Differences

This shows you the differences between two versions of the page.

--- exploring_lora [2018/09/29 23:36] – [5. Coverage Challenge] samer
+++ exploring_lora [2018/10/04 17:43] – [2. Theoretical Study] melhem
@@ Line 57: / Line 57: @@
   * What is the relation between processing gain and spreading factor in LoRa modulation? Explain.
   * How does the spreading factor impact the coverage of a LoRa transmitter?
-  * For each of the three possible configurations of your LoRa device, what is the transmission bit rate? Explain your computation.
+  * What is the transmission bit rate for each of the following configurations of your LoRa device? Explain your computation.
+    * Configuration 1: channel bandwidth = 125 kHz, spreading factor = 7, coding rate = 4/5.
+    * Configuration 2: channel bandwidth = 500 kHz, spreading factor = 7, coding rate = 4/5.
+    * Configuration 3: channel bandwidth = 125 kHz, spreading factor = 12, coding rate = 1/2.
   * Compute the receiver sensitivity, assuming the following parameters: channel bandwidth = 125 kHz, spreading factor = 7, coding rate = 4/5, bit error rate (BER) target = 10<sup>-4</sup>, and receiver noise figure = 6 dB. Refer to this {{ :1705.05899.pdf | article}} to determine the mapping between the BER and the SNR.
   * Compare the computed sensitivity to that provided by the {{ :an1200.22.pdf |Semtech Application Note AN1200.22}} for the same parameters.
@@ Line 69: / Line 72: @@
 Download the {{ :sketch-1819.zip | basic sketches}} that implement a simple LoRa communication between the two devices: a client and a server. Open the sketches with Arduino IDE. Make sure to choose the correct ''Board'' and ''Port'' in the ''Tools'' menu.
-Take a look at the source code in ''rf95_client.ino'' and ''rf95_server.ino''. Particularly, the ''setup'' function configures the radio parameters of your LoRa devices:
+Take a look at the source code in ''rf95_client.ino'' and ''rf95_server.ino''. Particularly, the following extract from the ''setup'' function configures the radio parameters of your LoRa devices:
-  * Central frequency (freq)
+  * Central frequency
-  * Spreading Factor (SF)
+  * Spreading Factor
-  * Bandwidth (Bw)
+  * Bandwidth
-  * Coding Rate (CR)
+  * Coding Rate
-  * Transmit power (Pow)
+  * Transmit power
 <code c++>
@@ Line 121: / Line 124: @@
 ==== -. Time on Air ====
-In this section, you will measure the Time on Air (ToA) that is given by the time necessary to transmit a message on the radio interface . You will assess the impact of the spreading factor, bandwidth, coding rate, and message size on the ToA.
+In this section, you will measure the Time on Air (ToA) that is given by the time necessary to transmit a message on the radio interface. You will assess the impact of the spreading factor, bandwidth, coding rate, and message size on the ToA.
 Start by implementing a function on the client that measures the time necessary for sending a message. For example, you can use the [[https://www.arduino.cc/en/Reference/Micros| micros()]] function available in the arduino libraries. Now, you can modify one of the parameters (spreading factor, bandwidth, coding rate, message size) and record the impact on the ToA. Note well that you may need to repeat the experiment multiple times in order to obtain the statistical distribution.
@@ Line 135: / Line 138: @@
 In this section, you will measure the coverage of LoRa under different radio configurations.
-Start by identifying a set of five geographical locations or Test Points (TP). These TPs should be astutely chosen to explore the limits of LoRa coverage. Then, you should implement a function on the server that measures the ratio of successfully delivered packets or PDR. Now, you should run the experiment for three different radio configurations: such configurations should ensure different reliability levels (high, medium, and low reliability).
+Start by identifying a set of five geographical locations or Test Points (TP). These TPs should be astutely chosen to explore the limits of LoRa coverage. Then, you should implement a function on the server that measures the ratio of successfully delivered packets or PDR (Packet Delivery Ratio). Now, you should run the experiment for three different radio configurations: such configurations should provide different reliability levels (high, medium, and low reliability).
 <WRAP center round help 100%>
@@ Line 159: / Line 162: @@
 ===== -. Coverage Challenge =====
-In this section, you are required to establish a record of LoRa coverage. Some rules must be followed to validate the record:
+In this section, you are required to establish a record of LoRa coverage. You can certainly unleash your scientific imagination, but some rules must be followed to validate the record:
   * Direct transmission between the two devices is only considered.
@@ Line 166: / Line 169: @@
 <WRAP center round help 100%>
-  * Provide the expression of the link budget.
+  * Compute the Fresnel zone for your transmission.
-  * Draw the RSSI values as a function of the distance.
+  * Provide the expression of the link budget and compute the received power using two different pathloss models.
-  * What is the path loss exponent?
+  * Compare the received power obtained experimentally with the theoretical results.
-  * Using regressions, compute a value of the path loss exponent. Analyze the result.
+  * Write an article (blog, wiki, ...) to describe your experiment.
-  * Compare the obtained sensitivity with the theoretical results computed in the previous section.
 </WRAP>
 ===== -. Grading =====