69 research outputs found
On the Effective Capacity of Two-Hop Communication Systems
In this paper, two-hop communication between a source and a destination with
the aid of an intermediate relay node is considered. Both the source and
intermediate relay node are assumed to operate under statistical quality of
service (QoS) constraints imposed as limitations on the buffer overflow
probabilities. It is further assumed that the nodes send the information at
fixed power levels and have perfect channel side information. In this scenario,
the maximum constant arrival rates that can be supported by this two-hop link
are characterized by finding the effective capacity. Through this analysis, the
impact upon the throughput of having buffer constraints at the source and
intermediate-hop nodes is identified.Comment: submitted to ICC 201
Channel Coding over Multiple Coherence Blocks with Queueing Constraints
This paper investigates the performance of wireless systems that employ
finite-blocklength channel codes for transmission and operate under queueing
constraints in the form of limitations on buffer overflow probabilities. A
block fading model, in which fading stays constant in each coherence block and
change independently between blocks, is considered. It is assumed that channel
coding is performed over multiple coherence blocks. An approximate lower bound
on the transmission rate is obtained from Feintein's Lemma. This lower bound is
considered as the service rate and is incorporated into the effective capacity
formulation, which characterizes the maximum constant arrival rate that can be
supported under statistical queuing constraints. Performances of variable-rate
and fixed-rate transmissions are studied. The optimum error probability for
variable rate transmission and the optimum coding rate for fixed rate
transmission are shown to be unique. Moreover, the tradeoff between the
throughput and the number of blocks over which channel coding is performed is
identified.Comment: submitted to ICC 201
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
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