  The virtualization of Radio Access Networks (RANs) has been proposed as one
of the important use cases of Network Function Virtualization (NFV). In VRAN!s
(VRAN!s), some functions from a Base Station (BS), such as those which make up
the Base Band Unit (BBU), may be implemented in a shared infrastructure located
at either a data center or distributed in network nodes. For the latter option,
one challenge is in deciding which subset of the available network nodes can be
used to host the physical BBU servers (the placement problem), and then to
which of the available physical BBUs each Remote Radio Head (RRH) should be
assigned (the assignment problem). These two problems constitute what we refer
to as the VRANPAP! (VRAN-PAP!). In this paper, we start by formally defining
the VRAN-PAP! before formulating it as a Binary Integer Linear Program (BILP)
whose objective is to minimize the server and front haul link setup costs as
well as the latency between each RRH and its assigned BBU. Since the BILP could
become computationally intractable, we also propose a greedy approximation for
larger instances of the VRAN-PAP!. We perform simulations to compare both
algorithms in terms of solution quality as well as computation time under
varying network sizes and setup budgets.
