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Nokia
Space diversity Alignment
Solution for Signal Ducting due of Ducting
1 © Nokia 21-01-2000
Nokia
Nokia
The free-space, reflection, and diffraction mechanisms described earlier explain signal level variations on a large scale, but other mechanisms introduce small-scale local fading
Slow Fading occurs as the user moves over hundreds of wavelengths due to shadowing by local obstructions
Rapid Fading occurs as signals received from many paths drift into and out of phase
• the fades are roughly λ/2 apart in space: 7 inches apart at 800 MHz., 3 inches apart at 1900 MHz
• fades also appear in the frequency domain and time domain
• Rayleigh distribution is a good model for these fades
Nokia
Space Diversity
Nokia
Fortunately, Rayleigh fades are very short and last a small percentage of the time
Two antennas separated by several wavelengths will not generally experience fades at the same time
“Space Diversity” can be obtained by using two receiving antennas and switching instant by-instant to whichever is best Signal received by Antenna 1 Signal received
Nokia
Nokia
Required separation D for good de-correlation is 10-20λ• 12-24 ft. @ 800 MHz.• 5-10 ft. @ 1900 MHz.
Nokia
Space Diversity Application Limitations
Nokia
Space Diversity can be applied only on the receiving end of a link.
Transmitting on two antennas would: • fail to produce diversity, since the two signals combine to produce only one value of signal level at a given point -- no diversity results. • produce objectionable nulls in the radiation at some angles
Therefore, space diversity is applied only on the “uplink”, i.e.., reverse path
• there isn’t room for two sufficiently separated antennas on a mobile or handheld
Nokia
Alignment Procedures
Nokia
A1
A2
B1
B2
Primary
Secondary
Nokia
Set Power ON for A1 and B1 ( main link), while A2 and B2 OFF 1- Fix antenna of B1 and move the one for A1. When you get the maximum
value on the voltmeter ( design parameter) tight antenna A1
A2-OFF
B1-ON
B2-OFF
A1- ON
Nokia
3- Now play with B1 till you get the maximum value, then tight antenna B1
A2-OFF
B1-ON
B2-OFF
A1- ON
Nokia
Set Power ON for A2 and B1, while B2 OFF Play with A2 till you get the maximum value, then tight antenna A2
A2-ON
B1-ON
B2-OFF
A1- OFF
Nokia
Set Power ON for A1,B2 while A2 OFF Play with B2 till you get the maximum value, then tight antenna B2
A2-OFF
B1-OFF
B2-ON
A1- ON