Information secrecy from multiple eavesdroppers in orthogonal relay channels

The secrecy capacity of relay channels with orthogonal components is studied in the presence of additional passive eavesdropper nodes. The relay and destination receive signals from the source on two orthogonal channels such that the destination also receives transmissions from the relay on its channel. The eavesdropper(s) can overhear either one or both of the orthogonal channels. For a single eavesdropper node, the secrecy capacity is shown to be achieved by a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">partial decode-and-forward</i> (PDF) scheme when the eavesdropper can overhear only one of the two orthogonal channels. For the case of two eavesdropper nodes, secrecy capacity is shown to be achieved by PDF for a sub-class of channels.