Next-generation networks demand robust security solutions at all layers. While Physical Layer Security (PLS) has emerged as a promising approach, the conventional PLS schemes are fundamentally limited, particularly when the Eve’s channel is of high quality. To solve this problem, we proposed a novel precoded STBC method. In this method, Alice and Bob use their Received Signal Strength Indicator (RSSI) to create a shared secret key, which they use to select a specific STBC encoding pattern from a set of unique, orthogonal STBC encoding patterns. This mechanism creates severe self-interference for Eve, significantly weakening her ability to decode the packet. This paper provides a quantitative performance analysis of Secrecy Rate (SR) with the different number of STBC encoding patterns and Bit Error Rate (BER) for the proposed method. As a result, analysis and simulation show that the proposed method achieves a significantly higher secrecy rate than the conventional STBC scheme and Beamforming while maintaining the BER performance of the conventional STBC scheme.