Hughes 9100 UMOD User manual

11717 Exploration Lane, Germantown, MD 20876
Tel: [phone] Fax: [phone]
HUGHES
NETWORK SYSTEMS
A HUGHES ELECTRONICS COMPANY
1022410–0001
Rev. 2
December 2, 1996
9100 UMOD
Universal Modem
1–PAK Chassis
Installation and Operation Manual

1022410–0001 Rev. 2 Introduction 1–1
Chapter 1
Introduction
The Hughes Network Systems, Inc. (HNS) 9100 Universal
Modem (UMOD) is a high-performance multifunction satellite
modem providing features that include multiple bit rates,
modulation types, coding schemes, terrestrial interfaces, and IF
frequency bands. The UMOD is operational as:
•A standalone, open–network modem for use with
INTELSAT (IDR/IBS) and EUTELSAT (SMS) standards.
•A standalone modem for closed networks.
•An integral part of the HNS Gemini VSAT, a private digital
data network for economical bypass of terrestrial data lines.
The 9100 UMOD is available in a single modem chassis referred
to as the 1–PAK as shown in figure 1-1 and in a ten–modem
chassis called the 10–PAK. The 10–PAK is described in the 9100
UMOD Universal Modem 10–PAK Chassis Installation and
Operation Manual, HNS document number 8051364.
0E
789•
456
123
HUGHES
NETWORK SYSTEMS
MODEM
UNIVERSAL
Figure 1-1 The 9100 Universal Modem single-modem chassis (1-PAK)
The UMOD supports IDR/IBS/SMS framing, single- or
twin-bearer drop-and-insert (D&I) multiplexing, an internal bit

1022410– 0001 Rev. 21–2 Introduction
error rate test set, and an EbNomonitor for use in Single Channel
Per Carrier (SCPC) and Multiple Channel Per Carrier (MCPC)
systems. Figure 1-2 shows a typical SCPC/MCPC application.
EXTERNAL MULTIPLEXER/DEMULTIPLEXER
VOICE DATA
COMBINED VOICE
AND DATA
9100
UNIVERSAL
MODEM
IFL
70/140-MHz RFT
(C- OR KU-BAND)
ANTENNA
RECEIVE
TRANSMIT
LNA
1 2 3
4 5 6
7 8 9
0 E
•
HUGHES
NETWORK SYSTEMS
PACKET
SWITCH PBX LAN
M&C FUNCTIONS
AVAILABLE THROUGH
KEYPAD/DISPLAY OR
BY USING OPTIONAL
M&C PERSONAL
COMPUTER (PC)
UPCONVERTER
HPA
DOWNCONVERTER
Figure 1-2 Typical SCPC/MCPC application
The UMOD meets the requirements demanded of modern satellite
modems as well as several features that offer flexibility for growth
from simple SCPC point-to-point applications to fully-networked
point-to-multipoint operation:
•Universal feature set—The feature set covers both current
and future applications with multiple bit rates, software
selectable in 1-bps increments from 9.6 kbps to 8.448
Mbps; BPSK and QPSK modulation methods; Viterbi,

1022410– 0001 Rev. 2 Introduction 1–3
Sequential, Reed-Solomon, and Concatenated FEC coding;
Internal framing to support IDR, IBS, and SMS framing,
single- and twin-bearer D&I multiplexing, and Engineering
Service Channel (ESC) supervisory overhead. All features
are software-selectable, there are no switches or jumpers to
configure.
•Single-card design—The entire modem, framing unit, and
multiple terrestrial and IF interfaces are integrated into a
single circuit board.
•Application-Specific Integrated Circuits (ASICs)—The
single-card design is made possible by using several
HNS-developed ASICs to perform UMOD functions.
•Bit rate: 9.6 kbps to 8.448 Mbps (selectable in 1-bps
increments)
•Baseband interface: RS-232, RS-422/449, V.35, or G.703
(T1, E1, T2, and E2)
•IF/RF interface: 70 MHz, 140 MHz, or L-Band
•Modulation methods: BPSK and QPSK
•FEC coding compatibility: Viterbi, Sequential,
Concatenated Viterbi/Reed-Solomon
•Internal framing unit supports IDR, IBS, and SMS framing,
single- and twin-bearer D&I multiplexing, and ESC
supervisory overhead
•Full redundancy switchover option in 1-for-1 (1:1)
redundancy

