# Joint Beam-Forming Optimization for Active-RIS-Assisted Internet-of-Things Networks with SWIPT
The Reconfigurable Intelligent Surface (RIS) is a programmable structure that can change the electromagnetic properties of its own surface in real-time, making the direction of signal propagation change, which is expected to build a new paradigm of 6G intelligent programmable wireless environment [13]. MIMO, as a key physical layer technology currently used in 5G communications, inevitably generates communication blocking, and RIS can effectively solve the blocking problem in this communication process, which is not only energy-efficient but also highly cost-effective [14]. Its basic principle is to arrange adjustable panels on the surface of an outdoor building to reflect passive signals sent from the base station in any desired direction, thus intrinsically manipulating the propagation environment and achieving the goal of improving energy and spectral efficiency [15; 16]. For RIS, there have been more research results [17; 18; 19; 20; 21]. For example, [17] investigated the electromagnetic and physical properties of RIS, and the authors developed a signal propagation attenuation model for wireless communication in free space after the inclusion of RIS, which is applicable in various scenarios, revealing that the signal propagation attenuation is not only related to the area of RIS, the distance from the transmitting end and the receiving end to the RIS, but also the direction of radiation between the antenna and the RIS unit, as well as the effect of the RIS's long-/short-range action. Ref. [18] focuses on the uplink of RIS-enabled multiuser MISO communication systems, and based on this, a channel estimation framework based on parallel factorization is proposed. Ref. [19] proposes a new concept of active RIS(A-RIS), which reduces the limitation of the \"multi-path fading\" effect and solves the optimization problem of maximizing the summation rate in an A-RIS-assisted MU-MISO system. The physical implementation of the active RIS consists of two parts; first, the element has an internal phase-shift circuit which is responsible for changing the phase of the signal; in addition to this, each active RIS element is additionally equipped with an active reflection-type amplifier, which can amplify the reflected signals at the cost of affordable power consumption and hardware cost. Particularly, the reflection-type amplifier can be realized by many low-cost methods, such as current-inverting converter or asymmetric current mirror. Ref. [20] also points out that, unlike passive RIS (P-RIS), A-RIS can both change the direction of the signal and increase its strength. The \"multiplicative fading\" effect due to the presence of BS to RIS channels and RIS to User K channels is overcome, and the size of the RIS is drastically reduced. Ref. [21] added P-RIS and A-RIS to the same communication system, respectively, and after comparing them, it was discovered that the A-RIS system saves more power than the P-RIS system when the same performance is achieved. The number of devices in 6G IoT communication has exploded, but the spectrum is becoming more and more scarce, and the energy is becoming more and more limited. To be able to effectively alleviate this problem, the Simultaneous Wireless Information and Power Transfer (SWIPT) technology came into being, which can effectively alleviate the spectrum and energy crisis [22; 23]. Specifically, this technology can transmit signals to users while performing information decoding (ID) and energy harvesting (EH). Since signal receivers have different sensitivities, there are two typical receiver architectures in information and energy co-transmission systems, namely, the time splitting (TS) architecture, which uses time as the dividing factor, and the power splitting (PS) architecture [24], which uses power as the splitting factor. With the PS architecture, any user can use a power divider to split the power of the received signal into two parts in a specified ratio, one for ID and the other for EH [25]. Ref.