The DS/CDMA system using transmission diversity for indoor wireless communications

In multipath fading channels, the direct-sequence spread spectrum (DS/SS) technique is often employed because of the capability to resolve signals from different paths and realize path diversity at the receiver. This advantage of DS/SS, however, is only when the time difference of propagation delay between paths is greater than a chip duration. In indoor communications, the delay spread is often very small and the above condition on the delay and chip duration is no longer satisfied, and this performance improvement by the path diversity with conventional DS/SS systems cannot be expected. In this paper we propose a new diversity technique for indoor wireless communication systems where delay spread is smaller than a chip duration. In this system, the transmitter sends signals at the same time from multiple antennas with intentional time delays, which allow a receiver to distinguish and combine the signals from different antennas.