1022410– 0001 Rev. 2 Specifications 2–1
Chapter 2
Specifications
This chapter lists UMOD physical, enironmental, system,
modulator, and demodulator specifications.
This section provides physical specifications for the Universal
Modem 1-PAK chassis.
Weight: 22.5 pounds (10.2 kg)
Refer to figure 2-1 for height, width, and depth dimensions.
1 2 3
4 5 6
7 8 9
0 E
•
HUGHES
NETWORK SYSTEMS
17.3 in.
(43.9 cm)
19.0 in.
(48.3 cm)
17.3 in.
(43.9 cm)
4.3 in.
(10.9 cm)
(LESS THAN 3U)
Figure 2-1 1-PAK chassis physical dimensions
2.1
Physical
dimensions
1-PAK chassis

1022410– 0001 Rev. 22–2 Specifications
This section describes the 9100 UMOD single-modem chassis
temperature, altitude, and humidity specifications.
The temperature requirements are:
•Operating range: 32 °F to 122 °F (0 °C to 50 °C)
•Storage range: -40 °F to 167 °F (-40 °C to 75 °C)
The altitude requirements are:
•Maximum operating altitude: 15,000 feet (4,752 meters)
•Maximum non-operating altitude: 50,000 feet
(15,240 meters)
The humidity requirements are:
•Maximum operating humidity: 95% relative humidity (RH)
at 122 °F (50 °C)
•Minimum operating humidity: 5% RH at 122 °F (50 °C)
This section describes 9100 Universal Modem system
specifications.
Single slot chassis (117VAC, 60 Hz) power consumption, see table
2-1 .
Table 2-1 Power Usage
Conditions Typical Pwr New Spec Pwr
PS only no Bd 61 W
With UMOD and no
RFM
122 W 150W
GEMINI with 5–watt
radio
197 W 240 W
Ranges: 52—88 MHz or 104—176 MHz (or 52—88 MHz and
104—176 MHz available as an option)
Step size: 100 Hz
Less than 0.5 dB degradation with two adjacent carriers 10 dB
higher at 1.4 X symbol rate
BPSK and QPSK
Range: 9.6 kbps—8.448 Mbps (BPSK 9.6 Kbps – 2.048 Mbps)
Step size: 1-bps steps
9.6 Ksps to 10 Msps
2.2
Environmental
specifications
Temperature
Altitude
Humidity
2.3
System
specifications
Single slot chassis
power consumption
Operating frequency
Channel spacing
Modulation types
Data rates
Symbol rates

1022410– 0001 Rev. 2 Specifications 2–3
Types: Viterbi, Sequential, Concatenated Viterbi/Reed-Solomon
Rates: 1/2, 3/4, 7/8, 1 (No coding)
(Sequential coding limited to R1/2 and 2.048 Mbps)
DIM: RS-232, RS-449, V.35
GIM: G.703 (T1, balanced and unbalanced E1, balanced and
unbalanced T2, E2)
CCITT V.35 and IESS-309 (IBS)
±2 ppm; ±1 ppm per year
Up to 512 Kbits or 32 ms (selectable in bytes or ms)
Front panel, ASCII terminal, remote (Hayes command set)
Configuration, loopbacks, alarms (local or remote)
Intelsat IDR and IBS (IESS-308 and IESS-309),
Eutelsat SMS (BS 7-40), or none
IDR, IBS, or none (for Open Network Applications)
See appendix H (for Closed Network Applications)
Bit Error Rate Test Function: 511-bit PN sequence; user-defined
8-bit repetitive mark/space; 1010 repetitive
Operational Eb/NoMonitor: ±1 dB accuracy
Uncoded: BPSK: 0.5 dB from theoretical; QPSK: 0.75 dB from
theoretical in IF-Back-to-Back, (see table 2-2 on page 2–5 ).
Coded: Intelsat specifications are guaranteed. Table 2-2
illustrates typical performance
Optional redundancy switchover support for all chassis is available
in the following configuration:1-PAK chassis: 1-for-1
1 MHz to10 MHz ("10 ppm, 100–Hz steps)
Forward error
correction
Data interfaces
Scrambling
Reference stability
Elastic buffer
Configuration
Monitor and control
(M&C)
Open-network framing
Engineering service
channel (ESC)
Overhead Channel
Diagnostics
Bit error rate
performance
Redundancy
switchover
Station clock input

