11 research outputs found
Throughput, Bit-Cost, Network State Information: Tradeoffs in Cooperative CSMA Protocols
In wireless local area networks, spatially varying channel conditions result
in a severe performance discrepancy between different nodes in the uplink,
depending on their position. Both throughput and energy expense are affected.
Cooperative protocols were proposed to mitigate these discrepancies. However,
additional network state information (NSI) from other nodes is needed to enable
cooperation. The aim of this work is to assess how NSI and the degree of
cooperation affect throughput and energy expenses. To this end, a CSMA protocol
called fairMAC is defined, which allows to adjust the amount of NSI at the
nodes and the degree of cooperation among the nodes in a distributed manner. By
analyzing the data obtained by Monte Carlo simulations with varying protocol
parameters for fairMAC, two fundamental tradeoffs are identified: First, more
cooperation leads to higher throughput, but also increases energy expenses.
Second, using more than one helper increases throughput and decreases energy
expenses, however, more NSI has to be acquired by the nodes in the network. The
obtained insights are used to increase the lifetime of a network. While full
cooperation shortens the lifetime compared to no cooperation at all, lifetime
can be increased by over 25% with partial cooperation.Comment: Some typos in v1 were corrected, to be presented at ISWCS 2010 in
York, United Kingdo
Experimental Comparison of Probabilistic Shaping Methods for Unrepeated Fiber Transmission
\u3cp\u3eThis paper studies the impact of probabilistic shaping on effective signal-to-noise ratios (SNRs) and achievable information rates (AIRs) in a back-to-back configuration and in unrepeated nonlinear fiber transmissions. For the back-to-back setup, various shaped quadrature amplitude modulation (QAM) distributions are found to have the same implementation penalty as uniform input. By demonstrating in transmission experiments that shaped QAM input leads to lower effective SNR than uniform input at a fixed average launch power, we experimentally confirm that shaping enhances the fiber nonlinearities. However, shaping is ultimately found to increase the AIR, which is the most relevant figure of merit, as it is directly related to spectral efficiency. In a detailed study of these shaping gains for the nonlinear fiber channel, four strategies for optimizing QAM input distributions are evaluated and experimentally compared in wavelength division multiplexing (WDM) systems. The first shaping scheme generates a Maxwell-Boltzmann (MB) distribution based on a linear additive white Gaussian noise channel. The second strategy uses the Blahut-Arimoto algorithm to optimize an unconstrained QAM distribution for a split-step Fourier method based channel model. In the third and fourth approach, MB-shaped QAM and unconstrained QAM are optimized via the enhanced Gaussian noise (EGN) model. Although the absolute shaping gains are found to be relatively small, the relative improvements by EGN-optimized unconstrained distributions over linear AWGN optimized MB distributions are up to 59%. This general behavior is observed in 9-channel and fully loaded WDM experiments.\u3c/p\u3