Constrained least squares detector for OFDM/SDMA-based wireless networks

The two major obstacles towards high-capacity indoor wireless networks are distortion due to the indoor channel and the limited bandwidth. A combined OFDM/SDMA approach efficiently tackles both obstacles and paves the way for low cost, high-capacity wireless indoor networks (see Vandenameele, P. et al., VTC Spring, p.1712-16, 1999; IEEE J. Selected Areas in Commun., vol.18, no.11, p.2312-21, 2000). Channel distortion due to multipath propagation is efficiently mitigated by orthogonal frequency division multiplexing (OFDM) while the bandwidth efficiency is increased by the use of spatial diversity multiple access (SDMA). To keep the WLAN cost low, simple SDMA processors with good performance are necessary. Hence, we propose a new, low-complexity multiuser SDMA detector, which is designed for constant modulus signals. This linear constrained least squares (CLS) receiver, which explicitly exploits the constant modulus nature of subcarrier modulation to achieve better separation, is compared in terms of performance and complexity with the zero forcing (ZF) and the minimum mean square error (MMSE) receivers. Simulations show that the CLS detector significantly outperforms the ZF detector and comes close to the performance of the MMSE detector for QPSK. For higher order MPSK, the CLS detector outperforms the MMSE detector substantially