1022410– 0001 Rev. 22–4 Specifications
The 9100 Universal Modem power supply automatically adjusts to
accept the following input voltage range: 1-PAK chassis: 100 to
240 Vac (47 to 63 Hz)
This section describes 9100 Universal Modem modulator
specifications.
Transmit power: -5 dBm to -30 dBm
Resolution: 0.1 dB
Accuracy: ±0.25 dB
On/Off isolation: > 60 dB
50 Ω(75 Ωoptional)
20 dB
±2 ppm all causes; ±1 ppm per year
Programmable (IDR, IBS, Custom)
> -50 dBc
-100 dBm/Hz at 0 dBm output level
-130 dBm/Hz at -30 dBm output level
This section describes 9100 Universal Modem demodulator
specifications.
Input impedance: 50 Ω(75 Ωoptional)
Input return loss: 20 dB
Desired carrier range: -30 to -55 dBm
Aggregate: -5 dBm Composite
Carrier: ±30 KHz
Clock: ±100 ppm
Input voltages
2.4
Modulator
specifications
Transmit power
Output impedance
Output return loss
Output frequency
stability
Spectral shape
Spurious and
Harmonics
Transmitted noise
2.5
Demodulator
specifications
Input power
Acquisition range

1022410– 0001 Rev. 2 Specifications 2–5
Refer to section 2.3, “System specifications” and table 2-2 .
Table 2-2 9100 Universal Modem typical bit error rate vs. Eb/Noperformance
specifications
Modulation
type
Forward Error
Correction
(FEC) Type
FEC
Rate Eb/Nofor BER shown below Remarks
(FEC) Type 1E–3 1E–4 1E–5 1E–6 1E–7 1E–10
BPSK None 1 8.6 9.9 10.9 11.7 12.4 – 0.5 dB from theoretical
BPSK Convolutional/
Viterbi
1/2 3.9 4.6 5.3 5.9 6.4 – K=7
BPSK Convolutional/
Viterbi
3/4 5.1 5.7 6.2 6.8 7.3 – K=7
BPSK Convolutional/
Viterbi
7/8 5.9 6.6 7.5 8.3 9.3 – K=7
BPSK Sequential 1/2 – 3.8 4.3 4.8 5.3 – 56Kbps
BPSK Sequential 1/2 – 4.5 4.9 5.3 5.7 – 1Mbps
BPSK Sequential 1/2 – 4.7 5.1 5.4 5.8 – 2Mbps
BPSK Concatenated
Vit/R–S
1/2,201
/219
– – – – – 4.3 K=7
BPSK Concatenated
Vit/R–S
3/4,201
/219
– – – – – 5.8 K=7
QPSK None 1 8.9 10.1 11.1 11.9 12.6 – 0.75 dB from theoretical
QPSK Convolutional/
Viterbi
1/2 4.1 4.8 5.5 6.1 6.6 – K=7
QPSK Convolutional/
Viterbi
3/4 5.3 5.9 6.4 7.0 7.5 – K=7
QPSK Convolutional/
Viterbi
7/8 5.9 6.8 7.6 8.3 9.1 – K=7
QPSK Sequential 1/2 – 4.0 4.5 5.0 5.5 – 56Kbps
QPSK Sequential 1/2 – 4.7 5.1 5.5 5.9 – 1Mbps
QPSK Sequential 1/2 – 5.0 5.3 5.7 6.0 – 2Mbps
QPSK Concatenated
Vit/R–S
1/2,201
/219
– – – – – 4.3 K=7
QPSK Concatenated
Vit/R–S
3/4,201
/219
– – – – – 5.8 K=7
All values are typical in IF back–to–back with V.35 scrambling
and differential encoding/decoding.
Bit error rate
performance

