In this paper, we discuss power spectrum overlapping of wideband/narrowband signals and wideband/wideband signals for increasing transmission efficiency. Here, in order to eliminate cross signal interference among those signals, we propose a generalized zero-forcing type decorrelating detection. Our numerical results show that, with the decorrelating detector, the overlapped wideband/wideband signal transmission can much improve the transmission efficiency. This implies that, for a given frequency bandwidth, in order to increase the information transmission rate, we should employ two different kinds of direct sequence spread spectrum-based signals with each power spectrum appropriately overlapped, not taking a single carrier-based approach nor an orthogonal multi-carrier approach.