A modified leakage-based transmit filter design for multi-user MIMO systems
25 Nov 2013-pp 912-916
TL;DR: A modified definition of signal-to-leakage-plus-noise ratio (SLNR) as a criterion for linear transmit filter design in Multi-user MIMO systems and an iterative precoding algorithm is proposed and is studied with two linear receivers.
Abstract: This paper proposes a modified definition of signal-to-leakage-plus-noise ratio (SLNR) as a criterion for linear transmit filter design in Multi-user MIMO systems. The proposed metric incorporates receiver structures into the precoder design, which can potentially exploit unused receive signal subspaces in cases where the available eigenmodes are not fully transmitted. The improvement in terms of the degrees of freedom of the precoder is also elaborated. In addition, an iterative precoding algorithm is proposed and is studied with two linear receivers, namely the matched filter (MF) and the minimum mean square error (MMSE) receivers. Simulation results show that the proposed scheme outperforms the conventional SLNR scheme and can achieve further improvement with an MMSE receiver, at the expense of increased computational complexity and slow convergence rate. Moreover, the proposed scheme is shown to reduce its form to the conventional scheme when full-eigenmode transmission is assumed.
Citations
More filters
TL;DR: Simulation results show that, for multiple users per cell, the proposed algorithms can effectively integrate user and substream selections and achieve multi-user diversity gain.
Abstract: In this study, linear transceiver designs are proposed based on modified definitions of signal-to-leakage-plus-noise ratio (mSLNR) for multi-cell coordinated beamforming scenarios. Two mSLNR definitions are presented, one of which modifies the computation of leakage and noise powers, while the other applies the modified procedure to the desired power calculation in addition to the computation of leakage and noise powers. The proposed mSLNRs are generally valid for any receiver types. Various linear receivers are studied, several of which, when applied with the first mSLNR definition, are shown to be equivalent. Moreover, a special case of the proposed scheme is shown to be equivalent to an existing algorithm. Iterative precoding algorithms are also presented with a discussion on their convergence properties. The proposed transceiver designs are further extended to incorporate scheduling functionalities. A weighted sum rate maximisation problem is formulated and is solved by two separate approaches, namely power allocation and data-substream selection methods. Simulation results show that, for multiple users per cell, the proposed algorithms can effectively integrate user and substream selections and achieve multi-user diversity gain.
7 citations
Dissertation•
21 Jun 2016
TL;DR: This thesis investigates the application of an iterative leakage-based precoding algorithm to practical multiuser-MIMO systems and proposes several modifications to the aforementioned method which demonstrated improved performance under certain practical conditions.
Abstract: This thesis investigates the application of an iterative leakage-based precoding algorithm to practical multiuser-MIMO systems. We consider the effect of practical impairments including imperfect channel state information, transmit antenna correlation, and timevarying channels. Solutions are derived which improve performance of the algorithm with imperfect channel state information at the transmitter by leveraging knowledge of the second-order statistics of the error. From this work we draw a number of conclusions on how imperfect channel state information may impact the system design including the importance of interference suppression at the receiver and the selection of the number of co-scheduled users. We also demonstrate an efficient approach to improve the convergence of the algorithm when using interference-rejection-combining receivers. Finally, we conduct simulations of an LTE-A system employing the improved algorithm to show its utility for modern communication systems. Iterative Leakage-Based Precoding for Multiuser-MIMO Systems Eric Sollenberger General Audience Abstract This thesis investigates several aspects of a particular method by which multiple users can share radio resources within a wireless system i.e. they may operate on the same frequency and at the same time. This is a desirable capability in modern wireless systems because it improves the efficiency of radio spectrum usage. Radio spectrum has become a very expensive resource in recent years so achieving high efficiency is crucial. Our investigation led us to propose several modifications to the aforementioned method which demonstrated improved performance under certain practical conditions. We further demonstrated the effects of several common system impairments and provided insight into how these impairments effect the system design. Finally, we demonstrated that using this method provides significant gains when used for the latest cellular technology.
2 citations
Cites background or methods from "A modified leakage-based transmit f..."
...One of the main concerns expressed in [8] was the slow convergence of the iSLNR algorithm when using IRC receivers compared to MF receivers, especially since the gain provided by using IRC receivers is marginal (under the assumption of perfect CSIT)....
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...The work in [8] proposed an iterative SLNR precoding scheme (iSLNR) that was shown to provide substantial gains in sum-rate and error rate assuming a known linear receiver structure....
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...This technique can be applied for any linear receiver structure, though the work in [8] discussed MF and IRC receivers....
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...The SLNR metric was used in an iterative algorithm (iSLNR) in [8] which considers the receiver processing and provides substantial gains for non-full-rank transmissions....
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...This is due to the effective decrease in required transmit degrees of freedom that results from using this algorithm, as explained in [8]....