1022410– 0001 Rev. 2 UMOD hardware theory of operation 3–1
Chapter 3
UMOD hardware theory of operation
The UMOD is a digital satellite modem that serves as a link
between the user’s baseband data terminal equipment (DTE) and
the IF frequency interface with a radio or up/downconverter. In
addition to the basic phase shift keying (BPSK and QPSK)
functions, the UMOD performs data processing such as forward
error correction (FEC), open-network framing, Doppler buffering,
and data multiplexing.
UMOD functions are divided as follows:
•Transmit and receive functions. The UMOD is typically
configured for full-duplex operation, transmitting user data
toward the satellite and receiving data from the satellite.
The two paths are independent for most applications.
•System functions. These include monitor and control
(M&C), self-test diagnostics, timing generation,
redundancy, loopbacks, and bit error rate testing (BERT).
Figure 3-1 on page 3–2 is a high-level diagram of the UMOD
that shows transmit, receive, and system functions. The following
sections describe UMOD functions in the order they appear in the
figure.
In the transmit direction (see figure 3-1 on page 3–2), the
UMOD accepts user data at the customer interface module (CIM)
and directs the data across the backplane to the transmit portion of
the terrestrial data interface daughtercard (either a data interface
module or a G.703 interface module) installed on the UMOD
motherboard.
After the terrestrial data interface converts the data from the user’s
electrical format (RS-232, RS-449, V.35, or G.703) to the format
used in the UMOD, the data is either routed to the UMOD
motherboard, or—if there is an optional internal framing unit
(IFU) installed on the UMOD motherboard—to the transmit
portion of the IFU for processing. After IFU processing, the data is
directed to the UMOD motherboard.
On the motherboard, the data is sent to the channel encoder, where
operations such as scrambling, differential encoding, and FEC
encoding are performed. After encoding, the data is routed to the
transmit filter for digital filtering and interpolation; then passed to
the modulator where the signal is PSK-modulated onto an IF
carrier provided by the transmit synthesizer. This modulated
carrier is amplified in the IF stage processor, then routed for
3.1
Transmit operations

1022410– 0001 Rev. 23–2 UMOD hardware theory of operation
Figure 3-1 UMOD functional block diagram

1022410– 0001 Rev. 2 UMOD hardware theory of operation 3–3
transmission across the backplane to the IF OUT connector on the
IF panel (located on the rear of the UMOD).
The CIM is the interface between the user’s equipment and the
UMOD. Transmit data from the DTE device can be input to the
UMOD at the CIM in the following electrical interface formats.
•EIA RS-232, EIA RS-422/449, or CCITT V.35. These
formats are supported by the 37-pin connector labeled TO
DTE.
•CCITT G.703. This format supports balanced T1 (also
called DS1), balanced or unbalanced E1 (also called CEPT),
balanced or unbalanced T2 (also referred to as DS2), and
unbalanced E2 electrical interfaces. The balanced G.703
port is labeled G.703 BAL, the unbalanced G.703 ports are
labeled SD (send data) and RD (receive data).
The CIM provides ports for drop-and-insert (D&I) multiplexing,
and a port for Engineering Service Channel (ESC) signals for use
with an optional internal framing unit (IFU). The D&I ports on the
CIM are labeled RD (receive data), SD (send data), IDI
(insert-data-in) and DDO (drop-data-out). ESC signals (including
audio ESC, octet alignment, and backward alarms) are supported
by the CIM port labeled ESC SIGNALS.
The CIM also has a station clock port (labeled STATION CLK) that
can receive a 1-MHz to 10-MHz TTL or 0 dBm to +25 dBm level
input.
Note
For more information about CIM ports, refer to appendix A, “CIM
interface port pinout information.”
Transmit traffic, D&I multiframes, ESC data, and clock signals are
passed from the CIM to the backplane.
The backplane serves as an internal electrical interface between
the CIM and the UMOD motherboard. Baseband transmit data,
ESC signals, D&I multiframes, and clock signals from the CIM
are routed across the backplane to the UMOD motherboard.
The backplane routes the 70- or 140-MHz IF to the BNC
connectors on the IF panel.
The terrestrial data interface daughtercard (installed on the UMOD
motherboard) converts the baseband transmit data to the TTL
format used by the UMOD motherboard. There are two types of
data interface daughtercards:
•Data interface module (DIM)
•G.703 interface module (GIM)
Customer interface
module
Backplane
Terrestrial data
interface

