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

Retroactive Anti-Jamming for MISO Broadcast Channels

Jamming attacks can significantly impact the performance of wireless communication systems. In addition to reducing the capacity, such attacks may lead to insurmountable overhead in terms of re-transmissions and increased power consumption. In this paper, we consider the multiple-input single-output (MISO) broadcast channel (BC) in the presence of a jamming attack in which a subset of the receivers can be jammed at any given time. Further, countermeasures for mitigating the effects of such jamming attacks are presented. The effectiveness of these anti-jamming countermeasures is quantified in terms of the degrees-of-freedom (DoF) of the MISO BC under various assumptions regarding the availability of the channel state information (CSIT) and the jammer state information at the transmitter (JSIT). The main contribution of this paper is the characterization of the DoF region of the two user MISO BC under various assumptions on the availability of CSIT and JSIT. Partial extensions to the multi-user broadcast channels are also presented.Comment: submitted to IEEE Transactions on Information Theor