ND SatCom SKYWAN IDU 1070, Руководство пользователя

Страница: 71 / 154

2010-10-26 Network Design and Engineering Guide 67
General Carrier Design
From Capacity Estimation to TDMA Structure
2.7 From Capacity Estimation to TDMA Structure
In chapter 2.4 the procedures to estimate the user traffic for a Sky WAN
®
network and for indi-
vidual Sky WAN
®
carriers were discussed. The TDMA Calculator tool allows the calculation of
a TDMA frame structure which fulfils the estimated requirements and which is optimized for the
applications used on the network.
Starting point for the ’TDMA Calculator’ Input is the work sheet TDMA Calc Input of the Capac-
ity Calculation tool described in chapter 2.4. For the example discussed there, this work sheet
provides the following results for the 3 carrier solution:
Figure 2-42 Results from Capacity Calculation Tool
The following results are important for the TDMA calculation:
-
The composition of the user traffic according to the different traffic types. These numbers
are used to define the corresponding channel input parameters in the TDMA Calculator.
- The user data rate per carrier for the single and multiple carrier solutions. The user data
rates calculated by the TDMA Calculator (shown in area ’Data output per frequency chan-
nel’) have to fulfill these requirements, i.e. they must be equal or larger than the estimated
user data rates.
The channel data rate input parameters in the TDMA Calculator are the modem rates. As a
starting point for these values, the Capacity Calculator proposes modem rates which are de-
rived from the user data rate by adding an estimated
TDMA overhead. A value of 15% for this
overhead is for most scenarios a reasonable approximation.
Using the values from the Capacity Calculation tool the TDMA calculation can now be per-
formed.