  Both dual-functional radar-communication (DFRC) and massive multiple-input
multiple-output (MIMO) have been recognized as enabling technologies for 6G
wireless networks. This paper considers the advanced waveform design for
hardware-efficient massive MIMO DFRC systems. Specifically, the transmit
waveform is imposed with the quantized constant-envelope (QCE) constraint,
which facilitates the employment of low-resolution digital-to-analog converters
(DACs) and power-efficient amplifiers. The waveform design problem is
formulated as the minimization of the mean square error (MSE) between the
designed and desired beampatterns subject to the constructive interference
(CI)-based communication quality of service (QoS) constraints and the QCE
constraint. To solve the formulated problem, we first utilize the penalty
technique to transform the discrete problem into an equivalent continuous
penalty model. Then, we propose an inexact augmented Lagrangian method (ALM)
algorithm for solving the penalty model. In particular, the ALM subproblem at
each iteration is solved by a custom-built block successive upper-bound
minimization (BSUM) algorithm, which admits closed-form updates, making the
proposed inexact ALM algorithm computationally efficient. Simulation results
demonstrate the superiority of the proposed approach over existing
state-of-the-art ones. In addition, extensive simulations are conducted to
examine the impact of various system parameters on the trade-off between
communication and radar performances.
