On the Degrees of freedom of the K-user MISO Interference Channel with imperfect delayed CSIT

This work investigates the degrees of freedom (DoF) of the K-user multiple-input single-output (MISO) interference channel (IC) with imperfect delayed channel state information at the transmitters (dCSIT). For this setting, new DoF inner bonds are provided, and benchmarked with cooperation-based outer bounds. The achievability result is based on a precoding scheme that aligns the interfering received signals through time, exploiting the concept of Retrospective Interference Alignment (RIA). The proposed approach outperforms all previous known schemes. Furthermore, we study the proposed scheme under channel estimation errors (CEE) on the reported dCSIT, and derive a closed-form expression for the achievable DoF with imperfect dCSIT.Comment: Draft version of the accepted manuscript at IEEE ICASSP 1

Optimal DoF Region of the Two-User MISO-BC with General Alternating CSIT

In the setting of the time-selective two-user multiple-input single-output (MISO) broadcast channel (BC), recent work by Tandon et al. considered the case where - in the presence of error-free delayed channel state information at the transmitter (delayed CSIT) - the current CSIT for the channel of user 1 and of user 2, alternate between the two extreme states of perfect current CSIT and of no current CSIT. Motivated by the problem of having limited-capacity feedback links which may not allow for perfect CSIT, as well as by the need to utilize any available partial CSIT, we here deviate from this `all-or-nothing' approach and proceed - again in the presence of error-free delayed CSIT - to consider the general setting where current CSIT now alternates between any two qualities. Specifically for $I_1$ and $I_2$ denoting the high-SNR asymptotic rates-of-decay of the mean-square error of the CSIT estimates for the channel of user~1 and of user~2 respectively, we consider the case where $I_1,I_2 \in\{\gamma,\alpha\}$ for any two positive current-CSIT quality exponents $\gamma,\alpha$. In a fast-fading setting where we consider communication over any number of coherence periods, and where each CSIT state $I_1I_2$ is present for a fraction $\lambda_{I_1I_2}$ of this total duration, we focus on the symmetric case of $\lambda_{\alpha\gamma}=\lambda_{\gamma\alpha}$, and derive the optimal degrees-of-freedom (DoF) region. The result, which is supported by novel communication protocols, naturally incorporates the aforementioned `Perfect current' vs. `No current' setting by limiting $I_1,I_2\in\{0,1\}$. Finally, motivated by recent interest in frequency correlated channels with unmatched CSIT, we also analyze the setting where there is no delayed CSIT