  Recently, Cloud-based Radio Access Network (C-RAN) has been proposed as a
potential solution to reduce energy cost in cellular networks. C-RAN
centralizes the baseband processing capabilities of Base Stations (BSs) in a
cloud computing platform in the form of BaseBand Unit (BBU) pool. In C-RAN,
power consumed by the traditional BS system is distributed as wireless
transmission power of the Remote Radio Heads (RRHs) and baseband processing
power of the BBU pool. Different from previous work where wireless transmission
power and baseband processing power are optimized individually and
independently, this paper focuses on joint optimization of allocation for these
two kinds of power and attempts to minimize the total power consumption subject
to Quality of Service (QoS) requirements from users in terms of data rates.
First, we exploit the load coupling model to express the coupling relations
among power, load and user data rates. Based on the load coupling mode, we
formulate the joint power optimization problem in C-RAN over both wireless
transmission power and baseband processing power. Second, we prove that
operating at full load may not be optimal in minimizing the total power
consumption in C-RAN. Finally, we propose an efficient iterative algorithm to
solve the target problem. Simulations have been performed to validate our
theoretical and algorithmic work. The results show that the proposed algorithm
outperforms existing schemes (without joint power optimization) in terms of
power consumption.
