1,621 research outputs found
Efficient Beam Alignment in Millimeter Wave Systems Using Contextual Bandits
In this paper, we investigate the problem of beam alignment in millimeter
wave (mmWave) systems, and design an optimal algorithm to reduce the overhead.
Specifically, due to directional communications, the transmitter and receiver
beams need to be aligned, which incurs high delay overhead since without a
priori knowledge of the transmitter/receiver location, the search space spans
the entire angular domain. This is further exacerbated under dynamic conditions
(e.g., moving vehicles) where the access to the base station (access point) is
highly dynamic with intermittent on-off periods, requiring more frequent beam
alignment and signal training. To mitigate this issue, we consider an online
stochastic optimization formulation where the goal is to maximize the
directivity gain (i.e., received energy) of the beam alignment policy within a
time period. We exploit the inherent correlation and unimodality properties of
the model, and demonstrate that contextual information improves the
performance. To this end, we propose an equivalent structured Multi-Armed
Bandit model to optimally exploit the exploration-exploitation tradeoff. In
contrast to the classical MAB models, the contextual information makes the
lower bound on regret (i.e., performance loss compared with an oracle policy)
independent of the number of beams. This is a crucial property since the number
of all combinations of beam patterns can be large in transceiver antenna
arrays, especially in massive MIMO systems. We further provide an
asymptotically optimal beam alignment algorithm, and investigate its
performance via simulations.Comment: To Appear in IEEE INFOCOM 2018. arXiv admin note: text overlap with
arXiv:1611.05724 by other author
Bandit Inspired Beam Searching Scheme for mmWave High-Speed Train Communications
High-speed trains (HSTs) are being widely deployed around the world. To meet
the high-rate data transmission requirements on HSTs, millimeter wave (mmWave)
HST communications have drawn increasingly attentions. To realize sufficient
link margin, mmWave HST systems employ directional beamforming with large
antenna arrays, which results in that the channel estimation is rather
time-consuming. In HST scenarios, channel conditions vary quickly and channel
estimations should be performed frequently. Since the period of each
transmission time interval (TTI) is too short to allocate enough time for
accurate channel estimation, the key challenge is how to design an efficient
beam searching scheme to leave more time for data transmission. Motivated by
the successful applications of machine learning, this paper tries to exploit
the similarities between current and historical wireless propagation
environments. Using the knowledge of reinforcement learning, the beam searching
problem of mmWave HST communications is formulated as a multi-armed bandit
(MAB) problem and a bandit inspired beam searching scheme is proposed to reduce
the number of measurements as many as possible. Unlike the popular deep
learning methods, the proposed scheme does not need to collect and store a
massive amount of training data in advance, which can save a huge amount of
resources such as storage space, computing time, and power energy. Moreover,
the performance of the proposed scheme is analyzed in terms of regret. The
regret analysis indicates that the proposed schemes can approach the
theoretical limit very quickly, which is further verified by simulation
results
End-to-End Simulation of 5G mmWave Networks
Due to its potential for multi-gigabit and low latency wireless links,
millimeter wave (mmWave) technology is expected to play a central role in 5th
generation cellular systems. While there has been considerable progress in
understanding the mmWave physical layer, innovations will be required at all
layers of the protocol stack, in both the access and the core network.
Discrete-event network simulation is essential for end-to-end, cross-layer
research and development. This paper provides a tutorial on a recently
developed full-stack mmWave module integrated into the widely used open-source
ns--3 simulator. The module includes a number of detailed statistical channel
models as well as the ability to incorporate real measurements or ray-tracing
data. The Physical (PHY) and Medium Access Control (MAC) layers are modular and
highly customizable, making it easy to integrate algorithms or compare
Orthogonal Frequency Division Multiplexing (OFDM) numerologies, for example.
The module is interfaced with the core network of the ns--3 Long Term Evolution
(LTE) module for full-stack simulations of end-to-end connectivity, and
advanced architectural features, such as dual-connectivity, are also available.
To facilitate the understanding of the module, and verify its correct
functioning, we provide several examples that show the performance of the
custom mmWave stack as well as custom congestion control algorithms designed
specifically for efficient utilization of the mmWave channel.Comment: 25 pages, 16 figures, submitted to IEEE Communications Surveys and
Tutorials (revised Jan. 2018
MAC Protocols for Terahertz Communication: A Comprehensive Survey
Terahertz communication is emerging as a future technology to support
Terabits per second link with highlighting features as high throughput and
negligible latency. However, the unique features of the Terahertz band such as
high path loss, scattering and reflection pose new challenges and results in
short communication distance. The antenna directionality, in turn, is required
to enhance the communication distance and to overcome the high path loss.
