Alice and Bob want to share a secret key and to communicate an independent message, both of which they desire to be kept secret from an eavesdropper Eve. We study this problem of secret communication and secret key generation when two resources are a
vailable -- correlated sources at Alice, Bob, and Eve, and a noisy broadcast channel from Alice to Bob and Eve which is independent of the sources. We are interested in characterizing the fundamental trade-off between the rates of the secret message and secret key. We present an achievable solution and prove its optimality for the parallel channels and sources case when each sub-channel and source component satisfies a degradation order (either in favor of the legitimate receiver or the eavesdropper). This includes the case of jointly Gaussian sources and an additive Gaussian channel, for which the secrecy region is evaluated.
The utility of limited feedback for coding over an individual sequence of DMCs is investigated. This study complements recent results showing how limited or noisy feedback can boost the reliability of communication. A strategy with fixed input distri
bution $P$ is given that asymptotically achieves rates arbitrarily close to the mutual information induced by $P$ and the state-averaged channel. When the capacity achieving input distribution is the same over all channel states, this achieves rates at least as large as the capacity of the state averaged channel, sometimes called the empirical capacity.
A fundamental problem in dynamic frequency reuse is that the cognitive radio is ignorant of the amount of interference it inflicts on the primary license holder. A model for such a situation is proposed and analyzed. The primary sends packets across
an erasure channel and employs simple ACK/NAK feedback (ARQs) to retransmit erased packets. Furthermore, its erasure probabilities are influenced by the cognitive radios activity. While the cognitive radio does not know these interference characteristics, it can eavesdrop on the primarys ARQs. The model leads to strategies in which the cognitive radio adaptively adjusts its input based on the primarys ARQs thereby guaranteeing the primary exceeds a target packet rate. A relatively simple strategy whereby the cognitive radio transmits only when the primarys empirical packet rate exceeds a threshold is shown to have interesting universal properties in the sense that for unknown time-varying interference characteristics, the primary is guaranteed to meet its target rate. Furthermore, a more intricate version of this strategy is shown to be capacity-achieving for the cognitive radio when the interference characteristics are time-invariant.
