Transcript
Wireless sensor network and its planning
Wireless networks are more and more often used for data acquisition from sensors. New standards are being designed and users are more and more meeting wireless communication on field of industrial or building automation. The design and development of wireless network is rather difficult task, especially inside buildings. The estimation of signal coverage before the wireless technology is bought and deployed seems to be an important step which may save time and money.
1. Switch on the PC and notebook (login student, password student) and run program WavenisTester (link on the desktop). Choose the serial port with radiomodem (COM1 on desktop PC, COM? on notebook – check in resource manager) and click on LoadDLL. Then write the A0 sequence into the program command line and send it. If the response is received from the modem (06 – positive acknowledgement and ID string), the communication channel between computer and modem is successfully established (all commands are in hexadecimal form). 2. Check the modems setting using the commands in the attached table (details can be found in the modem user manual): a)
Switch mode status (5010 command) should return 510000
b)
RF communication mode (66 command) should return 670000A3
c)
RSSI autocorrection (5A command) should return 5B0001
If there are differences, set the required values. 3. Check the communication between modems. Address of the modem is available on the bottom cover (below the bar code). The command to send the message is 22aaaaaaaaaaaadd..dd, where aa..aa is the destination MAC address and dd..dd is the transmitted data. 4. Check the level of the received signal is higher than –70 dBm. Use the command for RSSI (Received Signal Strength Indicator) readings. The level of locally received signal from the remote node can be obtained by 6Aaaaaaaaaaaaa command, the level of received signal at the remote node can be obtained by 68aaaaaaaaaaaa command, where aa..aa is a remote node address (in both cases !!!).
Approximate relation between the RSSI values and signal levels is provided by the table bellow: Input level (dBm)
RSSI
-69
0x1F
-74
0x1C
-79
0x19
-84
0x16
-89
0x12
-94
0x0E
-99
0x0A
-104
0x06
-109
0x02
RSSI range is 0 – 20h. 5. Run the I-Prop program on the notebook PC. It allows estimating the wireless network signal coverage inside the building. Read the chapter 9 (page 31) of I-Prop user manual. 6. Create a new project using the instructions in chapter 10 of the manual. Background bitmap is stored in „blok A3.bmp“ file. Set the scale of model (the distance from the stairs to the front wall of the block is 20 m). Try the „one-slope“ model, check the influence of different environment types. Add the second and fourth floors of the building by copying the 3rd floor and model the signal coverage again. The output level of the stationary modem is 14 dBm, do not take the antenna gain into account. 7. Define the walls and their types (necessary for „multi-wall“ model) using the background bitmap. Two wall types (thin and thick) are enough – ask instructor for details. Model the signal coverage for all three floors. 8. Disconnect the notebook from the power supply and measure the signal level at three different positions in the hall using the 6A command and repeat it for the second and fourth floors. 9. Analyze the quality of coverage estimation provided by the model. Take into account an additive error caused by non-calibrated antennas. 10. Switch on the WiFi access point and using a Winbox program check that it is configured in AP mode. 11. Change the model parameters in I-Prop program so that the 2.4 GHz frequency falls between fmin and fmax (ignore an error message).
12. Calibrate the model using one measurement at hall in the 3rd floor. 13. Measure the signal strength at complete 3rd and fourth floors. (Use the inSSIDer program or registered clients in Winbox program). 14. Evaluate the influence of antenna gain and polarization. (Use inSSIDer or Winbox program again.) 15. Compare the measured results with simulation. 16. Compare the quality of simulation for WiFi and 868 band radio. 17. Use all available antennas and estimate their gain (the gain of TPLink antenna – an antenna with stand – is 5 dBi). Test the influence of polarization and shielding (e.g. by hand) of the antennas.
Remarks to measurement Overview of modem commands and parameters: // Read and Write functional parameters 40=write, 50=read 5000 // read awakening period (multiples of 100 ms, 0 = 20 ms, max. 0A = 10s) 5001 // read wakeup type (0=long, 1=short - 50 ms) 5002 // read wakeup length (multiples of 1 ms, 1400 = 20 ms, 1027 = 10 s) 5003 // read polling group 5004 // read radio ACK (0 - no, 1 - yes) 5005 // read radio address 5006 // read relay route status (0 - disabled, 1 - enabled) 5007 // read relay route 5008 // read polling route 5009 // read polling group number 500A // read polling time (multiples of 100 ms) 500C // read radio user timeout (multiples of 100 ms) 500E // read exchange status 5010 // read switch mode status (automatic TX mode) 5016 // read multicast group 5017 // read broadcast reception timeout // Read and Select RF communication mode 66 // read RF communication mode 6400A1 // select 433 MHz, FH, 9600 640012 // select 868 MHz, SC, 4800 640094 // select 868 MHz, SC, 4800, Alarm Band 6400A2 // select 868 MHz, SC, 9600, channel select 6400A3 // select 868 MHz, FH, 9600 6400B3 // select 868 MHz, FH, 19200 6400B6 // select 869 MHz, 500 mW 6400B9 // select 915 MHz, FH, 19200 // Read and Select RF channel 62 // read RF channel 60xx // channel number 0 - 21
// Read and Select transmission power (only WaveCard) 54 // read TX power 44xx // select TX power (xx = 00 - 0A, -16dBm - +14dBm) // Read and Set RSSI threshold autocorrection 5A // read RSSI threshold autocorrection setting 4600 // set 4601 // reset // Read RSSI (response 00 = 0%, 2F = 100%) 6Axxxxxxxxxxxx // read local RSSI (xxxxxxxxxxxx = radio address of remote module) 68xxxxxxxxxxxx // read remote RSSI (xxxxxxxxxxxx = radio address of remote module) // Selecting serial BaudRate 4200 // 9600 4201 // 19200 4202 // 38400 4203 // 57600 4204 // 115200 // Read FW version A0
// read FW version
// Test Mode B000 B001 B002 B003
// continuous reception // continuous transmission without modulation // continuous transmission with modulation // stand-by
// Remote Services 80xxxxxxxxxxxxSSPP 80xxxxxxxxxxxx20 80xxxxxxxxxxxx28
// request service (xxxxxxxxxxxx = radio address, SS = service, PP = params) // get type // get FW version
// send message 22 xxxxxxxxxxxx 00
// send data 00
inSSIDer program It is a simple utility for wireless network signal strength measurement. Program sequentially scans all channels and looks for access points. During the measurement it provides a signal strength value in dBm and simultaneously it stores its time dependence into the graph. It can be therefore used to setup an antenna position or to map the signal coverage. For better visualization use the ESSID filtering for selected network. Use the Time Graph tab in the bottom half of the screen for time dependence presentation.
Winbox It is a simple utility used for configuration of network modules from Mikrotik company. These devices are based on RouterOS (Linux clone). Connectin to Routerboard RB411U Use a predefined account to connect. If not set, connect to IP address 192.168.88.1, login name is admin, keep password empty.
Checking/Setting of Access Point mode and transmitted power level After the login select the Wireless item in menu on the left. Setting starts by double-click on wlan1 item in the presented list (configuration takes place on Wireless and TX Power tabs). In the same way you can observe connected clients on Registration card (Signal).
