“…Here, we rely instead on the theory of online convex optimization (OCO) which: (i) does not require access to performance/cost functions or system/user-related parameters; and (ii) offers guarantees under a wide range of scenarios, including adversarial ones [92]. The robustness of OCO is particularly useful for vRANs which, due to the virtualized vBS functions, exhibit volatile performance and, importantly, high energy costs [18,26,38,40]. These experimental findings motivated the design of policies about the vBSs' transmission power, modulation and coding schemes, spectrum usage, and others, which aim to curb the vRANs energy costs [14,15,17].…”