User scheduling, beamforming and energy coordination are investigated in smart-grid powered cellular networks (SGPCNs), where the base stations are powered by a smart grid and natural renewable energy sources. Heterogeneous energy coordination is considered in SGPCNs, namely energy merchandizing with the smart grid and energy exchanging among the base stations. A long-term grid-energy expenditure minimization problem with proportional-rate constraints is formulated for SGPCNs. Since user scheduling is coupled with the beamforming vectors, the formulated problem is challenging to handle via standard convex optimization methods. In practice, the beamforming vectors need to be updated over each slot according to the channel variations. User scheduling needs to be updated over several slots (frame) since the frequent scheduling of user equipment can cause reliability issues. Therefore, the Lyapunov optimization method is used to decouple the problem. A practical two-scale algorithm is proposed to schedule users at each frame, and obtain the beamforming vectors and amount of exchanged natural renewable energy at each slot. We prove that the proposed two-scale algorithm can asymptotically achieve the optimal solutions via tuning a control parameter. Numerical results verify the performance of the proposed twoscale algorithm.
NOMENCLATURE
Variables DefinitionsM Number of BSTs L Number of antennas at each BST N m Number of associated UEs in the mth BST T Number of slots in each frame T k Set of slots in the kth frame h m,n (t k ) Channel-coefficient vector of the (m, n)th access link ω m,n Pathloss of the (m, n)th access link a m,n [k] Scheduled UE indicator y m,n (t k ) Received signal of the (m, n)th UE ).w m,n (t k ) Single-stream beamforming vector for the (m, n)th UE z m,n (t k ) AWGN at the (m, n)th UE σ 2 m,n Power of the AWGN at the (m, n)th UE SINR m,n Received SINR of the (m, n)th UE