4,157 research outputs found
Optimal Power Allocation by Imperfect Hardware Analysis in Untrusted Relaying Networks
By taking a variety of realistic hardware imperfections into consideration,
we propose an optimal power allocation (OPA) strategy to maximize the
instantaneous secrecy rate of a cooperative wireless network comprised of a
source, a destination and an untrusted amplify-and-forward (AF) relay. We
assume that either the source or the destination is equipped with a large-scale
multiple antennas (LSMA) system, while the rest are equipped with a single
antenna. To prevent the untrusted relay from intercepting the source message,
the destination sends an intended jamming noise to the relay, which is referred
to as destination-based cooperative jamming (DBCJ). Given this system model,
novel closed-form expressions are presented in the high signal-to-noise ratio
(SNR) regime for the ergodic secrecy rate (ESR) and the secrecy outage
probability (SOP). We further improve the secrecy performance of the system by
optimizing the associated hardware design. The results reveal that by
beneficially distributing the tolerable hardware imperfections across the
transmission and reception radio-frequency (RF) front ends of each node, the
system's secrecy rate may be improved. The engineering insight is that equally
sharing the total imperfections at the relay between the transmitter and the
receiver provides the best secrecy performance. Numerical results illustrate
that the proposed OPA together with the most appropriate hardware design
significantly increases the secrecy rate.Comment: 29 pages, 7 figures, Submitted to IEEE Transactions on Wireless
Communication
User Effects in Beam-Space MIMO
The performance and design of the novel single-RF-chain beam-space MIMO
antenna concept is evaluated for the first time in the presence of the user.
First, the variations of different performance parameters are evaluated when
placing a beam-space MIMO antenna in close proximity to the user body in
several typical operating scenarios. In addition to the typical degradation of
conventional antennas in terms of radiation efficiency and impedance matching,
it is observed that the user body corrupts the power balance and the
orthogonality of the beam-space MIMO basis. However, capacity analyses show
that throughput reduction mainly stems from the absorption in user body tissues
rather than from the power imbalance and the correlation of the basis. These
results confirm that the beam-space MIMO concept, so far only demonstrated in
the absence of external perturbation, still performs very well in typical human
body interaction scenarios.Comment: 4 pages, 7 figures, 2 table
AirSync: Enabling Distributed Multiuser MIMO with Full Spatial Multiplexing
The enormous success of advanced wireless devices is pushing the demand for
higher wireless data rates. Denser spectrum reuse through the deployment of
more access points per square mile has the potential to successfully meet the
increasing demand for more bandwidth. In theory, the best approach to density
increase is via distributed multiuser MIMO, where several access points are
connected to a central server and operate as a large distributed multi-antenna
access point, ensuring that all transmitted signal power serves the purpose of
data transmission, rather than creating "interference." In practice, while
enterprise networks offer a natural setup in which distributed MIMO might be
possible, there are serious implementation difficulties, the primary one being
the need to eliminate phase and timing offsets between the jointly coordinated
access points.
In this paper we propose AirSync, a novel scheme which provides not only time
but also phase synchronization, thus enabling distributed MIMO with full
spatial multiplexing gains. AirSync locks the phase of all access points using
a common reference broadcasted over the air in conjunction with a Kalman filter
which closely tracks the phase drift. We have implemented AirSync as a digital
circuit in the FPGA of the WARP radio platform. Our experimental testbed,
comprised of two access points and two clients, shows that AirSync is able to
achieve phase synchronization within a few degrees, and allows the system to
nearly achieve the theoretical optimal multiplexing gain. We also discuss MAC
and higher layer aspects of a practical deployment. To the best of our
knowledge, AirSync offers the first ever realization of the full multiuser MIMO
gain, namely the ability to increase the number of wireless clients linearly
with the number of jointly coordinated access points, without reducing the per
client rate.Comment: Submitted to Transactions on Networkin
Surface MIMO: Using Conductive Surfaces For MIMO Between Small Devices
As connected devices continue to decrease in size, we explore the idea of
leveraging everyday surfaces such as tabletops and walls to augment the
wireless capabilities of devices. Specifically, we introduce Surface MIMO, a
technique that enables MIMO communication between small devices via surfaces
coated with conductive paint or covered with conductive cloth. These surfaces
act as an additional spatial path that enables MIMO capabilities without
increasing the physical size of the devices themselves. We provide an extensive
characterization of these surfaces that reveal their effect on the propagation
of EM waves. Our evaluation shows that we can enable additional spatial streams
using the conductive surface and achieve average throughput gains of 2.6-3x for
small devices. Finally, we also leverage the wideband characteristics of these
conductive surfaces to demonstrate the first Gbps surface communication system
that can directly transfer bits through the surface at up to 1.3 Gbps.Comment: MobiCom '1
Single-RF spatial modulation requires single-carrier transmission: frequency-domain turbo equalization for dispersive channels
In this paper, we propose a broadband single-carrier (SC) spatial-modulation (SM) based multiple-input multipleoutput (MIMO) architecture relying on a soft-decision (SoD) frequency-domain equalization (FDE) receiver. We demonstrate that conventional orthogonal frequency-division multiplexing (OFDM)-based broadband transmissions are not readily suitable for the single–radio frequency (RF) assisted SM-MIMO schemes, since this scheme does not exhibit any substantial performance advantage over single-antenna transmissions. To circumvent this limitation, a low-complexity soft-decision (SoD) FDE algorithm based on the minimum mean-square error (MMSE) criterion is invoked for our broadband SC-based SM-MIMO scheme, which is capable of operating in a strongly dispersive channel having a long channel impulse response (CIR) at a moderate decoding complexity. Furthermore, our SoD FDE attains a near-capacity performance with the aid of a three-stage concatenated SC-based SM architecture
Modeling and Efficient Cancellation of Nonlinear Self-Interference in MIMO Full-Duplex Transceivers
This paper addresses the modeling and digital cancellation of
self-interference in in-band full-duplex (FD) transceivers with multiple
transmit and receive antennas. The self-interference modeling and the proposed
nonlinear spatio-temporal digital canceller structure takes into account, by
design, the effects of I/Q modulator imbalances and power amplifier (PA)
nonlinearities with memory, in addition to the multipath self-interference
propagation channels and the analog RF cancellation stage. The proposed
solution is the first cancellation technique in the literature which can handle
such a self-interference scenario. It is shown by comprehensive simulations
with realistic RF component parameters and with two different PA models to
clearly outperform the current state-of-the-art digital self-interference
cancellers, and to clearly extend the usable transmit power range.Comment: 7 pages, 5 figures. To be presented in the 2014 International
Workshop on Emerging Technologies for 5G Wireless Cellular Network
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