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H.1.5.3 Transmission Delays
The overall transmission time from the customer data source to the customer MOC is
determined by a series of delay components. These include transmission of sampled
data from the TDRS MA array antenna, processing of the sample to produce a signal
that can be demodulated, demodulation and decoding of the data, formatting the data
for transmission to the MOC, and transmission of the formatted data to the MOC. This
section discusses delay components associated with processing by DAS. Figure H-4
illustrates a simplified DAS signal flow.
Factors a customer may consider are the delays inherent in format processing at the
TDRSS ground terminal, the transmission delays possible in the IONet, and delays due
to forward error correction (FEC) processing. Although TDRS specifies the FEC
scheme, the delay is dependent on the data rate.
SGLT
Antenna/
EMC
SN Ground Terminal/DAS
Beamformer DMU PTP
Figure H-4. Simplified DAS Signal Flow
H.1.5.3.1 Beamformer
The DAS Beamformer receives data samples from the 30 elements of the MA antenna
array and creates a beam using a process of phase-shifting, summing, and filtering.
The Beamformer then passes the resulting signal to a DAS Demodulator Unit (DMU).
H.1.5.3.2 DAS DMU
The DAS DMU demodulation process performs signal acquisition, which includes PN
code and carrier acquisition, symbol synchronization and decoding. Acquisition, which
is described above in paragraph H.1.5.1, begins when the received signal achieves
sufficient C/N0.
The acquisition and symbol/decoder synchronization processes must be restarted every
time there is a disruption in the signal as described in paragraph H.1.5.2.
The recovered data are formatted in TCP/IP packets and transmitted by the
Programmable Telemetry Processor (PTP).
H.1.5.3.3 PTP
The PTP is responsible for distributing customer data as TCP/IP packets over the
Closed IONet or a Customer provided local interface, for storing a copy of the data, and
Revision 10 H-9 450-SNUG
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