RSS measurement

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Introduction

This tutorial helps you to understand how to measure Radio Signal Strength (RSS) received by a Tmote Sky. In this tutorial we have one sender and one receiver. Receiver receives the packet and display the RSS value of the packet received.

You can find the step by step simulation in the next section.

RSS Measurement Program on Cooja

Step 1

Create New Simulation on Cooja. Let's say we call our simulation as "RSS".

Step 2

Create Motes.

Step 3

Browse the firmware. You can find the code later in this tutorial.

Step 4

Compile the firmware.

Step 5

Select number of new motes=2. Note: We are uploading same firmware on both the motes. One will act as Sender and another will act as Receiver.

Step 6

Start the simulation.

Step 7

You can see the RSSI value in the mote output window.

Code

<HEADER FILES>
static struct collect_conn tc;

PROCESS(example_collect_process, "RSS Measurement");
AUTOSTART_PROCESSES(&example_collect_process);

static void recv(const rimeaddr_t *originator, uint8_t seqno, uint8_t hops)
{
  static signed char rss;
  static signed char rss_val;
  static signed char rss_offset;
  printf("Sink got message from %d.%d, seqno %d, hops %d: len %d '%s'\n",originator->u8[0], originator->u8[1],seqno, hops,packetbuf_datalen(),
         (char *)packetbuf_dataptr());
  rss_val = cc2420_last_rssi;
  rss_offset=-45;
  rss=rss_val + rss_offset;
  printf("RSSI of Last Packet Received is %d\n",rss);
}

static const struct collect_callbacks callbacks = { recv };

PROCESS_THREAD(example_collect_process, ev, data)
{
  static struct etimer periodic;
  static struct etimer et;
  
  PROCESS_BEGIN();

  collect_open(&tc, 130, COLLECT_ROUTER, &callbacks);

  if(rimeaddr_node_addr.u8[0] == 1 && rimeaddr_node_addr.u8[1] == 0) 
  {
    printf("I am sink\n");
    collect_set_sink(&tc, 1);
  }

  /* Allow some time for the network to settle. */
  etimer_set(&et, 120 * CLOCK_SECOND);
  PROCESS_WAIT_UNTIL(etimer_expired(&et));

  while(1) 
  {

    /* Send a packet every 1 seconds. */
    if(etimer_expired(&periodic)) 
    {
      etimer_set(&periodic, CLOCK_SECOND * 1 );
      etimer_set(&et, random_rand() % (CLOCK_SECOND * 1));
    }

    PROCESS_WAIT_EVENT();


    if(etimer_expired(&et)) 
    {
      static rimeaddr_t oldparent;
      const rimeaddr_t *parent;
      if(rimeaddr_node_addr.u8[0] != 1 )
      {
        printf("Sending\n");
        packetbuf_clear();
        packetbuf_set_datalen(sprintf(packetbuf_dataptr(),"%s", "Fight On") + 1);
        collect_send(&tc, 15);

        parent = collect_parent(&tc);
        if(!rimeaddr_cmp(parent, &oldparent)) 
        {
           if(!rimeaddr_cmp(&oldparent, &rimeaddr_null))
           {
              printf("#L %d 0\n", oldparent.u8[0]);
           }
           if(!rimeaddr_cmp(parent, &rimeaddr_null)) 
           {
              printf("#L %d 1\n", parent->u8[0]);
           }
           
           rimeaddr_copy(&oldparent, parent);
        }
      }
    }

  } //end of while

  PROCESS_END();
} //end of process thread
 

Understanding the Code

etimer_set(&et, CLOCK_SECOND * 2);

This will set the timer to repeat the iterations every 2 seconds.

SENSORS_ACTIVATE(light_sensor);

SENSORS_ACTIVATE(sht11_sensor);

We need to activate light_sensor for measuring the light intensity and sht11_sensor for the measurement of temperature and humidity.

val = sht11_sensor.value(SHT11_SENSOR_TEMP);

Here we are capturing the actual sensor value.

s = ((0.01*val) - 39.60);

We need to calibrate the sensor values by doing some calculations. You can find the calculations here: http://tinyos.stanford.edu/tinyos-wiki/index.php/Boomerang_ADC_Example

SENSORS_DEACTIVATE(light_sensor);

SENSORS_DEACTIVATE(sht11_sensor);

After we are done with the calculations, we need to deactivate the sensors.

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Edited by : Nitin http://web.stanford.edu/class/cs244e/papers/cc2420.pdf