SATCOM Modems For More Robust & Secure Communications
An Abstract
This article elaborates on the role of Satellite Communications (SATCOM) for military operations and as one of the means of establishing anti-access/area denial conditions over designated areas. The susceptibility and vulnerability of SATCOM systems to various conditions and attacks are briefly discussed. Trends and recent innovations in SATCOM systems and applications are mentioned. A short section is presented about factors and considerations for SATCOM modem design. Afterwards, C2Tech’s NATO STANAG-4606 standard compatible EPM modem is succinctly described. Finally, some general conclusions are drawn about the current status and the next steps.
1. INTRODUCTION
Military Satellite Communications (MILSATCOM) capability provides the main communication backbone for joint military operations where no infrastructure may exist. Establishing and sustaining robust, secure and reliable SATCOM On-The-Move (SOTM) links for operational forces is of primary importance. In peace times, they complement the existing military communication capabilities as back-up systems. MILSATCOM is a vital and irreplaceable ingredient of establishing Anti Access/Area Denial (A2/AD) conditions over the operational areas. A2/AD conditions can be fully established and maintained by fulfilling requirements of each and every component of Command, Control, Communications, Computers, Intelligence, Surveillance, Target Acquisition and Reconnaissance (C4ISTAR).
SATCOM communications are intrinsically susceptible and vulnerable to multitude of environmental and physical conditions, as well as various attacks. Furthermore, MILSATCOM systems are deliberately targeted by the adversaries for setting their own A2/AD conditions over conflict areas, and their vulnerabilities to kinetic/non-kinetic attacks, Electronic Warfare (EW), (alternately spectrum warfare), and cyber warfare attacks get exploited.
From users viewpoint, they have to provide large on-demand bandwidth for Internet Protocol (IP) and non-IP multimedia communications, must have easy and secure access to global networks, and must be easy and practical to use. The ground terminals have to be low cost, small in size, portable and quick to set up.
This article is mainly focused on SATCOM modems, which determine all the important characteristics of a SATCOM system in terms of spectral bandwidth, bit rate, resistance to anomalies in the communication medium, anti-jamming capability, data processing latency, in addition to the factors for compatibility, interoperability and standards compliance.
2. TRENDS AND INNOVATION IN SATCOM SYSTEMS
Adapting military and civil SATCOM systems to more contested medium and conditions, as well as attacks, is an incessant and a multi faceted effort covering all three system components in space, on ground stations and terminals, as well as at control centers. On one dimension, despite all the drawbacks in terms of weight, size, power and cost, active defences in the against Anti-Satellite (ASAT) weapons on the space segment, can be used to fight back.
On the second dimension, the bigger and more concentrated capabilities can be divided, dispersed, and disaggregated into smaller redundant capabilities, in a new proliferated architecture forming inter and intra connected satellite constellations, as well as multiple replaceable ground stations and control centers on the ground. The cost of production and launching of individual and less capable satellites may have a positive impact on the expenses. However; networking, management and control of the constellations may present even a bigger challenge in this case, and due to the increased redundancy in the overall system, the total cost of setting up and sustaining the proliferated constellations may have been substantially increased. Another option for dispersing the assets might be using capacity and bandwidth from the existing commercial SATCOM constellations, based on layered strategic and tactical needs.
On the third dimension, communication and bandwidth needs of the users can be significantly decreased by employing more autonomous and cognitive systems with “information processing and fusion” capability onboard, and just communicating the essentially needed end findings. A particular example of this can be given for the data links on Unmanned Aircraft Vehicles (UAVs), which carry multiples of sensors and collect a lot of information, and only the relevant data can be transmitted by UAV SATCOM links after performing the information fusion operation.
On the fourth dimension, passive defences and precautions, which constitute the main interest area of this article, can be broken down into many smaller components, such as incorporating nuclear hardening, data encryption, bit and block interleaving, stronger Forward Error Correction (FEC) codes, Spread Spectrum (SS) techniques against jamming both as Frequency Hopping SS (FHSS) and Direct Sequence SS (DSSS) and using Code Division Multiple Access (CDMA) on the latter. These techniques would make detection, interception and jamming more difficult, thus would be instrumental in fortifying the resistance against spectrum and cyber warfare attacks and assuring more dependable and survivable SATCOM capabilities. They provide low cost solutions to the problems in hand, and can easily be implemented in dedicated Hardware (HW) or in Firmware/Software (FW/SW) without requiring any substantial changes in the satellite and/or ground terminal design.
