883 research outputs found
Spectral Efficiency and Energy Efficiency Tradeoff in Massive MIMO Downlink Transmission with Statistical CSIT
As a key technology for future wireless networks, massive multiple-input
multiple-output (MIMO) can significantly improve the energy efficiency (EE) and
spectral efficiency (SE), and the performance is highly dependant on the degree
of the available channel state information (CSI). While most existing works on
massive MIMO focused on the case where the instantaneous CSI at the transmitter
(CSIT) is available, it is usually not an easy task to obtain precise
instantaneous CSIT. In this paper, we investigate EE-SE tradeoff in single-cell
massive MIMO downlink transmission with statistical CSIT. To this end, we aim
to optimize the system resource efficiency (RE), which is capable of striking
an EE-SE balance. We first figure out a closed-form solution for the
eigenvectors of the optimal transmit covariance matrices of different user
terminals, which indicates that beam domain is in favor of performing RE
optimal transmission in massive MIMO downlink. Based on this insight, the RE
optimization precoding design is reduced to a real-valued power allocation
problem. Exploiting the techniques of sequential optimization and random matrix
theory, we further propose a low-complexity suboptimal two-layer
water-filling-structured power allocation algorithm. Numerical results
illustrate the effectiveness and near-optimal performance of the proposed
statistical CSI aided RE optimization approach.Comment: Typos corrected. 14 pages, 7 figures. Accepted for publication on
IEEE Transactions on Signal Processing. arXiv admin note: text overlap with
arXiv:2002.0488
Joint Bit Allocation and Hybrid Beamforming Optimization for Energy Efficient Millimeter Wave MIMO Systems
In this paper, we aim to design highly energy efficient end-to-end
communication for millimeter wave multiple-input multiple-output systems. This
is done by jointly optimizing the digital-to-analog converter
(DAC)/analog-to-digital converter (ADC) bit resolutions and hybrid beamforming
matrices. The novel decomposition of the hybrid precoder and the hybrid
combiner to three parts is introduced at the transmitter (TX) and the receiver
(RX), respectively, representing the analog precoder/combiner matrix, the
DAC/ADC bit resolution matrix and the baseband precoder/combiner matrix. The
unknown matrices are computed as a solution to the matrix factorization problem
where the optimal fully digital precoder or combiner is approximated by the
product of these matrices. A novel and efficient solution based on the
alternating direction method of multipliers is proposed to solve these problems
at both the TX and the RX. The simulation results show that the proposed
solution, where the DAC/ADC bit allocation is dynamic during operation,
achieves higher energy efficiency when compared with existing benchmark
techniques that use fixed DAC/ADC bit resolutions.Comment: arXiv admin note: text overlap with arXiv:1909.1217
Performance Analysis of OTSM under Hardware Impairments in Millimeter-Wave Vehicular Communication Networks
Orthogonal time sequency multiplexing (OTSM) has been recently proposed as a
single-carrier (SC) waveform offering similar bit error rate (BER) to
multi-carrier orthogonal time frequency space (OTFS) modulation in
doubly-spread channels under high mobilities; however, with much lower
complexity making OTSM a promising candidate for low-power millimeter-wave
(mmWave) vehicular communications in 6G wireless networks. In this paper, the
performance of OTSM-based homodyne transceiver is explored under hardware
impairments (HIs) including in-phase and quadrature imbalance (IQI), direct
current offset (DCO), phase noise, power amplifier non-linearity, carrier
frequency offset, and synchronization timing offset. First, the discrete-time
baseband signal model is obtained in vector form under the mentioned HIs. Then,
the system input-output relations are derived in time, delay-time, and
delay-sequency (DS) domains in which the parameters of HIs are incorporated.
Analytical studies demonstrate that noise stays white Gaussian and effective
channel matrix is sparse in the DS domain under HIs. Also, DCO appears as a DC
signal at receiver interfering with only the zero sequency over all delay taps
in the DS domain; however, IQI redounds to self-conjugated fully-overlapping
sequency interference. Simulation results reveal the fact that with no HI
compensation (HIC), not only OTSM outperforms plain SC waveform but it performs
close to uncompensated OTFS system; however, HIC is essentially needed for OTSM
systems operating in mmWave and beyond frequency bands
Joint Waveform and Clustering Design for Coordinated Multi-point DFRC Systems
To improve both sensing and communication performances, this paper proposes a coordinated multi-point (CoMP) transmission design for a dual-functional radar-communication (DFRC) system. In the proposed CoMP-DFRC system, the central processor (CP) coordinates multiple base stations (BSs) to transmit both the communication signal and the dedicated probing signal. The communication performance and the sensing performance are both evaluated by the signal-to-interference-plus-noise ratio (SINR). Given the limited backhaul capacity, we study the waveform and clustering design from both the radar-centric perspective and the communication-centric perspective. Dinkelbach’s transform is adopted to handle the single-ratio fractional objective for the radar-centric problem. For the communication-centric problem, we adopt quadratic transform to convexitify the multi-ratio fractional objective. Then, the rank-one constraint of communication beamforming vector is relaxed by semidefinite relaxation (SDR), and the tightness of SDR is further proved to guarantee the optimal waveform design with fixed clustering. For dynamic clustering, equivalent continuous functions are used to represent the non-continuous clustering variables. Successive convex approximation (SCA) is further utilized to convexitify the equivalent functions. Simulation results are provided to verify the effectiveness of all proposed designs
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