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== Adapting MAC scheduling based on PHY parameters ==
Communication systems that need to operate over media with non stationary background noise and interference may benefit from having a close coordination between the [[Medium access control|MAC]] layer (which is responsible for scheduling transmissions) and the [[Physical layer|PHY]] layer (which manages actual transmission and reception of data over the media)
<ref>S. Shabdanov, P. Mitran, C. Rosenberg,
[http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6151784&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6151784 "Cross-Layer Optimization Using Advanced Physical Layer Techniques in Wireless Mesh Networks", in IEEE Transactions on Wireless Communications]</ref><ref name=Miao>{{cite book|author1=G. Miao|author2=G. Song|title=Energy and spectrum efficient wireless network design|publisher=[[Cambridge University Press]]|isbn=1107039886|year=2014}}</ref>
In some communications channels (for example, in power lines), noise and interference may be non-stationary and might vary synchronously with the 50 or 60 Hz [[AC current]] cycle. In scenarios like this, overall system performance can be improved if the MAC can get information from the PHY regarding when and how the noise and interference level is changing, so that the MAC can schedule transmission during the periods of time in which noise and interference levels are lower<ref name=Miao>{{cite book|author1=G. Miao|author2=G. Song|title=Energy and spectrum efficient wireless network design|publisher=[[Cambridge University Press]]|isbn=1107039886|year=2014}}</ref>.
An example of a communications system that allows this kind of Cross-layer optimization is the [[ITU-T]] [[G.hn]] standard, which provides high-speed local area networking over existing home wiring (power lines, phone lines and coaxial cables).
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