Issue link: https://resources.mouser.com/i/1520713
Beyond the Wires 20 receivers connected to an STM32WL—especially for applications like non-stationary asset tracking. A hub is also an STM32WL-based device, but it is configured as a master that controls baud rate, modulation type, and power to optimize link performance. More important, however, is that the hub controls the time slot generation and frequency- hopping configuration needed to meet FCC requirements and sets the communication timetable between itself, other hubs, and other nodes. Thus, each node or associated hub is completely aware of the communication time slot and frequency structure. Broadcasting this information to all elements of the network allows for a highly efficient network structure. The network topology decision to broadcast the information a priori to all network elements promotes higher bandwidths, frequency, and time re-use. The first enhancement that helps with network expandability is that each general node can also communicate with other general nodes in a peer- to-peer mode, essentially performing as a mesh network and extending the footprint of the network. As previously discussed, the main hub analyzes the time slot structure and broadcasts a connection table, where nodes may communicate within an unused sector of a time slot. A second enhancement in this architecture is that each general node can also join additional networks controlled by other hubs where those networks' coverage areas overlap, further extending the network footprint. Consequently, small local area wireless networks can be expanded by adding other local area wireless networks. The networks may operate in an overlapping manner or, if separated due to distance or obstructions blocking the wireless signals, may be connected using relay nodes. These relay nodes, as opposed to general nodes, are specialized nodes capable of connecting two or more hubs to overcome distance or physical barriers. A third enhancement further leverages the ability of nodes to interact with other hubs by ensuring that timing is tightly controlled between hubs, allowing for mobility at pedestrian speeds as the node moves from one hub's coverage area into another's. This new architecture enhancement takes advantage of the STM32WL's GFSK modulation support, its TimeServer function (which allows each time slot to be precisely set between hubs and nodes), and its inherent customizability. It does this through a frequency-hopped, time-division multiplexing (TDM) communications protocol (Figure 3). Along with mobility, the structured time slot patterns and broadcast information allow nodes to enter stop or sleep Tx Transmission Rx Transmission 400 mS (MAX) Time Slot Re-Use Node to Node Tx_Process Rx_Process Radio.Rx(400) Rx Window Tx Window Run Run Stop Modes Figure 3: Single time slot transaction summary, including node-to-node events. (Source: STMicroelectronics) Long Range connectivity with S2-LP