Demand of minimal hardware requirement and low energy consumption for internet of things (IoT) has gained the importance of techniques enhancing the physical layer security. Looking at this, we propose a channel-based mapping diversity (CBMD) scheme for a source (S), destination (D) pair to increase the average bit error rate (ABER) at an eavesdropper (E). CBMD leads to an ABER of 0.5 at E when the channels between S - D and S - E are independent. In the case where S - D and S - E are correlated (due to the proximity of E at D), we derive an optimal strategy at E which leads to the best performance at E. We also derive an optimal strategy at S, assuming E uses its optimal strategy, thereby, considering the worst case scenario. A sub-optimal strategy is also proposed at S which does not require any statistical information about the link S - E and hence, has low implementation complexity. We analyze the variation of ABER at E with the signal to noise ratio (SNR) and the channel correlation coefficient. Our simulation results demonstrate that CBMD indeed leads to significant performance degradation at E even at moderate channel correlation for a properly chosen strategy. © 2017 IEEE.