20,995 research outputs found
Energy efficiency-spectral efficiency trade-off of transmit antenna selection
We investigate the energy efficiency-spectral efficiency (EE-SE) trade-off of transmit antenna selection/maximum ratio combining (TAS) scheme. A realistic power consumption model (PCM) is considered, and it is shown that using TAS can provide significant energy savings when compared to multiple-input multiple-output (MIMO) in the low to medium SE region, regardless the number of antennas, as well as outperform transmit beamforming scheme (MRT) for the entire SE range. For a fixed number of receive antennas, our results also show that the EE gain of TAS over MIMO becomes even greater as the number of transmit antennas increases. The optimal value of SE that maximizes the EE is obtained analytically, and confirmed by numerical results. Moreover, the influence of receiver correlation is also evaluated and it is shown that considering a non-realistic PCM can lead to mistakes when comparing TAS and MIMO
Reduced Switching Connectivity for Large Scale Antenna Selection
In this paper, we explore reduced-connectivity radio frequency (RF) switching
networks for reducing the analog hardware complexity and switching power losses
in antenna selection (AS) systems. In particular, we analyze different hardware
architectures for implementing the RF switching matrices required in AS designs
with a reduced number of RF chains. We explicitly show that fully-flexible
switching matrices, which facilitate the selection of any possible subset of
antennas and attain the maximum theoretical sum rates of AS, present numerous
drawbacks such as the introduction of significant insertion losses,
particularly pronounced in massive multiple-input multiple-output (MIMO)
systems. Since these disadvantages make fully-flexible switching suboptimal in
the energy efficiency sense, we further consider partially-connected switching
networks as an alternative switching architecture with reduced hardware
complexity, which we characterize in this work. In this context, we also
analyze the impact of reduced switching connectivity on the analog hardware and
digital signal processing of AS schemes that rely on channel power information.
Overall, the analytical and simulation results shown in this paper demonstrate
that partially-connected switching maximizes the energy efficiency of massive
MIMO systems for a reduced number of RF chains, while fully-flexible switching
offers sub-optimal energy efficiency benefits due to its significant switching
power losses.Comment: 14 pages, 11 figure
On the Total Energy Efficiency of Cell-Free Massive MIMO
We consider the cell-free massive multiple-input multiple-output (MIMO)
downlink, where a very large number of distributed multiple-antenna access
points (APs) serve many single-antenna users in the same time-frequency
resource. A simple (distributed) conjugate beamforming scheme is applied at
each AP via the use of local channel state information (CSI). This CSI is
acquired through time-division duplex operation and the reception of uplink
training signals transmitted by the users. We derive a closed-form expression
for the spectral efficiency taking into account the effects of channel
estimation errors and power control. This closed-form result enables us to
analyze the effects of backhaul power consumption, the number of APs, and the
number of antennas per AP on the total energy efficiency, as well as, to design
an optimal power allocation algorithm. The optimal power allocation algorithm
aims at maximizing the total energy efficiency, subject to a per-user spectral
efficiency constraint and a per-AP power constraint. Compared with the equal
power control, our proposed power allocation scheme can double the total energy
efficiency. Furthermore, we propose AP selections schemes, in which each user
chooses a subset of APs, to reduce the power consumption caused by the backhaul
links. With our proposed AP selection schemes, the total energy efficiency
increases significantly, especially for large numbers of APs. Moreover, under a
requirement of good quality-of-service for all users, cell-free massive MIMO
outperforms the colocated counterpart in terms of energy efficiency
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