1022410– 0001 Rev. 23–4 UMOD hardware theory of operation
DIM
The DIM provides level translation to TTL, buffering, and
termination (if required) for the baseband transmit data. The DIM
supports the following electrical formats: EIA RS-232 (up to
64 kbps), EIA RS-422/449 (up to 8.448 Mbps), or CCITT V.35
(up to 8.448 Mbps).
The DIM takes transmit data from the backplane, converts it to
TTL level, performs retiming and phase correction on the
converted data, then outputs the data and clock signals to the
UMOD motherboard.
For more information on the DIM daughtercard, refer to section
3.6 on page 3–41, “Terrestrial data interface daughtercard.”
GIM
The GIM performs line decoding, jitter attenuation, level
translation to TTL, and buffering, for the baseband transmit data,
then outputs the resulting data to the UMOD motherboard for
further processing or to the optional internal framing unit.
The GIM supports two bipolar baseband interfaces. The first (or
main) interface is used by the UMOD for interfacing with the user
DTE device and is capable of operating with mixed T1 (balanced),
E1 (balanced or unbalanced), T2 (balanced or unbalanced), and E2
(unbalanced) transmit and receive data rates. The second interface,
along with an optional IFU daughtercard, supports a two-bearer
D&I framing multiplexer.
Transmit data entering the main G.703 interface is first converted
to TTL level. The GIM then performs active jitter suppression on
the signals, then codes the signal using one of the
AMI/HDB3/B8ZS/B6ZS line codes. If the signal is coded for
AMI, it can be scrambled using a 1 + X3+ X5scrambler, then
output to the UMOD motherboard. Otherwise, the signal is output
to the UMOD board—along with clock signals—once coding is
complete.
Transmit frames entering the D&I interface portion of the GIM are
first converted to TTL level. The GIM then performs active jitter
suppression on the frames, then codes the signal using one of the
AMI/HDB3/B8ZS line codes. The coded frames are then output to
the internal framing unit.
For more information on the GIM daughtercard, refer to section
3.6 on page 3–41, “Terrestrial data interface daughtercard.”

