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Massive MIMO systems, where base stations are equipped with hundreds of antennas, are an attractive way to handle the rapid growth of data traffic. As the number of users increases, the initial access and handover in contemporary networks will be flooded by user collisions. In this work, we propose a random access procedure that resolves collisions and also performs timing, channel, and power estimation...
Hardware calibration is a necessary procedure to establish the reciprocity of the uplink (UL) and downlink channels (DL) in a time division duplex (TDD) mode of operation. In practice, any calibration scheme is prone to errors. Such errors result in a residual mismatch between UL and DL channels, which, in turn, can significantly affect the quality of DL transmission. In this paper, we study the effects...
This paper investigates the performance of bidirectional dynamic networks (BDN) with massive multiple input multiple output (MIMO) systems. In BDN, dynamic allocation of the number of uplink and downlink remote radio heads (RRHs) is proposed, which offers a flexible solution to balance the data traffic asymmetry without requiring the time synchronization. Intuitively, the interference between the...
The idea of combining spatial modulation (SM) with massive multiple-input multiple-output (MIMO) system, i.e. massive SM-MIMO, has recently attracted plenty of academic interest, as it could simultaneously harness the advantages of SM and massive MIMO. However, the spectral efficiency (SE) analysis for massive SM-MIMO is still lack of exploring. To this end, a novel SE expression is derived in this...
This paper considers training-based transmissions in massive multi-input multi-output (MIMO) systems with one-bit analog-to-digital converters (ADCs). We assume that each coherent transmission block consists of a pilot training stage and a data transmission stage. The base station (BS) first employs the linear minimum mean-square-error (LMMSE) method to estimate the channel and then uses the maximum-ratio...
In this paper, we investigate the user pairing scheme in virtual multiple-input multiple-output (V- MIMO) systems, which can significantly improve system performance and spectral efficiency (SE) using multiuser diversity. Considering the development of green communication, we want to find the upper bound of energy efficiency (EE) under the constraint of SE. Firstly, the optimal transmit power allocation...
This paper presents the performance analysis of the self-interference cancellation (SIC) methods in full-duplex large-scale multiple-input multiple-output systems. To mitigate self-interference (SI), we assume that the full duplex-base station (BS) uses SI-subtraction or spatial suppression. Analytical and numerical results confirm that the SI-subtraction outperforms the spatial suppression for SIC...
In time-division duplex (TDD) massive multiple-input multiple-output (MIMO) systems, the spatial multiplexing gain cannot be fully achieved since available pilot resources in each channel coherence time interval are limited. In this paper, we propose OpSAC, an Opportunistic user Scheduling algorithm that uses Aged Channel state information (CSI) to increase the spatial multiplexing gain without incurring...
We propose a novel algorithm to design user load- achieving pilot sequences that mitigate pilot contamination in multi-cell massive multiple-input multiple-output (MIMO) networks. To this end, we first derive expressions for the user load and the load region of the network considering both small- scale and large-scale propagation effects. We then develop the pilot sequence algorithm for multi- cell...
In this paper, we propose a new frequency synchronization scheme for multiuser orthogonal frequency division multiplexing (OFDM) uplink with a large-scale uniform linear array (ULA) at base station (BS). Considering that the incident signal at BS from each user can be restricted within a narrow angular spread, the proposed scheme performs carrier frequency offset (CFO) estimation for each user individually...
The maximal ratio combining (MRC) receiver has excellent performance in the uplink of massive multiple-input-multiple-output (MIMO) systems under favorable propagation, but the performance degrades very much in a harsh channel because of interference. Theoretical analysis showing this phenomenon is given for a particular class of fading channel. A novel receiver, exploiting preemphasis/deemphasis...
In this paper, we analyze the benefits of including downlink pilots in a cell- free massive MIMO system. We derive an approximate per-user achievable downlink rate for conjugate beamforming processing, which takes into account both uplink and downlink channel estimation errors, and power control. A performance comparison is carried out, in terms of per-user net throughput, considering cell-free massive...
Narrowband satellite communications (SATCOM) in the ultra high frequency (UHF) band is an attractive option within the military SATCOM (MILSATCOM) community. The UHF user terminals (UTs) are typically low cost, easily deployable and have broad beamwidths so that precise pointing to the satellite is not a requirement for mobile users. At the same time, some inherent disadvantages of UHF SATCOM are...
Under the conditions where performance in a massive MIMO network is limited by pilot contamination, the uplink signal-to-interference ratio (SIR) exhibits different distributions when using different pilot allocation schemes. By utilising different sets of orthogonal pilot sequences, as opposed to reused sequences amongst adjacent cells, the resulting SIR distribution is more favourable with respect...
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