462 research outputs found
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
A Network Calculus Approach for the Analysis of Multi-Hop Fading Channels
A fundamental problem in the delay and backlog analysis across multi-hop
paths in wireless networks is how to account for the random properties of the
wireless channel. Since the usual statistical models for radio signals in a
propagation environment do not lend themselves easily to a description of the
available service rate on a wireless link, the performance analysis of wireless
networks has resorted to higher-layer abstractions, e.g., using Markov chain
models. In this work, we propose a network calculus that can incorporate common
statistical models of fading channels and obtain statistical bounds on delay
and backlog across multiple nodes. We conduct the analysis in a transfer
domain, which we refer to as the `SNR domain', where the service process at a
link is characterized by the instantaneous signal-to-noise ratio at the
receiver. We discover that, in the transfer domain, the network model is
governed by a dioid algebra, which we refer to as (min,x)-algebra. Using this
algebra we derive the desired delay and backlog bounds. An application of the
analysis is demonstrated for a simple multi-hop network with Rayleigh fading
channels and for a network with cross traffic.Comment: 26 page
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