Obviously, a dense cellular network based on conventional
independent BSs is not suitable for 5G systems. Therefore, a
centralized cellular network architecture has been proposed
and it has become a hot research topic in both academia and
industry. China Mobile announced a centralized radio access
network architecture (C-RAN) in 2009 [4], which incorporates
centralized baseband pool processing, cooperative radio with
distributed antennas equipped with remote radio heads (RRHs),
and real-time cloud infrastructures. Following C-RAN, wireless
network cloud (WNC) [5] by IBM and LightRadio [6] by AlcatelLucent
and Bells Labs are also proposed as possible solutions for
the future centralized wireless networks. Moreover, a RAN
evolution project P-CRAN is set up by NGMN in 2011 [7] to
study the requirement, solution and standardization of C-RAN
for a future radio access network architecture providing
optimized operations, higher efficiency and enhanced performance.
The main idea of these new architectures is to decouple
the radio frequency (RF) and baseband processing functions,
which have been co-located in traditional BSs. Only an RRH is
located in each cell site. The building baseband units, referred
to as BBUs, which perform the baseband processing functions in
traditional BSs are now aggregated and moved into a centralized
location, referred to as the BBU pool. The RRHs are
connected to the BBU pool through high bandwidth optical
networks. With this centralized network architecture, the