred to as the least symbol error rate (LBER) technique, is derived for allowing the adaptive implementation of the system to arrive from its initial beamforming weight solution to MSER beamforming solution. I.

A Novel MAC Layer Protocol for Space Division Multiple Access in Wireless Ad

by Dhananjay Lal, R. Toshniwal, R. Radhakrishnan, D. P. Agrawal, Rishi Toshniwal, Rajesh Radhakrishnan, Dharma P. Agrawal, J. Caffery Jr. - In IEEE 11th ICCCN , 2002
"... Use of directional antennas in cellular wireless networks offers many advantages such as range extension, reduced interference for signal detection and improved throughput. Recently, MAC protocols using directional antennas for wireless ad hoc networks that are based on and similar to IEEE 802.11 ty ..."
Abstract - Cited by 17 (3 self) - Add to MetaCart
Use of directional antennas in cellular wireless networks offers many advantages such as range extension, reduced interference for signal detection and improved throughput. Recently, MAC protocols using directional antennas for wireless ad hoc networks that are based on and similar to IEEE 802.11 type WLANs have been proposed. These protocols, however, are unable to attain substantial performance improvements because they do not enable the nodes to perform multiple simultaneous transmissions/receptions. In this paper, we propose a MAC layer protocol that exploits Space Division Multiple Access, thus using the property of directional reception to receive more than one packet from spatially separated transmitter nodes (under the assumption that the nodes are equipped with smart antenna systems). Our simulation results show that drastic throughput improvements may be achieved through this scheme.
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Quadratically Constrained Beamforming Robust Against Direction-of-Arrival Mismatch

by Chun-yang Chen, P. P. Vaidyanathan - IEEE TRANS. ON SIGNAL PROCESSING , 2007
"... It is well known that the performance of the minimum variance distortionless response (MVDR) beamformer is very sensitive to steering vector mismatch. Such mismatches can occur as a result of direction-of-arrival (DOA) errors, local scattering, near-far spatial signature mismatch, waveform distorti ..."
Abstract - Cited by 15 (1 self) - Add to MetaCart
It is well known that the performance of the minimum variance distortionless response (MVDR) beamformer is very sensitive to steering vector mismatch. Such mismatches can occur as a result of direction-of-arrival (DOA) errors, local scattering, near-far spatial signature mismatch, waveform distortion, source spreading, imperfectly calibrated arrays and distorted antenna shape. In this paper, an adaptive beamformer that is robust against the DOA mismatch is proposed. This method imposes two quadratic constraints such that the magnitude responses of two steering vectors exceed unity. Then, a diagonal loading method is used to force the magnitude responses at the arrival angles between these two steering vectors to exceed unity. Therefore, this method can always force the gains at a desired range of angles to exceed a constant level while suppressing the interferences and noise. A closed-form solution to the proposed minimization problem is introduced, and the diagonal loading factor can be computed systematically by a proposed algorithm. Numerical examples show that this method has excellent signal-to-interference-plus-noise ratio performance and a complexity comparable to the standard MVDR beamformer.

Direction estimation using compressive sampling array processing

by Ying Wang, Geert Leus, Ashish P - IEEE Workshop on Statistical Signal Processing , 2009
"... We propose a new architecture, the compressive sampling (CS) ar-ray, for array based applications, by exploiting compressive sam-pling in the spatial domain. With random projections (or selections) of the array elements, we can transform a large size array into a small size array. We also propose tw ..."
Abstract - Cited by 15 (4 self) - Add to MetaCart
We propose a new architecture, the compressive sampling (CS) ar-ray, for array based applications, by exploiting compressive sam-pling in the spatial domain. With random projections (or selections) of the array elements, we can transform a large size array into a small size array. We also propose two approaches of direction-of-arrival (DoA) estimation using our CS array, I. (joint) CS recovery, and II. CS beamformers. As a result we can greatly reduce the hardware complexity and software complexity while still maintaining the high resolution achieved as if a large size array were used. Index Terms — Compressive sampling, direction-of-arrival es-timation, beamforming.
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Kernel-based nonlinear beamforming construction using orthogonal forward selection with Fisher ratio class separability measure

by S. Chen, L. Hanzo, A. Wolfgang - IEEE Signal Process. Lett , 2004
"... Abstract — This letter shows that the wireless communication system capacity is greatly enhanced by employing nonlinear beamforming and the optimal Bayesian beamformer outperforms the standard linear beamformer significantly in terms of a reduced bit error rate, at a cost of increased complexity. Bl ..."
Abstract - Cited by 14 (9 self) - Add to MetaCart
Abstract — This letter shows that the wireless communication system capacity is greatly enhanced by employing nonlinear beamforming and the optimal Bayesian beamformer outperforms the standard linear beamformer significantly in terms of a reduced bit error rate, at a cost of increased complexity. Block-data adaptive implementation of the Bayesian beamformer is realized based on an orthogonal forward selection procedure with Fisher ratio for class separability measure. Keywords—Nonlinear beamforming, orthogonal least squares, Bayesian classification, Fisher ratio for class separability measure