Criteria for Making Valid Over the Air Measurements
The first step in making valid W-CDMA (with or without HSDPA) over the air measurements is to identify a target base station to measure. Then, for your measurements to be valid, you must find a location near the target base station with an unobstructed view of the base station antenna and a sufficiently strong W-CDMA or W-CDMA (with HSDPA) signal. W-CDMA or W-CDMA (with HSDPA) over the air measurements will experience interference from other W-CDMA or W-CDMA (with HSDPA) signals on the same RF channel and from multipath echoes. The code domain power view measures two key parameters to indicate these effects:
- Pilot dominance-The difference between the useful energy of the strongest pilot channel and the combined energy of the lower energy active pilot channels (expressed in dB). Ideally, this value should be very large (> 18 dB).
- The E7495A/B test set includes up to six lower energy active pilots in the pilot dominance calculation.
NOTE It is important to remember that the pilot dominance is always measured against the strongest signal. If you have specified your channel of interest manually, this channel might not necessarily be the strongest.
- Multipath power-The amount of power from the dominant pilot signal that is dispersed outside the main correlation peak, due to multipath echoes (expressed in dB). Ideally, this value should be very small (< 0.1 dB). Multipath power is the result of portions of the original broadcast signal arriving at the receiving antenna out of phase with the main power of the original signal. This can be caused by the signal being reflected off objects, such as buildings, or being refracted through the atmosphere differently from the main signal. These out of phase signals can cancel power from the main signal, or can appear as noise interference at the receiver.
The table below gives guidelines to the quality of the over the air code domain measurements with respect to pilot dominance and multipath power.
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Measurement Quality
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Pilot Dominance
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Multipath Power
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Very good
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>= 10 dB
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< 0.1 dB
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Fair
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> 8 dB
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< 0.4 dB
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Marginal
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> 5 dB
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< 0.7 dB
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The default measurement limits for pilot dominance and multipath power are set to give "fair" measurement quality. If these limits are met, the pilot dominance and multipath power values will be displayed in green. When the pilot dominance and multipath power parameters are outside the acceptable limits, the parameters will turn red. If this occurs, you must move to a different location that meets the "fair" criteria defined above.
In general, you should always use a preselector filter for the band of interest to prevent strong signals from overwhelming the signal of interest. Agilent offers the following preselector and antenna:
- Option 813-W-CDMA preselector filter and antenna for W-CDMA.