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Multicarrier transmission with limited feedback: Power loading over subchannel groups
 IEEE International Conference on Communications
, 2008
"... Abstract — Feedback of channel state information (CSI) enables a multicarrier transmitter to optimize the power allocation across subchannels. We consider a single user feedback scheme in which the entire set of subchannels is evenly divided into smaller groups of subchannels, and the receiver r ..."
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Abstract — Feedback of channel state information (CSI) enables a multicarrier transmitter to optimize the power allocation across subchannels. We consider a single user feedback scheme in which the entire set of subchannels is evenly divided into smaller groups of subchannels, and the receiver requests the use of a particular group if the gain of every subchannel in the group is above a threshold. The transmit power is then uniformly spread across the requested subchannel groups. The amount of feedback is therefore controlled by the group size and the threshold. For this scheme, given a total power constraint, we characterize how the channel capacity scales with the number of subchannels N as a function of the feedback rate. We then consider transmission over a block fading channel, assuming that each coherence block contains both feedback and data transmission. We optimize the fraction of feedback overhead as a function of the number of feedback bits per channel use and coherence time. Numerical results show that the asymptotic (largeN) analysis accurately predicts the behavior of finitesize systems of interest. I.
LimitedRate Channel State Feedback for Multicarrier Block Fading Channels 1
, 2008
"... The capacity of a fading channel can be substantially increased by feeding back channel state information from the receiver to the transmitter. With limitedrate feedback what state information to feed back and how to encode it are important open questions. This paper studies power loading in a mult ..."
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The capacity of a fading channel can be substantially increased by feeding back channel state information from the receiver to the transmitter. With limitedrate feedback what state information to feed back and how to encode it are important open questions. This paper studies power loading in a multicarrier system using no more than one bit of feedback per subchannel. The subchannels can be correlated and full channel state information is assumed at the receiver. First, a simple model with N parallel twostate (good/bad) memoryless subchannels is considered, where the channel state feedback is used to select a fixed number of subchannels to activate. The optimal feedback scheme is the solution to a vector quantization problem, and the associated performance for large N is characterized by a rate distortion function. As N increases, we show that the loss in forward rate from the asymptotic (ratedistortion) value decreases as (log N)/N and √ (log N)/N with optimal variable and fixedrate feedback codes, respectively. We subsequently extend these results to parallel Rayleigh block fading subchannels, where the feedback designates a set of subchannels, which are activated with equal power. Ratedistortion feedback codes are proposed for designating subsets of (good) subchannels with SignaltoNoise Ratios (SNRs) that exceed a threshold. The associated performance is compared with that of a simpler lossless source coding scheme, which designates groups of good subchannels, where both the group size and threshold are optimized. The ratedistortion codes can provide a significant increase in forward rate at low SNRs.
On resource allocation in twoway limited feedback beamforming systems
 in UCSD Info. Theory and
, 2008
"... Abstract — The benefits employing channel state information (CSI) at the transmitter in a multiple antenna wireless link are well documented in the literature. One of the most popular techniques to provide the transmitter with CSI in frequency division duplexing wireless links is by sending a finite ..."
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Abstract — The benefits employing channel state information (CSI) at the transmitter in a multiple antenna wireless link are well documented in the literature. One of the most popular techniques to provide the transmitter with CSI in frequency division duplexing wireless links is by sending a finite number of feedback bits. However, the effect of the overhead created by these feedback bits on the link performance is still not well understood. In this paper, we study a specific scenario of limited feedback known as limited feedback beamforming. We look at the effect of allocating resources to feedback and the scaling of these resources. Monte Carlo simulations also demonstrate the inherent tradeoff between the forward and reverse links in a wireless system. I.
Asymptotic performance of DSCDMA with linear MMSE receiver and limited feedback
 in Proc. IEEE Int. Conf. on Commun. (ICC
, 2008
"... Abstract—Signature quantization for reverselink Direct Sequence (DS) Code Division Multiple Access (CDMA) is considered. A receiver assumed to have perfect estimates of channel and interference covariance, selects the signature that maximizes signaltointerference plus noise ratio (SINR) for a de ..."
