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Abstract-The two major obstacles toward high-capacity indoor wireless networks are distortion due to the indoor channel and the limited bandwidth which necessitates a high spectral efficiency. A combined orthogonal frequency division multiplexing (OFDM) / spatial division multiple access (SDMA) approach can efficiently tackle both obstacles and paves the way for cheap, high-capacity wireless indoor networks [27], [26]. The channel distortion due to multipath propagation is efficiently mitigated with OFDM while the bandwidth efficiency can be increased with the use of SDMA. However, to keep the cost of an indoor wireless network comparable to its wired counterpart's cost, low-complexity SDMA processors with good performance are of special interest. In this paper, we propose a new multiuser SDMA detector which is designed for constant modulus signals. This constrained least squares (CLS) receiver, which deterministically exploits the constant modulus nature of the 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) receiver. Additionally, since the CLS detector relies on reliable channel knowledge at the receiver, we propose a strategy for estimating the multiple input multiple output (MIMO) channels. Simulations for a Hiperlan II-based [13] case-study 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 M-PSK, the CLS detector outperforms the MMSE detector. Furthermore, the estimation complexity for the CLS detector is substantially lower than that for the MMSE detector which additionally requires estimation of the noise power.Index Terms-Adaptive antennas, antenna diversity, channel estimation, orthogonal frequency division multiplexing (OFDM), space division multiple access (SDMA).

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Wireless LANs (WLAKs) still offer low capacity compared to wired LANs. The two major obstacles towards increasing the capacity are (a) distortion due to the indoor channel arid (b) limitations on the bandwidth-power budget. In this paper we propose an OFDM/SDBiA approach that conibines Orthogonal Frequency Division Multiplexing (OFDM), for multipath channel distortion mitigation, with SDhI.4, for bandwidth cfficiency. In addition, our approach concentrates all SDhIA functionality in the basestation, which reduces the overall system cost. We give algorithms for both the uplink and downlink, determine their performance and analyse thcir irnplernentation complexity. It is shown that OFDM/SDMA enables high-capacity WLANs at reasonable implementation complexity.