1022410– 0001 Rev. 2 UMOD hardware theory of operation 3–5
The optional internal framing unit (IFU) daughtercard connects
between the terrestrial data interface daughtercard (either a DIM
or a GIM) and the UMOD. In open-network configurations, it
provides single- or dual-bearer D&I multiplexing, and framing and
buffering support for the following Intelsat and Eutelsat services:
•Intelsat Intermediate Data Rate (IDR) service
•Intelsat Business Service (IBS)
•Eutelsat Satellite Multi-Services (SMS)
IDR mode
In IDR mode, the IFU supports 64 kbps rates defined by the
following services:
•64-, 192-, and 384-kbps rates. These data rates are passed
transparently without any overhead.
•1.544-, 2.048-, 6.312-, and 8.448-Mbps rates. A 96-kbps
overhead is added to the data.
•512-kbps through 15536 kbps. For this data rate, the IFU
adds an IBS-style overhead (1/15 or 6.7%). However, there
is no audio ESC, and no facility for the 64-kbps revenue
channel. IBS MODE MUST BE SELECTED.
•For IBS–style framing, use 64 kbps times nwhere n=1, 2, 4,
6, 8, 12, and 16.
In a standard framing operation, transmit data enters the IFU from
the GIM. The IFU adds ESC supervisory information to the data,
synchronously scrambles it, and then outputs the signals to the
UMOD motherboard for further processing.
Except for the 1.544-, 2.048-, 6.312-, and 8.448-Mbps rates, IDR
mode supports D&I operations. FOR ALL D&I OPERATIONS,
IBS MODE MUST BE SELECTED. For a D&I operation, the
T1 or E1 bearer from the DIM or GIM enters the IFU. The IFU
removes (drops) preselected frames (or timeslots) from the bearer,
assembles them in the framer, and (if appropriate) adds ESC
supervisory information. The data is then scrambled—using the
self-synchronizing scrambler specified in IESS-308 and
V.35—and output to the UMOD motherboard for further
processing.
IBS only mode
In IBS only mode, the IFU adds a 1/15 (or 6.7%) overhead to the
data. The following services are supported:
•48 kbps. Before satellite overhead is added, the IFU
performs an X.50 conversion on the 48-kbps data. The
conversion bit-stuffs the data up to 64-kbps.
•56 kbps. The IFU performs an X.50 conversion to bit-stuff
the 56-kbps data to 64-kbps.
Internal framing unit

1022410– 0001 Rev. 23–6 UMOD hardware theory of operation
•64 kbps. Data rate is 68.26667 kbps (64 x 16 / 15) after
overhead is added.
•512 kbps. Data rate is 546.1333 kbps (512 x 16 / 15) after
overhead is added.
•1544 kbps. Data rate is 1647 kbps (1544 x 16 / 15) after
overhead is added.
In a standard framing operation, transmit data enters the IFU from
the GIM. The IFU frames the data, adds ESC supervisory
information to the data, synchronously scrambles it, and then
outputs the signals to the UMOD motherboard for further
processing.
For a D&I operation, the T1 or E1 bearer from the GIM enters the
IFU. The IFU removes (drops) preselected DS0s (or timeslots)
from the bearer, assembles them in the framer, and adds ESC
supervisory information. The data is then synchronously
scrambled (as specified in IESS-309) and output to the UMOD
motherboard for further processing.
SMS only mode
In SMS only mode, the IFU adds a 1/15 (or 6.7%) overhead to the
data. A 1.152-kbps service is supported. Data rate is 1288.800
kbps (1152 x 16 / 15) after overhead is added.IBS MODE MUST
BE SELECTED.
In a standard framing operation, transmit data enters the IFU from
the DIM or GIM. The IFU frames the data, adds ESC supervisory
information to the data, synchronously scrambles it, and then
outputs the signals to the UMOD motherboard for further
processing.
For a D&I operation, the T1 or E1 bearer from the GIM enters the
IFU. The IFU removes (drops) preselected DS0s (or timeslots)
from the bearer, assembles them in the framer, and adds ESC
supervisory information. The data is then synchronously
scrambled (as specified in IESS-309) and output to the UMOD
motherboard for further processing.
IBS and SMS mode
In IBS and SMS mode, the IFU adds a 1/15 (or 6.7%) overhead to
the data. The following services are supported:
•64 kbps. Data rate is 68.26667 kbps (64 x 16 / 15) after
overhead is added.
•128 kbps. Data rate is 136.533 kbps (128 x 16 / 15) after
overhead is added.
•256 kbps. Data rate is 273.067 kbps (256 x 16 / 15) after
overhead is added.

