Adaptive Modulation in MIMO Eigenbeamforming with Outdated Channel State Information
01 Jan 2006-
TL;DR: A novel adaptive modulation scheme that loads power and integer bits over the eigenmodes in a MIMO communication system according to outdated CSI at the transmitter and simulations indicate that the proposed scheme provides a much higher spectral efficiency than the standard strategy which simply adds energy margin to achieve the target error performance.
Abstract: Channel state information(CSI) at the transmitter, even imperfect, can improve the capacity of a multiple-input multiple-output(MIMO) communication system and substantially reduce the receiver complexity. Eigenbeamforming has been proven to be the precoding scheme that not only achieves the channel capacity, but also minimizes the mean square error(MSE) at the output of the receiver in this case. This paper presents a novel adaptive modulation scheme that loads power and integer bits over the eigenmodes in a MIMO communication system according to outdated CSI at the transmitter. An un- coded narrowband system is considered in a time-varying and spatially uncorrelated fading channel. Simulations indicate that the proposed scheme provides a much higher spectral efficiency than the standard strategy which simply adds energy margin to achieve the target error performance. I. INTRODUCTION
Citations
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TL;DR: This letter studies peak-to-average power ratio (PAPR) reduction for orthogonal frequency-division multiplexing (OFDM) signals in eigenbeamformed multiple antenna systems with no modification of the receiver required.
Abstract: This letter studies peak-to-average power ratio (PAPR) reduction for orthogonal frequency-division multiplexing (OFDM) signals in eigenbeamformed multiple antenna systems The weak eigenmodes abandoned by the waterfilling allocation are intentionally filled in order to offset signal peaks in the time domainNumerical results indicate that this method can significantly increase the efficiency of peak power constrained systems with no modification of the receiver required
15 citations
14 Mar 2010
TL;DR: In this article, the per-subchannel signal-to-interference-and-noise ratio for the imperfect CSI case was derived to derive approximately optimal subchannel power levels and thresholds on the amount of CSI imperfections and noise tolerable in SVD-based multiplexing systems using M-ary quadrature amplitude modulation.
Abstract: In narrowband multiple-input multiple-output (MIMO) communication systems with perfectly known channel state information (CSI), the singular value decomposition (SVD) is commonly used to decompose the MIMO channel into independent single-input single-output subchannels. In theory, optimal interference-free data multiplexing may then be carried out using the subchannel power levels provided by the well-known waterfilling solution. In practice, however, when finite codebooks are used and perfect CSI is unavailable, adaptations to power levels and bit-loading schemes are often needed to maintain reasonable performance. In this paper, we use expressions for the per-subchannel signal-to-interference- and-noise ratio for the imperfect CSI case to derive approximately optimal subchannel power levels and thresholds on the amount of CSI imperfections and noise tolerable in SVD-based multiplexing systems using M-ary quadrature amplitude modulation. Numerical simulations demonstrate the usefulness of the derived expressions.
11 citations
Cites methods from "Adaptive Modulation in MIMO Eigenbe..."
...Some of the effects of imperfect CSI (ICSI) on MIMO SVD-based multiplexing methods that employ common signal constellations (such asM -ary quadrature amplitude modulation, or MQAM) have been examined in [3–5], and ad-hoc subchannel power and bit-loading methods have been proposed in [4, 5] to compensate for the effects of ICSI and nite symbol constellations....
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...In this paper, we present a more deterministic design approach that uses the per-subchannel SINR expression derived in [6] (also see [5]) to nd a subchannel power-loading scheme and multiplexing thresholds for SVD-based MIMO signaling with M-QAM constellations under ICSI conditions....
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...In the simulations, UPIBL will be compared with three other methods: conventional water lling (WF), beamforming with informed bit-loading (BFIBL), and the ad-hoc method of [5] which we refer to as power trimming with informed bit loading (PTIBL)....
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01 Jan 2010
TL;DR: In this article, the performance and impact of channel estimation in MIMO and OFDM systems is studied. But the authors focus on the channel state information (CSI) quality and do not consider the impact of imperfect CSI on the performance of the channel estimation.
