Page 51 - Complete Wireless Design
P. 51
Wireless Essentials
50 Chapter One
many digital signals unreadable. Space diversity is another common method
to mitigate multipath effects, but requires two antennas and the associated
diversity circuitry.
An important term to remember in discussing multipath transmission is
delay spread. Since multipath signals take longer to reach the receiver’s
antenna (the time is dependent on how far they have traveled compared to the
direct wave), the spread between the time the direct signal arrives and the
time the last multipath signal arrives is called the delay spread. Delay spread
causes increased ISI due to the received data actually overlapping. As stated
above, equalizers are typically employed in an attempt to mitigate this prob-
lem; but if the delay spread is excessive, then equalizers may not be able to
properly handle the multipath effects.
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