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Modular Integration Strategy

The EverTag Connectivity Module utilizes pre-certified RF modules (e.g., PAN B611-1, ESP32-C5, SIM7672E) to reduce the cost, time, and risk associated with full intentional radiator testing. However, maintaining the validity of these modular approvals requires strict adherence to integration guidelines.

Maintaining Modular Approvals

To legally leverage a module's existing FCC/CE certifications, the final product design must comply with the conditions specified in the module's grant.

Antenna and Trace Routing

  • Strict Adherence: The PCB layout must strictly follow the module manufacturer's antenna layout guidelines, including trace impedance, keep-out areas, and ground plane design.
  • Approved Antennas: Only antennas that are explicitly listed in the module's certification grant (or antennas of the same type with equal or lesser gain) may be used.
  • Consequence of Deviation: Any deviation from the approved trace routing or antenna selection voids the modular approval, requiring the entire system to undergo full intentional radiator testing (e.g., a Class II Permissive Change for FCC).

Firmware Power Limits

  • Tx Power Settings: The firmware must enforce the exact maximum transmit (Tx) power limits specified in the module's FCC/CE grants for each frequency band and modulation type.
  • Verification: The test lab will verify that the end product cannot be configured by the user to exceed these approved power levels.

Co-location and Multi-Transmitter Scenarios

The EverTag Connectivity Module may contain multiple radios (BLE, WiFi, LTE) that can transmit simultaneously. Pre-certified modules are typically evaluated in isolation. When integrated together, they require additional assessment.

Co-location Rules

  • Definition: Co-location occurs when two or more transmitting antennas are located within 20 cm of each other and can transmit simultaneously.
  • Assessment Required: Simultaneous transmission often requires additional RF Exposure (SAR/MPE) calculations and spurious emissions testing to ensure the radios do not cause intermodulation products or exceed exposure limits when operating together.

Strategy for EverTag

To manage co-location and simultaneous transmission, the EverTag architecture employs specific hardware and firmware coexistence mechanisms:

  1. 2.4 GHz (nRF54 + ESP32): BLE and Wirepas share the same nRF54 radio (internal time-division managed by the Wirepas stack). WiFi runs on a separate ESP32 chip with its own antenna. Wirepas built-in Adaptive Frequency Avoidance (AFA) automatically avoids WiFi-occupied channels, and Wirepas duty cycle is <0.1%. Configuring the ESP32 to prefer 5 GHz WiFi eliminates 2.4 GHz contention entirely. 3-wire coexistence GPIOs (REQUEST, PRIORITY, GRANT) are routed on the PCB for optional future firmware-based arbitration.
  2. WiFi + LTE: The ESP32 manages coexistence with the LTE modem via the LTE_TX_BLANK signal (GPIO25). Physical isolation (~20-30 dB) is achieved via diagonal antenna placement (~40-60mm separation) and orthogonal polarization (LTE vertical, WiFi horizontal).
  3. Radar (60 GHz): The 60 GHz radar operates in a completely different frequency band, resulting in zero coexistence/interference concern with the 2.4 GHz or LTE radios.
  4. RF Exposure Assessment: Perform Maximum Permissible Exposure (MPE) calculations for the combined RF output of all co-located transmitters to ensure compliance with human exposure limits.
  5. Spurious Emissions Testing: Conduct radiated spurious emissions testing with all co-located transmitters operating simultaneously at their maximum power to verify that no new, non-compliant emissions are generated.

Phase 2 Integration Rules (LTE & Radar)

Our two-phase certification strategy defers the LTE modem and 60 GHz radar to Phase 2.

Radar Pre-Certification Integration

The Acconeer A121 60 GHz radar sensor has achieved modular approval (e.g., FCC Part 15.255). To leverage this pre-certification and avoid full intentional radiator testing at 60 GHz, the integration must strictly follow Acconeer's guidelines. This includes adhering to the minimum ground plane requirements (≥20 × 20 mm) and using only approved lens configurations as specified in the A121 datasheet's Regulatory Approvals section.

Class II Permissive Change (C2PC)

When the LTE and radar features are ready for market, we will not need to start certification from scratch. Instead, we will submit a Class II Permissive Change (C2PC) to the FCC (and equivalent updates for CE).

Important Note on Lab Testing: A C2PC does not mean skipping the test lab. It means the scope of testing is drastically reduced. The lab will not need to re-evaluate the fundamental intentional radiator characteristics of the radios. However, the lab must still perform Radiated Spurious Emissions (RSE) and RF Exposure (MPE/SAR) testing on the fully assembled Phase 2 board. This proves that adding the new pre-certified transmitters (LTE and 60 GHz) to the Phase 1 radios (BLE/WiFi) does not cause illegal simultaneous co-location emissions.