ND SatCom SKYWAN IDU 7000, Manual

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68 Network Design and Engineering Guide 2010-10-26
General Carrier Design
From Capacity Estimation to TDMA Structure
One Carrier Solution
Besides the values provided by the Capacity Calculation tool we make the following additional
assumptions:
-
Reference burst mode: MRB.
- Frame time min: 109 ms (should lead to an actual frame time close to the target value of
110 ms).
- Available Eb/No = 5 dB, max. BER 10-7.
- Packet length for IP Real-time: 1500 Byte, IP Non Real-time: 200 Byte.
- Slot size optimization is performed on the FR Voice service, option “1” is selected.
With these assumptions the initial input values of the “TDMA Calculator” are inserted.
After clicking the button ’calculate’ an error message is displayed that the maximum number of
timeslots is exceeded. Perform the adjustments as described below to get an optimized 1 car-
rier solution; refer to .
Adjustment and Optimization Considerations
1. Evaluating the channel data output one notices that the number of time slots per TDMA
frame larger than the maximum supported by Sky WAN
®
networks. Adjusting the time slot
optimization rule to 3 calls per slot reduces this number to an allowed value (107).
2. A further optimization can be achieved by reducing the number of data slots required for-
request bursts. Starting from the default superframe size of 1, 5 slots are needed. Increas-
ingthe superframe size value to 5 reduces the number of request slots (parameter ’Length
req. frame [time slots] ) to the minimum of one slot only.
3. With these settings the available user data rate is exceeding the estimated user traffic on
carrier 1. In order to minimize the required space segment, it is now possible to reduce the
modem rate until the user requirement is just fulfilled.
i
If the number of time slots is exceeded, an error message is displayed in the
output window but a further calculated value in field ’Time slots per TDMA
frame’ is still visible (but no longer valid).