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--- reliable_lora_communication [2016/09/30 10:46] – [6. Modifying the Radio Parameters] samer
+++ reliable_lora_communication [2016/10/12 15:08] (current) – removed samer
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-====== Simple Prototype of LoRa Communications ======
-As defined by Semtech, LoRa(c) is //a wireless technology developed to create the low-power, wide-area networks (LPWANs) required for machine-to-machine (M2M) and Internet of Things (IoT) applications. The technology offers a very compelling mix of long range, low power consumption and secure data transmission and is gaining significant traction in IoT networks being deployed by wireless network operators//.
-In the following, we present a prototype of LoRa communication between two wireless modules. This enables to get basic insights on the implementation of the technology and prepares some advanced prototypes and experimentations.
-===== -. Hardware and Cost =====
-  * Arduino Uno or Mega (x2) for [[https://www.amazon.fr/SODIAL-ATmega2560-Microcontroleur-Arduino-Module/dp/B00OPO44UE/ref=sr_1_3?ie=UTF8&qid=1468680586&sr=8-3&keywords=arduino+mega | 10 USD]].
-  * Dragino shields (x2) for [[http://www.aliexpress.com/store/product/Long-distance-wireless-lora-shield-for-Arduino-Leonardo-UNO-Mega2560-Duemilanove-Due/1390863_32591527766.html|20 USD]].
-  * 868 MHz Antenna (x2) for [[http://fr.farnell.com/rf-solutions/ant-8whip3h-sma/ant-868mhz-whip-hinged-sma-3dbi/dp/2305899?MER=BN-2305899| 5 USD]].
-===== -. Software =====
-  * RadioHead: The Packet Radio library for embedded microprocessors can be downloaded from [[http://www.airspayce.com/mikem/arduino/RadioHead/]] or from this [[http://www.airspayce.com/mikem/arduino/RadioHead/RadioHead-1.61.zip|direct link]].
-  * Arduino IDE: Specific OS versions can be downloaded from [[https://www.arduino.cc/en/Main/Software]].
-===== -. Compatibility =====
-This tutorial is written for :
-  * Arduino IDE 1.6.9.
-  * RadioHead 1.61.
-  * Dragino hardware release v1.3.
-  * Mac OS 10.11.5.
-Beware of the necessary modifications, if any of the previous specifications is not supported in your case.
-===== -. Installation =====
-Start by plugging the Dragino shields on the Arduino devices and mounting the antennas as shown in Fig. 1.
-[{{ :dragino-arduino-mega.jpg?nolink&300 |Figure 1. Arduino with LoRa Dragino shield.}}]
-Connect the two Arduino devices to USB ports on your computer. If this is the first time you use Arduino IDE, make sure to install the necessary USB drivers by selecting ''Tools'' > ''Boards Manager'' and installing Arduino AVR boards.
-Now, you have to select the corresponding ''Board'' and ''Port'' in the ''Tools'' menu to program your Arduino. For example, you can use the following:
-  * For Arduino Uno: Board = Arduino/Genuino Uno Mega, Port = /dev/cu.wchusbserial1420.
-  * For Arduino Mega: Board = Arduino/Genuino Mega 2560, Port = /dev/cu.usbmodem141511.
-Unzip the RadioHead library and copy it to your sketchbook library folder as detailed in [[https://www.arduino.cc/en/Guide/Libraries]].
-===== -. Running Basic Sketches =====
-Start by setting the central frequency of the LoRa modules. For this, open the ''RH_RF95.cpp'' file locate in the ''RadioHead'' folder and change the frequency to 868.1 Mhz:
-<file cpp RH_RF95.cpp>
-setFrequency(868.1);
-</file>
-Download the {{ :client-server-reliable-lora.zip | basic sketches}} that implement a reliable LoRa communication between the two modules. Open the sketches with Arduino IDE, compile and upload on the two arduino modules, respectively. On the serial interfaces, you should obtain similar results as in Fig. 2 and Fig. 3.
-[{{ :client-radiohead.png?direct&600 ||Figure 2. Client serial monitor}}]
-[{{ :server-radiohead.png?direct&600 ||Figure 3. Server serial monitor}}]
-===== -. Modifying the Radio Parameters =====
-The typical configuration for loRa modules consists of 125 KHz sub-channels, a coding rate of 4/5 and a spreading factor equal to 7. This configuration ensures higher data rate but is more vulnerable in harsh radio conditions. You want to ensure more robustness to noise on the radio channel or extend the coverage, you may change the module configuration to a stronger coding rate of 4/8 and a spreading factor of 12. This obviously comes at the expense of lower data rates ! The procedure is explained in the following.
-Start by modifying in modem config in ''RH_RF95.cpp'':
-<file cpp RH_RF95.cpp>
-//setModemConfig(Bw125Cr45Sf128); // Radio default
-setModemConfig(Bw125Cr48Sf4096); // slow and reliable?
-</file>
-As the data rate is lower, you may need to increase the timeout before declaring a lot transmission. Thus, you need to add a variable in ''RH_LONG_TIMEOUT.h'' that equals 8 seconds and set the timeout in ''RHReliableDatagram.cpp''.
-<file cpp RHReliableDatagram.h>
-#define RH_LONG_TIMEOUT 8000
-</file>
-<file cpp RHReliableDatagram.cpp>
-RHReliableDatagram::RHReliableDatagram(RHGenericDriver& driver, uint8_t thisAddress)
-    : RHDatagram(driver, thisAddress)
-{
-    _retransmissions = 0;
-    _lastSequenceNumber = 0;
-    //_timeout = RH_DEFAULT_TIMEOUT;
-    _timeout = RH_LONG_TIMEOUT;
-    _retries = RH_DEFAULT_RETRIES;
-}
-</file>