Space-Time/Frequency Coding for MIMO-OFDM in Next Generation Broadband Wireless Systems
IEEE Wireless Communications
Representation theory for high-rate multiple-antenna code design
IEEE Transactions on Information Theory
IEEE Transactions on Information Theory
Optimal space-time constellations from groups
IEEE Transactions on Information Theory
Full-rate full-diversity space-frequency codes with optimum coding advantage
IEEE Transactions on Information Theory
Wiretap Channel With Side Information
IEEE Transactions on Information Theory
Anonymous Networking Amidst Eavesdroppers
IEEE Transactions on Information Theory
Protocol-aided channel equalization in wireless ATM
IEEE Journal on Selected Areas in Communications
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Recently, Li, Hwu and Ratazzi have proposed a physical-layer security design to guarantee low probability of interception (LPI) for MIMO systems without relying on upper-layer data encryption. The proposed scheme utilizes antenna array redundancy to deliberately randomize the transmitted signals to prevent eavesdropping. Motivated by their idea, in this paper we design a physical-layer transmission scheme to achieve LPI in cooperative systems. There are two major differences in cooperative systems: 1) each relay node may have only one antenna that can not provide antenna array redundancy for signal randomization; 2) there may exist timing errors due to the asynchronous nature of cooperative systems. Considering the two differences, we propose a distributed differentially encoded OFDM transmission scheme with deliberate signal randomization to prevent eavesdropping and exploit the available spatial and frequency diversities in asynchronous cooperative systems. We use diagonal unitary codes to perform the differential encoding in the frequency domain over subcarriers within each OFDM block, or we use general (not necessarily diagonal) unitary codes to perform the differential encoding in the frequency domain across several OFDM blocks. By some deliberate signal randomization, the eavesdropper can not detect the transmitted symbols, while the authorized receiver can perform differential decoding successfully without the knowledge of the channels or the timing errors.