15,945 research outputs found
On the Performance of Optimized Dense Device-to-Device Wireless Networks
We consider a D2D wireless network where users are densely deployed in a
squared planar region and communicate with each other without the help of a
wired infrastructure. For this network, we examine the 3-phase hierarchical
cooperation (HC) scheme and the 2-phase improved HC scheme based on the concept
of {\em network multiple access}. Exploiting recent results on the optimality
of treating interference as noise in Gaussian interference channels, we
optimize the achievable average per-link rate and not just its scaling law. In
addition, we provide further improvements on both the previously proposed
hierarchical cooperation schemes by a more efficient use of TDMA and spatial
reuse. Thanks to our explicit achievable rate expressions, we can compare HC
scheme with multihop routing (MR), where the latter can be regarded as the
current practice of D2D wireless networks. Our results show that the improved
and optimized HC schemes yield very significant rate gains over MR in realistic
conditions of channel propagation exponents, signal to noise ratio, and number
of users. This sheds light on the long-standing question about the real
advantage of HC scheme over MR beyond the well-known scaling laws analysis. In
contrast, we also show that our rate optimization is non-trivial, since when HC
is applied with off-the-shelf choice of the system parameters, no significant
rate gain with respect to MR is achieved. We also show that for large pathloss
exponent the sum rate is a nearly linear function of the number of users in
the range of networks of practical size. This also sheds light on a
long-standing dispute on the effective achievability of linear sum rate scaling
with HC. Finally, we notice that the achievable sum rate for large is
much larger than for small . This suggests that HC scheme may be a very
effective approach for networks operating at mm-waves.Comment: Revised and resubmitted to IEEE Transactions on Information Theor
Individual Preference Aware Caching Policy Design in Wireless D2D Networks
Cache-aided wireless device-to-device (D2D) networks allow significant
throughput increase, depending on the concentration of the popularity
distribution of files. Many studies assume that all users have the same
preference distribution; however, this may not be true in practice. This work
investigates whether and how the information about individual preferences can
benefit cache-aided D2D networks. We examine a clustered network and derive a
network utility that considers both the user distribution and channel fading
effects into the analysis. We also formulate a utility maximization problem for
designing caching policies. This maximization problem can be applied to
optimize several important quantities, including throughput, energy efficiency
(EE), cost, and hit-rate, and to solve different tradeoff problems. We provide
a general approach that can solve the proposed problem under the assumption
that users coordinate, then prove that the proposed approach can obtain the
stationary point under a mild assumption. Using simulations of practical
setups, we show that performance can improve significantly with proper
exploitation of individual preferences. We also show that different types of
tradeoffs exist between different performance metrics and that they can be
managed through caching policy and cooperation distance designs.Comment: Accepted by IEEE Transactions on Wireless Communication
DeepWear: Adaptive Local Offloading for On-Wearable Deep Learning
Due to their on-body and ubiquitous nature, wearables can generate a wide
range of unique sensor data creating countless opportunities for deep learning
tasks. We propose DeepWear, a deep learning (DL) framework for wearable devices
to improve the performance and reduce the energy footprint. DeepWear
strategically offloads DL tasks from a wearable device to its paired handheld
device through local network. Compared to the remote-cloud-based offloading,
DeepWear requires no Internet connectivity, consumes less energy, and is robust
to privacy breach. DeepWear provides various novel techniques such as
context-aware offloading, strategic model partition, and pipelining support to
efficiently utilize the processing capacity from nearby paired handhelds.
