Inter-user interference (IUI) suppression is a prime matter for mobile communication systems. Channel state information (CSI), meanwhile, is severely affected by the receiver additive noise effect. Sample matrix inversion (SMI) based minimum mean square error (MMSE) adaptive array is a powerful means to suppress noise enhancement with the aid of data symbols. However, its effectiveness is limited under an insufficient number of symbols available. Based on the multi-carrier transmission system, this paper proposes an adaptive subcarrier grouping to expand the number of received symbols for a covariance matrix calculation. The grouping size is adaptively adjusted by observing the dispersion of adjacent subcarriers. Simulative results reveal the effectiveness of the proposed adaptive algorithm; superior bit error rate (BER) performance can be attained under various Rician K factors. INDEX TERMS Adaptive array, Interference suppression, Channel estimation, Sample matrix inversion, Subcarrier grouping, Rician fading I. INTRODUCTION M OBILE data traffic is continuously increasing due to widespread mobile terminals such as smartphones or tablets. Besides, machine to machine (M2M) communications will induce further explosion of wireless connectivity. Global Internet Protocol (IP) traffic is expected to grow more than triple from 2017 to 2022 , and 14.6 billion M2M devices, which accounts for half of all devices, will be connected to the network in 2022 [1]. The fifth-generation (5G) [2] mobile communications system and beyond are promising technologies to support these enormous traffic and connections increase. They require the realization of huge capacity, outstanding throughput, and high dense connectivity. Key solutions for these demands are massive multiple-input multiple-output (MIMO) system and usage of millimeterwave (mmWave) [3], [4]. The former can be utilized in various means such as beamforming [5], suppressing unknown interference from other cells and inter-user interference (IUI) [6], and mobility resistance [7]. Its high directivity also heightens the connection density. Although mmWave contributes to enhancing throughput

This paper expands an analytical formulation of maximal ratio transmission (MRT) precoded massive multiple-input multiple-output (MIMO) systems. Evaluating performance on massive MIMO systems where both base station (BS) and user terminals (UTs) have array antennas could impose impractical computation complexity. The existing work derived the power distribution of inter-user interference (IUI) but that of the desired signal was treated as fixed. This paper enhances its modeling accuracy by deriving the latest. The consistency of the proposed model is confirmed by comparing it to the simulation results.

This letter adopts higher-order modulation scheme than 16QAM to our previously proposed semi-blind uplink interference suppression scheme for multicell multiuser massive MIMO systems. Our semi-blind approach is attained by the decision feedback channel estimation (DFCE) and the sample matrix inversion (SMI) spatial adaptive filtering. However, its efficiency depended on inter-cell interference (ICI), in particular for higher-order QAM. We propose to employ cell partitioning-based M-ary QAM to avoid ICI at the initial condition and verify overall spectral efficiency improvement.

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