In this paper, we propose a high diversity achievement algorithm for dual carrier modulation (DCM) in multiband-orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) systems. The proposed algorithm uses additional precoding to the conventional DCM symbols with 25 subcarrier separation. The proposed algorithm exploits not only frequency diversity between 50 subcarrier separation by using DCM, but also frequency diversity between 25 subcarrier separation by using additional precoding, resulting in better performance than the conventional DCM. We also propose a method for detecting the proposed algorithm by sharing the modified dual carrier modulation (MDCM) detection block which is basically included MB-OFDM UWB systems. The proposed detection method prevents the increase in hardware complexity caused by additional precoding. Simulation results show that the performance of the proposed algorithm was improved by 3 dB in CM1 at an uncoded BER of 105, compared to DCM.