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DMD50 Universal Satellite Modem
3.1.3 Tx Baseband Processing
The Tx Data and Clock enters the Baseband Processor, passes through a Rate Adapting FIFO
and enters the Framer/Drop Processor. In IDR, IBS, and D&I Modes, the framer adds the
appropriate framing and ESC as defined in IESS-308 and 309. In D&I Mode, the framer acquires
the terrestrial framing structure, E1 or T1, and synchronizes the Drop Processor. The Drop
Processor extracts the desired time slots from the terrestrial data stream and feeds these
channels back to the framer. The framer then places the 'dropped' terrestrial time slots into the
desired satellite channel slots. The data is then sent to the Reed-Solomon Encoder.
When enabled, the Reed-Solomon Encoder, encodes the data into Reed-Solomon Blocks. The
blocks are then interleaved and synchronized to the frame pattern as defined by the selected
specification (IESS-308, IESS-309, DVB, etc.). After Reed-Solomon Encoding, the composite
data and clock are applied to the BB Loopback Circuit.
3.1.4 Rx Baseband Processing
The Receive Processor performs the inverse function of the Tx Processor. Data received from
the satellite passes through the BB Loopback Circuit to the Reed-Solomon Decoder to the
Deframer. The Deframer acquires the IBS/IDR/DVB frame, synchronizes the Reed-Solomon
Decoder and extracts the received data and overhead from the frame structure, placing the data
into the PD Buffer, sending the overhead data to the UIM. The data is extracted from the buffer
and is sent to the UIM. Backward Alarm indications are sent to the M&C Subsystem. In Drop
and Insert Mode, the Insert Processor synchronizes to the incoming terrestrial T1/E1 Data
Stream, extracts satellite channels from the PD Buffer, and then inserts them into the desired
terrestrial time slots in the T1/E1 Data Stream.
3.2 Monitor & Control (M&C) Subsystem
The modems M&C system is connected to most of the circuitry on any board contained in the
modem. These connections provide status on the working condition of the circuitry as well as
providing the data required for the various measurements the modem provides. The M&C
processes this information and generates status indications as well as alarms when necessary.
Detailed status information is available via the modems various user interfaces including the
remote and terminal ports. An external summary fault is available on the RS422 Data interface
The M&C contains a high-performance microprocessor and is responsible for overall command
and control of modem functions. The M&C is constantly monitoring all subsystems of the modem
by performing a periodic poll routine and configures the modem by responding to commands
input to the system. During each poll cycle, the status of each of the subsystems is collected and
reported to each of the external ports. Performance statistics such as Eb/No, buffer fill %, etc.
are compiled. If faults are detected, the M&C will take appropriate actions to minimize the effect
of such faults on the system (refer to the Fault Matrices in Section 6).
The modem supports the following M&C protocols:
Terminal Interface (Section 3.2.1)
Remote Port Interface (Section 3.2.2)
Ethernet M&C, Web Browser & SNMP (Section 3.2.3)
Modem Status, Alarms & Contact Closures (Section 3.2.4)
TM118 – Rev. 1.1
Theory of Operation
3-5
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