However, these features in combine negate the use of traditional Medium access
protocols. Therefore novel MAC protocol designs are required to fully exploit
their potential benefits including efficient channel access, control message
exchange, link establishment, mobility management, and line-of-sight blockage
mitigation. An in-depth survey of Terahertz MAC protocols is presented in this
paper. The paper highlights the key features of the Terahertz band which should
be considered while designing an efficient Terahertz MAC protocol, and the
decisions which if taken at Terahertz MAC layer can enhance the network
performance. Different Terahertz applications at macro and nano scales are
highlighted with design requirements for their MAC protocols. The MAC protocol
design issues and considerations are highlighted. Further, the existing MAC
protocols are also classified based on network topology, channel access
mechanisms, and link establishment strategies as Transmitter and Receiver
initiated communication. The open challenges and future research directions on
Terahertz MAC protocols are also highlighted.Comment: Submitted to IEEE Communication Surveys and Tutorials Journa
On the Beamformed Broadcast Signaling for Millimeter Wave Cell Discovery: Performance Analysis and Design Insight
Availability of abundant spectrum has enabled millimeter wave (mm-wave) as a
prominent candidate solution for the next generation cellular networks. Highly
directional transmissions are essential for exploitation of mm-wave bands to
compensate high propagation loss and attenuation. The directional transmission,
nevertheless, necessitates a specific design for mm-wave initial cell
discovery, as conventional omni-directional broadcast signaling may fail in
delivering the cell discovery information. To address this issue, this paper
provides an analytical framework for mm-wave beamformed cell discovery based on
an information theoretical approach. Design options are compared considering
four fundamental and representative broadcast signaling schemes to evaluate
discovery latency and signaling overhead. The schemes are then simulated under
realistic system parameters. Analytical and simulation results reveals four key
findings: (i) For cell discovery without knowledge of beacon timing,
analog/hybrid beamforming performs as well as digital beamforming in terms of
cell discovery latency; (ii) Single beam exhaustive scan optimize the latency,
however leads to overhead penalty; (iii) Multi-beam simultaneous scan can
significantly reduce the overhead, and provide the flexibility to achieve
trade-off between the latency and the overhead; (iv) The latency and the
overhead are relatively insensitive to extreme low block error rates
Millimeter Wave Cellular Networks: A MAC Layer Perspective
The millimeter wave (mmWave) frequency band is seen as a key enabler of
multi-gigabit wireless access in future cellular networks. In order to overcome
the propagation challenges, mmWave systems use a large number of antenna
elements both at the base station and at the user equipment, which lead to high
directivity gains, fully-directional communications, and possible noise-limited
operations. The fundamental differences between mmWave networks and traditional
ones challenge the classical design constraints, objectives, and available
degrees of freedom. This paper addresses the implications that highly
directional communication has on the design of an efficient medium access
control (MAC) layer. The paper discusses key MAC layer issues, such as
synchronization, random access, handover, channelization, interference
management, scheduling, and association. The paper provides an integrated view
on MAC layer issues for cellular networks, identifies new challenges and
tradeoffs, and provides novel insights and solution approaches.Comment: 21 pages, 9 figures, 2 tables, to appear in IEEE Transactions on
Communication
Codebook-Based Beam Tracking for Conformal ArrayEnabled UAV MmWave Networks
Millimeter wave (mmWave) communications can potentially meet the high
data-rate requirements of unmanned aerial vehicle (UAV) networks. However, as
the prerequisite of mmWave communications, the narrow directional beam tracking
is very challenging because of the three-dimensional (3D) mobility and attitude
variation of UAVs. Aiming to address the beam tracking difficulties, we propose
to integrate the conformal array (CA) with the surface of each UAV, which
enables the full spatial coverage and the agile beam tracking in highly dynamic
UAV mmWave networks. More specifically, the key contributions of our work are
three-fold. 1) A new mmWave beam tracking framework is established for the
CA-enabled UAV mmWave network. 2) A specialized hierarchical codebook is
constructed to drive the directional radiating element (DRE)-covered
cylindrical conformal array (CCA), which contains both the angular beam pattern
and the subarray pattern to fully utilize the potential of the CA. 3) A
