291,245 research outputs found
Predictor-based robust control of uncertain nonlinear systems subject to input delay
10th IFAC Workshop on Time Delay Systems, TDS-2012; Boston, MA; United States; 22 June 2012 through 24 June 2012In this paper, a tracking controller is developed for a class of nonlinear systems subject to time delay in the control input, uncertainties in the dynamic model, and additive disturbances. The control development is based on a novel predictor-like method to address the time delay in the control input. Lyapunov based stability analysis is used to prove semi-global asymptotic tracking. © 2012 IFAC
Adaptive Network Coding Schemes for Satellite Communications
In this paper, we propose two novel physical layer aware adaptive network
coding and coded modulation schemes for time variant channels. The proposed
schemes have been applied to different satellite communications scenarios with
different Round Trip Times (RTT). Compared to adaptive network coding, and
classical non-adaptive network coding schemes for time variant channels, as
benchmarks, the proposed schemes demonstrate that adaptation of packet
transmission based on the channel variation and corresponding erasures allows
for significant gains in terms of throughput, delay and energy efficiency. We
shed light on the trade-off between energy efficiency and delay-throughput
gains, demonstrating that conservative adaptive approaches that favors less
transmission under high erasures, might cause higher delay and less throughput
gains in comparison to non-conservative approaches that favor more transmission
to account for high erasures.Comment: IEEE Advanced Satellite Multimedia Systems Conference and the 14th
Signal Processing for Space Communications Workshop (ASMS/SPSC), 201
On the ergodic sum-rate performance of CDD in multi-user systems
The main focus of space-time coding design and analysis for MIMO systems has
been so far focused on single-user systems. For single-user systems, transmit
diversity schemes suffer a loss in spectral efficiency if the receiver is
equipped with more than one antenna, making them unsuitable for high rate
transmission. One such transmit diversity scheme is the cyclic delay diversity
code (CDD). The advantage of CDD over other diversity schemes such as
orthogonal space-time block codes (OSTBC) is that a code rate of one and delay
optimality are achieved independent of the number of transmit antennas. In this
work we analyze the ergodic rate of a multi-user multiple access channel (MAC)
with each user applying such a cyclic delay diversity (CDD) code. We derive
closed form expressions for the ergodic sum-rate of multi-user CDD and compare
it with the sum-capacity. We study the ergodic rate region and show that in
contrast to what is conventionally known regarding the single-user case,
transmit diversity schemes are viable candidates for high rate transmission in
multi-user systems. Finally, our theoretical findings are illustrated by
numerical simulation results.Comment: to appear in Proceedings of 2007 IEEE Information Theory Workshop
(ITW) in Lake Taho
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