Advances in MIMO Techniques for Mobile Communications—A Survey <s> SMMSE SIC MUD <s> Wireless networks are under constant pressure to provide ever-higher data rates to increasing numbers of users with greater reliability. This book is an accessible introduction to every fundamental aspect of space-time wireless communications. Space-time processing technology is a powerful tool for improving system performance that already features in the UMTS and CDMA2000 mobile standards. The ideal volume for graduate students and professionals, it features homework problems and other supporting material on a companion website. <s> BIB001 </s> Advances in MIMO Techniques for Mobile Communications—A Survey <s> SMMSE SIC MUD <s> In this paper we study space-time coding schemes for a novel MIMO transceiver which performs adaptive signal combining in radio-frequency (RF). The limitations of the RF circuitry make necessary to develop specific designs for this architecture. For instance, the space and time encoders must operate separately (the former works in the RF domain and the latter works in baseband), and at different time scales: the spatial encoder or RF beamformer must remain fixed during the transmission of a probably large number of symbols, whereas the time-encoder can work at the symbol rate. We show in the paper that although the multiplexing gain of the system is limited to one, we are still able to achieve the full spatial diversity of the MIMO channel as well as to increase the received signal-to-noise ratio through array gain. Specifically, when perfect channel state information (CSI) is available only at the receiver we propose to use a scheme referred to as orthogonal beam division multiplexing (OBDM). With this scheme the symbols are time-precoded with a unitary discrete Fourier transform (DFT) matrix, then they are successively transmitted through orthogonal directions and, finally, we use a receiver comprising maximal ratio combining (MRC) followed by a minimum mean-square error (MMSE) decoder. The performance of the proposed techniques in terms of outage capacity and bit error rate is illustrated by means of several simulations examples. <s> BIB002
A MUD scheme for MIMO-OFDM systems referred to as successive MMSE receive filtering with SIC (SMMSE SIC) is presented in BIB002 . The MMSE SIC MUD suffers from performance loss in scenarios with multiple closely spaced antennas located at the same UE. The proposed scheme tackles this problem by successively calculating the rows of the receive matrix at the BS for each of the UE transmit antennas, followed by SIC thus transforming the uplink MU-MIMO channel into a set of parallel SU-MIMO channels.  where is the MIMO channel matrix between user i and the BS for 1, , i K " . The R T M M u receive filter matrix at the BS is given by where The SMMSE SIC detection in BIB002 has been considered for STBC based MIMO transmission i.e. the Alamouti scheme and also for dominant eigenmode transmission (DET). The open-loop Alamouti scheme provides MIMO diversity without the need for any CSI at the UEs. On the other hand, DET requires full CSI at both the transmitter and the receiver, which means that the UE transmit matrices need to be computed at the BS and then fed forward to the UEs. However, beside the full diversity gain equal to that of STBC, DET also provides the maximum array gain by transmitting over the strongest eigenmode of the MIMO channel BIB001 BIB002  . i D Figure 34 shows the BER performance of SMMSE SIC Alamouti in comparison with V-BLAST. The impact of channel estimation errors is also shown. The simulated MIMO-OFDM system consists of 6 BS antennas and 3 UEs equipped with 2 antennas each, denoted as 6 u {2, 2, 2} MU-MIMO configuration. The MIMO channel H is assumed to be frequency selective with the power delay profile defined by IEEE 802.11n -D for non-line-of-sight (NLOS) conditions. The channel model for each user's channel takes into account the antenna correlation at the BS. However, the antennas at each UE are considered to have low spatial correlation assuming large angular spread at the user. A total of 64 OFDM subcarriers are used with subcarrier spacing of 150 kHz. The user data is encoded using a 1/2 rate convolutional code. 4-QAM modulation is used for each subcarrier of SMMSE SIC Alamouti system while BPSK is used for V-BLAST so that the data rate remains the same for both systems. Figure 35 shows the performance gain of SMMSE SIC DET over SMMSE SIC Alamouti. SMMSE SIC DET shows substantial gains in the high SNR region and these become more significant as the no. of users in the system increases.