Femtocell self-organzation



Keith Briggs 2013-12-19 (This project can interact with the other femtocell
timeslot synchronization project which I am simultaneously proposing.  The 
first three paragraphs of general background information are identical.)



LTE is the technology currently being deployed for 4G wireless services.  As
well as providing the new generation of mobile phone services, its potential
application to other areas is being investigated.



A basic principle of LTE is the division of the two dimensions of frequency and
time into so-called resource blocks (RB); a RB can be imagined as a rectangular
unit capable of carrying a certain amount of data.   In the time dimensions,
RBs are 1 millisecond long. 



A possible application is to have a small LTE base-station ("femtocell") in
every house, as a replacement for a wifi homehub.  But there is a risk of 
interference, causing reductions in the data rate, and so various kinds of
interference mitigation mechanisms are being considered.  Roughly speaking, we
want to achieve a self-organizating network (SON), in which each femtocell
manages its own resource in response to its local environment, without any
central planning or management.  In mathematical terms, we have a complex
system, with femtocells as nodes, and a graph with edges representing neighbour
relationships.  This project would use complex systems ideas, rather than
specifics of the LTE technology (though some specifics cannot be ignored).   



Each femtocell can use a range of radio modulation schemes, dependent on the
signal-to-interference ratio (SIR).  As the SIR reduces, a more robust
modulation scheme can be switched to, but this carries less data, so more RBs
are needed in compensation.  This means that more interference is caused to
neighbours, and these neighbours in turn will have to react to maintain their
data rate, for example by also using more RBs.   So it is not obvious that the
global dynamics of this process is stable; there might be a convergence to a
fully-blocked state where no femtocell can transmit data.



This this project would be to develop a formal model of this interaction of
femtocells with neighbours, and either prove by analytical methods that it is 
stable, or demonstrate stability by computer simulation.