One of the most significant recent innovations in SATCOM has been introduced by the use of High Throughput Satellites (HTS), which provide multiples of GBits/s total bandwidths, and have a high level of frequency reuse due to the employment of highly focused multiple spot beams on Ka and Ku bands. Another recent innovation has been implemented as the advancement in the auto-pointing and auto-tracking solutions, which brought back the use of non-geostationary Low Earth Orbit (LEO) satellite constellations for SATCOM applications. The last but not least miniaturization of SATCOM terminals, even bringing SATCOM capability to smart phones with small attachments and/or sleeves, can be regarded as a great innovation.
3. DESIGN CONSIDERATIONS FOR SATCOM MODEMS
Designing state of the art data communication systems, especially for the highly stressed satellite communication conditions, starts by a good and thorough understanding and evaluation of the anomalies and disturbances in the transmission medium and the characteristics of the transmission channel.
For SATCOM solutions, Rician and Rayleighian channels with multipath fading, shadowing effect due to buildings and shrubs, atmospheric effects (rain, snow, dust and humidity), Ionospheric and Tropospheric scintillation effects, as well as Doppler shift for mobile receivers, need to be considered for both up and down links. The channel, for geostationary orbits, is 36 000 km long one way and is mainly dominated by the path loss, which may go up to 205 dB at X-Band. The following information would be consequential in constructing reliable link budgets and determining the modem design parameters to build systems that can overcome all the adverse effects and conditions:
Channel characteristics:
Multi-path channel
Deep fades
Frequency selective fading
Group and phase delay
Path loss
Rain/Snow fading
Atmospheric absorption
Scintillation effects (Ionospheric & Tropospheric)
Doppler shift (if mobile)
Channel availability
Spectral channelization
Data packetization and MAC Layer requirements
Application requirements
Encryption/Decryption requirements
Diversity requirements
Supported net bit rate(s)
Anti-jamming techniques
Supported modulation/demodulation type(s)
Spectral efficiency
Required BER & PER
Required SNR(s)
Symbol rate(s)
Interleave/De-interleave depth(s) (bit and block)
FEC rate(s) (inner and outer)
Resultant symbol rate(s)
Latency
Baseband filter characteristics and filter roll-off
IF/RF filter characteristics and filter roll-off
Antenna characteristics
Polarization
Diversity
Gain & G/T
Efficiency
Beam-width
Tracking/Tuning error
Side-lobes
Multi-Band
Transmit power level(s)
Required link margin(s)
After all the parameters have been determined, a behavioral model of the system has to be constructed, and the system simulations have to be run for different combinations of data rates, FEC rates and modulation types. The parameters have to be optimized after running successive and iterative system simulations. Architectural design of the system, including hardware (FPGA & dedicated) vs. firmware/software (DSP & uC) partitioning, has to be determined, and a more detailed block diagram needs to be drawn with the block descriptions, specifications and interfaces. The physical realization/construction of the blocks and the modem follows with HW circuit synthesis and verifications. DSP FW and SW are handled simultaneously on a separate path. System integration and testing may constitute the final steps and the system evaluation tests against the calculated and simulated values have to be performed. In case of large discrepancies for any combination, the process reverts back to the simulation, synthesis, functional realization and verification steps.
4. C2Tech & ELECTRONIC PROTECTIVE MODEM (EPM) SOLUTIONS
C2Tech Information Technologies Inc. is a young, growing, dynamic and ambitious technology and innovation company. Since its founding in 2005, C2Tech has been providing state of the art complete system solutions for a wide range of applications in Defence and Aerospace (D&A) industries, in forms of HW, FW/SW and mixed technology implementations. Digital data communication solutions, and specifically satellite communications, are expertise areas for C2tech. To develop the expertise areas, generous investments have been made in engineering infrastructure and system engineering in terms of tools and people, and technology libraries have been developed for re-use purposes.
