Meaning
Technical standards established by Japanese regulatory bodies define the transmission characteristics and operational parameters for 920 MHz band telemeter, telecontrol, and low-power data communication systems. Under ARIB STD-T108, radio equipment operating in the frequency range from 920.5 MHz to 928 MHz must conform to strict power thresholds, carrier sense intervals, and frequency stability limits. The specification governs both 20 mW specified low-power radio stations and 250 mW high-output systems, establishing clear physical radio boundaries for smart meters, environmental sensors, and localized wireless controllers.
Its jurisdiction stops at national spectrum limits, leaving wideband cellular networks and non-Japanese sub-gigahertz allocations outside its purview.
Channel Arbitration
Listen-before-talk protocols embedded in the standard require devices to assess spectrum availability before transmitting a signal. Under ARIB STD-T108, nodes must measure signal energy across a selected channel for a minimum duration of 128 microseconds to 5 milliseconds depending on the designated channel spacing and transmission power class. If the sensed energy exceeds negative 80 dBm, the radio postpones transmission and executes an exponential backoff sequence.
This mechanism prevents collision cascades across shared mesh networks deployed in dense residential or industrial clusters. Transmission bursts face mandatory duration ceilings, restricting single continuous packet transmissions to 400 milliseconds or 4 seconds according to station classification. Consecutive transmissions necessitate mandatory pause intervals of at least 2 milliseconds or 50 milliseconds.
Hardware timers configured within baseband microcontrollers manage these duration boundaries, preventing stuck firmware loops from permanently seizing local channel access.
Emission Mask
Adjacent channel power ratios enforced across the band prevent out-of-band energy from desensitizing adjacent receivers. Compliance requires transmitter leakage outside the assigned channel to drop by at least 20 dB at the adjacent channel boundary and 40 dB across non-adjacent bands. Harmonic suppression thresholds demand attenuation down to 2.5 microwatts or lower for spurious emissions detected above 1 GHz.
Achieving these levels forces developers to select low-phase-noise local oscillators and clean power amplifier supply decoupling on the radio frequency board. Poorly routed traces between the radio module and the matched trace antenna generate common-mode noise that invalidates these emission boundaries.
Regulatory Verification
Construction design certification testing evaluates the radio in both conducted and radiated arrangements inside an accredited test house. Technicians verify frequency tolerance within 20 parts per million across the designated temperature operating range of negative 10 to positive 55 degrees Celsius. Receiver spurious emissions must not exceed 4 nanowatts across sub-1 GHz bands, protecting co-located radios from local oscillator radiation.
The technical conformit mark registered under Japanese Radio Law validates the physical integration and fixes the module firmware revision against tampering. Modifications to board traces, enclosure dielectric properties, or operational firmware require delta evaluation to uphold the certified status of the hardware.
