It is shown that the use of chaos shift keying (CSK) with a transmit diversity technique such as beamforming and space-time coding can provide a secure communication link with improvement in the system error performance. Spreading sequences that are used to scramble data in spread spectrum (SS) systems can be generated using a single mathematical relationship of a chaotic generator. These chaotic sequences are very difficult to predict over long-term chaotic pattern unless the exact initial condition of the chaotic generator is known, providing security. On the other hand, beamforming and orthogonal space-time block coding (OSTBC) transmit diversity techniques are known to provide optimal transmitting structures for communication systems, especially if combined. Based on the signal angle-of-arrival (AoA) estimates, the channel correlation matrix can be constructed, and it is shown that signal transmission of OSTBC codes in the eigen-modes of this matrix gives an effective array weighting gain which improves system error performance without sacrificing any diversity and coding gain. A performance study of CSK with beamforming and space-time encoded is carried out in this paper.
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