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MINIATURE
SATELLITE TERMINALS
The SC2001
ASTRA and the SC3001
DIRAC ICs provide the full digital baseband
transceiver resp. receiver functionality for CDMA-based satcom terminals.
Application examples include 'little LEO' and 'big LEO' terminals for voice,
data, messaging and geolocation.
An example
of a ‘little LEO’ application in which the SC2001 ASTRA is used, is the
LLMS (Little LEO Messaging System), also called IRIS (Intercontinental
Retrieval of Information by Satellite) from SAIT Systems. This network
allows worldwide bi-directional communications to between small terminals
and a number of satellites, which demodulate and store incoming data streams,
and forward them when designated ground stations are in the footprint.
In the terminals, the SC2001 ASTRA is the key component for the CDMA/spread
spectrum processing of up- and downlink streams of a few kbps, with a processing
gain of over 20 dB. The on-chip decimating filter and SRRC filter, together
with the sufficiently long PN sequence length allow proper data recovery
in the heavily interference-polluted VHF ‘little LEO’ band.
NAVIGATION
TERMINALS
Navigation
is one of the best known spread spectrum applications. Sirius Communications’
IC’s and CDMA technology are applied in various ways in the architecture
of navigation terminals.
The SC2001
ASTRA can be applied in combination with a GPS or a GPS/GLONASS OEM
module, providing a bi-directional communications channel, complementary
to the receiver of the navigation channel.The SC2001
ASTRA can be configured as the baseband PHY layer of specialty GPS
and GPS/GLONASS receivers.
Sirius Communications’
NAVICOMTM patented baseband IC architecture
providing solutions for GPS and GLONASS codes, as well as the GNSS-1 EGNOS
codes and the WAAS augmentation codes. Low power, small size and low cost
are the key advantages of this novel approach.
Sirius Communications’
CDMA technology is also adopted for alternative (non-GPS based) navigation
systems. Read the Wireless
Design and Development article on a custom designed
ASIC for 2-way paging and geolocation using a LEO bentpipe constellation,
exploiting both pseudorange and Doppler information to obtain an accurate
position fix.
Sirius Communications
is developing chip sets for use in the future GNSS-2 satellite navigation
system.
High-precision
RTK receiver baseband chips, exploiting both GPS and GLONASS reception,
are designed on request, through Sirius Communications’ CDMA
ASIC Design Service.
VSAT
TERMINALS AND HUBSTATIONS
CDMA/Spread
Spectrum gets an increasing attention as the technology of choice
for VSAT (Very Small Aperture Terminal) applications. The SC2001
ASTRA is present in several commercial products
and products under development. Feedback from the market confirms the following
benefits of an SC2001 ASTRA-based CDMA VSAT implementation:
Low psd (power spectral density) of the transmitted signal;
Robustness against adjacent channel and in-channel interference, through
processing gains over 30 dB, if required. This allows operation in bands
suffering from interference, or using the CDMA/Spread Spectrum channel
as an overlay simultaneously with other, non-CDMA applications. An example
of this is the implementation of a D-SNG (Digital Satellite News Gathering)
channel on a DVB transponder in use;
Versatility in the assignment of number of channels per user;
User data rate can be traded off for robustness, occupying the same bandwidth;
Proprietary codes can be used (downloadable in on-chip RAMs of the SC2001
ASTRA), supporting any custom framing and clock frequency planning for
the terminal;
LPD/LPI for secure communications through the support of any custom PN
code sequences and the possibility for dynamic PN code allocation;
On-chip module for the support of QS-CDMA (Quasi-Synchronous CDMA), which
provides a superior bandwidth efficiency (capacity) for star networks.
The dual receiver architecture provides parallel demodulation of a Pilot
and a Traffic channel;
In the hub, several (tens of) SC2001 ASTRA chips can be put in a Master-Slave
configuration (symbol clock and oversampled chip clock) for the processing
of many simultaneous channels.
70
MHz Intermediate Frequency up/down converters
are available, which plug in directly on the SC2002 ASTRA
Development Board.
