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Maximizing Energy Efficiency in the Vector Precoded MU-MISO Downlink by Selective Perturbation

IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2014年第9期13卷 4974-4984页

作者： Masouros, Christos Sellathurai, Mathini Ratnarajah, Tharmalingam UCL Dept Elect & Elect Engn London WC1E 7JE England Heriot Watt Univ Sch Engn & Phys Sci Edinburgh EH14 4AS Midlothian Scotland Univ Edinburgh Sch Engn Edinburgh EH9 3JL Midlothian Scotland

We propose an energy-efficient vector perturbation (VP) technique for the downlink of multiuser multiple-input-single-output (MU-MISO) systems. In contrast to conventional VP where the search for perturbation vectors involves all users' symbols, here, the perturbation is applied to a subset of the transmitted symbols. This, therefore, introduces a performance-complexity tradeoff, where the complexity is greatly reduced compared to VP by limiting the dimensions of the sphere search, at the expense of a performance penalty compared to VP. By changing the size of the subset of perturbed users, the aforementioned tradeoff can be controlled to maximize energy efficiency. We further propose three distinct criteria for selecting which users' symbols to perturb, each of which yields a different performance-complexity tradeoff. The presented analytical and simulation results show that partially perturbing the data provides a favorable tradeoff, particularly at low-power transmission where the power consumption associated with the signal processing becomes dominant. In fact, it is shown that diversity close to the one for conventional VP can be achieved at energy efficiency levels improved by up to 300% compared to VP.

关键词： Vector perturbation energy efficiency complexity reduction multi-user MIMO non-linear precoding

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Vector Perturbation Based on Symbol Scaling for Limited Feedback MISO Downlinks

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2014年第3期62卷 562-571页

作者： Masouros, Christos Sellathurai, Mathini Ratnarajah, Tharmalingam UCL Dept Elect & Elect Engn London WC1E 6BT England Heriot Watt Univ Sch Engn & Phys Sci Edinburgh EH14 4AS Midlothian Scotland Univ Edinburgh Sch Engn Edinburgh EH9 3JL Midlothian Scotland

We propose a low-complexity vector precoding (VP) scheme for the downlink of multi-user multiple input single output (MU-MISO) systems with limited feedback. Conventional VP requires the use of modulo operation and knowledge of the scaling factor used at the transmitter in order to remove the perturbation quantity at the receiver. The latter may be problematic in certain limited feedback scenarios where only quantized versions of the scaling factor can be made available at the receiver. To circumvent this shortcoming, we propose a modified VP technique where the search of perturbing vectors is limited to the area in the symbol constellation which is constrictive to the information symbols, i.e., the area where the distances from the decision thresholds are increased with respect to a distance threshold. By doing this, the perturbation quantities can only enhance detection and need not be removed at the receiver. Successful detection can therefore be done without the use of the modulo operation and the scaling factor, which makes the proposed VP scheme applicable to limited feedback scenarios. Analytical and simulation results show that the performance of the proposed scheme is free of the error floor typically encountered with conventional VP in the presence of limited feedback.

关键词： Limited feedback multi-user MIMO non-linear precoding vector precoding

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Limited Feedback Vector Perturbation precoding By MinMax Optimization

Limited Feedback Vector Perturbation Precoding By MinMax Opt...

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IEEE Global Communications Conference

作者： Christos Masouros Mathini Sellathurai Tharmalingam Ratnarajah Dep. of Electrical & Electronic Eng. University College London School of Eng. and Physical Sciences Herriot Watt University School of Engineering University of Edinburgh

ISBN: (纸本)9781479935130

A vector perturbation (VP) scheme is proposed for the downlink of multi-user multiple input multiple output (MU-MIMO) systems with limited feedback. Instead of a computationally expensive sphere search used in conventional VP, the proposed scheme uses a MinMax Optimization to select the perturbation quantities. In addition, the proposed VP circumvents the need for receive-scaling by constraining the search of perturbing vectors to the area in the symbol constellation which is constrictive to the information symbols, i.e. the area where the distances from the decision thresholds are increased with respect to a distance threshold. Consequently, while conventional VP requires the feed-forwarding of the scaling factor to the receiver for correct detection, the proposed scheme does not require the scaling of the received symbols. This advantage is particularly pronounced in limited feedback scenarios where the scaling factors forwarded to the receiver are prone to quantization errors. As illustrated by the results, the error floor encountered in conventional VP in limited feedback scenarios is avoided in the proposed scheme.