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Abstract—Signature quantization for reverselink Direct Sequence (DS) Code Division Multiple Access (CDMA) is considered. A receiver assumed to have perfect estimates of channel and interference covariance, selects the signature that maximizes signaltointerference plus noise ratio (SINR) for a desired user from a signature codebook. The codebook index corresponding to the optimal signature is relayed to the user with finite number of bits via a feedback channel. Previously, it was shown that a Random Vector Quantization (RVQ) codebook, which contains independent isotropically distributed vectors, is optimal (i.e., maximizes SINR) in a large system limit in which number of interfering users, processing gain, and feedback bits tend to infinity with fixed ratios. Here we derive exact expressions for a large system SINR for the user whose signature is selected from RVQ codebook. We assume that the receiver is linear minimum mean squared error (MMSE) and consider both ideal and multipath fading channels. I.
On optimal training and beamforming in uncorrelated MIMO systems with feedback,”
 in Proceedings of the 42nd Annual Conference on Information Sciences and Systems,
, 2008
"... AbstractThis paper studies the design and analysis of optimal trainingbased beamforming in uncorrelated multipleinput multipleoutput (MIMO) channels with known Gaussian statistics. First, given the response of the MIMO channel to a finite sequence of training vectors, the beamforming vector whic ..."
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AbstractThis paper studies the design and analysis of optimal trainingbased beamforming in uncorrelated multipleinput multipleoutput (MIMO) channels with known Gaussian statistics. First, given the response of the MIMO channel to a finite sequence of training vectors, the beamforming vector which maximizes the average received signaltonoise ratio (SNR) over all channel realizations is found. Secondly, the question of what consists of optimal training for a given amount of training is addressed. Upper and lower bounds for the maximum achievable SNR using beamforming are established. Furthermore, optimal training sequences are conjectured to satisfy the Welch bound. The conjecture is supported by the evidence that such sequences achieve close to the upper bound with moderate to large amount of trainings.
Adaptive Transceivers for Wireless Spread Spectrum Networks
"... The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comm ..."
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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggesstions for reducing this burden, to Washington
1 LimitedRate Channel State Feedback for Multicarrier Block Fading Channels
, 2009
"... The capacity of a fading channel can be substantially increased by feeding back channel state information from the receiver to the transmitter. With limitedrate feedback what state information to feed back and how to encode it are important open questions. This paper studies power loading in a mult ..."
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The capacity of a fading channel can be substantially increased by feeding back channel state information from the receiver to the transmitter. With limitedrate feedback what state information to feed back and how to encode it are important open questions. This paper studies power loading in a multicarrier system using no more than one bit of feedback per subchannel. The subchannels can be correlated and full channel state information is assumed at the receiver. First, a simple model with N parallel twostate (good/bad) memoryless subchannels is considered, where the channel state feedback is used to select a fixed number of subchannels to activate. The optimal feedback scheme is the solution to a vector quantization problem, and the associated performance for large N is characterized by a rate distortion function. As N increases, we show that the loss in forward rate from the asymptotic (ratedistortion) value decreases as (log N)/N and √ (log N)/N with optimal variable and fixedrate feedback codes, respectively. We subsequently extend these results to parallel Rayleigh block fading subchannels, where the feedback designates a set of subchannels, which are activated with equal power. Ratedistortion feedback codes are proposed for designating subsets of (good) subchannels with SignaltoNoise Ratios (SNRs) that exceed a threshold. The associated performance is compared with that of a simpler lossless
1Optimization of Twoway Communication with ARQ Feedback
"... Abstract—In this paper, we study ARQ feedback in the context of twoway wireless communications. In particular, we consider two nodes which wish to exchange data over a frequency division duplex, timevarying wireless additive white Gaussian noise with Rayleigh fading, channel. In twoway scenarios, ..."
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Abstract—In this paper, we study ARQ feedback in the context of twoway wireless communications. In particular, we consider two nodes which wish to exchange data over a frequency division duplex, timevarying wireless additive white Gaussian noise with Rayleigh fading, channel. In twoway scenarios, unlike the more well studied oneway data scenarios, the data and resources allocated to feedback and channel estimation may share the same link, leading to interesting tradeoffs. To analyze these, we present a twoway framework in which 1) training (estimation of channel state), 2) feedback (in the form of ARQ), and 3) data are taken into account, and share the same noisy fading channel. We obtain an expression which captures the tradeoffs between allocating resources for these three tasks on the overall throughput achievable in each direction, which we numerically evaluate. In particular, we obtain the optimal resource allocations corresponding to different channel conditions, SNR regimes, and receiver feedback protocols under fast and slow fading conditions. Index Terms—bidirectional communication, feedback, throughput, timevarying channel