  With the increase of physical antenna and subcarrier numbers in MIMO-OFDM
systems, channel side information feedback amount and signal precoding
complexity overburden will consume much more system resource, even become
intolerable. To solve this problem, previous works mainly focused on fixed
subcarrier grouping size and precoded MIMO signals in the same group with
unitary channel state information (CSI). It could reduce the system overburden,
but such a process would lead to system capacity loss due to the channel
mismatch in precoding procedure. In this paper, we consider a MIMOOFDM system
over double-selective i.i.d. Rayleigh channels and investigate the quantitative
relation between group size and capacity loss theoretically. By exploiting our
developed theoretical results, we also propose an adaptive subcarrier grouping
algorithm, which not only enables to have a good control of system service
quality but also to reduce system overburden significantly. Numerical results
are shown to provide valuable insights on the system design of MIMO-OFDM
systems and indicate that the proposed subcarrier grouping scheme is extremely
efficient in some common scenarios.