关键词： Vector perturbation Limited feedback Multi-user MIMO non-linear precoding

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Computationally Efficient Vector Perturbation precoding Using Thresholded Optimization

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IEEE TRANSACTIONS ON COMMUNICATIONS 2013年第5期61卷 1880-1890页

作者： Masouros, C. Sellathurai, M. Ratnarajah, T. UCL Dept Elect & Elect Eng London WC1E 7JE England Heriot Watt Univ Dept Elect Elect & Comp Eng Edinburgh Midlothian Scotland Univ Edinburgh Inst Digital Commun Edinburgh EH9 3JL Midlothian Scotland

We propose a low-complexity vector perturbation (VP) precoding scheme for the downlink of multi-user multiple input multiple output (MU-MIMO) systems. While conventional VP performs a computationally intensive sphere search through multiple candidate perturbation vectors to minimize the norm of the precoded signal, the proposed precoder applies a threshold to the desired norm to reduce the number of search nodes visited by the sphere encoder. This threshold is determined by the performance requirements of the mobile users. Once the threshold is met, the search for the perturbation vectors finishes thus saving significant computational burden at the transmitter. To evaluate the advantages of the proposed technique compared to VP, we further derive the computational complexity in terms of the volume of the associated search space and the resulting numerical operations. In addition, we use a new performance-complexity metric to study the relevant tradeoff and look at the power efficiency of the system, both of which metrics can be used to optimize the user-determined threshold accordingly. The presented analysis and results show that the proposed thresholded VP (TVP) offers a favorable tradeoff between performance and complexity where significant complexity reduction is attained while the user threshold performance is guaranteed.

关键词： Vector perturbation sphere encoding complexity reduction multi-user MIMO non-linear precoding

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Low Complexity Vector precoding for Fast Fading MIMO Downlinks

Low Complexity Vector Precoding for Fast Fading MIMO Downlin...

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IEEE Global Communications Conference (GLOBECOM)

作者： Masouros, Christos Sellathurai, Mathini Ratnarajah, Tharm UCL Dept Elect & Elect Engn London England Heriot Watt Univ Sch Engn & Phys Sci Edinburgh Midlothian Scotland Univ Edinburgh Sch Engn Edinburgh Midlothian Scotland

ISBN: (纸本)9781479913534

Vector precoding (VP) requires the feed-forwarding of the transmit scaling factor to the receiver for correct detection. This can be problematic in fast fading scenarios where the statistics of the scaling factor change frequently and in limited feedback scenarios where the feed-forwarding to the receiver is prone to quantization errors. In response to this, a new VP scheme is proposed for the downlink of multi-user multiple input multiple output (MU-MIMO) systems with limited feedback. The proposed VP circumvents the need for receive-scaling by constraining the search of perturbing vectors to the area in the symbol constellation which is constrictive to the information symbols, i.e. the area where the distances from the decision thresholds are increased with respect to a distance threshold. By doing this, the perturbation quantities need not be removed at the receiver and successful detection can be done without the use of the modulo operation and the scaling factor. In addition, instead of a computationally expensive sphere search used in conventional VP, the proposed scheme uses a MinMax Optimization to select the perturbation quantities. As illustrated by the analysis and results, the error floor encountered in conventional VP in limited feedback scenarios is avoided in the proposed scheme.

关键词： Terms Vector precoding limited feedback multi-user MIMO non-linear precoding

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COMPLEXITY REDUCTION FOR VECTOR precoding USING QOS REQUIREMENTS

COMPLEXITY REDUCTION FOR VECTOR PRECODING USING QOS REQUIREM...

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IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)

作者： Masouros, Christos Ratnarajah, Tharm Sellathurai, Mathini UCL Dept Elect & Elect Eng London England Univ Edinburgh Sch Engn Edinburgh Midlothian Scotland Heriot Watt Univ Sch Engn & Phys Sci Edinburgh Midlothian Scotland

ISBN: (纸本)9781479903566

We propose a low-complexity vector precoding (VP) scheme for the downlink of multi-user multiple input multiple output (MU-MIMO) systems. Instead of performing a full sphere search to maximize the receive signal to noise ratio (SNR), the search for the perturbation vectors finishes once a threshold SNR value is reached, thus saving significant computational burden at the transmitter. This threshold is determined by the quality of service (QoS) requirements of the mobile users. To evaluate the advantages of the proposed technique compared to VP, we analytically calculate its computational complexity in terms of the volume of the associated search space. The results show that the proposed thresholded VP (TVP) offers a significantly reduced complexity compared to VP.

