2,370 research outputs found
Secure Communications in Millimeter Wave Ad Hoc Networks
Wireless networks with directional antennas, like millimeter wave (mmWave)
networks, have enhanced security. For a large-scale mmWave ad hoc network in
which eavesdroppers are randomly located, however, eavesdroppers can still
intercept the confidential messages, since they may reside in the signal beam.
This paper explores the potential of physical layer security in mmWave ad hoc
networks. Specifically, we characterize the impact of mmWave channel
characteristics, random blockages, and antenna gains on the secrecy
performance. For the special case of uniform linear array (ULA), a tractable
approach is proposed to evaluate the average achievable secrecy rate. We also
characterize the impact of artificial noise in such networks. Our results
reveal that in the low transmit powerregime, the use of low mmWave frequency
achieves better secrecy performance, and when increasing transmit power, a
transition from low mmWave frequency to high mmWave frequency is demanded for
obtaining a higher secrecy rate. More antennas at the transmitting nodes are
needed to decrease the antenna gain obtained by the eavesdroppers when using
ULA. Eavesdroppers can intercept more information by using a wide beam pattern.
Furthermore, the use of artificial noise may be ineffective for enhancing the
secrecy rate.Comment: Accepted by IEEE Transactions on Wireless Communication
Tractable Resource Management with Uplink Decoupled Millimeter-Wave Overlay in Ultra-Dense Cellular Networks
The forthcoming 5G cellular network is expected to overlay millimeter-wave
(mmW) transmissions with the incumbent micro-wave ({\mu}W) architecture. The
overall mm-{\mu}W resource management should therefore harmonize with each
other. This paper aims at maximizing the overall downlink (DL) rate with a
minimum uplink (UL) rate constraint, and concludes: mmW tends to focus more on
DL transmissions while {\mu}W has high priority for complementing UL, under
time-division duplex (TDD) mmW operations. Such UL dedication of {\mu}W results
from the limited use of mmW UL bandwidth due to excessive power consumption
and/or high peak-to-average power ratio (PAPR) at mobile users. To further
relieve this UL bottleneck, we propose mmW UL decoupling that allows each
legacy {\mu}W base station (BS) to receive mmW signals. Its impact on mm-{\mu}W
resource management is provided in a tractable way by virtue of a novel
closed-form mm-{\mu}W spectral efficiency (SE) derivation. In an ultra-dense
cellular network (UDN), our derivation verifies mmW (or {\mu}W) SE is a
logarithmic function of BS-to-user density ratio. This strikingly simple yet
practically valid analysis is enabled by exploiting stochastic geometry in
conjunction with real three dimensional (3D) building blockage statistics in
Seoul, Korea.Comment: to appear in IEEE Transactions on Wireless Communications (17 pages,
11 figures, 1 table
Spatial networks with wireless applications
Many networks have nodes located in physical space, with links more common
between closely spaced pairs of nodes. For example, the nodes could be wireless
devices and links communication channels in a wireless mesh network. We
describe recent work involving such networks, considering effects due to the
geometry (convex,non-convex, and fractal), node distribution,
distance-dependent link probability, mobility, directivity and interference.Comment: Review article- an amended version with a new title from the origina
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Millimeter wave wearable communication networks : analytic modeling and MIMO support
Future high-end wearable electronic devices including virtual reality goggles and augmented reality glasses require rates of the order of gigabits-per-second and potentially very low latency. Supporting high data rate wireless connectivity for applications such as uncompressed video streaming among wearable devices in a densely crowded environment is challenging. This is primarily due to bandwidth scarcity when many users operate multiple devices simultaneously. The millimeter wave (mmWave) band has the potential to address this bottleneck, thanks to more spectrum and less interference because of signal blockage at these frequencies. This dissertation addresses key questions that need to be answered before realizing mmWave-based wearables in practice: (i) what are the expected achievable rates in a crowded user environment, with mmWave devices using a given hardware configuration? (ii) how is the wireless connectivity affected in an indoor operation, which is prone to surface reflections? (iii) can multi-stream data transmission, involving large bandwidth communication under hardware constraints be realized? To answer these, tools from stochastic geometry and compressive sensing, and architectures involving hybrid analog/digital multiple-input multiple-output (MIMO) are leveraged. The main contributions of this dissertation are 1) analytical modeling to compute average achievable rates in mmWave wearable networks consisting of finite number of user devices and human blockages, 2) characterizing the impact of reflections and non-isotropic performance of mmWave wearable networks in crowded indoor environments, 3) channel estimation to support MIMO for wideband mmWave wearable devices using hybrid architecture, and 4) designing optimal, but easy-to-implement, precoding/combining strategies in frequency-selective mmWave systems. Both analysis and numerical simulations show how the proposed evaluation methodology and solutions serve to enable mmWave based communication among next generation wearable electronic devices.Electrical and Computer Engineerin
HBF MU-MIMO with Interference-Aware Beam Pair Link Allocation for Beyond-5G mm-Wave Networks
Hybrid beamforming (HBF) multi-user multiple-input multiple-output (MU-MIMO)
is a key technology for unlocking the directional millimeter-wave (mm-wave)
nature for spatial multiplexing beyond current codebook-based 5G-NR networks.
In order to suppress co-scheduled users' interference, HBF MU-MIMO is
predicated on having sufficient radio frequency chains and accurate channel
state information (CSI), which can otherwise lead to performance losses due to
imperfect interference cancellation. In this work, we propose IABA, a 5G-NR
standard-compliant beam pair link (BPL) allocation scheme for mitigating
spatial interference in practical HBF MU-MIMO networks. IABA solves the network
sum throughput optimization via either a distributed or a centralized BPL
allocation using dedicated CSI reference signals for candidate BPL monitoring.
We present a comprehensive study of practical multi-cell mm-wave networks and
demonstrate that HBF MU-MIMO without interference-aware BPL allocation
experiences strong residual interference which limits the achievable network
performance. Our results show that IABA offers significant performance gains
over the default interference-agnostic 5G-NR BPL allocation, and even allows
HBF MU-MIMO to outperform the fully digital MU-MIMO baseline, by facilitating
allocation of secondary BPLs other than the strongest BPL found during initial
access. We further demonstrate the scalability of IABA with increased gNB
antennas and densification for beyond-5G mm-wave networks.Comment: 13 pages, 11 figures. This work has been submitted to IEEE for
possible publication (copyright may be transferred without notice, after
which this version may no longer be accessible
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