User's Manual

112
Copyright © 2004-2012 by InfiNet Wireless
ςΙ.
Recommendations
1. Using InfiNet devices for High Bitrates
Using InfiNet devices on bitrates 48 and 54 Mbps (standard series), 104…130
Mbps (Xm-series, 20 MHz) and 240…300 Mbps (Xm-series, 40 MHz) has specific
requirements because of low noise immunity of high-order modulation
techniques (64 QAM).
One should take all possible precautions to prevent exceeding of parasite signals
over receiver sensitivity threshold. The problem is aggravated by the presence of
this parasite signal in entire spectrum.
Nevertheless, when using MINT architecture in most cases it is recommended to
set the maximal bitrate on the radio interface and switch on autobitrate function.
This will allow the system automatically and dynamically determine the most
appropriate bitrate for the current environment conditions.
2. Design of Multi-sectored Base Stations
Using of multiple Base Station sectors with high output power with limited
frequency and special gap between them increases noise level on the
neighboring sectors. This can lead to the decrease of its performance. So we
have ultimate choice: either optimizing base station for more bitrate/less range
(without amplifiers) or optimize base station for more range/less bitrate (with
amplifiers).
To deal with this problem most effectively it is recommended:
1. To increase number of sectors (commonly, up to 4-6)
2. Switch to the narrower bandwidth (5 or 10 MHz)
3. Use amplifiers and directional antennas at remote subscriber CPEs.
Remote subscribers can be configured for significantly lower than average
bitrates providing more stable operating modes but those subscribers can
decrease overall cell performance; so try to avoid mix solutions when the
BS-CPE has a big difference for different subscribers.
4. Use Xm-series devices that have much higher performance, NLOS and
robust characteristics than standard-series ones.
3. Asymmetrical System Design
Following conclusions regarding using base station can be made:
• Downstream bitrate (base to CPE) is usually higher than upstream;
• Beam width of base station sectored antenna is 10 times wider than
beam width of subscriber antenna;
• Trying to deploy base stations on area heights leads to raising overall
noise level and reducing noise immunity;
• Subscriber SNR measured at a base station is significantly worse than
that of subscriber side.
• Increasing transmit bitrate does not influence the overall working
conditions and network performance;
• Increasing receive bitrate does worsen noise immunity and network
performance.