A Subspace Method for Signature Waveform
Hui Liu, Guanghan Xu · 1996
Synchronous code-division multiple-access (CDMA) techniques possess intrinsic protection against co-channel in- terference due to orthogonal codes employed and thus, offers higher capacity than existing frequency-division multiple-access (FDMA) or time-division multiple-access (TDMA) systems. In the presence of multipath, however, each signal is subject to frequency-selective fading and the orthogonality condition does not necessarily hold leading to increased cross correlation. In these scenarios, multiuser detection need to be performed to suppress interference and recover the message symbols. To imple- ment such a technique, explicit knowledge of the (nonorthogonal) signature waveforms of all users is required. Here, we propose a blind estimation scheme that provides closed-form estimates of the signature waveforms by exploiting the structure information of the data output. In particular, we show that the subspace of the data matrix contains sufficient information for unique determination of the signature waveforms. Based on this obser- vation, a multiple signal classification (MUSIC)-like (l) algorithm is derived. Performance analysis of the new approach is also presented.