218 research outputs found
The Spatial Outage Capacity of Wireless Networks
We address a fundamental question in wireless networks that, surprisingly,
has not been studied before: what is the maximum density of concurrently active
links that satisfy a certain outage constraint? We call this quantity the
spatial outage capacity (SOC), give a rigorous definition, and analyze it for
Poisson bipolar networks with ALOHA. Specifically, we provide exact analytical
and approximate expressions for the density of links satisfying an outage
constraint and give simple upper and lower bounds on the SOC. In the
high-reliability regime where the target outage probability is close to zero,
we obtain an exact closed-form expression of the SOC, which reveals the
interesting and perhaps counter-intuitive result that all transmitters need to
be always active to achieve the SOC, i.e., the transmit probability needs to be
set to 1 to achieve the SOC.Comment: 32 pages, 9 figure
Delay Analysis of Spatially-Coded MIMO-ZFBF with Retransmissions in Random Networks
For a low-mobile Poisson bipolar network and under
line-of-sight/non-line-of-sight (LOS/NLOS) path-loss model, we study repetitive
retransmissions (RR) and blocked incremental redundancy (B-IR). We consider
spatially-coded multiple-input multiple-output (MIMO) zero-forcing beamforming
(ZFBF) multiplexing system, whereby the packet success reception is determined
based on the aggregate data rate across spatial dimensions of the MIMO system.
Characterization of retransmission performance in this low-mobile configuration
is practically important, but inherently complex due to a substantial rate
correlation across retransmissions and intractability of evaluating the
probability density function (pdf) of aggregate data rate. Adopting tools of
stochastic geometry, we firstly characterize the rate correlation coefficient
(RCC) for both schemes. Our results show that, compared to RR scheme, B-IR
scheme has higher RCC while its coverage probability is substantially larger.
We demonstrate that the spotted contention between coverage probability and RCC
causes the mean transmission delay (MTD) of B-IR to become either smaller or
larger than the MTD of RR scheme. Finally, we develop a numerical approximation
of MTD, and evaluate the effective spatial throughput (EST), which is
reciprocal to MTD, of RR and B-IR schemes. Our numerical results highlight
fundamental tradeoffs between densification, multiplexing gain, block length,
and activity factor of nodes. We further observe that for dense networks 1) LOS
component is considerably instrumental to enhance EST; 2) EST of B-IR scheme
can be much higher than that of RR scheme; 3) When Doppler spread exists, it
can improve MTD of B-IR while it does not cast any meaningful effect on the MTD
of RR.Comment: 16 page
Outage Analysis of Cooperative NOMA in Millimeter Wave Vehicular Network at Intersections
In this paper, we study the impact and the improvement of using cooperative
non-orthogonal multiple access scheme (NOMA) on a millimeter wave (mmWave)
vehicular network at intersection roads. The intersections consists of two
perpendicular roads. The transmission occurs between a source, and two
destinations nodes with a help of a relay. We assume that the interference
comes from as set of vehicles that are distributed as a one dimensional
homogeneous Poisson point process (PPP). We derive closed form outage
probability expressions for cooperative NOMA, and compare them with cooperative
orthogonal multiple access (OMA). We show that, NOMA offers a significant
improvement, especially for high data rates. However, there a condition imposed
to the data rate, otherwise, the performance of NOMA will decreases
dramatically. We show that as the nodes approach the intersection, the outage
probability increases. Counter-intuitively, We show that, the non line of sigh
(NLOS) scenario has a better performance than the line of sigh (LOS) scenario.
The analysis is conducted using tools from stochastic geometry and is verified
with Monte Carlo simulations
SIR Meta Distribution of K-Tier Downlink Heterogeneous Cellular Networks with Cell Range Expansion
Heterogeneous cellular networks (HCNs) constitute a necessary step in the
evolution of cellular networks. In this paper, we apply the
signal-to-interference ratio (SIR) meta distribution framework for a refined
SIR performance analysis of HCNs, focusing on K-tier heterogeneous cellular
networks based on the homogeneous independent Poisson point process (HIP)
model, with range expansion bias (offloading bias) in each tier. Expressions
for the b-th moment of the conditional success probability for both the entire
network and each tier are derived, based on which the exact meta distributions
and the beta approximations are evaluated and compared. Key performance metrics
including the mean success probability, the variance of the conditional success
probability, the mean local delay and the asymptotic SIR gains of each tier are
obtained. The results show that the biases are detrimental to the overall mean
success probability of the whole network and that the b-th moment curve (versus
the SIR threshold) of the conditional success probability of each tier can be
excellently approximated by the horizontal shifted versions of the first moment
curve of the single-tier PPP network. We also provide lower bounds for the
region of the active probabilities of the base stations to keep the mean local
delay of each tier finite.Comment: 29 pages, 11 figure
Efficient Calculation of Meta Distributions and the Performance of User Percentiles
Meta distributions (MDs) are refined performance metrics in wireless networks
modeled using point processes. While there is no known method to directly
calculate MDs, the moments of the underlying conditional distributions (given
the point process) can often be expressed in exact analytical form. The problem
of finding the MD given the moments has several solutions, but the standard
approaches are inefficient and sensitive to the choices of a number of
parameters. Here we propose and explore the use of a method based on binomial
mixtures, which has several key advantages over other methods, since it is
based on a simple linear transform of the moments
Accuracy of Distance-Based Ranking of Users in the Analysis of NOMA Systems
We characterize the accuracy of analyzing the performance of a NOMA system
