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AN-100U/UX Base Station
Manual
70-00058-01-04
Proprietary Redline Communications © 2010
Page 117 of 136
April 19, 2010
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.
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.
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:
system to not change modulation:
Table 59: 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.
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.
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.
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.
7.5
Interference Issues
7.5.1 General Interference
Redline has introduced several techniques to mitigate interference issues:
1. OFDM: multiple carriers using both time and frequency diversity to provide high
tolerance to co-channel and adjacent channel interference, remove inter-symbol
interference (ISI) due to multipath and recover data from carriers falling in regions of
deep channel fades.
interference (ISI) due to multipath and recover data from carriers falling in regions of
deep channel fades.
2. Multiple channels (twenty-eight non-overlapping at 3.5 MHz) for diversity and
interference mitigation.
3. Adaptive modulation using six transmission rates to suit varying link conditions.
4. Adaptive encoding is heavily coded to substantially increase robustness. State of the
art forward error correction (FEC) using Convolutional-coding gives the base station
superior frequency selective fading mitigation capability.
superior frequency selective fading mitigation capability.
5. Narrow beam antennas with high sidelobe and backlobe isolation and very low
VSWR.
6. Antenna cross-polarization enabling equipment co-location as well as effective
frequency planning.