A time-frequency domain approach to synchronization, channel estimation, and detection for DS-CDMA impulse-radio systems

This paper deals with synchronization, channel estimation, and detection in ultrawideband (UWB) biphase impulse-modulated systems. We address both the single-user scenario, and the multiuser scenario assuming a direct-sequence code-division multiple-access (DS-CDMA) scheme. The users´ binary-codeword elements modulate short-duration pulses. Codewords span a transmission frame. Frames are separated by a guard time to cope with the channel time dispersion. The detection approach is single-user-based and it operates in the frequency domain (FD). The algorithm first acquires frame synchronization with the desired user. It runs a discrete Fourier transform (DFT), and it performs FD channel estimation for the desired user via a recursive least-squares (RLS) algorithm. Finally, detection is directly accomplished in the FD. Frame synchronization is achieved in the time domain with a two-step procedure that first acquires coarse timing, then finely estimates where the desired user´s signal energy is located. In the presence of multiple-access interference (MAI), the algorithm is appropriately modified to include the capability of canceling the interference through the exploitation of its FD correlation. Simulation results show that the proposed approach exhibits fast convergence, and high performance with and without synchronous/asynchronous MAI.