ND SatCom SKYWAN IDU 1070, Руководство пользователя

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2010-10-26 Network Design and Engineering Guide 57
General Carrier Design
TDMA Carrier Design with ’TDMA Calculator’
2.6.1 Section ’General Data Input’
The parameters in the fields of the ’General Data Input’ section have the following meaning:
’Minimum TDMA frame time’: Fill in the target value for the TDMA frame time, i.e. the time in-
terval between two reference bursts. The
Sky WAN
®
system will automatically select the
number of time slots such that the actual TDMA frame time (see also chapter 2.6.3 “General
Data Output”) will be larger but as close as possible to the target frame time.
The range for this value is 40-400 ms. Small frame times reduce the burst delay jitter for real
time traffic (streaming) but will also reduce the user data rate due to a higher TDMA overhead.
Large values increase the user data rate but also the burst delay jitter. A good compromise be-
tween jitter and efficiency is a TDMA frame time of 110 ms if both real-time and non real-time
services should be supported. If some of the real-time services are very sensitive to network
delay, smaller values for TDMA frames may be chosen. A network with pure non real-time serv-
ices may use larger frame times to increase efficiency, but values larger than 200 ms are not
recommended.
’Number of uplink populations’ and ’Size of uplink populations’:
If ’Number of uplink populations’ is selected to ’1’, MRB mode will be used. If it is selected to
’2’, a DUB mode is specified. In this case, additional input fields will appear, refer to figure 2-40.
The input field ’Size of UL population 1’ defines the number of stations in the network.
Figure 2-40 TDMA Calculator - two Uplink Populations specified
If ’Number of uplink populations’ is specified to ’2’, the following input fields will appear addi-
tionally:
- In the select box ’Masterstation with self reception’ the reference burst run mode is speci-
fied:
-
select entry ’Yes’ to choose the MRB-DUB;
- select entry ’No’ to choose the NFB-DUB mode (without self reception).
- Use the input fields ’Size of uplink population 1’ and ’Size of uplink population 2’ to define
the number of stations in uplink population 1 and 2.
’Number of frequency channels’: The number of Sky WAN
®
carriers used in this network. This
number includes both carriers with and without reference bursts.
’Number of downlink populations’: The number of downlink populations in the network, which
is identical to the number of carriers with a reference burst.
’Size superframe (max.) [TDMA frames]’: The number of TDMA frames between transmissions
of a request burst from a station.
A value range of 1-16 is supported, however superframe sizes larger than 5 should only be
used, if the applications support a long latency between capacity requirement and assignment.
If services with a real-time characteristic are supported using dynamic slot assignment, super-
frame size should be set to 1. This parameter allows for increasing the user data rate on carrier
1 (and carrier 2 for DUB modes) by reducing the number of base slots used for the request
slots.