Adaptive connected hybrid beamforming for energy efficiency maximization in multi-user millimeter wave systems

Energy efficiency (EE) is a key enabler for sustainable green millimeter wave (mmWave) communication. However, conventional hybrid beamforming methods suffer from energy efficiency performance loss due to hardware limitations and the connected structure. To overcome these limitations, this work investigates a novel adaptive connected (AC) hybrid beamforming (HBF) design for multi-user mmWave systems. We formulate the problem as an EE maximization problem subject to the constraints of the adaptive connected structure, constant modulus, and power budget. Addressing this complicated non-convex problem, we harness the characteristics of the AC structure and introduce an iterative HBF design algorithm grounded in fractional programming. Numerical results demonstrate the effectiveness and flexibility of the proposed AC-based HBF design in terms of EE enhancement.