Energy Efficiency of Indoor THz Communication Systems with Finite-bit DACs/ADCs under Minimum Rate Constraints

Terahertz (THz) communication is expected to be a key technology of next-generation wireless communication. In this paper, we study the energy efficiency of an indoor THz communication system employing array-of-subarray structure. In the system, each radio frequency (RF) chain is connected with one antenna subarray and finite-bit digital-to-analog converters (DACs) at the access point (AP) side or analog-to-digital converters (ADCs) at user side. We assume minimum achievable rate constraint to satisfy the communication requirements and propose a joint power and subarray optimization policy to maximize the energy efficiency, which is the division of the sum achievable rate and total power consumption including the transmission power and circuit power given by the up-to-date studies. Specifically, the energy efficiency maximization problem is decomposed into subproblems of finding the optimal power allocation and optimal subarray number. An algorithm is proposed to find the optimal settings. Through numerical results, the proposed scheme outperforms other benchmark schemes in terms of energy efficiency. Also, it is shown that the optimal configuration of the number of subarrays is essential for energy efficiency maximization in the considered system.