Deployed as a user-space library, DeepWear offers developer-friendly APIs that
are as simple as those in traditional DL libraries such as TensorFlow. We have
implemented DeepWear on the Android OS and evaluated it on COTS smartphones and
smartwatches with real DL models. DeepWear brings up to 5.08X and 23.0X
execution speedup, as well as 53.5% and 85.5% energy saving compared to
wearable-only and handheld-only strategies, respectively
Cooperative HARQ Assisted NOMA Scheme in Large-scale D2D Networks
This paper develops an interference aware design for cooperative hybrid
automatic repeat request (HARQ) assisted non-orthogonal multiple access (NOMA)
scheme for large-scale device-to-device (D2D) networks. Specifically,
interference aware rate selection and power allocation are considered to
maximize long term average throughput (LTAT) and area spectral efficiency
(ASE). The design framework is based on stochastic geometry that jointly
accounts for the spatial interference correlation at the NOMA receivers as well
as the temporal interference correlation across HARQ transmissions. It is found
that ignoring the effect of the aggregate interference, or overlooking the
spatial and temporal correlation in interference, highly overestimates the NOMA
performance and produces misleading design insights. An interference oblivious
selection for the power and/or transmission rates leads to violating the
network outage constraints. To this end, the results demonstrate the
effectiveness of NOMA transmission and manifest the importance of the
cooperative HARQ to combat the negative effect of the network aggregate
interference. For instance, comparing to the non-cooperative HARQ assisted
NOMA, the proposed scheme can yield an outage probability reduction by %.
Furthermore, an interference aware optimal design that maximizes the LTAT given
outage constraints leads to % throughput improvement over HARQ-assisted
orthogonal multiple access (OMA) scheme.Comment: submitted to IEEE Transactions on Communication
Caching at the Wireless Edge: Design Aspects, Challenges and Future Directions
Caching at the wireless edge is a promising way of boosting spectral
efficiency and reducing energy consumption of wireless systems. These
improvements are rooted in the fact that popular contents are reused,
asynchronously, by many users. In this article, we first introduce methods to
predict the popularity distributions and user preferences, and the impact of
erroneous information. We then discuss the two aspects of caching systems,
namely content placement and delivery. We expound the key differences between
wired and wireless caching, and outline the differences in the system arising
from where the caching takes place, e.g., at base stations, or on the wireless
devices themselves. Special attention is paid to the essential limitations in
wireless caching, and possible tradeoffs between spectral efficiency, energy
efficiency and cache size.Comment: Published in IEEE Communications Magazin
On Green Energy Powered Cognitive Radio Networks
Green energy powered cognitive radio (CR) network is capable of liberating
the wireless access networks from spectral and energy constraints. The
limitation of the spectrum is alleviated by exploiting cognitive networking in
which wireless nodes sense and utilize the spare spectrum for data
communications, while dependence on the traditional unsustainable energy is
assuaged by adopting energy harvesting (EH) through which green energy can be
harnessed to power wireless networks. Green energy powered CR increases the
network availability and thus extends emerging network applications. Designing
green CR networks is challenging. It requires not only the optimization of
dynamic spectrum access but also the optimal utilization of green energy. This
paper surveys the energy efficient cognitive radio techniques and the
optimization of green energy powered wireless networks. Existing works on
energy aware spectrum sensing, management, and sharing are investigated in
detail. The state of the art of the energy efficient CR based wireless access
network is discussed in various aspects such as relay and cooperative radio and
small cells. Envisioning green energy as an important energy resource in the
future, network performance highly depends on the dynamics of the available
spectrum and green energy. As compared with the traditional energy source, the
arrival rate of green energy, which highly depends on the environment of the
energy harvesters, is rather random and intermittent. To optimize and adapt the
usage of green energy according to the opportunistic spectrum availability, we
discuss research challenges in designing cognitive radio networks which are
powered by energy harvesters
Ambient RF Energy Harvesting in Ultra-Dense Small Cell Networks: Performance and Trade-offs
In order to minimize electric grid power consumption, energy harvesting from
ambient RF sources is considered as a promising technique for wireless charging
of low-power devices. To illustrate the design considerations of RF-based
