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LMIC_low_power

This is a first attempt to add low-power mode to the Arduino LMIC port. The lmic folder contains the modified version of the LMIC port based on version 1.5.0+arduino-2. Modified files are:

Arduino_LoRa_LMIC_ABP_temp is the LMIC-based Arduino example similar to the Arduino_LoRa_temp example of the our low-cost LoRa IoT framework. Its structure and features are the same (simple temperature sensor, keep track of sequence number on reset, low-power consumption down to 5uA in sleep mode) except that it uses the LMIC port to build a LoRaWAN device. For smallest power consumption, please look at our YouTube video tutorial Extreme low-cost & low-power LoRa IoT for real-world deployment.

Arduino_LoRa_LMIC_OTAA_temp is the OTAA version of Arduino_LoRa_LMIC_ABP_temp. This example is for demonstrating the usage of an SX1301-based concentrator hat (e.g. RAK831/2245) with our gateway framework. Please refer to this README for more details.

The main reason of this contribution is because low-power mode on AVR microcontrollers makes both millis() and micros() to be not updated, causing timing issues in the LMIC stack, especially the time to complete the EV_TXCOMPLETE event. The idea is to store the amount of sleep time in order to add it to the value returned by hal_ticks(). A new function hal_sleep_lowpower(u1_t sleepval) is introduced to allow the main low-power loop to indicate to the LMIC stack how much sleep time (in seconds) it has to take into account when returning hal_ticks().

Installation

Flash a device

You will need an Arduino device such as the Arduino Pro Mini in 8MHz and 3.3v version. Connect a LoRa radio module and change the DIO mapping in Arduino_LoRa_LMIC_ABP_temp and Arduino_LoRa_LMIC_OTAA_temp according to your configuration. The example uses DR_SF12.

You have several options of PCBs:

In order to use Arduino_LoRa_LMIC_ABP_temp, you need to create an ABP device on TTN for instance to get the device short address (32 bits) and, if you want, both NwkSKey and AppSKey. These information have to be filled in the example code. A nice tutorial can be found on https://medium.com/kkbankol-events/tutorial-build-a-open-source-smart-city-based-on-lora-7ca76b9a098.

In order to use Arduino_LoRa_LMIC_ABP_temp, you need to create an OTAA device on TTN.

The default sleep time is 5min, unsigned int TX_INTERVAL = 5*60;. In a real-world application, set it to more than 10mins or higher.

Output from Serial Monitor

Here is a typical output from Arduino IDE's Serial Monitor with both #define SHOW_LOW_POWER_CYCLE and #define SHOW_LMIC_LOWPOWER_TIMING uncommented. To deploy a sensor device for a real-world scenario, comment these lines.

LoRa temperature sensor, LMIC extended version
Arduino Pro Mini detected
ATmega328P detected
Get back previous sx1272 config
Using seqnoUp of 1
Forced to use default parameters
Using idle period of 300
Reading 244
Reading 238
Reading 235
Reading 233
Reading 230
Mean temp is 22.25
Sending \!TC/22.25
Real payload size is 10
234974: Packet queued
454645: EV_TXCOMPLETE (includes waiting for RX windows)
diff in ticks: 219671
diff in seconds: 3
now micros: 7287424
cumulated sleep: 0
now ticks: 455464
now ticks from os_getTime(): 455464
Switch to power saving mode
8888888888888888888888888888888888881D[860]
Reading 305
Reading 302
Reading 299
Reading 296
Reading 292
Mean temp is 22.25
Sending \!TC/22.25
Real payload size is 10
18623475: Packet queued
18843145: EV_TXCOMPLETE (includes waiting for RX windows)
diff in ticks: 219670
diff in seconds: 3
now micros: 12504112
cumulated sleep: 289
now ticks: 18844007
now ticks from os_getTime(): 18844007
Switch to power saving mode
888888888888

As you can see, after the wake up from the sleep period of 5mins, EV_TXCOMPLETE happens after about 3s ("diff in seconds: 3") which means that the transmission happen almost immediately. This is actually the normal behavior as a sleep time of 5mins is more than the minimum off-time imposed by the LMIC's duty-cycle rule (about 146s for DR_SF12). Therefore the transmission can be scheduled to happen immediately, validating the correct timing of the LMIC stack after a sleep period.