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TL;DR: A robust design of the proposed schemes for the case of imperfect channel state information (CSI) is presented, and adequate knowledge of effective receive subspaces can be attained by simply assuming matched filters in the iterative precoding process, while further improvement can be obtained by an actual implementation of interference-mitigation-capable receivers.
2 citations
References
More filters
TL;DR: While the proposed algorithms are suboptimal, they lead to simpler transmitter and receiver structures and allow for a reasonable tradeoff between performance and complexity.
Abstract: The use of space-division multiple access (SDMA) in the downlink of a multiuser multiple-input, multiple-output (MIMO) wireless communications network can provide a substantial gain in system throughput. The challenge in such multiuser systems is designing transmit vectors while considering the co-channel interference of other users. Typical optimization problems of interest include the capacity problem - maximizing the sum information rate subject to a power constraint-or the power control problem-minimizing transmitted power such that a certain quality-of-service metric for each user is met. Neither of these problems possess closed-form solutions for the general multiuser MIMO channel, but the imposition of certain constraints can lead to closed-form solutions. This paper presents two such constrained solutions. The first, referred to as "block-diagonalization," is a generalization of channel inversion when there are multiple antennas at each receiver. It is easily adapted to optimize for either maximum transmission rate or minimum power and approaches the optimal solution at high SNR. The second, known as "successive optimization," is an alternative method for solving the power minimization problem one user at a time, and it yields superior results in some (e.g., low SNR) situations. Both of these algorithms are limited to cases where the transmitter has more antennas than all receive antennas combined. In order to accommodate more general scenarios, we also propose a framework for coordinated transmitter-receiver processing that generalizes the two algorithms to cases involving more receive than transmit antennas. While the proposed algorithms are suboptimal, they lead to simpler transmitter and receiver structures and allow for a reasonable tradeoff between performance and complexity.
3,291 citations
TL;DR: Under certain mild conditions, this scheme is found to be throughput-wise asymptotically optimal for both high and low signal-to-noise ratio (SNR), and some numerical results are provided for the ergodic throughput of the simplified zero-forcing scheme in independent Rayleigh fading.
Abstract: A Gaussian broadcast channel (GBC) with r single-antenna receivers and t antennas at the transmitter is considered. Both transmitter and receivers have perfect knowledge of the channel. Despite its apparent simplicity, this model is, in general, a nondegraded broadcast channel (BC), for which the capacity region is not fully known. For the two-user case, we find a special case of Marton's (1979) region that achieves optimal sum-rate (throughput). In brief, the transmitter decomposes the channel into two interference channels, where interference is caused by the other user signal. Users are successively encoded, such that encoding of the second user is based on the noncausal knowledge of the interference caused by the first user. The crosstalk parameters are optimized such that the overall throughput is maximum and, surprisingly, this is shown to be optimal over all possible strategies (not only with respect to Marton's achievable region). For the case of r>2 users, we find a somewhat simpler choice of Marton's region based on ordering and successively encoding the users. For each user i in the given ordering, the interference caused by users j>i is eliminated by zero forcing at the transmitter, while interference caused by users j
2,616 citations
01 Jan 2004
2,180 citations
TL;DR: A simple encoding algorithm is introduced that achieves near-capacity at sum rates of tens of bits/channel use and regularization is introduced to improve the condition of the inverse and maximize the signal-to-interference-plus-noise ratio at the receivers.
Abstract: Recent theoretical results describing the sum capacity when using multiple antennas to communicate with multiple users in a known rich scattering environment have not yet been followed with practical transmission schemes that achieve this capacity. We introduce a simple encoding algorithm that achieves near-capacity at sum rates of tens of bits/channel use. The algorithm is a variation on channel inversion that regularizes the inverse and uses a "sphere encoder" to perturb the data to reduce the power of the transmitted signal. This work is comprised of two parts. In this first part, we show that while the sum capacity grows linearly with the minimum of the number of antennas and users, the sum rate of channel inversion does not. This poor performance is due to the large spread in the singular values of the channel matrix. We introduce regularization to improve the condition of the inverse and maximize the signal-to-interference-plus-noise ratio at the receivers. Regularization enables linear growth and works especially well at low signal-to-noise ratios (SNRs), but as we show in the second part, an additional step is needed to achieve near-capacity performance at all SNRs.
1,796 citations
TL;DR: This paper proposes designing precoders by maximizing the so-called signal-to-leakage-and-noise ratio (SLNR) for all users simultaneously, and it also avoids noise enhancement.
Abstract: In multiuser MIMO downlink communications, it is necessary to design precoding schemes that are able to suppress co-channel interference. This paper proposes designing precoders by maximizing the so-called signal-to-leakage-and-noise ratio (SLNR) for all users simultaneously. The presentation considers communications with both single- and multi-stream cases, as well as MIMO systems that employ Alamouti coding. The effect of channel estimation errors on system performance is also studied. Compared with zero-forcing solutions, the proposed method does not impose a condition on the relation between the number of transmit and receive antennas, and it also avoids noise enhancement. Simulations illustrate the performance of the scheme
871 citations