# A Spectrum Management Platform Architecture to Enable a Sharing Economy in 6G
## 4 HODNET Architecture
### Description of HODNET Planes  
The HODNET architecture defines a set of planes that facilitate the low-level programmability necessary to achieve scalable, logically centralised spectrum trading as depicted in Figure 3c. While Wi-5 only considered a single centralised physical controller for a specific scenario, HODNET can be deployed in a distributed manner, making use of  
Figure 3: Description of HODNET architecture: (**a**) high-level description of HODNET architecture; (**b**) illustration of the difference between HODNET and SDWN control paths; (**c**) planes in HODNET architecture; (**d**) Interaction between Agent and Master in HODNET architecture.  
dynamic Edge Computing platforms, and partly being implemented through NFV and Service Function Chaining architectures to facilitate multi-operator deployments. This will further reinforce the scalability aspects of HODNET (req. 2) and address the availability issues discussed above (req. 1). The planes presented in Figure 2(c) can be described as follows:  
* Infrastructure Plane. This plane includes the nodes through which the radio resources of each RAN can be accessed and shared, such as 5G Base Stations (gNBs) or Wi-Fi APs. The nodes each run software agents which expose the parameters to configure these nodes, such as transmission power, transmission and reception channel, coding scheme, and the number of connected devices.
* Heterogeneous Spectrum Programming Plane. This plane defines the primitives that enable access to and configuration of the RAN parameters. The configurations are applied to the nodes via a Master/Agent system which translates them to be specific to the underlying technology (e.g., 802.11 channel and transmission strength) and also includes a monitoring primitive that gathers information related to the radio resources available at each RAN.
* Control Plane. This plane includes the HODNET controller as well as the SDWN controller. The difference between the roles of each controller is depicted in Figure 2(b). The SDWN controller is responsible for managing the data path, depicted by a blue dashed line. The HODNET controller is responsible for managing the spectrum path (depicted by a red dashed line), i.e., the radio configuration of the access nodes. The control plane will, for example, coordinate vertical handovers between operators and technologies via the SDWN Controller but manage interference using the HODNET Controller.
* Radio Resources Sharing Plane. This plane implements a variety of Radio Resource Management (RRM) algorithms and monitoring mechanisms, communicating with the available RANs about their resources via the control plane. The algorithms use the collected monitoring information and apply heterogeneous RRM techniques such as cell aggregation. Note that the techniques used to manage the heterogeneous radio resource will be limited to the RATs accessed by the controller through the Heterogeneous Spectrum Programming Plane.
* Brokering Interface. This is the interface between the Radio Resources Sharing Plane and the various operators. It automates the negotiation process, in which the RANs and offers are each represented by agents. The agents then barter a deal, e.g., using a negotiating algorithm as described in [13]. While an in-depth analysis of this functionality is beyond the scope of this paper, an example of what the architecture for such a Brokering Platform could look like has been published in [27].