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The K-user cyclic Z-interference channel models a situation in which the kth transmitter causes interference only to the (k-1)th receiver in a cyclic manner, e.g., the first transmitter causes interference only to the Kth receiver. The impact of noiseless feedback on the capacity of this channel is studied by focusing on the Gaussian cyclic Z-interference channel. To this end, the symmetric feedback capacity of the linear shift deterministic cyclic Z-interference channel is completely characterized for all interference regimes. Using insights from the linear deterministic channel model, the symmetric feedback capacity of the Gaussian cyclic Z-interference channel is characterized up to within a constant number of bits. As a byproduct of the constant gap result, the symmetric generalized degrees of freedom with feedback for the Gaussian cyclic Z-interference channel are also characterized. These results highlight that the symmetric feedback capacities for both linear and Gaussian channel models are in general functions of K, the number of users. Furthermore, the capacity gain obtained due to feedback decreases as K increases. [ABSTRACT FROM PUBLISHER]

The symmetric K-user interference channel with fully connected topology is considered, in which 1) each receiver suffers interference from all other (K-1) transmitters, and 2) each transmitter has causal and noiseless feedback from its respective receiver. The number of generalized degrees of freedom ( \ssr GDoF) is characterized in terms of \alpha , where the interference-to-noise ratio ( \ssr INR) is given by \ssr INR= \ssr SNR^\alpha . It is shown that the per-user \ssr GDoF of this network is the same as that of the two-user interference channel with feedback, except for \alpha =1, for which existence of feedback does not help in terms of \ssr GDoF. The coding scheme proposed for this network, termed cooperative interference alignment, is based on two key ingredients, namely, interference alignment and interference decoding. Moreover, an approximate characterization is provided for the symmetric feedback capacity of the network, when the \ssr SNR and \ssr INR are far apart from each other. [ABSTRACT FROM PUBLISHER]

The two-user multiple-input multiple-output (MIMO) interference channel (IC) with arbitrary numbers of antennas at each terminal is considered and the degrees of freedom (DoF) region is characterized in the presence of noiseless channel output feedback from each receiver to its respective transmitter and availability of delayed channel state information at the transmitters (CSIT). It is shown that having output feedback and delayed CSIT can strictly enlarge the DoF region of the MIMO IC when compared to the case in which only delayed CSIT is present. The proposed coding schemes that achieve the corresponding DoF region with feedback and delayed CSIT utilize both resources, i.e., feedback and delayed CSIT in a nontrivial manner. It is also shown that the DoF region with local feedback and delayed CSIT is equal to the DoF region with global feedback and delayed CSIT, i.e., local feedback and delayed CSIT is equivalent to global feedback and delayed CSIT from the perspective of the DoF region. The converse is proved for a stronger setting in which the channels to the two receivers need not be statistically equivalent. [ABSTRACT FROM AUTHOR]