| 192 | | == 9. Signal quality measurements == |
| 193 | | After deploying the BS on site, we will need to measure the signal quality such as Received Signal Strength Indication (RSSI) and Carrier to Interference plus Noise Ratio (CINR). |
| 194 | | The measured signal quality information may help to configure the transmission power of the radio signal from antenna at the BS to control the coverage area and the propagation range of the WiMAX system. |
| 195 | | |
| 196 | | === Measurement tools === |
| 197 | | We use the signal measurement application ''wimax_gps_oml2'' for WiMAX which can be found in the following site: [http://wimax.orbit-lab.org/wiki/WiMAX/30/02#WimaxMeasurementApplication:wimax_gps_oml2 Orbit-Lab.org] |
| 198 | | This tool utilizes signal quality measurement according to the location which is gathered by GPS receiver (GlobalSat BU-383, connected via USB). |
| 199 | | |
| 200 | | === First measurement survey === |
| 201 | | 1. Measurement procedure |
| 202 | | - Set the transmission power of the antenna (''bs_tx_power'') to 30dBm |
| 203 | | - Defined 30 locations at Columbia Campus |
| 204 | | - Mesured WiMAX signal strehgth parameters (RSSI, CINR, Client Transmission Power) |
| 205 | | - Recorded WiMAX radio link parameters with corresponding GPS coordinates on the WiMAX client |
| 206 | | 1. Results |
| 207 | | - A wide outdoor area of the campus is exposed to the WiMAX signal so that WiMAX clients are capable to get Internet connectivity via WiMAX base station |
| 208 | | - Areas behind buildings and near the edge of the campus are bad covered, or rather not covered |
| 209 | | - The results of the RSSI and CINR measurement are shown in the following figures (drawn through http://gpsvisualizer.com ): |
| 210 | | |
| 211 | | || a. Measured RSSI || b. Measured CINR || |
| 212 | | || [[ThumbImage(0626_mexp1_30dBm.png, thumb=450)]] || [[ThumbImage(0626_mexp1_30dBm_cinr.png, thumb=450)]] || |
| 213 | | |
| 214 | | - Identified two major problems with the recording through ''wimax_gps_oml2'': |
| 215 | | i. The recorded GPS data are inaccurate. |
| 216 | | Caused by the urban area with a lot of high buildings the number of reachable GPS satellites alternates between two and ten and consequently the accuracy the calculated GPS position is low and the calculated position alternates between locations that are several hundred feet apart. |
| 217 | | ii. The recorded RSSI is not synchronized with the calculated GPS position. |
| 218 | | We identified that the GPS position is recorded delayed in comparison to the RSSI. The longer the measurement survey the more delayed is the recorded GPS position. Due this delay the recorded data are not meaningful. |
| 219 | | |
| 220 | | === Measurement survey to create a coverage map === |
| 221 | | 1. Measurement procedure |
| 222 | | - We solved the synchronization problem of GPS and RSSI data |
| 223 | | - We could not solve the accurancy problem. We tried to use an other GPS receiver (HOLUX GR-213 instead of GlobalSat BU-383) but the results were worst. |
| 224 | | - Consequently, we decided to select 128 locations on the campus to create the coverage map |
| 225 | | - Additionally, we increased the transmission power of the WiMAX BS to 40dBm (max. ODU) to cover a wider area of the campus |
| 226 | | 1. Results |
| | 192 | == 9. Signal Strength Measurements == |
| | 193 | We measured the signal quality such as Received Signal Strength Indication (RSSI) and Carrier to Interference plus Noise Ratio (CINR) across campus using the 'wimax_gps_oml2' tool. The tool writes the current location obtained from a GPS received connected via USB and various WiMAX signal parameters and writes them into an sqlite based database. The data from the database was then used to plot the results using http://gpsvisualizer.com. |
| | 194 | |
| | 195 | The base station TX power was set to 40 dBm. We also had to fix the 'wimax_gps_oml2' tool in the process to make sure that the measured WiMAX signal strength is paired with correct GPS location. |
