In heterogeneous dense networks where spectrum is shared, users privacy remains one of the major challenges. When the receivers are not only interested in their own signals but also in eavesdropping other users' signals, the cross talk becomes information leakage.We propose a novel and efficient secrecy rate enhancing relay strategy EFFIN for information leakage neutralization. The relay matrix is chosen such that the effective leakage channel (spectral and spatial) is zero. Thus, it ensures secrecy regardless of receive processing employed at eavesdroppers and does not rely on wiretaps codes to ensure secrecy, unlike other physical layer security techniques such as artificial noise. EFFIN achieves a higher sum secrecy rate over several state-of-the-art baseline methods.

本論文は、多端子通信路に対するマルチユーザ符号化および復号の研究成果をまとめたものである。多重接続加算通信路による情報伝送において、複数ユーザの稼働状態を識別するための誤り訂正可能なシグネチャ符号の構成を論ず,全伝送率の高いシグネチャ符号の一般的な構成法を解明する.双方向中継通信路では、2ユーザターボ符号に対する復号の演算量を低減させる復号法を提案する。加法性白色ガウス雑音環境下では復号性能を劣化することなく、レイリーフェージング環境下では僅かな劣化にとどめながら、復号の演算量を約半分程度に低減することができる. / Coding and decoding for multiuser communication systems are investigated. For MAAC, we propose a coding scheme of (k + 1)-ary error-correcting signature codes. We give binary and non-binary signature codes. They are the best error-correcting signature codes for MAAC, in the sense that they have highest sum rates known. For TWRC, we propose a low-complexity two-user turbo decoding scheme when turbo codes are applied in two users. The approximate decoding algorithm preserves low decoding complexity over the Gaussian TWRC, without much performance degradation. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University

In heterogeneous dense networks where spectrum is shared, users' privacy remains one of the major challenges. On a multi-antenna relay-assisted multi-carrier interference channel, each user shares the spectral and spatial resources with all other users. When the receivers are not only interested in their own signals but also in eavesdropping other users' signals, the cross talk on the spectral and spatial channels becomes information leakage. In this paper, we propose a novel secrecy rate enhancing relay strategy that utilizes both spectral and spatial resources, termed as information leakage neutralization. To this end, the relay matrix is chosen such that the effective channel from the transmitter to the colluding eavesdropper is equal to the negative of the effective channel over the relay to the colluding eavesdropper and thus the information leakage to zero. Interestingly, the optimal relay matrix in general is not block-diagonal which encourages users' encoding over the frequency channels. We proposed two information leakage neutralization strategies, namely efficient information leakage neutralization (EFFIN) and local-optimized information leakage neutralization (LOPTIN). EFFIN provides a simple and efficient design of relay processing matrix and precoding matrices at the transmitters in the scenario of limited power and computational resources. LOPTIN, despite its higher complexity, provides a better sum secrecy rate performance by optimizing the relay processing matrix and the precoding matrices jointly. The proposed methods are shown to improve the sum secrecy rates over several state-of-the-art baseline methods.