Abstract: Studies on the Performance and Impact of Channel Estimation in MIMO and OFDM Systems Michael David Larsen Department of Electrical and Computer Engineering Doctor of Philosophy The need for reliable, high-throughput, mobile wireless communication technologies has never been greater as increases in the demand for on-the-go access to information, entertainment, and other electronic services continues. Two such technologies, which are at the forefront of current research efforts, are orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output (MIMO) systems, their union being known simply as MIMO-OFDM. The successful performance of these technologies depends upon the availability of accurate information concerning the wireless communication channel. In this dissertation, several issues related to quality of this channel state information (CSI) are studied. Specifically, the first part of this dissertation considers the design of optimal pilot signals for OFDM systems. The optimization is addressed via lower bounds on the estimation error variance, which bounds are given by formulations of the Cramer-Rao bound (CRB). The second part of this dissertation uses the CRB once again, this time as a tool for evaluating the potential performance of MIMO-OFDM channel estimation and prediction. Bounds are found for several parametric time-varying wideband MIMO-OFDM channel models, and numerical evaluations of these bounds are used to illuminate several interesting features regarding the estimation and prediction of MIMO-OFDM channels. The final part of this dissertation considers the problem of MIMO multiplexing using SVD-based methods when only imperfect CSI is available. For this purpose, general per-MIMO-subchannel signal and interference-plus-noise power expressions are derived to quantify the effects of CSI imperfections, and these expressions are then used to find robust MIMO-SVD power and bit allocations which maintain good overall performance in spite of imperfect CSI.
Cites background or methods from "Adaptive Modulation in MIMO Eigenbe..."
...Also note that the adaptive modulation algorithm of [73], which is the best performing method from the papers discussed here, is used for the purpose of comparison in Chapter 5....
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...The second method is essentially the ad-hoc method of [73], though modified to use our SINR expressions and the SER and bit expressions of (5....
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...The SINR expression used in [73] is equivalent to one of the SINR expressions derived in Chapter 5 for the special case of identical CSI at both the transmitter and receiver, referred to in the chapter as the common CSI (CCSI) case....
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...For instance, having derived an expression for the BER, [73] proposes an ad-hoc method to select power and bit-loading levels in each subchannel to meet...
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...Note that in [73], excess power from the smallest subchannel could also be reallocated from one temporal transmission to the next....
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References
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AT&T1
TL;DR: This paper presents a simple two-branch transmit diversity scheme that provides the same diversity order as maximal-ratio receiver combining (MRRC) with one transmit antenna, and two receive antennas.
Abstract: This paper presents a simple two-branch transmit diversity scheme. Using two transmit antennas and one receive antenna the scheme provides the same diversity order as maximal-ratio receiver combining (MRRC) with one transmit antenna, and two receive antennas. It is also shown that the scheme may easily be generalized to two transmit antennas and M receive antennas to provide a diversity order of 2M. The new scheme does not require any bandwidth expansion or any feedback from the receiver to the transmitter and its computation complexity is similar to MRRC.
13,706 citations
01 Nov 1999
TL;DR: In this paper, the authors investigate the use of multiple transmitting and/or receiving antennas for single user communications over the additive Gaussian channel with and without fading, and derive formulas for the capacities and error exponents of such channels, and describe computational procedures to evaluate such formulas.
Abstract: We investigate the use of multiple transmitting and/or receiving antennas for single user communications over the additive Gaussian channel with and without fading. We derive formulas for the capacities and error exponents of such channels, and describe computational procedures to evaluate such formulas. We show that the potential gains of such multi-antenna systems over single-antenna systems is rather large under independenceassumptions for the fades and noises at different receiving antennas.
12,542 citations
TL;DR: This paper addresses digital communication in a Rayleigh fading environment when the channel characteristic is unknown at the transmitter but is known (tracked) at the receiver with the aim of leveraging the already highly developed 1-D codec technology.
