121 research outputs found
On Low-Resolution ADCs in Practical 5G Millimeter-Wave Massive MIMO Systems
Nowadays, millimeter-wave (mmWave) massive multiple-input multiple-output
(MIMO) systems is a favorable candidate for the fifth generation (5G) cellular
systems. However, a key challenge is the high power consumption imposed by its
numerous radio frequency (RF) chains, which may be mitigated by opting for
low-resolution analog-to-digital converters (ADCs), whilst tolerating a
moderate performance loss. In this article, we discuss several important issues
based on the most recent research on mmWave massive MIMO systems relying on
low-resolution ADCs. We discuss the key transceiver design challenges including
channel estimation, signal detector, channel information feedback and transmit
precoding. Furthermore, we introduce a mixed-ADC architecture as an alternative
technique of improving the overall system performance. Finally, the associated
challenges and potential implementations of the practical 5G mmWave massive
MIMO system {with ADC quantizers} are discussed.Comment: to appear in IEEE Communications Magazin
Hardware-Impaired Rician-Faded Cell-Free Massive MIMO Systems With Channel Aging
We study the impact of channel aging on the uplink of a cell-free (CF)
massive multiple-input multiple-output (mMIMO) system by considering i)
spatially-correlated Rician-faded channels; ii) hardware impairments at the
access points and user equipments (UEs); and iii) two-layer large-scale fading
decoding (LSFD). We first derive a closed-form spectral efficiency (SE)
expression for this system, and later propose two novel optimization techniques
to optimize the non-convex SE metric by exploiting the
minorization-maximization (MM) method. The first one requires a numerical
optimization solver, and has a high computation complexity. The second one with
closed-form transmit power updates, has a trivial computation complexity. We
numerically show that i) the two-layer LSFD scheme effectively mitigates the
interference due to channel aging for both low- and high-velocity UEs; and ii)
increasing the number of AP antennas does not mitigate the SE deterioration due
to channel aging. We numerically characterize the optimal pilot length required
to maximize the SE for various UE speeds. We also numerically show that the
proposed closed-form MM optimization yields the same SE as that of the first
technique, which requires numerical solver, and that too with a much reduced
time-complexity.Comment: This work has been submitted to the IEEE Transactions on
Communications for possible publication. Copyright may be transferred without
notice, after which this version may no longer be accessible, 32 pages, 14
figure
Massive MIMO Systems With Low-Resolution ADCs: Baseband Energy Consumption vs. Symbol Detection Performance
In massive multiple-input multiple-output (MIMO) systems using a large number of antennas, it would be difficult to connect high-resolution analog-to-digital converters (ADCs) to each antenna component due to high cost and energy consumption problems. To resolve these issues, there has been much work on implementing symbol detectors and channel estimators using low-resolution ADCs for massive MIMO systems. Although it is intuitively true that using low-resolution ADCs makes it possible to save a large amount of energy consumption in massive MIMO systems, the relationship between energy consumption using low-resolution ADCs and detection performance has not been properly analyzed yet. In this paper, the tradeoff between different detectors and total baseband energy consumption including flexible ADCs is thoroughly analyzed taking the optimal fixed-point operations performed during the detection processes into account. In order to minimize the energy consumption for the given channel condition, the proposed scheme selects the best mode among various processing options while supporting the target frame error rate. The numerous case studies reveal that the proposed work remarkably saves the energy consumption of the massive MIMO processing compared with the existing schemes.11Ysciescopu
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