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Space diversity Alignment

Solution for Signal Ducting due of Ducting

1 © Nokia 21-01-2000

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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

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Space Diversity

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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

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Required separation D for good de-correlation is 10-20λ• 12-24 ft. @ 800 MHz.• 5-10 ft. @ 1900 MHz.

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Space Diversity Application Limitations

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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

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Alignment Procedures

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A1

A2

B1

B2

Primary

Secondary

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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

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3- Now play with B1 till you get the maximum value, then tight antenna B1

A2-OFF

B1-ON

B2-OFF

A1- ON

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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

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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