close

Enter

Log in using OpenID

Adjacent Channel Interference

embedDownload
Adjacent Channel Interference
• Interference resulting from signals which are adjacent in
frequency to signal is called Adjacent channel interference.
• Comes from imperfect filters that allow frequency leakage into
the pass band.
• Serious problem if adjacent channel user is transmitting in very
close to subscriber’s receiver, while the receiver attempts to
receive a base station on desired channel.
• This referred as near-far effect
– Nearby mobile transmits on a frequency near to that of a
weak mobile
• It can be minimized by careful filtering, use of guard bands and
channel assignment
• A cell need not be assigned channels which are all adjacent in
frequency
• The frequency separation between channels in given cell
maximize
1
Near-Far (N – F) Problem
• The near-far problem is a situation that is
common in 3G cellular systems.
• The problem is this: consider a receiver and
two transmitters one close to the receiver
and the other far away.
2
Near-Far (N – F) Problem
• If both transmitters transmit simultaneously
and both have equal powers, then the
receiver will receive more power from the
nearer transmitter.
3
Near-Far (N – F) Problem
• Thus reception from the farther transmitter
is more difficult, if not impossible to
"understand the voice."
• One user useful transmission's signal is the
other user harmful interference (noise).
4
Near-Far (N – F) Problem
• The signal received from the farther
transmitter is totally corrupted by signal
from nearer transmitter and may be below
detectability and the farther transmitter may
just as well not transmit.
• The nearer Transmitter is effectively
jamming the communication channel of the
farthest user.
5
What is the Solution
• The N-F problem is commonly solved by
dynamic output power adjustment of the
transmitters.
• Transmitters need enough power so that the
received power from all transmitters at the
receiver is roughly the same.
6
What is the Solution
• This is called dynamic power control which
when implemented has to be a cooperation
between handheld device and the base
station using two methods:
Open-loop power control where handheld
increase/decrease its power relative to a
threshold level.
7
Author
Document
Category
Uncategorized
Views
0
File Size
74 KB
Tags
1/--pages
Report inappropriate content