# Multi-RAT Orchestration Method for Heterogeneous Wireless Networks
## 2 State-of-the-Art
It refers to the development of the 5G network (beyond 5G) toward future 6G network solutions, where new KPIs will be introduced, not defined currently within the 5G framework (e.g., link energy efficiency, battery saving, and others), the implementation of which can be ensured by a properly managed multi-RAT network orchestrator. The latest trends in the use of software in the network, such as Software Defined Networking (SDN) and Network Function Virtualization (NFV), are opening new opportunities for operators, especially in deploying highly adaptive networks and offering defined specific requirements to end users. The centralized nature of SDN can directly help in obtaining network context information that can be used to optimize resources. The use of SDN allows for an even better implementation of the multi-RAT concept. For example, in [11], the authors proposed an SDN-based multi-RAT LTE and Wi-Fi data flow management system. In this case, a multi-RAT solution for automatic off-loading was proposed. Another paper [12] analyzes the multi-RAT solution in low-power, low-bitrate LPWAN networks (NB-IoT, Sigfox, and LoRaWAN) used to optimize the energy consumption and extend the life of battery transmitters. It should be noted that various terms referring to \"heterogeneous networks\" exist. For some, even a single mobile network operator's environment, consisting of different 3 GPP RATs (3G, 4G, 5G) or different cell types (macro, micro, pico), may be treated as a heterogeneous network. In other cases, it is also referred to as a cellular network, but with different radio band accesses, i.e., licensed, unlicensed LAAs, and/or shared LSAs). In this paper, we are using the broader concept of the heterogeneous wireless network term, which includes mobile networks (4G/LTE, 5G/NR, 6G) along with other non-3 GPP RAT radio solutions (WLAN, LPWAN, RLAN), transmitting in licensed, unlicensed, and shared frequency bands--a new type of hybrid heterogeneous wireless network managed at the highest level while orchestrated on the hypernetwork layer setting. At the radio level, there is the emergence of various multi-RAT radio network managers and the current development trend of software-defined radio solutions (SDR--Software Defined Radio) that can also be observed. SDR is a radio system in which transceiver components that are typically implemented in hardware (to name a few: implemented digital multiplexers, filters, equalizers, modulators/demodulators, multiple antenna techniques in an ASIC, i.e., application-specific integrated circuit) are instead implemented by computer software or an embedded system equipped with programmablehardware such as an ASIP (Application Specific Instruction Set Processor) or an FPGA (Field Programmable Gate Array). The combination of the multi-RAT technique with SDR solutions allows for modeling and predicting the emergence of new cases of its application, e.g., single radio systems (front-end) implementing many radio interfaces on one transmitting device (SDR/FPGA) or others. This may in the future further simplify the configuration and management of the radio interface, especially its analog radio part. Table 1 presents an overview of the currently available open source SDR software solutions dedicated for mobile system emulation and testing. The projects presented encompass both the Radio Access Network (RAN) and the core network (CN). RANs for the following solutions have a fully implemented Layer 1-3 radio protocol stack (i.e., PHY, MAC, RLC, PDCP, and RRC). Programmable radio systems using the software solutions listed in Table 1 have been used in many research projects thus far, such as network coexistence analyzing using shared access to spectrum, smart metering in LTE networks [18], managing radio resources between Wi-Fi and LTE-U networks [19], developing a solution supporting the search for people after a disaster [20].