ambient energy harvesting networks, this article first points out the primary
challenges of implementing and operating such networks, including
non-deterministic energy arrival patterns, energy harvesting mode selection,
energy-aware cooperation among base stations (BSs), etc. A brief overview of
the recent advancements and a summary of their shortcomings are then provided
to highlight existing research gaps and possible future research directions. To
this end, we investigate the feasibility of implementing RF-based ambient
energy harvesting in ultra-dense small cell networks (SCNs) and examine the
related trade-offs in terms of the energy efficiency and
signal-to-interference-plus-noise ratio (SINR) outage probability of a typical
user in the downlink. Numerical results demonstrate the significance of
deploying a mixture of on-grid small base stations (SBSs)~(powered by electric
grid) and off-grid SBSs~(powered by energy harvesting) and optimizing their
corresponding proportions as a function of the intensity of active SBSs in the
network.Comment: IEEE Wireless Communications, to appea
High Throughput Opportunistic Cooperative Device-to-Device Communications With Caching
To achieve the potential in providing high throughput for cellular networks
by device-to-device (D2D) communications, the interference among D2D links
should be carefully managed. In this paper, we propose an opportunistic
cooperation strategy for D2D transmission by exploiting the caching capability
at the users to control the interference among D2D links. We consider overlay
inband D2D, divide the D2D users into clusters, and assign different frequency
bands to cooperative and non-cooperative D2D links. To provide high opportunity
for cooperative transmission, we introduce a caching policy. To maximize the
network throughput, we jointly optimize the cluster size and bandwidth
allocation, where the closed-form expression of the bandwidth allocation factor
is obtained. Simulation results demonstrate that the proposed strategy can
provide 400%-500% throughput gain over traditional D2D communications when the
content popularity distribution is skewed, and can provide 60%-80% gain even
when the content popularity distribution is uniform.Comment: A part of this work was published in IEEE VTCSpring 2016
[arXiv:1603.04664
Combined Spatial and Temporal Blocking for High-Performance Stencil Computation on FPGAs Using OpenCL
Recent developments in High Level Synthesis tools have attracted software
programmers to accelerate their high-performance computing applications on
FPGAs. Even though it has been shown that FPGAs can compete with GPUs in terms
of performance for stencil computation, most previous work achieve this by
avoiding spatial blocking and restricting input dimensions relative to FPGA
on-chip memory. In this work we create a stencil accelerator using Intel FPGA
SDK for OpenCL that achieves high performance without having such restrictions.
We combine spatial and temporal blocking to avoid input size restrictions, and
employ multiple FPGA-specific optimizations to tackle issues arisen from the
added design complexity. Accelerator parameter tuning is guided by our
performance model, which we also use to project performance for the upcoming
Intel Stratix 10 devices. On an Arria 10 GX 1150 device, our accelerator can
reach up to 760 and 375 GFLOP/s of compute performance, for 2D and 3D stencils,
respectively, which rivals the performance of a highly-optimized GPU
implementation. Furthermore, we estimate that the upcoming Stratix 10 devices
can achieve a performance of up to 3.5 TFLOP/s and 1.6 TFLOP/s for 2D and 3D
stencil computation, respectively.Comment: FPGA '18: 2018 ACM/SIGDA International Symposium on
Field-Programmable Gate Array
Fair Stochastic Interference Orchestration with Cellular Throughput Boosted via Outband Sidelinks
Time-domain Inter-Cell Interference Coordination (ICIC) is recognized as the
main driver towards efficient and effective ultra-dense network deployments.
Almost Blank Subframe (ABS), as key-example of ICIC, has been recently
standardized so as to achieve high spectral efficiency. As we show in this
article, adopting ABS implies non-trivial complexity to be effective in
multicellular environments with heterogeneous cell coverage and user density.
Nonetheless, no fairness determinism is guaranteed by ICIC and ABS in
particular. Instead, we analytically show that a compound exploitation of ABS
with outband sidelinks used for Device-to-Device (D2D) communications on
unlicensed bands not only allows to abate the complexity of operating ABS, but
also results in unexpectedly high levels of fairness. Based on the analysis, we
formulate a convex optimization problem to stochastically make ABS decisions
while providing proportional fairness guarantees. Our results prove that,
compared to a legacy system, stochastically orchestration of ABS largely boosts
fairness while retaining a notable throughput gain offered by mmWave outband
sidelinks used for relay
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