Covert communication, also known as low probability of detection (LPD)communication, prevents the adversary from knowing that a communication istaking place. Recent work has demonstrated that, in a three-party scenario witha transmitter (Alice), intended recipient (Bob), and adversary (Warden Willie),the maximum number of bits that can be transmitted reliably from Alice to Bobwithout detection by Willie, when additive white Gaussian noise (AWGN) channelsexist between all parties, is on the order of the square root of the number ofchannel uses. In this paper, we begin consideration of network scenarios bystudying the case where there are additional "friendly" nodes present in theenvironment that can produce artificial noise to aid in hiding thecommunication. We establish achievability results by considering constructionswhere the system node closest to the warden produces artificial noise anddemonstrate a significant improvement in the throughput achieved covertly,without requiring close coordination between Alice and the noise-generatingnode. Conversely, under mild restrictions on the communication strategy, wedemonstrate no higher covert throughput is possible. Extensions to theconsideration of the achievable covert throughput when multiple wardensrandomly located in the environment collaborate to attempt detection of thetransmitter are also considered.
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