4,433 research outputs found
A generalisation of the nonlinear small-gain theorem for systems with abstract initial conditions
We consider the development of a general nonlinear small-gain theorem for systems with abstract initial conditions. Systems are defined in a set theoretic manner from input-output pairs on a doubly infinite time axis, and a general construction of the initial conditions (i.e. a state at time zero) is given in terms of an equivalence class of trajectories on the negative time axis. By using this formulation, an ISS-type nonlinear small-gain theorem is established with complete disconnection between the stability property and the existence, uniqueness properties. We provide an illustrative example
Energy efficient hybrid satellite terrestrial 5G networks with software defined features
In order to improve the manageability and adaptability
of future 5G wireless networks, the software orchestration mechanism,
named software defined networking (SDN) with Control
and User plane (C/U-plane) decoupling, has become one of the
most promising key techniques. Based on these features, the hybrid
satellite terrestrial network is expected to support flexible
and customized resource scheduling for both massive machinetype-
communication (MTC) and high-quality multimedia requests
while achieving broader global coverage, larger capacity and lower
power consumption. In this paper, an end-to-end hybrid satellite
terrestrial network is proposed and the performance metrics,
e. g., coverage probability, spectral and energy efficiency (SE and
EE), are analysed in both sparse networks and ultra-dense networks.
The fundamental relationship between SE and EE is investigated,
considering the overhead costs, fronthaul of the gateway
(GW), density of small cells (SCs) and multiple quality-ofservice
(QoS) requirements. Numerical results show that compared
with current LTE networks, the hybrid system with C/U split
can achieve approximately 40% and 80% EE improvement in
sparse and ultra-dense networks respectively, and greatly enhance
the coverage. Various resource management schemes, bandwidth
allocation methods, and on-off approaches are compared, and the
applications of the satellite in future 5G networks with software
defined features are proposed
Massive MIMO Performance - TDD Versus FDD: What Do Measurements Say?
Downlink beamforming in Massive MIMO either relies on uplink pilot
measurements - exploiting reciprocity and TDD operation, or on the use of a
predetermined grid of beams with user equipments reporting their preferred
beams, mostly in FDD operation. Massive MIMO in its originally conceived form
uses the first strategy, with uplink pilots, whereas there is currently
significant commercial interest in the second, grid-of-beams. It has been
analytically shown that in isotropic scattering (independent Rayleigh fading)
the first approach outperforms the second. Nevertheless there remains
controversy regarding their relative performance in practice. In this
contribution, the performances of these two strategies are compared using
measured channel data at 2.6 GHz.Comment: Submitted to IEEE Transactions on Wireless Communications,
31/Mar/201
STAR-IOS Aided NOMA Networks: Channel Model Approximation and Performance Analysis
Simultaneous transmitting and reflecting intelligent omini-surfaces
(STAR-IOSs) are able to achieve full coverage "smart radio environments". By
splitting the energy or altering the active number of STAR-IOS elements,
STAR-IOSs provide high flexibility of successive interference cancellation
(SIC) orders for non-orthogonal multiple access (NOMA) systems. Based on the
aforementioned advantages, this paper investigates a STAR-IOS-aided downlink
NOMA network with randomly deployed users. We first propose three tractable
channel models for different application scenarios, namely the central limit
model, the curve fitting model, and the M-fold convolution model. More
specifically, the central limit model fits the scenarios with large-size
STAR-IOSs while the curve fitting model is extended to evaluate multi-cell
networks. However, these two models cannot obtain accurate diversity orders.
Hence, we figure out the M-fold convolution model to derive accurate diversity
orders. We consider three protocols for STAR-IOSs, namely, the energy splitting
(ES) protocol, the time switching (TS) protocol, and the mode switching (MS)
protocol. Based on the ES protocol, we derive analytical outage probability
expressions for the paired NOMA users by the central limit model and the curve
fitting model. Based on three STAR-IOS protocols, we derive the diversity gains
of NOMA users by the M-fold convolution model. The analytical results reveal
that the diversity gain of NOMA users is equal to the active number of STAR-IOS
elements. Numerical results indicate that 1) in high signal-to-noise ratio
regions, the central limit model performs as an upper bound, while a lower
bound is obtained by the curve fitting model; 2) the TS protocol has the best
performance but requesting more time blocks than other protocols; 3) the ES
protocol outperforms the MS protocol as the ES protocol has higher diversity
gains
Underactuated Source Seeking by Surge Force Tuning: Theory and Boat Experiments
We extend source seeking algorithms, in the absence of position and velocity
measurements, and with tuning of the surge input, from velocity-actuated
(unicycle) kinematic models to force-actuated generic Euler-Lagrange dynamic
underactuated models. In the design and analysis, we employ a symmetric product
approximation, averaging, passivity, and partial-state stability theory. The
proposed control law requires only real-time measurement of the source signal
at the current position of the vehicle and ensures semi-global practical
uniform asymptotic stability (SPUAS) with respect to the linear motion
coordinates for the closed-loop system. The performance of our source seeker
with surge force tuning is illustrated with both numerical simulations and
experiments of an underactuated boat
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