5 research outputs found
Mixed RF/FSO Relaying Systems with Hardware Impairments
In this work, we provide a detailed analysis of a dual-hop fixed gain (FG)
amplify-and-forward relaying system, consisting of a hybrid radio frequency
(RF) and free-space optical (FSO) channels. We introduce an impairment model
which is the soft envelope limiter (SEL). Additionally, we propose the partial
relay selection (PRS) protocol with outdated channel state information (CSI)
based on the knowledge of the RF channels in order to select one relay for the
communication. Moreover, the RF channels of the first hop experience Rayleigh
fading while we propose a unified fading model for the FSO channels, called the
unified Gamma Gamma (GG), taking into account the atmospheric turbulence, the
path loss and the misalignment between the transmitter and the receiver
aperture also called the pointing error. Novel closed-forms of the outage
probability (OP), the bit error probability (BEP) and the average ergodic
capacity (EC) are derived in terms of Meijer-G and Fox-H functions.
Capitalizing on these metrics, we also derive the asymptotical high
signal-to-noise ratio (SNR) in order to get engineering insights into the
impacts of the hardware impairments and the system parameters as well. Finally,
using Monte Carlo simulations, we validate numerically the derived mathematical
formulations.Comment: arXiv admin note: text overlap with arXiv:1901.0424
Zero-Forcing Max-Power Beamforming for Hybrid mmWave Full-Duplex MIMO Systems
Full-duplex (FD) systems gained enormous attention because of the potential
to double the spectral efficiency. In the context of 5G technology, FD systems
operating at millimeter-wave (mmWave) frequencies become one of the most
promising solutions to further increase the spectral efficiency and reduce the
latency. However, such systems are vulnerable to the self-interference (SI)
that significantly degrades the performance. To overcome this shortcoming,
analog-only beamforming techniques have been developed to mitigate the SI.
Because of the huge power consumption, systems operating at mmWave frequencies
beamform the power by only tunning the phase shifters while maintaining
constant amplitudes. Such a hardware constraint, known as the constant
amplitude (CA) constraint, severely limits the system performance. In this
work, we propose a digital and analog hybrid beamforming design that completely
eliminates the SI while substantially minimizing the losses imposed by the CA
constraint. Further, we develop a fully-digital beamforming design and derive
the upper bound for the spectral efficiency as benchmarking tools to quantify
the losses of our proposed hybrid design
Adaptive Gradient Search Beamforming for Full-Duplex mmWave MIMO Systems
In this work, we present a framework analysis of full-duplex (FD) systems for
Millimeter Wave (mmWave) analog architecture. Given that FD systems can double
the ergodic capacity, such systems experience large losses caused by the
loopback self-interference (SI). In addition, systems with analog architecture
also suffer from other forms of losses mainly incurred by the constant
amplitude (CA) constraint. For this purpose, we propose the projected Gradient
Ascent algorithm to maximize the sum rate under the unit-norm and CA
constraints. Unlike previous works, our approach achieves the best spectral
efficiency while minimizing the losses incurred by the CA constraint. We also
consider an adaptive step size to compensate for the perturbations that may
affect the cost function during the optimization. The results will show that
the proposed algorithm converges to the same optimal value for different
initializations while the number of iterations required for the convergence
changes for each case. In this context, we primarily consider the gradient
search method for a two-nodes FD systems and then we extend the analysis for a
dual-hop FD relaying systems. Finally, we evaluate the robustness of our method
in terms of rate and outage probability and compare with previous approaches
Tractable Approach to MmWaves Cellular Analysis with FSO Backhauling under Feedback Delay and Hardware Limitations
In this work, we investigate the performance of a millimeter waves (mmWaves)
cellular system with free space optical (FSO) backhauling. MmWave channels are
subject to Nakagami-m fading while the optical links experience the Double
Generalized Gamma including atmospheric turbulence, path loss and the
misalignment between the transmitter and the receiver aperture (also known as
the pointing errors). The FSO model also takes into account the receiver
detection technique which could be either heterodyne or intensity modulation
and direct detection (IM/DD). Each user equipment (UE) has to be associated to
one serving base station (BS) based on the received signal strength (RSS) or
Channel State Information (CSI). We assume partial relay selection (PRS) with
CSI based on mmWaves channels to select the BS associated with the highest
received CSI. Each serving BS decodes the received signal for denoising,
converts it into modulated FSO signal, and then forwards it to the data center.
Thereby, each BS can be viewed as a decode-and-forward (DF) relay. In practice,
the relay hardware suffers from nonlinear high power amplification (HPA)
impairments which, substantially degrade the system performance. In this work,
we will discuss the impacts of three common HPA impairments named respectively,
soft envelope limiter (SEL), traveling wave tube amplifier (TWTA), and solid
state power amplifier (SSPA). Novel closed-forms and tight upper bounds of the
outage probability, the probability of error, and the achievable rate are
derived. Capitalizing on these performance, we derive the high SNR asymptotes
to get engineering insights into the system gain such as the diversity order.Comment: arXiv admin note: substantial text overlap with arXiv:1901.0424
Asymmetric RF/FSO Relaying with HPA non-Linearities and Feedback Delay Constraints
In this work, we investigate the performance of a dual-hop multiple relays
system consisting of mixed Radio-Frequency (RF)/Free Space Optical (FSO)
channels. The RF channels are subject to Rayleigh fading while the optical
links experience the Double Generalized Gamma including atmospheric turbulence,
path loss and the misalignment between the transmitter and the receiver
aperture (also known as the pointing error). The FSO model also takes into
account the receiver detection technique which could be either heterodyne or
intensity modulation and direct detection. Partial Relay Selection with
outdated Channel State Information is assumed based on the RF channels to
select a relay and we also consider fixed and variable Amplify-and-Forward
relaying schemes. In addition, we assume that the relays are affected by the
high power amplifier non-linearities and herein we discuss two power amplifiers
called Soft Envelope Limiter and Traveling Wave Tube Amplifier. Furthermore,
novel closed-forms and tight upper bounds of the outage probability, the bit
error probability, and the ergodic capacity are derived. Capitalizing on these
performance, we derive the high SNR asymptotic to get engineering insights
about the system gains such as the diversity and the coding gains. Finally, the
mathematical expressions are validated using the Monte Carlo simulation