User's Manual
Table Of Contents
16
AVR2043
8345A-AVR-11/10
From Figure 5-8, page 17, one can conclude key parameters for such an indoor
scenario:
1. For one antenna, multipath fades can exceed 30dB
2. For the 2.4GHz ISM band, a local fading minimum is typically below 5cm (~2in).
This number is expected considering the wavelength. Conclusion: an antenna
diversity design should place antennas at a distance larger than that.
3. For almost all positions, only one antenna is in a deep fade. The setup prepared
for this test demonstrates the advantage of using antenna diversity.
Figure 5-7. Coupling between left and right antennas.
If practical situations are further analyzed (see Figure 5-8, pag
e 17), one can derive a
practical “antenna gain” for the diversity setups. To ensure robust and reliable
communication, a single antenna system has to consider at least a 30dB link margin
as fade margin.
Considering the multipath setup used for the experiment, a signal level of -70dBm is
the worst case receiver signal strength when operating on antenna diversity. A single
antenna system could get into a spot where the receive power is as low as -85dBm.
It might be too optimistic in an indoor environment to take the 15dB and state that an
antenna diversity system has four times the range compared to a non-antenna
diversity system. But antenna diversity cuts deep fades and strongly increases the
stability of a radio link. This is essential for radio nodes that get installed in a fixed
position, as with wall mounted equipment. The location of deep fades can move over
time due to small changes inside the room or building as there are doors, windows,
furniture, and people that may move.