C2Tech has been the second company in NATO to design and build a STANAG 4606 standard compatible Electronic Protective Measures (EPM) modem solution. The NATO STANAG-4606 standard compatible EPM modem provides robust anti-jam, low probability of exploitation and low probability of intercept SATCOM capability for joint operations in land, air and sea, including SOTM applications, under interference, jamming and fading conditions.
Further details of C2Tech’s EPM modem solution is summarized presented below:
4.1 General Description
Using EPM waveform is the key for establishing a secure and robust communication link, especially when a communication system is wide open to electronic threats and unexpected interferences. SW Defined Modem (SDM) employs a Frequency Hopping (FH) EPM waveform which has strong resiliency against jamming. FH on wide IF band is performed according to TRANSEC algorithm, and the control messages in the network are protected based on NETSEC algorithm. DSP and FPGA based implementation of the modem makes easy and quick HW and FW upgrades possible. Operation of the modem is easily managed, configured and monitored by means of a user friendly web interface. Up to 6 communication channels can be installed in a single modem enclosure.
4.2 Control & Monitoring
User friendly web interface enables setting up and controlling all of the modem features and options, as well as monitoring run time parameters of each communication unit. Other than hard control, soft control of ESM and EMCON is also available via the web interface. Time reference is accepted through GPS (automatically) or web interface (manually).
4.3 Interfaces
L-Band IF input and output
Encryption key loading
Ethernet interface for remote control and monitoring
E1 and RS449 data interfaces
ESM, EMCON and Emergency Zeroizing
GPS (IRIGB 200-98)
External clock interface
4.4 TRANSEC/NETSEC
NATO or any National TRANSEC/NETSEC Algorithm can be easily installed upon request. Each channel has its own embedded TRANSEC/NETSEC unit.
4.5 Mechanical
EPM Modem enclosure is manufactured to fit in an 9U Rack where up to 6 identical hot swappable communication units (channels) can be inserted. Control of the physical features of the modem box, such as heat, power and
air flow, is achieved through the web interface.
Completing the design work, manufacturing the prototypes, completing the field tests and getting the approvals for this modem, which have already been achieved, are not the end of the road. C2Tech continues its development work on further editions of STANAG-4606 compatible modems (Editions 2 & 3), while completing preparations for the serial production of these modems for the modernization, augmentation and upgrade of MILSATCOM capabilities. Establishing compatibility and interoperability with the similar modems from other manufacturers and integrating the modems into the existing SATCOM infrastructure still remain as the future steps.
As a last note, it should be mentioned that, C2tech has already built, and is continuing to build, significant management and field experience in providing integrated satellite communications solutions and as a satellite service provider, through its sister company Martin Telecom under the brand name of ClickNet, while serving a large customer base.
5. CONCLUSIONS
MILSATCOM capability provides the main communication backbone for joint military operations where no infrastructure may exist. Establishing and sustaining robust, secure and reliable SATCOM On-The-Move (SOTM) links for operational forces is of primary importance.
SATCOM communications are intrinsically susceptible and vulnerable to multitude of environmental and physical conditions, as well as various kinetic/non-kinetic, electronic and cyber attacks.
Designing SATCOM modems is an elaborate and tedious job involving consideration of many parameters and conditions. In addition, it requires a well established design infrastructure and expertise.
C2Tech has been the second company in NATO to design and build a STANAG-4606 standard compatible Electronic Protective Measures (EPM) modem solution that provides robust anti-jam, low probability of exploitation and low probability of intercept SATCOM capability.
C2Tech continues its development work on new editions (Edition 2 & 3) of STANAG-4606 compatible modems. Establishing compatibility and interoperability with the similar modems from other manufacturers and integrating the modems into the existing SATCOM infrastructure still remain as the future steps.
In addition to its in-house satellite system and modem design engineering expertise, C2Tech has gained considerable management and field experience as an integrated satellite communications solutions provider as well as a satellite service provider, while serving a large customer base, through its sister company Martin Telecom under the brand name of ClickNet.
