IEEE Information Theory Workshop (ITW)
K-user degraded broadcast channel with secrecy outside a bounded range
Shaofeng Zou, Yingbin Liang, Lifeng Lai, H. Vincent Poor, Shlomo Shitz Shamai
Abstract
A K-receiver degraded broadcast channel with secrecy outside a bounded range is studied, in which a transmitter sends K messages respectively to K receivers, and the channel quality gradually degrades from receiver K to receiver 1. Each receiver k is required to decode messages W1, …, Wk, for 1 ≤ k ≤ K. Furthermore, each message Wkshould be kept secure from receivers with two-level worse channel quality, i.e., receivers 1, …, k − 2. The secrecy capacity region is fully characterized. The achievable scheme designates one superposition layer to each message with random binning employed for each layer for protecting all upper-layer messages from lower-layer receivers. Furthermore, the scheme allows adjacent layers to share rates so that part of the rate of each message can potentially be shared with its immediate upper-layer message to enlarge the rate region. More importantly, an induction approach is developed to perform Fourier-Motzkin elimination over 2K variables among Θ(K2) bounds to obtain a close-form achievable rate region. A converse proof is developed that matches the achievable rate region, which involves recursive construction of the rate bounds.