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MISO Broadcast Channels with Delayed FiniteRate Feedback: Predict or Observe?
"... Abstract—Most multiuser precoding techniques require accurate channel state information at the transmitter (CSIT) to maintain orthogonality between the users. Such techniques have proven quite fragile in timevarying channels because the CSIT is inherently imperfect due to quantization error and fe ..."
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Cited by 10 (2 self)
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Abstract—Most multiuser precoding techniques require accurate channel state information at the transmitter (CSIT) to maintain orthogonality between the users. Such techniques have proven quite fragile in timevarying channels because the CSIT is inherently imperfect due to quantization error and feedback delay. An alternative approach recently proposed by MaddahAli and Tse (MAT) allows for significant multiplexing gain in the multiinput singleoutput (MISO) broadcast channel (BC) even with CSIT that is “completely stale”, i.e., uncorrelated with the current channel state. With K users, their scheme claims to lose only a log(K) factor relative to the full K degrees of freedom (DoF) attainable in the MISO BC with perfect CSIT for large K. However, their result does not consider the cost of the feedback, which is potentially very large in high mobility (short channel coherence time). In this paper, we more closely examine the MAT scheme and compare its maximum net DoF gain to single user transmission (which always achieves 1 DoF) and partial CSIT linear precoding (which achieves up to K). In particular, assuming the channel coherence time isN symbol periods and the feedback delay is Nfd, we show that when N < (1+o(1))K logK (short coherence time), single user transmission performs best, whereas for N> (1+o(1))(Nfd+K / logK)(1−log−1K)−1 (long coherence time), zeroforcing precoding outperforms the other two. The MAT scheme is optimal for intermediate coherence times, which for practical parameter choices is indeed quite a large and significant range, even accounting for the feedback cost. Index Terms—MIMO, channel state information, quantization. I.
MISO broadcast channel with delayed and evolving CSIT,” Nov. 2012, submitted to
 IEEE Trans. Inform. Theory
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Effects of Channel Aging in Massive MIMO Systems
, 2013
"... MIMO communication may provide high spectral efficiency through the deployment of a very large number of antenna elements at the base stations. The gains from massive MIMO communication come from the use of multiuser MIMO on the uplink and downlink, but with a large excess of antennas at the base ..."
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Cited by 6 (1 self)
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MIMO communication may provide high spectral efficiency through the deployment of a very large number of antenna elements at the base stations. The gains from massive MIMO communication come from the use of multiuser MIMO on the uplink and downlink, but with a large excess of antennas at the base station compared to the number of served users. Initial work on massive MIMO did not fully address several practical issues associated with its deployment. This paper considers the impact of channel aging on the performance of massive MIMO systems. The effects of channel variation are characterized as a function of different system parameters assuming a simple model for the channel time variations at the transmitter. Channel prediction is proposed to overcome channel aging effects. The analytical results on aging show how capacity is lost due to time variation in the channel. Numerical results in a multicell network show that massive MIMO works even with some channel variation and that channel prediction could partially overcome channel aging effects.
1 On the Capacity Region and the Generalized Degrees of Freedom Region for the MIMO Interference Channel with Feedback
"... Abstract—In this paper, we study the effect of feedback on the twouser MIMO interference channel. The capacity region of the MIMO interference channel with feedback is characterized within a constant number of bits, where this constant is independent of the channel matrices. Further, it is shown th ..."
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Cited by 4 (4 self)
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Abstract—In this paper, we study the effect of feedback on the twouser MIMO interference channel. The capacity region of the MIMO interference channel with feedback is characterized within a constant number of bits, where this constant is independent of the channel matrices. Further, it is shown that the capacity region of the MIMO interference channel with feedback and its reciprocal interference channel are within a constant number of bits. Finally, the generalized degrees of freedom region for the MIMO interference channel with feedback is characterized.
Precoding methods for MISO broadcast channel with delayed CSIT,” arXiv preprint arXiv:1207.2103
, 2012
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1MISO Broadcast Channels with Delayed FiniteRate Feedback: Predict or Observe?
"... Abstract—Most multiuser precoding techniques require accurate channel state information at the transmitter (CSIT) to maintain orthogonality between the users. Such techniques have proven quite fragile in timevarying channels because the CSIT is inherently imperfect due to quantization error and fe ..."
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Abstract—Most multiuser precoding techniques require accurate channel state information at the transmitter (CSIT) to maintain orthogonality between the users. Such techniques have proven quite fragile in timevarying channels because the CSIT is inherently imperfect due to quantization error and feedback delay. An alternative approach recently proposed by MaddahAli and Tse (MAT) allows for significant multiplexing gain in the multiinput singleoutput (MISO) broadcast channel (BC) even with CSIT that is “completely stale”, i.e., uncorrelated with the current channel state. With K users, their scheme claims to lose only a log(K) factor relative to the full K degrees of freedom (DoF) attainable in the MISO BC with perfect CSIT for large K. However, their result does not consider the cost of the feedback, which is potentially very large in high mobility (short channel coherence time). In this paper, we more closely examine the MAT scheme and compare its maximum net DoF gain to single user transmission (which always achieves 1 DoF) and partial CSIT linear precoding (which achieves up to K). In particular, assuming the channel coherence time is N symbol periods and the feedback delay is Nfd, we show that when N < (1+o(1))K logK (short coherence time), single user transmission performs best, whereas for N> (1+o(1))(Nfd+K / logK)(1−log−1 K)−1 (long coherence time), zeroforcing precoding outperforms the other two. The MAT scheme is optimal for intermediate coherence times, which for practical parameter choices is indeed quite a large and significant range, even accounting for the feedback cost. Index Terms—MIMO, channel state information, quantization I.
1On the Capacity Region and the Generalized Degrees of Freedom Region for the MIMO Interference Channel with Feedback
"... In this paper, we study the effect of feedback on the twouser MIMO interference channel. The capacity region of the MIMO interference channel with feedback is characterized within a constant number of bits, where this constant is independent of the channel matrices. Further, it is shown that the ca ..."
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In this paper, we study the effect of feedback on the twouser MIMO interference channel. The capacity region of the MIMO interference channel with feedback is characterized within a constant number of bits, where this constant is independent of the channel matrices. Further, it is shown that the capacity region of the MIMO interference channel with feedback and its reciprocal interference channel are within a constant number of bits. Finally, the generalized degrees of freedom region for the MIMO interference channel with feedback is characterized.