Quantum and Evolution Series Installation and Operating Handbook
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8.16 FastLink Low-latency LDPC
FEC design is a trade-off between good BER performance and low latency. TPC has low
latency but BER performance can be 1dB or more worse than conventional LDPC. (For
example, TPC 8QAM ¾ at 5e-8 BER has an Eb/No of 6.4dB compared to LDPC at
5.5dB.) Conventional LDPC latency can be many times that of TPC. (For example, LDPC
16QAM ¾ at 64kbps has a latency of 395ms compared to TPC latency of 47ms, which is
a factor of over eight different.)
With satellite delay in addition, LDPC can exhibit over ½ second one-way delay for very
low data rates. Low-latency LDPC FECs are becoming available that provide comparable
BER performance to LDPC with latency nearer to TPC. FastLink low-latency LDPC from
Paradise does precisely this. FastLink also offers an extensive range of modulations
ranging from BPSK to 64QAM (including both 8PSK and 8QAM, 16APSK and 16QAM
and 32APSK).
One of the key advantages of FastLink is its flexibility. As mentioned, FECs offer a trade-
off between BER performance and latency. While the default settings for FastLink
achieve this balance, two other modes are also available. The first mode optimises
performance for particularly low latency, at the cost of a slight increase in Eb/No required
to achieve a specific BER. The second mode optimises BER performance and is suitable
when latency is not an issue (e.g. when higher data rates are being used). This flexibility
means that FastLink LDPC has now superseded Paradise’s conventional LDPC offering.
This flexibility also means that FastLink can be used in a wide range of demanding
applications, allowing a single FEC to potentially replace the use of multiple existing
FECs.
If one FEC is to be used in place of all others then Paradise believes you should choose
one with flexible configuration as opposed to a fixed set of modulation and code rates that
are inevitably a compromise.
FastLink is available on all Paradise SCPC modems at all data rates up to 60Mbps.
FastLink LDPC is compatible with
Paired Carrier
. FastLink does not interoperate with any
other LDPC.
