| Summary: | 碩士 === 國立清華大學 === 通訊工程研究所 === 100 === This thesis examines the use of vector quantization to generate secret keys over correlated wireless fading channels. In channel-based secret key generation schemes, common randomness of the channel between two users are utilized to generate secret keys at the two terminals. These key generation schemes should be designed to ensure low key disagreement probability (KDP) among the two users and also high key entropy so that the generated keys cannot be easily inferred by the eavesdropper. Conventional channel-based secret key generation schemes utilize scalar quantization over individual channel observations, which is simple to implement but yields high KDP at low SNR and low key entropy when the channel is correlated. In this thesis, two vector quantization schemes are proposed to exploit the temporal correlation of channels: the minimum quadratic distortion (MQD) and the minimum key disagreement probability (MKDP) secret key generation schemes. In these schemes, the Lloyd-Max algorithm is used with the quadratic distortion and the KDP as their respective distortion measures to compute the quantizers. The MKDP scheme achieves low KDP but requires high complexity whereas the MQD yields low complexity but slightly higher KDP. The unitary transformation is performed on the channel vectors before quantization to avoid key disagreement caused by channel vectors lying on the boundary of quantization cells. Furthermore, to ensure high entropy of the secret keys, an entropy constraint is further incorporated into the objective of the quantization design. Computer simulations are provided to demonstrate the effectiveness of the proposed vector quantization schemes.
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