Multiuser MIMO achievable rates with downlink training and channel state feedback (original) (raw)
Related papers
2007
Abstract We consider a MIMO fading broadcast channel and compute achievable ergodic rates when channel state information is acquired at the receivers via downlink training and explicit channel feedback is performed to provide transmitter channel state information (CSIT). Both “analog” and quantized (digital) channel feedback are analyzed, and digital feedback is shown to be potentially superior when the feedback channel uses per channel coefficient is larger than 1.
2012
We derive the ergodic channel capacity of a closedloop MIMO broadcast system under both random user selection (RUS) and semi-orthogonal user selection (SUS) principles, when considering the effects of channel estimation errors, channel state information (CSI) quantization errors and CSI feedback-delay. We intend to answer the question of "How many simultaneous users should be active in a time slot in order to achieve the maximum sum-rate in a MIMO broadcast system?". It is shown that we should refrain from supporting full-rank transmissions due to the excess inter-user interference caused by imperfect CSI at both the receiver and transmitter under RUS. By contrast, fullrank transmissions may be feasible under the SUS principle. An approximate ergodic capacity equation is also derived for RUS, and then an adaptive-rank transmission strategy is derived, which is capable of maximizing the achievable ergodic capacity.
Feedback schemes for multiuser MIMO-OFDM downlink
2008
Abstract We consider a MIMO-OFDM broadcast channel and compare achievable ergodic rates under three channel state feedback schemes: analog feedback, direction quantized feedback and ldquotime-domainrdquo channel quantized feedback. The third scheme is new, and it is inspired by rate-distortion theory of Gaussian correlated sources. For each scheme we derive the conditions under which the system achieves full multiplexing gain.
2006
Abstract We consider a MIMO fading broadcast channel and compare the achievable ergodic rates when the channel state information at the transmitter is provided by" analog" noisy feedback or by quantized (digital) feedback. The superiority of digital feedback is shown whenever the number of feedback channel uses per channel coefficient is larger than 1. Also, we show that by proper design of the digital feedback link, errors in the feedback have a minor effect even by using very simple uncoded modulation.
Ergodic and Outage Performance of Fading Broadcast Channels With 1-Bit Feedback
IEEE Transactions on Vehicular Technology, 2010
In this paper, the ergodic sum-rate and outage probability of a downlink single-antenna channel with K users are analyzed in the presence of Rayleigh flat fading, where limited channel state information (CSI) feedback is assumed. Specifically, only 1-bit feedback per fading block per user is available at the base station. We first study the ergodic sumrate of the 1-bit feedback scheme, and consider the impact of feedback delay on the system. A closed-form expression for the achievable ergodic sum-rate is presented as a function of the fading temporal correlation coefficient. It is proved that the sumrate scales as log log K, which is the same scaling law achieved by the optimal non-delayed full CSI feedback scheme. The sumrate degradation due to outdated CSI is also evaluated in the asymptotic regimes of either large K or low SNR. The outage performance of the 1-bit feedback scheme for both instantaneous and outdated feedback is then investigated. Expressions for the outage probabilities are derived, along with the corresponding diversity-multiplexing tradeoffs (DMT). It is shown that with instantaneous feedback, a power allocation based on the feedback bits enables to double the DMT compared to the case with shortterm power constraint in which a dynamic power allocation is not allowed. But, with outdated feedback, the advantage of power allocation is lost, and the DMT reverts to that achievable with no CSI feedback. Nevertheless, for finite SNR, improvement in terms of outage probability can still be obtained.
Training and feedback optimization for multiuser MIMO downlink
2011
Abstract We consider a MIMO fading broadcast channel where the fading channel coefficients are constant over time-frequency blocks that span a coherent time xa coherence bandwidth. In closed-loop systems, channel state information at transmitter (CSIT) is acquired by the downlink training sent by the base station and an explicit feedback from each user terminal. In open-loop systems, CSIT is obtained by exploiting uplink training and channel reciprocity.
Reduced feedback for selective fading MIMO broadcast channels
In this article, we analyze the selective multiple-input multiple-output broadcast channel, where links are assumed to be selective in both time and frequency. The assumption of full channel knowledge at the transmitter side requires a large amount of feedback, and it is therefore not practical to be implemented in real systems. A more feasible solution with finite rate feedback originally proposed by Jindal in IEEE Trans. Inf. Theory is applied here to the selective fading case, where the minimal number of feedback bits required to achieve the full multiplexing is derived. We show that the correlation between time frequency channels can be used in order to minimize the number of feedback bits to the transmitter side while conserving the maximal multiplexing gain. Finally, the practical implementation of a time-frequency channel quantization scheme is addressed, and a low-complexity scheme that also achieves the multiplexing gain is proposed.
On the Achievable Rate of ZF-DPC for MIMO Broadcast Channels with Finite Rate Feedback
2009
In this paper we study a MIMO fading broadcast channel where each receiver has perfect channel state information (CSI) while the transmitter only acquires quantized CSI by finite rate feedback. We analyze the zero-forcing dirty-paper coding (ZF-DPC) scheme, which is a nonlinear preceding scheme inherently superior to linear ZF beamforming. Lower bound in closed-form expression and upper bound on the achievable ergodic rate of ZF-DPC with Gaussian inputs and uniform power allocation are derived. Based on the closed-form lower bound, sufficient conditions on the feedback channels to ensure non-zero and full downlink multiplexing gain are obtained. Specifically, in order to achieve the downlink multiplexing gain of alphaM (0 < alpha les 1), it is sufficient to scale the number of feedback bits B per user as B = alpha (M- 1) log2 P/N0 where M is the number of transmit antennas and P/N0 is the average downlink SNR.