User's Manual

Table Of Contents

InfiNet Wireless R5000 Technical User Manual

VIII.Recommendations

1. Using InfiNet Devices for High Speeds (48, 54 Mbps)

Using InfiNet devices on greater speeds 48 and 54 Mbps can specific limitations

and 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. This practically is not impossible to

achieve when there are other active devices in neighborhood and therefore such

high speed devices can be used only in autonomous links.

2. Design of Multi-sectored Base Stations

Based on the above, we can resume that it is possible to build only single-

sectored base station for high speeds and building multi-sectored base stations is

possible only for speeds less than 36 Mbps. More than that, there is trade-off

between coverage and speed. The more powerful base station we have

(amplifiers, greater range), the less speeds can be defined for this base station.

So we have ultimate choice: either optimizing base station for more speed/less

range (without amplifiers) or optimize base station for more range/less speed

(with amplifiers).

Compromise is achieved by using amplifiers and directional antennas at remote

subscribers, but this approach essentially is more costly.

Remote subscribers can be configured for significantly lower than average

speeds 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.

3. Asymmetrical System Design

Following conclusions regarding using base station can be made:

• Downstream speed (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 speed does not influence the overall working

conditions and network performance;

• Increasing receive speed does worsen noise immunity and network

performance.

Every step in speed increasing requires 3 dB step improvements SNR.

Asymmetry in 8 times corresponds to 9 dB. It means that without link quality

losses we can have 2 times speed difference between upstream and

downstream. In order to maintain energetic parameters, we have to increase

base station output power by 9 dB by means of built-in amplifier. Other option is

to install external amplifier at subscriber side, because it has more gain for

receiving than for transmitting.