codebook-based multiuser beam tracking scheme is proposed, where the Gaussian
process machine learning enabled UAV position/attitude predication is developed
to improve the beam tracking efficiency in conjunction with the tracking-error
aware adaptive beamwidth control. Simulation results validate the effectiveness
of the proposed codebook-based beam tracking scheme in the CA-enabled UAV
mmWave network, and demonstrate the advantages of CA over the conventional
planner array in terms of spectrum efficiency and outage probability in the
highly dynamic scenarios
Enhanced Random Access and Beam Training for mmWave Wireless Local Networks with High User Density
As low frequency band becomes more and more crowded, millimeter-wave (mmWave)
has attracted significant attention recently. IEEE has released the 802.11ad
standard to satisfy the demand of ultra-high-speed communication. It adopts
beamforming technology that can generate directional beams to compensate for
high path loss. In the Association Beamforming Training (A-BFT) phase of
beamforming (BF) training, a station (STA) randomly selects an A-BFT slot to
contend for training opportunity. Due to the limited number of A-BFT slots,
A-BFT phase suffers high probability of collisions in dense user scenarios,
resulting in inefficient training performance. Based on the evaluation of the
IEEE 802.11ad standard and 802.11ay draft in dense user scenarios of mmWave
wireless networks, we propose an enhanced A-BFT beam training and random access
mechanism, including the Separated A-BFT (SA-BFT) and Secondary Backoff A-BFT
(SBA-BFT). The SA-BFT can provide more A-BFT slots and divide A-BFT slots into
two regions by defining a new `E-A-BFT Length' field compared to the legacy
802.11ad A-BFT, thereby maintaining compatibility when 802.11ay devices are
mixed with 802.11ad devices. It can also reduce the collision probability in
dense user scenarios greatly. The SBA-BFT performs secondary backoff with very
small overhead of transmission opportunities within one A-BFT slot, which not
only further reduces collision probability, but also improves the A-BFT slots
utilization. Furthermore, we propose a three-dimensional Markov model to
analyze the performance of the SBA-BFT. The analytical and simulation results
show that both the SA-BFT and the SBA-BFT can significantly improve BF training
efficiency, which are beneficial to the optimization design of dense user
wireless networks based on the IEEE 802.11ay standard and mmWave technology.Comment: 13 pages, 17 figures, accepted by IEEE Transactions on Wireless
Communications, Sep. 201
Millimeter Wave communication with out-of-band information
Configuring the antenna arrays is the main source of overhead in millimeter
wave (mmWave) communication systems. In high mobility scenarios, the problem is
exacerbated, as achieving the highest rates requires frequent link
reconfiguration. One solution is to exploit spatial congruence between signals
at different frequency bands and extract mmWave channel parameters from side
information obtained in another band. In this paper we propose the concept of
out-of-band information aided mmWave communication. We analyze different
strategies to leverage information derived from sensors or from other
communication systems operating at sub-6 GHz bands to help configure the mmWave
communication link. The overhead reductions that can be obtained when
exploiting out-of-band information are characterized in a preliminary study.
Finally, the challenges associated with using out-of-band signals as a source
of side information at mmWave are analyzed in detail.Comment: 14 pages, 6 figure
Enabling UAV Cellular with Millimeter-Wave Communication: Potentials and Approaches
To support high data rate urgent or ad hoc communications, we consider mmWave
UAV cellular networks and the associated challenges and solutions. To enable
fast beamforming training and tracking, we first investigate a hierarchical
structure of beamforming codebooks and design of hierarchical codebooks with
different beam widths via the sub-array techniques. We next examine the Doppler
effect as a result of UAV movement and find that the Doppler effect may not be
catastrophic when high gain directional transmission is used. We further
explore the use of millimeter wave spatial division multiple access and
demonstrate its clear advantage in improving the cellular network capacity. We
also explore different ways of dealing with signal blockage and point out that
possible adaptive UAV cruising algorithms would be necessary to counteract
signal blockage. Finally, we identify a close relationship between UAV
positioning and directional millimeter wave user discovery, where update of the
former may directly impact the latter and vice versa.Comment: This paper explores the potentials and approaches to exploit mmWave
communication to establish a UAV cellular. It is to appear in IEEE
Communications Magazin
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