Wang Yong, Ma Lin, Xu Yubin
School of Electronics and Information Engineering, Harbin Institute of Technology, Harbin 150080, China.
Sensors (Basel). 2017 Jun 26;17(7):1498. doi: 10.3390/s17071498.
In the downlink cloud radio access network (C-RAN), fronthaul compression has been developed to combat the performance bottleneck caused by the capacity-limited fronthaul links. Nevertheless, the state-of-arts focusing on fronthaul compression for spectral efficiency improvement become questionable for energy efficiency (EE) maximization, especially for meeting its requirements of large-scale implementation. Therefore, this paper aims to develop a low-complexity algorithm with closed-form solution for the EE maximization problem in a downlink C-RAN with limited fronthaul capacity. To solve such a non-trivial problem, we first derive an optimal solution using branch-and-bound approach to provide a performance benchmark. Then, by transforming the original problem into a parametric subtractive form, we propose a low-complexity two-layer decentralized (TLD) algorithm. Specifically, a bisection search is involved in the outer layer, while in the inner layer we propose an alternating direction method of multipliers algorithm to find a closed-form solution in a parallel manner with convergence guaranteed. Simulations results demonstrate that the TLD algorithm can achieve near optimal solution, and its EE is much higher than the spectral efficiency maximization one. Furthermore, the optimal and TLD algorithms are also extended to counter the channel error. The results show that the robust algorithms can provide robust performance in the case of lacking perfect channel state information.
在下行链路云无线接入网络（C-RAN）中，前传压缩技术已得到发展，以应对由容量受限的前传链路所导致的性能瓶颈。然而，专注于通过前传压缩来提高频谱效率的现有技术，对于实现能效（EE）最大化而言，尤其是在满足大规模实施的要求方面，变得值得怀疑。因此，本文旨在针对前传容量受限的下行链路C-RAN中的能效最大化问题，开发一种具有闭式解的低复杂度算法。为了解决这一具有挑战性的问题，我们首先使用分支定界法推导最优解，以提供性能基准。然后，通过将原始问题转化为参数减法形式，我们提出了一种低复杂度的两层分布式（TLD）算法。具体而言，外层采用二分搜索，而在内层，我们提出一种乘子交替方向法算法，以并行方式找到闭式解并保证收敛。仿真结果表明，TLD算法能够实现接近最优的解，并且其能效远高于频谱效率最大化算法。此外，最优算法和TLD算法还被扩展以应对信道误差。结果表明，在缺乏完美信道状态信息的情况下，鲁棒算法能够提供稳健的性能。
