Multiuser MIMO Achievable Rates With Downlink Training and Channel State Feedback

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 it is provided to the transmitter by channel state feedback. Unquantized (analog) and quantized (digital) channel state feedback schemes are analyzed and compared under various assumptions. Digital feedback is shown to be potentially superior when the feedback channel uses per channel state 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 if simple uncoded modulation is used on the feedback channel. We discuss first the case of an unfaded AWGN feedback channel with orthogonal access and then the case of fading MIMO multi-access (MIMO-MAC). We show that by exploiting the MIMO-MAC nature of the uplink channel, a much better scaling of the feedback channel resource with the number of base station antennas can be achieved. Finally, for the case of delayed feedback, we show that in the realistic case where the fading process has (normalized) maximum Doppler frequency shift 0 ≤ F < 1/2, a fraction 1 − 2F of the optimal multiplexing gain is achievable. The general conclusion of this work is that very significant downlink throughput is achievable with simple and efficient channel state feedback, provided that the feedback link is properly designed.

Degrees of Freedom of Two-Hop MISO Broadcast Networks With Mixed CSIT

“…f21 (2) and y R2 (3). A linear combination of the two codewords in X [1] o is also available at R 2 as an interference term F…”

“…In general, nonnegligible CSIT estimation errors lead to a reduced DOF. For example, if the variance of the estimation error decays as O(P −α ) for some constant α ∈ [0, 1] and transmission power P , 2α DOF (i.e., only a fraction of the DOF when perfect CSIT is available) can be achieved by LBF [3]. If the channel varies rapidly, feedback delay may be comparable to channel coherence time.…”

“…Therefore, increasing α increases the quality of CSIT. Furthermore, since α > 1 implies that estimation error is negligible compared to noise, the instantaneous CSIT can be regarded as accurate from the DOF perspective [3]. Hence we only consider α ∈ [0, 1] throughout the paper.…”

Joint Scheduling and ARQ for MU-MIMO Downlink in the Presence of Inter-Cell Interference

“…4 pseudoinverse (e.g., see [14], [16], [18], [31], [32] and references therein) of the channel matrix restricted to the active users, i.e., to the columns {h k,c,c [t] : k ∈ S c [t]}. It follows that the transmit covariance matrix takes on the form with those users with positive powers, i.e.,…”

Ergodic Capacity of Multi-User MIMO Systems Using Pilot-Based Channel Estimation, Quantized Feedback and Outdated Feedback as Well as User Selection

“…Most of these contributions were based on the block fading channel and assumed delay-free feedback. The authors of [4] considered the effects of imperfect and outdated CSI, and presented the comparison of different quantization strategies associated with a delayed feedback link. However, most of the previous contributions ignored the impact of the number of active users M and assumed that exactly N t users are supported in each slot, which meant…”