在本文中，我們在可重構智慧反射板之秘密通訊系統中探索主動與被動式波束成型設計的問題，我們考慮在多個使用者的情況下，將使用者分為複數個合法使用者以及複數個竊聽者。在不希望竊聽者接受合法使用者資訊的情況下，將可重構智慧反射板加入通訊系統中，並在一定傳送能量限制下，結合基地台之波束成型設計使得任一合法使用者之保密率有所加強。由於原命題並不具有凹性，並且其中多個變數纏疊，直接解決此問題之複雜度極高且無法有效找到最佳解，基於以上原因，必須先將此問題轉換至具有凹性，並嘗試引入交換最佳化來切割變數，如次方能有效解決問題，除此之外，我們也比較上述方法與低複雜度的逼零線性波束成型設計之保密率表現。

In this work, we explore the joint design problem of both active and passive beamforming for reconfigurable intelligent surface (RIS) assisted secrecy communication. We consider the multi-user system with multiple legitimate receivers, referred to Bob. Besides, there are a number of eavesdroppers, referred as Eve, that intercept Bob’s information. In this scenario, RIS is deployed to enhance the secrecy rate of each Bob subject to the maximum power constraint. We jointly design passive beamforming and active beamforming to maximize the secrecy rate at each Bob. Since the optimization problem is non-concave with coupled optimization variables, direct solving it incurs very high complexity and thus we transform the original problem into concave one and then apply the alternating optimization (AO) to find the optimal solution. We evaluate the performance of the proposed algorithm numerically in comparison with the linear beamforming based on the principle of zero forcing (ZF).

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