Showing papers by "Nuno Souto published in 2005"

Iterative turbo multipath interference cancellation for WCDMA systems with non-uniform modulations

Abstract: In this paper we consider the use of non-uniform QAM constellations (quadrature amplitude modulation) for the transmission of multicast and broadcast services in the downlink connection of a WCDMA (wideband code division multiplexing) system. The objective is to increase the efficiency of the transmission by splitting the information in classes with different importance and mapping the bit streams of these classes to more or less protected positions of the modulation symbols. With this strategy, the most important information streams can be received by all users while the less relevant information will only be extracted by users with good propagation conditions. It is shown that the multipath interference introduced by the channel induces a severe performance loss for these modulations. A low complexity iterative turbo multipath interference canceller (MPIC) that uses feedback information from the turbo-decoder is proposed for suppressing this interference. Computer simulation results are presented, showing that a considerable performance gain can be obtained with the use of the iterative MPIC.

Iterative MMSE Detection for MIMO/BLAST DS-CDMA Systems in Frequency Selective Fading Channels – Achieving High Performance in Fully Loaded Systems

Abstract: A MMSE (Minimum Mean Square Error) DS-CDMA (Direct Sequence-Code Division Multiple Access) receiver coupled with a low-complexity iterative interference suppression algorithm was devised for a MIMO/BLAST (Multiple Input, Multiple Output / Bell Laboratories Layered Space Time) system in order to improve system performance, considering frequency selective fading channels. The scheme is compared against the simple MMSE receiver, for both QPSK and 16QAM modulations, under SISO (Single Input, Single Output) and MIMO systems, the latter with 2Tx by 2Rx and 4Tx by 4Rx (MIMO order 2 and 4 respectively) antennas. To assess its performance in an existing system, the uncoded UMTS HSDPA (High Speed Downlink Packet Access) standard was considered.