Everactive’s second and third generation technology are built upon its ultra-low power (ULP), always-on network, Evernet. As shown in Figure 1, Evernet connects Eversensor devices to our gateways using this proprietary protocol that we designed to leverage our custom ULP receiver chips. Evernet gateways are installed on-site, and provide an intermediate control plane for our network, as well as a local data buffer in the case of cloud connectivity outages. Most often, LTE is used as the backhaul connection from the Evergateways to our Evercloud to simplify the IT infrastructure and installation. Wi-Fi and Ethernet backhaul connections are also supported.
The main advantages of Evernet are:
- Batteryless – Everactive has redefined ultra-low power (ULP) for radios and built custom receiver chips that operate on trace amounts of power.
- Always-on, millisecond latency – the power of Everactive’s receiver chip is so low that we never have to turn it off; therefore, sensors are continuously connected to gateways and can be reached instantly, if necessary.
- Scalable, 1,000+ sensors per gateway – our always-on receiver significantly reduces wireless traffic for network synchronization, therefore allowing many more nodes to share the spectrum.
- Secure – all data is encrypted using AES, and our ULP receiver includes a cryptographic checksum to eliminate replay attacks.
- Designed for dense environments (industrial / buildings / commercial) – Eversensors communicate on a sub-GHz frequency for deep penetration in dense settings with severe non-line-of-sight channels.
Chip Block Diagram
The core of our technology, and one of Everactive’s key pieces of differentiation, is our custom, ULP system-on-chip (SoC). A simplified system diagram of one application is shown in Figure 2. Our SoC includes energy-harvesting power management, timers, digital signal processing, and memory, as well as our ULP receiver. The key components of the SoC for Evernet are the ULP receiver and the Arm Cortex M0 32-bit processor which executes the networking software stack. The SoC is combined with a commercial off-the-shelf (COTS) IEEE 802.15.4g compliant radio to offload the data communication traffic. Both radios are connected to a single integrated antenna inside the body of the Eversensor.
Evernet uses the always-on ULP receiver on the SoC to handle all network synchronization traffic through an encrypted broadcast channel from the gateway. In addition, this receiver can decode basic operational instructions and process global and/or local network-level interrupts. While the COTS radio is used for bidirectional data traffic, time division multiple access (TDMA) coordination is achieved with the ULP radio and local timing references provided by our SoC. These network-level synchronization functions are necessary in order to provide a robust communication solution, and they are often the most power-hungry functions of any standard wireless protocol, such as Bluetooth. By bringing these functions inside our SoC and using Everactive’s proprietary ULP circuit design expertise, the power is reduced by 1000x, while also providing a more scalable and low-latency networking solution.
Comparison to Other Solutions
The plot in Figure 3 shows how Everactive’s ULP receivers compare to state-of-the-art published research results in terms of active power and sensitivity (a measure of wireless range). This plot highlights the 1000x reduction in power compared to the best-in-class COTS receiver. As a comparison, standard compliant receivers such as Bluetooth and Zigbee operate in the 5,000-30,000uW range.
Table 1, below, compares Evernet 2.0 to some commonly used IoT networks. Other networks are forced to adopt a “duty-cycled” operation of their radios, leaving them off most of the time, in order to save power. This impacts the power required for synchronization overhead to align the narrow on-times of each sensor, as well as the latency to communicate to any single device.