1022410– 0001 Rev. 2 UMOD hardware theory of operation 3–7
•384 kbps. Data rate is 409.600 kbps (384 x 16 / 15) after
overhead is added.
•768 kbps. Data rate is 819.200 kbps (768 x 16 / 15) after
overhead is added.
•1536 kbps. Data rate is 1638.400 kbps (1536 x 16/15) after
overhead is added.
•1920 kbps. This is a 2048 kbps data stream with a
32-channel PCM frame format (referred to as CCITT G732
or CEPT). The 30 timeslots available to the user yield the
1.920 Mbps rate. The terrestrial rate is therefore 2048 kbps,
not 1920 kbps.
Because the G723 format already has a 32 / 30 overhead
factor (actual rate / available rate) there is no satellite
overhead, and some bits of TS0 are borrowed for satellite
use. The IFU provides the option to leave the spare TS0 bits
transparent end-to-end, or to set the bits “high” over the
satellite link.
•2048 kbps (unformatted). Data rate is 2184.533 kbps. At
this rate, the 2184.533 kbps is handled as if it were
unformatted, and the 16/15 overhead is added. No frame
formatting is required. If the signal is a G732 signal, all bits
are passed transparently.
In a standard framing operation, transmit data enters the IFU from
the DIM or GIM. The IFU frames the data, adds ESC supervisory
information to the data, synchronously scrambles it, and then
outputs the signals to the UMOD motherboard for further
processing.
For a D&I operation, the T1 or E1 bearer from the GIM enters the
IFU. The IFU removes (drops) preselected frames (or timeslots)
from the bearer, assembles them in the framer, and adds ESC
supervisory information. The data is then synchronously
scrambled (as specified in IESS-309) and output to the UMOD
motherboard for further processing.
For more information on the IFU daughtercard, refer to section 3.7
on page 3–51, “Internal framing unit daughtercard.”
A user–definable overhead channel is available for closed network
applications. See appendix H for details.
Overhead channel

1022410– 0001 Rev. 23–8 UMOD hardware theory of operation
88The channel encoding section of the UMOD motherboard
formats the data before it is modulated.
The encoding circuitry (see figure 3-2 on page 3–8) performs the
functions specified in IESS-308 (IDR) and IESS-309 (IBS) that
relate to forward error correction and scrambling. [In addition, this
circuit performs the channel coding functions required to operate
in a closed HNS Telephony Earth Station (TES) network as well
as the HNS Personal Earth Station (PES) network.]
Figure 3-2 Channel encoding circuit block diagram
The channel encoding circuit performs the following functions:
•Scrambling data for energy dispersion purposes
•[Inserting the Overhead Channel Frame Marker and Data
Packet]
•Differential encoding for resolution of phase ambiguity in
the demodulator during initial acquisition and following
cycle slips
•Converting FEC Rate 1/2 to Rate 3/4 or Rate 7/8
(Puncturing)
•FEC convolutional encoding
•Reed-Solomon encoding (IESS-308 Rev. 6A)
•4-level interleaver per IESS-308.
•Concatenated Viterbi/Reed-Solomon encoding
The encoding circuit operates in the following modes:
•BPSK—Rate 1 (no FEC); Rates 1/2, 3/4, and 7/8 Viterbi
only; Rate 1/2 Sequential only; Rates 1/2 and 3/4 with
Viterbi and Reed-Solomon concatenated
•QPSK—Rate 1; Rates 1/2, 3/4, and 7/8 Viterbi only; Rate
1/2 Sequential only; Rates 1/2 and 3/4 with Viterbi and
Reed-Solomon concatenated
Channel coding transmit interfaces
Text inside of brackets—[ ]—denotes features currently under development.
Channel encoding