Abstract: This paper addresses digital communication in a Rayleigh fading environment when the channel characteristic is unknown at the transmitter but is known (tracked) at the receiver. Inventing a codec architecture that can realize a significant portion of the great capacity promised by information theory is essential to a standout long-term position in highly competitive arenas like fixed and indoor wireless. Use (n T , n R ) to express the number of antenna elements at the transmitter and receiver. An (n, n) analysis shows that despite the n received waves interfering randomly, capacity grows linearly with n and is enormous. With n = 8 at 1% outage and 21-dB average SNR at each receiving element, 42 b/s/Hz is achieved. The capacity is more than 40 times that of a (1, 1) system at the same total radiated transmitter power and bandwidth. Moreover, in some applications, n could be much larger than 8. In striving for significant fractions of such huge capacities, the question arises: Can one construct an (n, n) system whose capacity scales linearly with n, using as building blocks n separately coded one-dimensional (1-D) subsystems of equal capacity? With the aim of leveraging the already highly developed 1-D codec technology, this paper reports just such an invention. In this new architecture, signals are layered in space and time as suggested by a tight capacity bound.
6,812 citations
TL;DR: An overview of the extensive results on the Shannon capacity of single-user and multiuser multiple-input multiple-output (MIMO) channels is provided and it is shown that the capacity region of the MIMO multiple access and the largest known achievable rate region (called the dirty-paper region) for the M IMO broadcast channel are intimately related via a duality transformation.
Abstract: We provide an overview of the extensive results on the Shannon capacity of single-user and multiuser multiple-input multiple-output (MIMO) channels. Although enormous capacity gains have been predicted for such channels, these predictions are based on somewhat unrealistic assumptions about the underlying time-varying channel model and how well it can be tracked at the receiver, as well as at the transmitter. More realistic assumptions can dramatically impact the potential capacity gains of MIMO techniques. For time-varying MIMO channels there are multiple Shannon theoretic capacity definitions and, for each definition, different correlation models and channel information assumptions that we consider. We first provide a comprehensive summary of ergodic and capacity versus outage results for single-user MIMO channels. These results indicate that the capacity gain obtained from multiple antennas heavily depends on the available channel information at either the receiver or transmitter, the channel signal-to-noise ratio, and the correlation between the channel gains on each antenna element. We then focus attention on the capacity region of the multiple-access channels (MACs) and the largest known achievable rate region for the broadcast channel. In contrast to single-user MIMO channels, capacity results for these multiuser MIMO channels are quite difficult to obtain, even for constant channels. We summarize results for the MIMO broadcast and MAC for channels that are either constant or fading with perfect instantaneous knowledge of the antenna gains at both transmitter(s) and receiver(s). We show that the capacity region of the MIMO multiple access and the largest known achievable rate region (called the dirty-paper region) for the MIMO broadcast channel are intimately related via a duality transformation. This transformation facilitates finding the transmission strategies that achieve a point on the boundary of the MIMO MAC capacity region in terms of the transmission strategies of the MIMO broadcast dirty-paper region and vice-versa. Finally, we discuss capacity results for multicell MIMO channels with base station cooperation. The base stations then act as a spatially diverse antenna array and transmission strategies that exploit this structure exhibit significant capacity gains. This section also provides a brief discussion of system level issues associated with MIMO cellular. Open problems in this field abound and are discussed throughout the paper.
2,480 citations
28 Apr 1996
TL;DR: There is a constant power gap between the spectral efficiency of the proposed technique and the channel capacity, and this gap is a simple function of the required bit-error rate (BER).
Abstract: We propose a variable-rate and variable-power MQAM modulation scheme for high-speed data transmission over fading channels. We first review results for the Shannon capacity of fading channels with channel side information, where capacity is achieved using adaptive transmission techniques. We then derive the spectral efficiency of our proposed modulation. We show that there is a constant power gap between the spectral efficiency of our proposed technique and the channel capacity, and this gap is a simple function of the required bit-error rate (BER). In addition, using just five or six different signal constellations, we achieve within 1-2 dB of the maximum efficiency using unrestricted constellation sets. We compute the rate at which the transmitter needs to update its power and rate as a function of the channel Doppler frequency for these constellation sets. We also obtain the exact efficiency loss for smaller constellation sets, which may be required if the transmitter adaptation rate is constrained by hardware limitations. Our modulation scheme exhibits a 5-10-dB power gain relative to variable-power fixed-rate transmission, and up to 20 dB of gain relative to nonadaptive transmission. We also determine the effect of channel estimation error and delay on the BER performance of our adaptive scheme. We conclude with a discussion of coding techniques and the relationship between our proposed modulation and Shannon capacity.
2,355 citations