In the cooperative cellular network, relay-like base stations are connected to the central processor (CP) via rate-limited fronthaul links and the joint processing is performed at the CP, which thus can effectively mitigate the multiuser interference. In this paper, we consider the joint beamforming and compression problem with per-antenna power constraints in the cooperative cellular network. We first establish the equivalence between the considered problem and its semidefinite relaxation (SDR). Then we further derive the partial Lagrangian dual of the SDR problem and show that the objective function of the obtained dual problem is differentiable. Based on the differentiability, we propose two efficient projected gradient ascent algorithms for solving the dual problem, which are projected exact gradient ascent (PEGA) and projected inexact gradient ascent (PIGA). While PEGA is guaranteed to find the global solution of the dual problem (and hence the global solution of the original problem), PIGA is more computationally efficient due to the lower complexity in inexactly computing the gradient. Global optimality and high efficiency of the proposed algorithms are demonstrated via numerical experiments.

翻译：在协作蜂窝网络中，类似中继的基站通过速率受限的前传链路连接到中央处理器，并在中央处理器处进行联合处理，从而能有效抑制多用户干扰。本文研究协作蜂窝网络中带有每根天线功率约束的联合波束赋形与压缩问题。首先建立了该问题与其半定松弛之间的等价性，然后进一步推导了半定松弛问题的部分拉格朗日对偶，并证明所得对偶问题的目标函数是可微的。基于该可微性，我们提出了两种高效的投影梯度上升算法来求解对偶问题，即投影精确梯度上升法和投影非精确梯度上升法。投影精确梯度上升法能保证找到对偶问题的全局最优解（从而也是原始问题的全局最优解），而投影非精确梯度上升法由于非精确计算梯度时复杂度更低，因此计算效率更高。数值实验验证了所提算法的全局最优性和高效性。