We propose an extended one-shot decorrelating detector (EOS-DD) which may be viewed as a generalized double window multiuser detector (DW-MD) for asynchronous direct-sequence code-division multiple-access (DS/CDMA) systems in frequency selective fading environments. The EOS-DD extends a processing window and the received signal over an extended window is utilized for decorrelating. The effects of the window size on BER performance are investigated by numerical analysis. Analysis and simulation show that the EOS-DD is superior to the one-shot decorrelating detector (OS-DD) and finite memory length truncated decorrelating detector (FIR-DD) in terms of noise enhancement and near-far resistance. It is also shown that the EOS-DD with window size 4 can provide significantly improved performance compared to the EOS-DD with window size 2.

As a new type of a linear decorrelating receiver, the Pseudo-Decorrelator was presented for asynchronous code division multiple access systems in [6]. In this paper, the concept of the Pseudo-Decorrelator is extended to derive a suboptimal receiver for WCDMA uplink systems in a Rayleigh fading environment. Starting with the analysis of the multiple access components of the decision statistics, a non-square cross-correlation matrix for each bit is obtained. This cross-correlation matrix is then inverted and the inverted matrix is applied to the decision statistics obtained from a conventional receiver. Simulation results are presented for K-user systems over a Rayleigh fading channel. The effects of the synchronization errors, such as time delays and carrier phase errors, are also examined through simulations in this paper.

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.

This paper proposes a new multiuser detector, quasi-decorrelating detector (QDD), for a synchronous CDMA system. The QDD has the same complexity as that of decorrelator detector (DD) although it uses feedback loops, the number of which is adjustable to balance the near-far resistance and noise enhancement. The results show that the QDD outperforms the DD under various operational conditions. The impact of different spreading codes on the performance of the QDD is studied. It is shown that the Gold code is the best spreading code suitable for the QDD.