227 research outputs found
On the Performance of the Relay-ARQ Networks
This paper investigates the performance of relay networks in the presence of
hybrid automatic repeat request (ARQ) feedback and adaptive power allocation.
The throughput and the outage probability of different hybrid ARQ protocols are
studied for independent and spatially-correlated fading channels. The results
are obtained for the cases where there is a sum power constraint on the source
and the relay or when each of the source and the relay are power-limited
individually. With adaptive power allocation, the results demonstrate the
efficiency of relay-ARQ techniques in different conditions.Comment: Accepted for publication in IEEE Trans. Veh. Technol. 201
On the Performance of Millimeter Wave-based RF-FSO Multi-hop and Mesh Networks
This paper studies the performance of multi-hop and mesh networks composed of
millimeter wave (MMW)-based radio frequency (RF) and free-space optical (FSO)
links. The results are obtained in cases with and without hybrid automatic
repeat request (HARQ). Taking the MMW characteristics of the RF links into
account, we derive closed-form expressions for the networks' outage probability
and ergodic achievable rates. We also evaluate the effect of various parameters
such as power amplifiers efficiency, number of antennas as well as different
coherence times of the RF and the FSO links on the system performance. Finally,
we determine the minimum number of the transmit antennas in the RF link such
that the same rate is supported in the RF- and the FSO-based hops. The results
show the efficiency of the RF-FSO setups in different conditions. Moreover,
HARQ can effectively improve the outage probability/energy efficiency, and
compensate for the effect of hardware impairments in RF-FSO networks. For
common parameter settings of the RF-FSO dual-hop networks, outage probability
of 10^{-4} and code rate of 3 nats-per-channel-use, the implementation of HARQ
with a maximum of 2 and 3 retransmissions reduces the required power, compared
to cases with open-loop communication, by 13 and 17 dB, respectively.Comment: Submitted to IEEE Transactions on Wireless Communication
On the Performance of Millimeter Wave-based RF-FSO Links with HARQ Feedback
This paper studies the performance of hybrid radio-frequency (RF) and
free-space optical (FSO) links in the cases with and without hybrid automatic
repeat request (HARQ). Considering millimeter wave (mmwave) characteristics in
the RF link and pointing errors in the FSO link, we derive closed-form
expressions for the message decoding probabilities as well as the throughput
and the outage probability of the RF-FSO setups. We also evaluate the effect of
various parameters such as power amplifiers efficiency, different transmission
techniques in the FSO link, pointing errors in the FSO link as well as
different coherence times/symbol rates of the RF and the FSO links on the
throughput and outage probability. The results show the efficiency of the
RF-FSO links in different conditions. Moreover, the HARQ can effectively
improve the outage probability/energy efficiency, and compensate the effect of
hardware impairments in RF-FSO links.Comment: Under review in PIMRC'201
On the Throughput of Large-but-Finite MIMO Networks using Schedulers
This paper studies the sum throughput of the {multi-user}
multiple-input-single-output (MISO) networks in the cases with large but finite
number of transmit antennas and users. Considering continuous and bursty
communication scenarios with different users' data request probabilities, we
derive quasi-closed-form expressions for the maximum achievable throughput of
the networks using optimal schedulers. The results are obtained in various
cases with different levels of interference cancellation. Also, we develop an
efficient scheduling scheme using genetic algorithms (GAs), and evaluate the
effect of different parameters, such as channel/precoding models, number of
antennas/users, scheduling costs and power amplifiers' efficiency, on the
system performance. Finally, we use the recent results on the achievable rates
of finite block-length codes to analyze the system performance in the cases
with short packets. As demonstrated, the proposed GA-based scheduler reaches
(almost) the same throughput as in the exhaustive search-based optimal
scheduler, with substantially less implementation complexity. Moreover, the
power amplifiers' inefficiency and the scheduling delay affect the performance
of the scheduling-based systems significantly
Performance analysis of RF-FSO multi-hop networks
We study the performance of multi-hop networks composed of millimeter wave
(MMW)-based radio frequency (RF) and free-space optical (FSO) links. The
results are obtained in the cases with and without hybrid automatic repeat
request (HARQ). Taking the MMW characteristics of the RF links into account, we
derive closed-form expressions for the network outage probability. We also
evaluate the effect of various parameters such as power amplifiers efficiency,
number of antennas as well as different coherence times of the RF and the FSO
links on the system performance. Finally, we present mappings between the
performance of RF-FSO multi-hop networks and the ones using only the RF- or the
FSO-based communication, in the sense that with appropriate parameter settings
the same outage probability is achieved in these setups. The results show the
efficiency of the RF-FSO setups in different conditions. Moreover, the HARQ can
effectively improve the outage probability/energy efficiency, and compensate
the effect of hardware impairments in RF-FSO networks. For common parameter
settings of the RF-FSO dual-hop networks, outage probability 10^{-4} and code
rate 3 nats-per-channel-use, the implementation of HARQ with a maximum of 2 and
3 retransmissions reduces the required power, compared to the cases with no
HARQ, by 13 and 17 dB, respectively.Comment: Presented at IEEE WCNC 201
Beamforming Techniques for Non-Orthogonal Multiple Access in 5G Cellular Networks
In this paper, we develop various beamforming techniques for downlink
transmission for multiple-input single-output (MISO) non-orthogonal multiple
access (NOMA) systems. First, a beamforming approach with perfect channel state
information (CSI) is investigated to provide the required quality of service
(QoS) for all users. Taylor series approximation and semidefinite relaxation
(SDR) techniques are employed to reformulate the original non-convex power
minimization problem to a tractable one. Further, a fairness-based beamforming
approach is proposed through a max-min formulation to maintain fairness between
users. Next, we consider a robust scheme by incorporating channel
uncertainties, where the transmit power is minimized while satisfying the
outage probability requirement at each user. Through exploiting the SDR
approach, the original non-convex problem is reformulated in a linear matrix
inequality (LMI) form to obtain the optimal solution. Numerical results
demonstrate that the robust scheme can achieve better performance compared to
the non-robust scheme in terms of the rate satisfaction ratio. Further,
simulation results confirm that NOMA consumes a little over half transmit power
needed by OMA for the same data rate requirements. Hence, NOMA has the
potential to significantly improve the system performance in terms of transmit
power consumption in future 5G networks and beyond.Comment: accepted to publish in IEEE Transactions on Vehicular Technolog
Reliability performance analysis of half-duplex and full-duplex schemes with self-energy recycling
Abstract. Radio frequency energy harvesting (EH) has emerged as a promising option for improving the energy efficiency of current and future networks. Self-energy recycling (sER), as a variant of EH, has also appeared as a suitable alternative that allows to reuse part of the transmitted energy via an energy loop. In this work we study the benefits of using sER in terms of reliability improvements and compare the performance of full-duplex (FD) and half-duplex (HD) schemes when using multi-antenna techniques at the base station side. We also assume a model for the hardware energy consumption, making the analysis more realistic since most works only consider the energy spent on transmission. In addition to spectral efficiency enhancements, results show that FD performs better than HD in terms of reliability. We maximize the outage probability of the worst link in the network using a dynamic FD scheme where a small base station (SBS) determines the optimal number of antennas for transmission and reception. This scheme proves to be more efficient than classical HD and FD modes. Results show that the use of sER at the SBS introduces changes on the distribution of antennas for maximum fairness when compared to the setup without sER. Moreover, we determine the minimum number of active radio frequency chains required at the SBS in order to achieve a given reliability target
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