POWERLINE
MODEMS
The SC2001
ASTRA is successfully applied for powerline
communications by taking advantage of the following features:
Bandwidth
and band position can be accurately tuned in accordance with the local
regulations, by exploiting the programmability of the user data rates,
PN code lengths, digital up- and downconversion frequencies;
Different
types of powerline communications can be mixed by selecting different PN
code lengths for different QoS (Quality of Service), and hence different
BERs (Bit Error Rates);
An
efficient burst communication protocol is available as part of the
SC2002 ASTRA Development Board software.
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UMTS
APPLICATIONS
UMTS
has an enormous potential for the upcoming third generation
(3G) mobile telecommunication systems. Code Division Multiple
Access (CDMA) plays an important role in these developments. Also it is
acknowledged that satellite communications business in relation to its
integration in UMTS will become very important too.
Taking into
account this vast potential, Sirius Communications, as an industry
innovator, has already established collaboration and started W-CDMA developments
with major telecommunication partners in 1997, 1998 and 1999 and offers
its W-CDMA ASIC design skills
to other interested companies.
Later in 1999,
Sirius Communications will announce more information on its W-CDMA solutions
in the Sirius Communications'
line of products.
CATV
UPSTREAM MODEMS
Spread Spectrum/CDMA
has many advantages over PSK-based solutions for CATV upstream modems.
The SC2001 ASTRA provides
the following features:
Ingress
noise is effectively cancelled through processing gain;
High
aggregate data rates are obtained through efficient CDMA/FDMA multiplexing;
The
SC2001 ASTRA can be configured for different data rates and different processing
gains, depending on the application (data transfer, Internet communication)
by run-time programming the data rate, PN code and code length and the
number of channels per user.
The SC9002
ASAP Development Board provides an optimal
balance between network capacity and interference rejection.
TERRESTRIAL
WIRELESS TERMINALS
Terrestrial
wireless communications have been boosted by the (almost) worldwide allocation
of the license-free ISM (Industrial, Scientific and Medical) bands, such
as the 902-928 MHz band in the US, and the 2.4-2.4835 GHz band worldide
available. These bands offer at the same time an opportunity and a challenge:
As
a user license is not required, rapid development and deployment is possible,
taking into account the FCC part 15.247 (US) or ETS 300 328 (Europe) regulations;
The
bands are per definition to be shared with other applications, which means
that the interference levels are unpredictable, both in space and in time.
In order to guarantee a future-proof robust link, sufficient processing
gain is required, together with the possibility of trading off user data
rate for PN code length, preserving the same bandwidth occupation.
The SC2001
ASTRA and SC3001
DIRAC ICs satisfy the above requirements.
This chip is used both in the terminals and in the central stations (base
stations). Depending on the data rates, duty cycles and aggregate throughput
requirements of the application at hand, the communication can be organized
through polling, through random Aloha-type access or using QS-CDMA.
Important features
which make the Sirius Communications products the right choice for use
in medium- and long-range terrestrial networks (for voice and data communication),
SCADA (Supervisory Control And Data Acquisition) networks, remote monitoring,
remote control, surveillance applications are the following:
High-end components: implementation loss <0.1dB;
High-speed data communications with SC9002
ASAP Development Board
On-chip filters and up/down converters to/from IF;
4 parallel BPSK/CDMA or 2 parallel (O)QPSK/DMA communication channels for
transmission and reception per chip (SC2001
ASTRA);
Integrated 32-bit RISC ARM6 processor (SC3001
DIRAC);
High robustness: programmable codes with lengths up till 1,023 give over
30dB of Processing Gain, providing a high immunity to interference and
multipath fading (reflections);
9.6 kbaud, 19.2 kbaud or higher data rates are possible;
Development boards are equipped with RS-232 interfaces;
The SC3001 DIRAC IC has on-chip UART VL16C550 from VLSI Technologies, Inc.;
Low power consumption;
License-free operation when combined with 902-928 MHz frontend (USA) or
2.4
GHz Frontend (Europe, Japan);
Pilot channel and on-chip synchronization functions allow for QS-CDMA (Quasi
Synchronous CDMA) networks and Dynamic Multiple Access.
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