Redline Communications Inc. AN100UA 用户手册
Red
MAX
™
Base Station
User Manual
Doc. #70-00058-01-01
Proprietary Redline Communications © 2007
July 13, 2007
Page 92 of 119
This formula corresponds with an expectation that a very strong signal (high C/N) is able
to withstand higher levels of interference (low C/I). If the signal is weak, even low
interference levels will significantly degrade the useful signal. Consider the following
examples:
Case 1: The threshold CINR for 64 QAM 3/4 is around 23.25 dB. If the C/N ratio is 24
dB, the system will operate at 64 QAM 3/4 (signal is close to the 64 QAM 3/4 threshold,
but still above it). If we introduce an interferer with a signal 30 dB weaker than the
system signal (i.e., C/I = 30 dB), the overall CINR will drop to around 23 dB, forcing the
system to change the modulation rate to 64 QAM 2/3.
Case 2: If the signal is very strong and the C/N ratio is around 28 dB, it will require a
much stronger interferer to force a drop in modulation. According to the formula above,
for a C/N of 28 dB, the C/I should be 25 dB in order to force a drop in modulation. In this
case the interferer was 5 dB stronger than the first case.
The following table lists experimentally obtained minimal C/I ratios required for the
system to not change modulation:
to withstand higher levels of interference (low C/I). If the signal is weak, even low
interference levels will significantly degrade the useful signal. Consider the following
examples:
Case 1: The threshold CINR for 64 QAM 3/4 is around 23.25 dB. If the C/N ratio is 24
dB, the system will operate at 64 QAM 3/4 (signal is close to the 64 QAM 3/4 threshold,
but still above it). If we introduce an interferer with a signal 30 dB weaker than the
system signal (i.e., C/I = 30 dB), the overall CINR will drop to around 23 dB, forcing the
system to change the modulation rate to 64 QAM 2/3.
Case 2: If the signal is very strong and the C/N ratio is around 28 dB, it will require a
much stronger interferer to force a drop in modulation. According to the formula above,
for a C/N of 28 dB, the C/I should be 25 dB in order to force a drop in modulation. In this
case the interferer was 5 dB stronger than the first case.
The following table lists experimentally obtained minimal C/I ratios required for the
system to not change modulation:
Table 35: Op. Notes - Co-channel C/I dB Measured Results
Modulation/Coding
CINR threshold dB
C/I: Case 1 dB
C/I: Case 2 dB
64 QAM 3/4
23.25
34
24.4
64 QAM 2/3
21.75
32
22.7
16 QAM 3/4
18
28
18.2
16 QAM 1/2
15
26
16.4
QPSK 3/4
11.6
21
12.1
QPSK 1/2
6.75
19
9.4
In case 1 the signal is already very close the threshold rate (C/N is less than 1 dB above
the CINR threshold) and even weak interference can force the system to change to a
lower modulation. A moderately high C/I ratio is required for the modulation to remain
unchanged.
In case 2 the signal is very strong (C/N is more than 10 dB above the CINR threshold)
and can experience more severe interference without being forced to change modulation.
The amount of interference required to force the system to go to the lower modulation
rate in these two extreme cases is very different, and in an actual deployment scenario a
full range of results are possible. Careful planning is necessary when frequency reuse is
required, and sufficient fade margin must be included to anticipate fluctuations of both
C/I and C/N.
the CINR threshold) and even weak interference can force the system to change to a
lower modulation. A moderately high C/I ratio is required for the modulation to remain
unchanged.
In case 2 the signal is very strong (C/N is more than 10 dB above the CINR threshold)
and can experience more severe interference without being forced to change modulation.
The amount of interference required to force the system to go to the lower modulation
rate in these two extreme cases is very different, and in an actual deployment scenario a
full range of results are possible. Careful planning is necessary when frequency reuse is
required, and sufficient fade margin must be included to anticipate fluctuations of both
C/I and C/N.
6.4 Interference
Issues
6.4.1 Multipath Interference
The base station is designed with high immunity to interference and multipath signals. Its
core technology is Orthogonal Frequency Division Multiplexing (OFDM), capable of
reliable performance under multi-path and frequency selective fading known to have
severe signal fading and distortion effects in the sub-11 GHz frequencies.
Multipath interference is a significant problem in long-range links, and in near line-of-
sight, and non line-of-sight links. Multipath is a form of self-interference occurring when
core technology is Orthogonal Frequency Division Multiplexing (OFDM), capable of
reliable performance under multi-path and frequency selective fading known to have
severe signal fading and distortion effects in the sub-11 GHz frequencies.
Multipath interference is a significant problem in long-range links, and in near line-of-
sight, and non line-of-sight links. Multipath is a form of self-interference occurring when