Achievable Degrees of Freedom in MIMO Correlatively Changing Fading   Channels
  The relationship between the transmitted signal and the noiseless received signals in correlatively changing fading channels is modeled as a nonlinear mapping over manifolds of different dimensions. Dimension counting argument claims that the dimensionality of the neighborhood in which this mapping is bijective with probability one is achievable as the degrees of freedom of the system.We call the degrees of freedom achieved by the nonlinear decoding methods the nonlinear degrees of freedom. 
Mina Karzand and Lizhong Zheng
cs.IT math.IT