关键词： Vector precoding sphere encoding complexity reduction multi-user MIMO non-linear precoding

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COMPLEXITY REDUCTION FOR VECTOR precoding USING QOS REQUIREMENTS

COMPLEXITY REDUCTION FOR VECTOR PRECODING USING QOS REQUIREM...

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IEEE International Conference on Acoustics, Speech and Signal Processing

作者： Christos Masouros Tharm Ratmrajah Mathmi Sellathurai Dept. of Electrical & Electronic Eng. University College London London UK School of Engineering University of Edinburgh Edinburgh UK School of Eng. and Physical Sciences Herriot Watt University Edinburgh UK

ISBN: (纸本)9781479903573

关键词： Vector precoding sphere encoding complexity reduction multi-user MIMO non-linear precoding

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Low Complexity Vector precoding for Fast Fading MIMO Downlinks

Low Complexity Vector Precoding for Fast Fading MIMO Downlin...

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IEEE Global Communications Conference

作者： Christos Masouros Mathini Sellathurai Tharm Ratnarajah Dep. of Electrical & Electronic Eng. University College London London UK School of Eng. and Physical Sciences Herriot Watt University Edinburgh UK School of Engineering University of Edinburgh Edinburgh UK

ISBN: (纸本)9781479913510

关键词： Vector precoding limited feedback multi-user MIMO non-linear precoding Scale factor multiple input multiple output systems fast fading Receivers multi-user prediction coding Threshold error floor Cloning Vectors Quantization Feedback

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A Practical GDFE Precoder for Multiuser MIMO Systems

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2012年第10期11卷 3668-3676页

作者： Gaur, Sudhanshu Gao, Long Acharya, Joydeep Hitachi Amer Ltd Wireless Syst Res Lab Santa Clara CA 95050 USA

Generalized decision feedback equalizer (GDFE) achieves MIMO broadcast channel (BC) capacity but suffers from huge computational complexity and feedback overhead making it unsuitable for practical systems. Much of the complexity is due to the computation of the covariance matrix corresponding to the least favorable noise. Additionally GDFE implementation requires the base stations (BS) to feedback filter coefficients to the users thus increasing overhead. In this paper, we address both the aspects - computational complexity and feedback overhead. We first propose an alternative framework for realizing the GDFE precoder, which avoids the explicit computation of the least favorable noise. We show that, while maintaining capacity optimality of the GDFE precoder, the proposed algorithm has significantly lower complexity. Next, we propose another algorithm which does not require the feedback of filter coefficients from BS to users with minimal loss in achievable capacity. Thus our algorithms are a step towards adopting GDFE precoders in future wireless systems.

关键词： Broadcast channel multiuser MIMO non-linear precoding GDFE

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A Transmit-Power Efficient MIMO-THP Design

A Transmit-Power Efficient MIMO-THP Design

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IEEE International Symposium on Information Theory

作者： Masouros, Christos Sellathurai, Mathini Ratnarajah, Tharm Queens Univ Belfast ECIT Belfast BT3 9DT Antrim North Ireland

ISBN: (纸本)9781467325790

In this paper, an improved multiple input multiple output Tomlinson-Harashima precoder (MIMO-THP) is introduced, where the transmit power loss is reduced based on optimizing the interference to be canceled. The concept behind the proposed technique builds on the fact that both the desired and interfering signals originate from the base station (BS) of the downlink system itself. Based on this observation, the proposed method influences the resulting interference, to reduce the transmission power required to cancel it, without altering the information content of the downlink message. The aim is to bring the interference closer to the replicas of the desired symbols for all users in the THP modulo-extended constellation. In this way, the power required to pre-subtract interference is decreased. Theoretical and simulation results both confirm that, by optimizing the interference to be canceled, the proposed technique offers a considerable transmit power reduction compared to conventional THP while securing an equal error rate performance.

关键词： Tomlinson-Harashima precoding power loss known interference multi-user MIMO non-linear precoding

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