  In spatially distributed multiuser antenna systems, the received signal
contains multiple carrier-frequency offsets (CFOs) arising from mismatch
between the oscillators of transmitters and receivers. This results in a
time-varying rotation of the data constellation, which needs to be compensated
at the receiver before symbol recovery. In this paper, a new approach for blind
CFO estimation and symbol recovery is proposed. The received base-band signal
is over-sampled, and its polyphase components are used to formulate a virtual
Multiple-Input Multiple-Output (MIMO) problem. By applying blind MIMO system
estimation techniques, the system response can be estimated and decoupled
versions of the user symbols can be recovered, each one of which contains a
distinct CFO. By applying a decision feedback Phase Lock Loop (PLL), the CFO
can be mitigated and the transmitted symbols can be recovered. The estimated
MIMO system response provides information about the CFOs that can be used to
initialize the PLL, speed up its convergence, and avoid ambiguities usually
linked with PLL.