If you compared to the output below when there is no specific low-power management (unmodified LMIC stack) then you can see that in addition to sleeping for 5mins, on wake up LMIC schedules the next transmission to be 146s in the future ("diff in seconds: 146") as its internal clock based on micros() has not advanced while the microcontroller was put in sleep mode.

LoRa temperature sensor, LMIC extended version
Arduino Pro Mini detected
ATmega328P detected
Get back previous sx1272 config
Using seqnoUp of 1
Forced to use default parameters
Using idle period of 300
Reading 232
Reading 226
Reading 222
Reading 219
Reading 216
Mean temp is 22.25
Sending \!TC/22.25
Real payload size is 10
235132: Packet queued
454801: EV_TXCOMPLETE (includes waiting for RX windows)
diff in ticks: 219669
diff in seconds: 3
now micros: 7289896
now ticks: 455618
now ticks from os_getTime(): 455619
Switch to power saving mode
8888888888888888888888888888888888881D[866]
Reading 291
Reading 287
Reading 283
Reading 279
Reading 275
Mean temp is 22.25
Sending \!TC/22.25
Real payload size is 10
560285: Packet queued
9722398: EV_TXCOMPLETE (includes waiting for RX windows)
diff in ticks: 9162113
diff in seconds: 146
now micros: 155572568
now ticks: 9723285
now ticks from os_getTime(): 9723286
Switch to power saving mode
88888888888888888841D[484]

Using single-channel gateway

There is also a modification to discuss with a single-channel gateway:

static void initJoinLoop (void) {
    //added by C. Pham
#ifdef LMIC_SCG
    LMIC.txChnl = 0;
#else
    LMIC.txChnl = os_getRndU1() % 3;
    setDrJoin(DRCHG_SET, DR_SF7);
#endif
    LMIC.adrTxPow = 14;
    initDefaultChannels(1);
    ASSERT((LMIC.opmode & OP_NEXTCHNL)==0);
    LMIC.txend = LMIC.bands[BAND_MILLI].avail + rndDelay(8);
}

static ostime_t nextJoinState (void) {
    u1_t failed = 0;
    //added by C. Pham
#ifdef LMIC_SCG
    setDrJoin(DRCHG_NOJACC, (dr_t)LMIC.datarate);
#else
    // Try 869.x and then 864.x with same DR
    // If both fail try next lower datarate
    if( ++LMIC.txChnl == 3 )
        LMIC.txChnl = 0;
    if( (++LMIC.txCnt & 1) == 0 ) {
        // Lower DR every 2nd try (having tried 868.x and 864.x with the same DR)
        if( LMIC.datarate == DR_SF12 )
            failed = 1; // we have tried all DR - signal EV_JOIN_FAILED
        else
            setDrJoin(DRCHG_NOJACC, decDR((dr_t)LMIC.datarate));
    }
#endif
    // Clear NEXTCHNL because join state engine controls channel hopping
    LMIC.opmode &= ~OP_NEXTCHNL;
    ...

Using 433MHz band

There is also a modification to work in the 433MHz band. In config.h uncomment BOTH #define CFG_eu868 1 and #define CFG_eu433 1 to have your device sending on the 433MHz band. The 3 mandatory frequencies are then 433.175, 433.375 and 433.575 while the frequency for downlink in the RX2 window is set to 434.665 (according to LoRaWAN EU433 plan). If #define LMIC_SCG is on then only the first channel, i.e. 433.175MHz, will be used for both data uplink and join-request for OTAA.

Important notice

This modified LMIC distribution has by default:

Comment #define LMIC_SCG if you want to benefit from the low-power features but talking to a multi-channel LoRaWAN gateway. Enjoy! C. Pham