2,485 research outputs found
Millimeter Wave Communications
Millimeter wave (mmWave) technologies promise to revolutionize wireless networks by enabling multi-gigabit data rates. However, they suffer from high attenuation, and hence have to use highly directional antennas to focus their power on the receiver. Existing radios have to scan the space to find the best alignment between the transmitter’s and receiver’s beams, a process that takes up to a few seconds. This delay is problematic in a network setting where the base station needs to quickly switch between users and accommodate mobile clients.
We present Agile-Link, the first mmWave beam steering system that is demonstrated to find the correct beam alignment without scanning the space. Instead of scanning, Agile- Link hashes the beam directions using a few carefully chosen hash functions. It then identifies the correct alignment by tracking how the energy changes across different hash functions. Our results show that Agile-Link reduces beam steering delay by orders of magnitude.National Science Foundation (U.S.
Millimeter Wave Communications with Reconfigurable Antennas
The highly sparse nature of propagation channels and the restricted use of
radio frequency (RF) chains at transceivers limit the performance of millimeter
wave (mmWave) multiple-input multiple-output (MIMO) systems. Introducing
reconfigurable antennas to mmWave can offer an additional degree of freedom on
designing mmWave MIMO systems. This paper provides a theoretical framework for
studying the mmWave MIMO with reconfigurable antennas. We present an
architecture of reconfigurable mmWave MIMO with beamspace hybrid analog-digital
beamformers and reconfigurable antennas at both the transmitter and the
receiver. We show that employing reconfigurable antennas can provide throughput
gain for the mmWave MIMO. We derive the expression for the average throughput
gain of using reconfigurable antennas, and further simplify the expression by
considering the case of large number of reconfiguration states. In addition, we
propose a low-complexity algorithm for the reconfiguration state and beam
selection, which achieves nearly the same throughput performance as the optimal
selection of reconfiguration state and beams by exhaustive search.Comment: presented at IEEE ICC 201
High temperature superconductor analog electronics for millimeter-wavelength communications
The performance of high temperature superconductor (HTS) passive microwave circuits up to X-band was encouraging when compared to their metallic counterparts. The extremely low surface resistance of HTS films up to about 10 GHz enables a reduction in loss by as much as 100 times compared to copper when both materials are kept at about 77 K. However, a superconductor's surface resistance varies in proportion to the frequency squared. Consequently, the potential benefit of HTS materials to millimeter-wave communications requires careful analysis. A simple ring resonator was used to evaluate microstrip losses at Ka-band. Additional promising components were investigated such as antennas and phase shifters. Prospects for HTS to favorable impact millimeter-wave communications systems are discussed
Conformal Antenna Array for Millimeter-Wave Communications: Performance Evaluation
In this paper, we study the influence of the radius of a cylindrical
supporting structure on radiation properties of a conformal millimeter-wave
antenna array. Bent antenna array structures on cylindrical surfaces may have
important applications in future mobile devices. Small radii may be needed if
the antenna is printed on the edges of mobile devices and in items which human
beings are wearing, such as wrist watches, bracelets and rings. The antenna
under study consists of four linear series-fed arrays of four patch elements
and is operating at 58.8 GHz with linear polarization. The antenna array is
fabricated on polytetrafluoroethylene substrate with thickness of 0.127 mm due
to its good plasticity properties and low losses. Results for both planar and
conformal antenna arrays show rather good agreement between simulation and
measurements. The results show that conformal antenna structures allow
achieving large angular coverage and may allow beam-steering implementations if
switches are used to select between different arrays around a cylindrical
supporting structure.Comment: Keywords: conformal antenna, millimeter-wave communications, patch
antenna array. 11 pages, 10 figures, 1 tabl
Beam-searching and Transmission Scheduling in Millimeter Wave Communications
Millimeter wave (mmW) wireless networks are capable to support multi-gigabit
data rates, by using directional communications with narrow beams. However,
existing mmW communications standards are hindered by two problems: deafness
and single link scheduling. The deafness problem, that is, a misalignment
between transmitter and receiver beams, demands a time consuming beam-searching
operation, which leads to an alignment-throughput tradeoff. Moreover, the
existing mmW standards schedule a single link in each time slot and hence do
not fully exploit the potential of mmW communications, where directional
communications allow multiple concurrent transmissions. These two problems are
addressed in this paper, where a joint beamwidth selection and power allocation
problem is formulated by an optimization problem for short range mmW networks
with the objective of maximizing effective network throughput. This
optimization problem allows establishing the fundamental alignment-throughput
tradeoff, however it is computationally complex and requires exact knowledge of
network topology, which may not be available in practice. Therefore, two
standard-compliant approximation solution algorithms are developed, which rely
on underestimation and overestimation of interference. The first one exploits
directionality to maximize the reuse of available spectrum and thereby
increases the network throughput, while imposing almost no computational
complexity. The second one is a more conservative approach that protects all
active links from harmful interference, yet enhances the network throughput by
100% compared to the existing standards. Extensive performance analysis
provides useful insights on the directionality level and the number of
concurrent transmissions that should be pursued. Interestingly, extremely
narrow beams are in general not optimal.Comment: 5 figures, 7 pages, accepted in ICC 201
Low-Latency Millimeter-Wave Communications: Traffic Dispersion or Network Densification?
This paper investigates two strategies to reduce the communication delay in
future wireless networks: traffic dispersion and network densification. A
hybrid scheme that combines these two strategies is also considered. The
probabilistic delay and effective capacity are used to evaluate performance.
For probabilistic delay, the violation probability of delay, i.e., the
probability that the delay exceeds a given tolerance level, is characterized in
terms of upper bounds, which are derived by applying stochastic network
calculus theory. In addition, to characterize the maximum affordable arrival
traffic for mmWave systems, the effective capacity, i.e., the service
capability with a given quality-of-service (QoS) requirement, is studied. The
derived bounds on the probabilistic delay and effective capacity are validated
through simulations. These numerical results show that, for a given average
system gain, traffic dispersion, network densification, and the hybrid scheme
exhibit different potentials to reduce the end-to-end communication delay. For
instance, traffic dispersion outperforms network densification, given high
average system gain and arrival rate, while it could be the worst option,
otherwise. Furthermore, it is revealed that, increasing the number of
independent paths and/or relay density is always beneficial, while the
performance gain is related to the arrival rate and average system gain,
jointly. Therefore, a proper transmission scheme should be selected to optimize
the delay performance, according to the given conditions on arrival traffic and
system service capability
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