High-load processing is performed at the receiving station side. Since processing on the user device side is just for the simple operation of sending the data acquired by sensors, its power consumption can be minimized.
The transmitter transmits the same data four times, and the receiver aligns the timings of the four sets of data and synthesizes the waveform. This waveform synthesis can be expected to improve the sensitivity by up to 6 dB.
Transmission is performed with known synchronization bits periodically inserted between the data, and the receiver estimates the influence of the communication channel characteristics based on this synchronization bits. This influence is then canceled to correct the fading factor due to fast movements.
The LDPC error correction method, which is generally used for high volume streaming data like TV broadcasts, is optimized for LPWA low-bit packets and applied. This improves the sensitivity by 7 dB and enables robust communications.
Chirp modulation that varies the frequency over time enables multiplexing of many signals while making full use of the channel bandwidth. In addition, the spread spectrum effect also improves immunity to interference from other systems.
The frequency channel used for transmission is changed for every transmission. In addition, for the Japanese specification, when the carrier of another system is detected in the desired transmission channel, the system transmits on a different channel to reduces the effect of interference from other systems.
Synchronous communication is performed between the transmitting devices and the receiving station using accurate GNSS time information. This enables multiplexing with a high time density. In addition, no preamble is required for each transmission, which helps to shorten transmission times.
* The ELTRES™core protocol has been standardized as the ETSI TS 103 357 “Lfour Family.”
|Antenna Radiated power||20 mW|
|Communication direction||Uplink only|
|Frequency band||923.5 MHz to 928.1 MHz (23-channel frequency hopping)|
|Main modulation system||π/2 Shift BPSK|
|Sub-modulation system||Linear chirp modulation|
|Transmission system||Four repeated transmissions of 0.4 sec or shorter packets|
|Reduction of interference with other systems||CSMA (Carrier Sense Multiple Access)|
|Error correction code||LDPC (Low Density Parity Check) code|
|User payload length||128 bits|
|Transmission modes||Periodically repeated transmission mode, Event-triggered transmission mode|
|Minimum transmission interval||1 minute|
* The above are the ELTRES™ system specifications, and may differ slightly from the actual service specifications.