User's Manual

SATELLAR Radio Unit User manual v.0.7
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In addition the factors affecting the latency are
o Forward error correction: The principle of forward error correction is to read a few bits to
a data register and generate a codeword based on a certain mathematical formula and
the stored data bits. This at first generates some delay in the transmitter but especially in
the receiver where a longer bit sequence must be stored before being able to decode the
incoming codeword.
o Encryption in the radio path: The principle of encryption is to collect a certain amount of
data to a shift register and manipulate it according to a certain rule. The process of
encryption adds delay in the data flow and must be avoided in the cases where low
latency is the most important requirement.
Strictly speaking the last two factors violate the principle of transparent data transmission (no
modifications to the content of the data). However, this is more or less a matter of definition.
More important is to understand that switching these on affects the latency and must not be
done in applications where low latency is a critical requirement.
To use the Radio unit in transparent mode:
o Configure the data port settings as required by the used data transmission protocol (data
rate, number of data bits, number of stop bits, parity).
o Set the network protocol mode to basic (see chapter 6.5 for explanation)
o If required modify the pause length parameter (see chapter 6.3.5. for explanation)
o Modify the synchronization interval parameter: Data stream in transparent data
transmission can be in principle of infinite length. If the receiver looses the
synchronization it will not be able to continue reception until it gets a new synchronization
sequence. If the data stream is very long a lot of data disappears. To minimize this effect
the transmitter adds a new synchronization sequence after a period called sync interval.
The receiver then detects the new synchronization sequence and is able to continue the
reception. Repeated synchronization sequences cause some extra delay in the system and
the interval must be defined experimentally in the application.
o Set all the radio parameters as required (unless already set in the factory): radio
frequency, channel spacing, RF output power, modulation method, forward error
correction, encryption, and the length of the synchronization sequence.