User Manual

DELTANODE FIBER DAS MANUAL
©DeltaNode Solutions 2012
28
Revision 12-03
3 System design
Fiber-DAS is a way of distributing radio signals from a base station to a remotely located antenna where
the coaxial cable losses would be too high or there is impractical to install coaxial cables. Fiber-DAS can
be used indoor to cover large building where outside penetration of radio signals is not enough, it can be
used to cover structures such as tunnels for rail and road, airports, metro lines and many other places.
This part of the manual aims at giving you some idea on how to do your systems design and avoid
common pitfalls. All fiber-DAS share some common properties as they are an extension of an existing
signal into an area where there is little or no coverage.
3.1 The basics
There are some basic knowledge you should be familiar with when you design your system. In this part
we will go through the most important ones and help you get through the design of your system.
A link budget is a way of calculating the required signal levels for the base station and the mobile station
and matching this against your system design, the losses in the cables, the antenna factors and other
such parameters goes into a link budget.
When you have done a rough link budget you should use the DAS calculator and calculate the settings of
each uplink and downlink in the system.
Example: You have a system with 3 remote units and they are all dual band 850/1900 for CDMA and
GSM. Your system has 6 uplinks and 6 downlinks where the signal may proceed from antenna to base
station or vice versa, in unit one there is one 850 RF strip and one 1900 RF strip forming two RF chains
with uplinks and downlinks.
The DAS calculator may yield a different noise figure from the one you initially assumed when you did
your link budget. This is fine, you may insert the new noise figure in your link budget and observe the
result.
When you have done your calculations you already know the settings of the system in principle and you
can now commission it. Using the settings from the DAS calculator as a basis you can connect to the
system and set it up one unit at a time, more about that in chapter 5 Commissioning of the system.
3.2 Link budgets
The starting point is to create a viable link budget for your system. As link budgets are calculated
different for different systems you may want to take some time and study typical link budget calculations
for the type of services you are using.
You do not need to create link budgets for all of your remotes and all frequency bands. Do it for the
worst case only for each service, that should be enough. This is the normal procedure and it is usually not
difficult to find the worst case scenario. Look for the highest loss between the base station and the
antenna, including the fiber loss between Master Unit and Remote Unit and any split loss after the
Remote Unit until you get to the last antenna.