where users are ranked according to their distances instead of instantaneous
channel gains, i.e., product of distance-based path-loss and fading channel
gains. Distance-based ranking is analytically tractable and can lead to
important insights. However, it may not be appropriate in a multipath fading
environment where a near user suffers from severe fading while a far user
experiences weak fading. Since the ranking of users in a NOMA system has a
direct impact on coverage probability analysis, impact of the traditional
distance-based ranking, as opposed to instantaneous signal power-based ranking,
needs to be understood. This will enable us to identify scenarios where
distance-based ranking, which is easier to implement compared to instantaneous
signal power-based ranking, is acceptable for system performance analysis. To
this end, in this paper, we derive the probability of the event when
distance-based ranking yields the same results as instantaneous signal
power-based ranking, which is referred to as the accuracy probability. We
characterize the probability of accuracy considering Nakagami-m fading channels
and three different spatial distribution models of user locations in NOMA. We
illustrate the impact of accuracy probability on uplink and downlink coverage
probability
Intrinsic Secrecy in Inhomogeneous Stochastic Networks
Network secrecy is vital for a variety of wireless applications and can be accomplished by exploiting network interference. Recently, interference engineering strategies (IESs) have been developed to harness network interference, depending on the wireless environment (node distribution, transmission policy, and channel conditions). Typically, the node spatial distribution has been modeled according to a homogeneous Poisson point process for mathematical tractability. However, such a model can be inadequate for inhomogeneous (e.g., sensor and vehicular) networks. This paper develops a framework for the design and analysis of inhomogeneous wireless networks with intrinsic secrecy. Based on the characterization of the network interference and received signal-to-interference ratio for different receiver selection strategies. Local and global secrecy metrics are introduced for characterizing the level of intrinsic secrecy in inhomogeneous wireless networks from a link and a network perspective. The benefits of IESs are quantified by simulations in various scenarios, thus corroborating the analysis. Results show that IESs can elevate the network secrecy significantly
An Outage Probability Analysis of Full-Duplex NOMA in UAV Communications
As unmanned aerial vehicles (UAVs) are expected to play a significant role in
fifth generation (5G) networks, addressing spectrum scarcity in UAV
communications remains a pressing issue. In this regard, the feasibility of
full-duplex non-orthogonal multiple access (FD-NOMA) UAV communications to
improve spectrum utilization is investigated in this paper. Specifically,
closed-form outage probability expressions are presented for FD-NOMA,
half-duplex non-orthogonal multiple access (HD-NOMA), and half-duplex
orthogonal multiple access (HD-OMA) schemes over Rician shadowed fading
channels. Extensive analysis revealed that the bottleneck of performance in
FD-NOMA is at the downlink UAVs. Also, FD-NOMA exhibits lower outage
probability at the ground station (GS) and downlink UAVs than HD-NOMA and
HD-OMA under low transmit power regimes. At high transmit power regimes,
FD-NOMA is limited by residual SI and inter-UAV interference at the downlink
UAVs and FD-GS, respectively. The impact of shadowing is also shown to affect
the reliability of FD-NOMA and HD-OMA at the downlink UAVs.Comment: To appear in Proc. IEEE Wireless Commun. Netw. Conf. (WCNC),
Marrakech, Morocco, 201
On the Performance of Cooperative NOMA Using MRC at Road Intersections in the Presence of Interference
As the traffic safety has become of utmost importance, much attention is
given to intelligent transportation systems (ITSs), and more particularly to
vehicular communications (VCs). Moreover, 50 % of all crashes happen at road
intersections, which makes theme a critical areas. In this paper, we
investigate the improvement when implementing maximum ratio combining (MRC) in
cooperative VCs transmission schemes using non-orthogonal multiple access
scheme (NOMA) at road intersections. We consider that a source transmits a
message to two destinations with a aid of a relay. The transmission undergoes
interference generated from a set of vehicles on the roads. We obtained closed
form outage probability expressions, and we extend the derivation for a
scenario involving K destination nodes and several road lanes. The performance
of MRC cooperative NOMA is compared with the standard cooperative NOMA, and we
show that implementing MRC with NOMA offers a significant improvement over the
standard cooperative NOMA. Also, we compare the performance of MRC using NOMA
with MRC cooperative orthogonal multiple access (OMA), and demonstrate that
NOMA significantly outperforms OMA. We conclude that it is always beneficial to
use MRC and NOMA even at the cost of implementation complexity. Finally, we
demonstrate that the outage probability increases drasticallyen the vehicles
are closer to the road intersection, and that using MRC with NOMA improves
significantly the performance in this context. To verify the correctness of our
analysis, extensive Monte-Carlo simulations are carried out.Comment: arXiv admin note: text overlap with arXiv:1909.0198
Wireless Access in Ultra-Reliable Low-Latency Communication (URLLC)
The future connectivity landscape and, notably, the 5G wireless systems will
feature Ultra-Reliable Low Latency Communication (URLLC). The coupling of high
reliability and low latency requirements in URLLC use cases makes the wireless
access design very challenging, in terms of both the protocol design and of the
associated transmission techniques. This paper aims to provide a broad
perspective on the fundamental tradeoffs in URLLC as well as the principles
used in building access protocols. Two specific technologies are considered in
the context of URLLC: massive MIMO and multi-connectivity, also termed
interface diversity. The paper also touches upon the important question of the
proper statistical methodology for designing and assessing extremely high
reliability levels.Comment: Invited paper, submitted for revie
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