2,529 research outputs found
A Normalization Model for Analyzing Multi-Tier Millimeter Wave Cellular Networks
Based on the distinguishing features of multi-tier millimeter wave (mmWave)
networks such as different transmit powers, different directivity gains from
directional beamforming alignment and path loss laws for line-of-sight (LOS)
and non-line-of-sight (NLOS) links, we introduce a normalization model to
simplify the analysis of multi-tier mmWave cellular networks. The highlight of
the model is that we convert a multi-tier mmWave cellular network into a
single-tier mmWave network, where all the base stations (BSs) have the same
normalized transmit power 1 and the densities of BSs scaled by LOS or NLOS
scaling factors respectively follow piecewise constant function which has
multiple demarcation points. On this basis, expressions for computing the
coverage probability are obtained in general case with beamforming alignment
errors and the special case with perfect beamforming alignment in the
communication. According to corresponding numerical exploration, we conclude
that the normalization model for multi-tier mmWave cellular networks fully
meets requirements of network performance analysis, and it is simpler and
clearer than the untransformed model. Besides, an unexpected but sensible
finding is that there is an optimal beam width that maximizes coverage
probability in the case with beamforming alignment errors.Comment: 7 pages, 4 figure
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
Device-to-Device Communications in the Millimeter Wave Band: A Novel Distributed Mechanism
In spite of its potential advantages, the large-scale implementation of the
device-to-device (D2D) communications has yet to be realized, mainly due to
severe interference and lack of enough bandwidth in the microwave (W)
band. Recently, exploiting the millimeter wave (mmW) band for D2D
communications has attracted considerable attention as a potential solution to
these challenges. However, its severe sensitivity to blockage along with its
directional nature make the utilization of the mmW band a challenging task as
it requires line-of-sight (LOS) link detection and careful beam alignment
between the D2D transceivers. In this paper, we propose a novel distributed
mechanism which enables the D2D devices to discover unblocked LOS links for the
mmW band communication. Moreover, as such LOS links are not always available,
the proposed mechanism allows the D2D devices to switch to the W band if
necessary. In addition, the proposed mechanism detects the direction of the LOS
links to perform the beam alignment. We have used tools from stochastic
geometry to evaluate the performance of the proposed mechanism in terms of the
signal-to-interference-plus-noise ratio (SINR) coverage probability. The
performance of the proposed algorithm is then compared to the one of the single
band (i.e., W/mmW) communication. The simulation results show that the
proposed mechanism considerably outperforms the single band communication.Comment: 6 Pages, 6 Figures, Accepted for presentation in Wireless
Telecommunication Symposium (WTS'18
Throughput Optimal Beam Alignment in Millimeter Wave Networks
Millimeter wave communications rely on narrow-beam transmissions to cope with
the strong signal attenuation at these frequencies, thus demanding precise beam
alignment between transmitter and receiver. The communication overhead incurred
to achieve beam alignment may become a severe impairment in mobile networks.
This paper addresses the problem of optimizing beam alignment acquisition, with
the goal of maximizing throughput. Specifically, the algorithm jointly
determines the portion of time devoted to beam alignment acquisition, as well
as, within this portion of time, the optimal beam search parameters, using the
framework of Markov decision processes. It is proved that a bisection search
algorithm is optimal, and that it outperforms exhaustive and iterative search
algorithms proposed in the literature. The duration of the beam alignment phase
is optimized so as to maximize the overall throughput. The numerical results
show that the throughput, optimized with respect to the duration of the beam
alignment phase, achievable under the exhaustive algorithm is 88.3% lower than
that achievable under the bisection algorithm. Similarly, the throughput
achievable by the iterative search algorithm for a division factor of 4 and 8
is, respectively, 12.8% and 36.4% lower than that achievable by the bisection
algorithm
Common Codebook Millimeter Wave Beam Design: Designing Beams for Both Sounding and Communication with Uniform Planar Arrays
Fifth generation (5G) wireless networks are expected to utilize wide
bandwidths available at millimeter wave (mmWave) frequencies for enhancing
system throughput. However, the unfavorable channel conditions of mmWave links,
e.g., higher path loss and attenuation due to atmospheric gases or water vapor,
hinder reliable communications. To compensate for these severe losses, it is
essential to have a multitude of antennas to generate sharp and strong beams
for directional transmission. In this paper, we consider mmWave systems using
uniform planar array (UPA) antennas, which effectively place more antennas on a
two-dimensional grid. A hybrid beamforming setup is also considered to generate
beams by combining a multitude of antennas using only a few radio frequency
chains. We focus on designing a set of transmit beamformers generating beams
adapted to the directional characteristics of mmWave links assuming a UPA and
hybrid beamforming. We first define ideal beam patterns for UPA structures.
Each beamformer is constructed to minimize the mean squared error from the
corresponding ideal beam pattern. Simulation results verify that the proposed
codebooks enhance beamforming reliability and data rate in mmWave systems.Comment: 14 pages, 10 figure
- …