LoRa multiple communication

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Hi all, I have a problem regarding “LoRa multiple communication” on ESP32.

I am doing a project with 3 wifi sniffer nodes as 3 slaves. They will always be active, keeping sniffering/listening to the nearby packets data. They send the data to the server only when a specific request has been sent by the master. The workflow will be like: master send requests to slave 1 and wait for answer from slave 1 at 0~1s. When the slave 1 got the request, it will send the data to the server. Same applies to slave 2 and 3 in every second afterwards.

My problem is that not every request sent by master will be answered by the specific slave. I.e., it might request 5 times and only got 1 response, like the picture below. Also, the program became blocked forever when around 32 packets have been set to the master (Not sure if it’s relevant to LoRa.endPacket())
2020-12-21 13 54 18
The (part of) master code is:

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loop(){if (millis() - lastRequestSentTime > 500){ if (turn == 1) { SendRequest("1#"); // Send request to Client 1 receiveFromSlaveDevice("1#"); // This is data from Client 1 lastRequestSentTime = millis(); // trun = 2; // contintues to turn 2 and 3 } } vTaskDelay( 100 / portTICK_PERIOD_MS );}

Code: [[Select]](javascript:void(0):wink:

void SendRequest( String request ){ LoRa.beginPacket(); // start packet LoRa.print(request); // send request LoRa.endPacket(); // finish packet and send it} // SendRequest

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void receiveFromSlaveDevice( String nodeID ){ int packetSize = LoRa.parsePacket(); if (packetSize) { Serial.println( "Received packet from: " + nodeID ); String incomingMessage = ""; // payload of incoming packet while ( LoRa.available() ) { String incomingMessage = LoRa.readString(); // incomingMessage (WiFi device data) format: Timestamp \t MAC Address \t RSSI \n int pos1 = incomingMessage.indexOf('\t'); int pos2 = incomingMessage.indexOf('\t', pos1 + 1); int pos3 = incomingMessage.indexOf('\n', pos2 + 1); std::vector<String> wifiDevicePayload(3); wifiDevicePayload[0] = incomingMessage.substring(0, pos1); // Timestamp wifiDevicePayload[1] = incomingMessage.substring(pos1 + 1, pos2); // MAC Address wifiDevicePayload[2] = incomingMessage.substring(pos2 + 1, pos3); // RSSI Serial.println("Index 1: " + wifiDevicePayload[0]); printWiFiDeviceData( wifiDevicePayload ); xQueueSend( g_queueBetweenReceiveAndWebServer, &wifiDevicePayload, portMAX_DELAY ); } }}

The (part of) slave code is:

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int packetSize = LoRa.parsePacket();if (packetSize){ while ( LoRa.available() ) { String request = LoRa.readString(); if ( request == "1#" ) { Serial.println( "Client 1 got request, answering Server..." ); sendToMasterDevice( WiFiDeviceData ); } else { Serial.println( "ERROR - No requests from Server." ); } }}

It seems there is some transition time needed for the LoRa chip to switch from sending mode to receiving mode. But there is not a function can be used to wait until a message is received… (Like

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RF95.waitAvailableTimeout()
in RadioHead Library, RadioHead: RHGenericDriver Class Reference).
I was mainly refering to this: https://miliohm.com/multi-clients-lora-with-a-server-communication/. And I wonder if it is possible to achieve the same thing by using arduino-LoRa library (GitHub - sandeepmistry/arduino-LoRa: An Arduino library for sending and receiving data using LoRa radios.)

Any suggestions or ideas will be of highly appreciated! Many thanks!