Journal of Signal Processing Systems https://doi.org/10.1007/s11265-018-1335-1 Two Low Complexity MRC and EGC Based Receivers for SC-FDE Modulations with Massive MIMO Schemes David Borges 1 · Paulo Montezuma 1,2,3 · Afonso Ferreira 1 · Rui Dinis 1,2 Received: 14 April 2017 / Revised: 10 January 2018 / Accepted: 24 January 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Massive multiple-input and multiple-output (MIMO) schemes involving several tens or even hundreds of antenna elements are pointed as one of the key technologies for 5G systems. However the huge capacity gains attainable by these schemes, are only possible with receivers able to cope with the frequency selective fading that may affect the signals. These systems can be combined with single-carrier with frequency domain equalization (SC-FDE) schemes to improve the power efficiency in uplink due to the low envelope fluctuations. However, when more antennas are involved in the communication link, channel matrix size grows and the complexity involved in equalization process can be an obstacle to power consumption and low latency. In this paper we will focus on the equalization applied in massive MIMO schemes, more specifically in two new low complexity receivers based on an iterative block decision feedback equalizer (IB-DFE) that avoid matrix inversion operation by replacing in the equalizer the feedforward part by an equal gain combiner (EGC) or a maximum ratio combiner (MRC) module. Keywords Massive MIMO · Low latency · Low complexity receivers · SC-FDE 1 Introduction Massive multiple-input and multiple-output (MIMO) schemes, involving several tens or even hundreds of antenna elements are expected to one of the key technologies for 5G systems [2]. The integration of millimeter-wave (mmWave) and MIMO can achieve increments of several orders of magnitude in rates due to larger bandwidth and greater spectral efficiency [1, 2]. This makes mmWave MIMO a promising technique for future 5G wireless communication systems. The smaller wavelength associated with higher frequencies of mmWave enables to pack a large antenna array in a small physical dimension. This large number of antennas can provide sufficient antenna gain to compensate the severe attenuation of mmWave signals. Additionally,  Paulo Montezuma pmc@uninova.pt 1 DEE, FCT Universidade Nova de Lisboa, Almada, Portugal 2 IT, Instituto de Telecomunicac¸˜ oes, Av. Rovisco Pais, Lisboa, Portugal 3 Uninova, Instituto de Desenvolvimento de Novas Tecnologias, Quinta da Torre, Caparica, Almada, Portugal the large antenna array can also support the transmission of multiple data streams to improve the spectral efficiency through the use of precoding [3, 4]. Despite the huge capac- ity gains achieved by these techniques, the implementation complexity precludes the use of conventional MIMO detec- tion schemes [5]. For this reason, massive MIMO schemes should avoid the usual matrix inversion inherent to MIMO receivers, which makes receivers based on the maximum ratio combiner (MRC) particularly interesting. On the other hand, higher data rates and large bandwidth (BW), usually are associated to an higher sensitivity to channel effects. As consequence, multi-path effects and intersymbol interference (ISI) may increase which which may involve the use of more complex equalizers. The complexity of the equalization process is increased even more in massive MIMO systems due to the addition of extra transmit and receive antennas [6]. Block transmission techniques have been used inten- sively due to their performance in high data rate trans- mission over severely time-dispersive channel. The two alternatives are orthogonal frequency division multiplexing (OFDM) and single carrier with frequency domain equal- ization (SC-FDE) modulation. In this paper we will use the SC-FDE technique which is more suitable for uplink