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The Mean Effective Gain

The Mean Effective Gain (MEG) is a very good measure of how well the antenna performs in a specific environment but often the measurements are carried out by using only a single “test person” or with a head phantom.

This may explain why validation made by different mobile net operators of the same handset model has often led to very different performance assessment. This has led to the question:

How much influence does the mobile user has on the antenna performance? To answer this question this measurement campaign was carried out.

The Mean Effective Gain (MEG) is used as the performance measure for three candidate antennas, a   wavelength whip, a helical and a directive patch. These antenna types were selected because they are the three basic types used on today’s handheld phones.

MEASUREMENTS

The measurements were carried out at 1880 MHz having 200 test persons using the handsets in normal speaking position. The mock-up handheld consists of a commercially available GSM-1800 handheld equipped with a retractable whip and helical antenna which was modified to also include a back mounted patch antenna. Two 50 ohms cables were used to connect the antennas to the receiving equipment. The mock-up consists therefore of three antennas connected to two connectors, a patch antenna on one connector and either the whip or the normal mode helical (when not retracted) on the other connector.

The measurements were carried out by asking each test person to hold the handheld in what he or she felt was a natural speaking position. Then the person was asked to follow a path marked by tape on the floor. The path was a square of some 2 by 4 meters and each record of data lasts one minute corresponding to 3 - 4 rounds. To record all three antennas each person had to follow the path for one minute, change the whip antenna to the helix and walk the path once again. Hence, firstly reclord the whip antenna and the patch and next to record the helix antenna and the patch once again.

Altogether four locations were selected, one path on each floor and 50 test persons were used on for each floor. The windows on level 3, level 2 and the ground level were facing towards the transmitter but there was no line of sight due to higher buildings in-between. On first floor the windows were facing opposite the transmitter.

The handset was connected to a dual-channel wide-band correlation sounder in order to record two antennas at a time. The carrier frequency was 1890MHz and a bandwidth of 20 MHz was used to suppress the fast fading. The instantaneous dynamic range of the sounder was 45 dB and the over all dynamic range is 80 dB with a linearity of f 1dB.

To match a typical urban GSM- 1800 micro cell the transmitter antenna was located approximately 700 meter away on the sixteenth level of a high building in an urban environment. The transmit antenna was a 60 degrees sector antenna with a beamwidth of 5 degrees in elevation and it was tilted mechanically some 4 degrees down. The building in which the measurements were performed is hidden by other buildings on the picture and therefore no line of sight exist between the transmitter and the handheld receiver.

DATA PROCESSING

Each recorded path lasts one minute and consists of 1000 impulse responses for both channels, and each impulse response has a depth of 6 micro seconds. To obtain the received power the noise power was first estimated and removed for each impulse response in similar ways as in [5]. Also the back-to-back measurements were used in equalizing the gain difference between

the two channels of the sounder (0.3 dB +OS dB). Then the average of the received power for each path was taken and used as the average received power for one path, antenna and person etc.. As a reference, sets of three measurements for the same path were taken with no person present. These measurements were recorded the same way as with a person present except that the handheld was mounted on a wooden stick whit a 60 degrees tilt angle from vertical. The measurement without the person present was repeated three times in order to find the repeatability of the measured path. For each set of three measurements without a person present both the mean and the spread were calculated.

  
نویسنده : امیر حسین بیک ; ساعت ٤:٢٠ ‎ب.ظ روز چهارشنبه ٢۸ بهمن ۱۳۸۸
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