1022410– 0001 Rev. 2 UMOD hardware theory of operation 3–9
The channel coding circuitry interfaces to the internal framing unit
or directly to the terrestrial interface via processor control. Serial
data from either source is processed by the transmit channel
coding and then routed to the modulator interface where preamble
and postamble insertion occurs only when in TES mode of
operation. During BPSK and QPSK operation transmit symbol
rate data at the modulator interface consists of two serial channels:
I and Q. When BPSK modulation is selected only the I channel is
used.
Scrambling
Data scrambling ensures uniform spectral spreading of the
transmitted carrier. Two types of scramblers are provided:
IESS-309 (IBS) and V.35.
The IESS-309 (IBS) scrambler is selected when the UMOD is
operating in an IBS network. To aid the descrambling
synchronization process, the sequence 001001001001001 is
loaded at the start of each multiframe. In addition, the frame
alignment and message fields (bytes 0 and 32 respectively) of the
IBS frame are left unscrambled for the same purpose. Loading of
the synchronization sequence and disabling of the scrambler
output during bytes 0 and 32 is controlled by the internal framing
unit.
The V.35 scrambler used when operating within an IDR or TES
network is self-synchronizing and meets CCITT V.35
specifications. The scrambler is reset to a known state between
bursts and is enabled during a burst. When operating in TES
asynchronous data (burst) mode the preamble and postamble
portions of the burst are not scrambled. Only the message segment
of a burst is scrambled.
Differential encoding
The channel encoding section supports both binary-phase shift
keying (BPSK) and quadrature-phase shift keying (QPSK)
differential encoding. When BPSK modulation is used, the BPSK
differential encoder and BPSK differential decoder resolve
180-degree phase ambiguity in the received data when a
demodulator carrier cycle slip causes inversion of the data.
Because the Viterbi decoder will decode and correct errors but
produce inverted data in such an event, biphase differential coding
is required. In the case of QPSK modulation the QPSK encoder
and decoder resolve 90-degree phase ambiquity.
The QPSK differential encoder is used only in R1 QPSK; the
BPSK encoder is used for BPSK, and QPSK, when in Viterbi or
Viterbi-Reed-Solomon modes. The selection of differential coding
type is software controlled.

1022410– 0001 Rev. 23–10 UMOD hardware theory of operation
Forward error correction encoding
The following is a list of the forward error correction (FEC)
encoding methods supported by the UMOD channel coding
section:
•Rate 1/2, 3/4, and 7/8 convolutional encoding (K=7)
•Rate 1/2 and 3/4 convolutional encoding (K=36)
•Rate 1/2 and 3/4 concatenated Viterbi and Reed-Solomon
encoding
•4-level interleaver used with Reed-Solomon encoder (per
IESS-308)
TES shuffler
This circuit is included as part of the UMOD channel coding to
allow compatible operation within a TES network.
Modulator interface (preamble and postamble insertion)
This circuit is included as part of the UMOD channel coding to
allow compatible operation within a TES network.

1022410– 0001 Rev. 2 UMOD hardware theory of operation 3–11
Transmit filtering is performed digitally on the data from the
channel encoding section (see figure 3-3 on page 3–11). Dual
finite impulse response (FIR) filters—part of the FIR/NCO
ASIC—perform baseband spectral shaping on the I and Q
channels. To meet UMOD requirements, the filter coefficients are
programmable, not fixed. In most cases either a linear-phase
raised-cosine filter or a square-root raised-cosine filter response is
used, although the FIR filter is capable of almost any response
desired, including Butterworth and Bessel responses. Corrections
for sinx/x distortions in the digital-to-analog (D/A) converter are
included in the filter coefficient set.
Figure 3-3 Transmit filter circuit block diagram
Alias spectra will appear at multiples of the sampling rate of the
FIR filter which lie within the passband of the anti-alias filter. To
remove these spectral components, a series of interpolation filters
are used after the main FIR filter to upsample the data from the
FIR filter to a final sample rate in the range of 10 to 20 Msps. This
upsampling places the alias components within the stopband of the
anti-alias filters.
Following the FIR filters, D/A converters convert the digital
output sequence into rectangular pulses whose amplitude is
proportional to the value of the data word.
The D/A converters are followed by fixed-bandwidth anti-alias
filters to suppress the alias spectra created by the discrete time
nature of the FIR filter. The cutoff frequency of the lowpass filters
is approximately 5 MHz to accommodate the highest design
symbol rate of 9.3 Msps. The filter incorporates group-delay
equalization.
Transmit filtering