741 research outputs found
Optimal Pilot Symbols Ratio in terms of Spectrum and Energy Efficiency in Uplink CoMP Networks
In wireless networks, Spectrum Efficiency (SE) and Energy Efficiency (EE) can
be affected by the channel estimation that needs to be well designed in
practice. In this paper, considering channel estimation error and non-ideal
backhaul links, we optimize the pilot symbols ratio in terms of SE and EE in
uplink Coordinated Multi-point (CoMP) networks. Modeling the channel estimation
error, we formulate the SE and EE maximization problems by analyzing the system
capacity with imperfect channel estimation. The maximal system capacity in SE
optimization and the minimal transmit power in EE optimization, which both have
the closed-form expressions, are derived by some reasonable approximations to
reduce the complexity of solving complicated equations. Simulations are carried
out to validate the superiority of our scheme, verify the accuracy of our
approximation, and show the effect of pilot symbols ratio.Comment: 5 pages, 3 figures, 2017 IEEE 85th Vehicular Technology Conference
(VTC Spring
The Impact of QoS Constraints on the Energy Efficiency of Fixed-Rate Wireless Transmissions
Transmission over wireless fading channels under quality of service (QoS)
constraints is studied when only the receiver has channel side information.
Being unaware of the channel conditions, transmitter is assumed to send the
information at a fixed rate. Under these assumptions, a two-state (ON-OFF)
transmission model is adopted, where information is transmitted reliably at a
fixed rate in the ON state while no reliable transmission occurs in the OFF
state. QoS limitations are imposed as constraints on buffer violation
probabilities, and effective capacity formulation is used to identify the
maximum throughput that a wireless channel can sustain while satisfying
statistical QoS constraints. Energy efficiency is investigated by obtaining the
bit energy required at zero spectral efficiency and the wideband slope in both
wideband and low-power regimes assuming that the receiver has perfect channel
side information (CSI). In both wideband and low-power regimes, the increased
energy requirements due to the presence of QoS constraints are quantified.
Comparisons with variable-rate/fixed-power and variable-rate/variable-power
cases are given. Energy efficiency is further analyzed in the presence of
channel uncertainties. The optimal fraction of power allocated to training is
identified under QoS constraints. It is proven that the minimum bit energy in
the low-power regime is attained at a certain nonzero power level below which
bit energy increases without bound with vanishing power
Performance Analysis and Enhancement of Multiband OFDM for UWB Communications
In this paper, we analyze the frequency-hopping orthogonal frequency-division
multiplexing (OFDM) system known as Multiband OFDM for high-rate wireless
personal area networks (WPANs) based on ultra-wideband (UWB) transmission.
Besides considering the standard, we also propose and study system performance
enhancements through the application of Turbo and Repeat-Accumulate (RA) codes,
as well as OFDM bit-loading. Our methodology consists of (a) a study of the
channel model developed under IEEE 802.15 for UWB from a frequency-domain
perspective suited for OFDM transmission, (b) development and quantification of
appropriate information-theoretic performance measures, (c) comparison of these
measures with simulation results for the Multiband OFDM standard proposal as
well as our proposed extensions, and (d) the consideration of the influence of
practical, imperfect channel estimation on the performance. We find that the
current Multiband OFDM standard sufficiently exploits the frequency selectivity
of the UWB channel, and that the system performs in the vicinity of the channel
cutoff rate. Turbo codes and a reduced-complexity clustered bit-loading
algorithm improve the system power efficiency by over 6 dB at a data rate of
480 Mbps.Comment: 32 pages, 10 figures, 1 table. Submitted to the IEEE Transactions on
Wireless Communications (Sep. 28, 2005). Minor revisions based on reviewers'
comments (June 23, 2006
On space-time trellis codes over rapid fading channels with channel estimation
Ph.DDOCTOR OF PHILOSOPH
BER and optimal power allocation for amplify-and-forward relaying using pilot-aided maximum likelihood estimation
Bit error rate (BER) and outage probability for amplify-and-forward (AF) relaying systems with two different channel estimation methods, disintegrated channel estimation and cascaded channel estimation, using pilot-aided maximum likelihood method in slowly fading Rayleigh channels are derived. Based on the BERs, the optimal values of pilot power under the total transmitting power constraints at the source and the optimal values of pilot power under the total transmitting power constraints at the relay are obtained, separately. Moreover, the optimal power allocation between the pilot power at the source, the pilot power at the relay, the data power at the source and the data power at the relay are obtained when their total transmitting power is fixed. Numerical results show that the derived BER expressions match with the simulation results. They also show that the proposed systems with optimal power allocation outperform the conventional systems without power allocation under the same other conditions. In some cases, the gain could be as large as several dB's in effective signal-to-noise ratio
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