Printer Friendly

Enabling wideband SATCOM on-the-move communications.

[FIGURE 1 OMITTED]

There are several anticipated operational benefits associated with implementing high capacity, beyond line-of-sight communications on mobile tactical warfighting platforms. These benefits are more commonly referred to as satellite communications on-the-move. These include improvements in situational understanding, lethality, survivability, and overall combat effectiveness.

The Warfighter Information Network--Tactical Increment 2 program is currently implementing solutions to enable this capability using components originally developed under the United States Army's KaSAT Development Program and the Affordable Directional Antenna and Pointing Technologies Army Technology Objective-Demonstration. These components include the MPM-1000 modem, which implements the Network-Centric Waveform, as well as an on-the-move antenna system, which includes a positioner, feed assembly, aperture and an inertial navigation unit. Multiple technical, operational, and statutory issues, however, must be addressed in order to fully realize this vision.

These challenges are discussed herein, as well as the status of their corresponding solutions. A roadmap for implementation of the capability in the field is provided, as well as a forecast for future SOTM technology evolution.

Technical challenges

There are numerous technical challenges related to vehicle platform dynamics, size, weight, and power constraints, varying radio frequency link conditions, and the use of layer three networking protocols, which must be considered in the development of a mobile high capacity beyond line-of-sight communication system. Each of these challenges must be addressed with a cost effective solution in order to comply with WIN-T program objectives.

Vehicle platform dynamics

WIN-T Increment 2 will deploy multiple configuration items using fixed, at-the-halt, and/or satellite communications on-the-move terminals. (See Figure 1. Above.) Two different types of SOTM terminals will be provided under Increment 2. Both SOTM systems require an antenna positioner, which must reliably and accurately point to a fixed absolute azimuth, elevation, and polarization angle regardless of vehicular motion. This is normally accomplished by feeding a three axis positioner with input from an external Inertial Navigation Unit device. The external commercial-off-the shelf INU devices are relatively expensive and contribute substantially to the overall cost of the SOTM system. Many external INUs were originally developed for fixed wing aircraft applications. Although this approach is acceptable for the Tactical Communication Node and Point of Presence Configuration Items, which are fielded in relatively low densities, it becomes an issue for the Soldier Network Extension CI, which is projected to be fielded in densities exceeding 34 units per BCT.

In order to address this challenge, the U.S. Army Communications-Electronics Research, Development and Engineering Center developed a prototype two-axis positioner with an embedded low cost INU, in lieu of an external commercial off-the-shelf device under the ADAPT ATO-D. This positioner relies on a satellite beacon, along with its internal INU to stay accurately pointed at the satellite.

Prototype antennas were delivered to the CERDEC in the fourth quarter of fiscal year 2008. PM WIN-T, working with MIT/ Lincoln Labs, developed a unique testing capability for these prototypes since they required a live satellite beacon, motion table and precise pointing measurement system.

Testing of the prototypes confirmed that the initial ADAPT ATO-D design goals were satisfied. Eventually, 34 SNE Engineering Development Models were subsequently procured under WIN-T Increment 2. See (Figure 2. Above right) Additional testing on the SNE EDMs will be completed in the third quarter of FY 08, to ensure that the low cost positioner is capable of satisfying all FCC/ITU criteria for SOTM platforms, while subjected to the U.S. Army's Perryman and Churchville-B road profiles. The overall pointing accuracy and throughput performance requirements for the SNE CI are less than that of the TCN/PoP SOTM terminals. However, the projected Average Procurement Unit Cost for the SNE is less than 55 percent of that for a standard three axis/ external INU implementation.

[FIGURE 2 OMITTED]

Vehicular platform considerations also present an issue with respect to the modem used for SOTM applications. The MPM-1000 modem technology used in WIN-T Increment 2 was originally developed under the Army's KaSAT program. The KaSAT modem configuration was neither affordable nor suitable for use within warfighting platforms. Consequently, PM WIN-T needed to reduce the modem's APUC and ruggedize the system to withstand platform induced shock and vibration, as well as exposure to warfighter environments.

Working with the modem contractor, PM WIN-T identified several candidate cost savings opportunities in the modem design. These included selection of a commercial off-the-shelf-based modem controller, design of a new carrier board for the controller, and replacement of expensive FPGAs with more affordable alternatives.

At the same time, PM WIN-T applied funding to redesign the mechanical structure of the modem to withstand shock and vibration profiles in accordance with MIL-STD-810F. The new modem design will also comply with significantly increased stringent environmental requirements, including exposure to sand, dust, fungus, humidity, electromagnetic interference, and greater operating temperature ranges. Notwithstanding the improvements in the modem design to address the vehicular platform concerns, the overall projected APUC for the modem has decreased by more than 40 percent, as compared to units procured in FY 07.

Size, weight, and power constraints

Size, weight, and power are critical system characteristics for all SOTM systems. WIN-T SOTM systems will be fielded as B-Kits to be integrated into user owned vehicles that have tight SWAP constraints. Integrating SOTM B-Kits into tactical mobile platforms, such as Humvees, Bradleys, Strykers, and Mine Resistant Ambush Protected vehicles is a packaging challenge. The surface area to mount an antenna is minimal and different on each vehicle.

Also, antenna height must be minimized, as well, for Soldier survivability reasons. Considerable development focused on reducing antenna size, weight, and power to enable integration into these types of tactical vehicles. Early vendor models delivered antennas with 24 inch apertures, which proved too large for mobile tactical vehicles. WIN-T has performed multiple tradeoff studies between throughput performance and antenna size, weight, and power to define the optimal antenna system for each of the mobile vehicle platforms. WIN-T Increment 2 will provide 18 inch aperture antennas for the TCN and PoP CIs and 16.5 inch antenna for the SNE CI.

In support of future WIN-T Increments, PM WIN-T is working closely with the CERDEC to further reduce SWAP requirements for SOTM antennas via sponsorship of the SOTM Active Quasioptical array antenna. This hybrid design combines the benefits from both phase arrays and real aperture technology to provide electronic switchable Ku/ Ka-band in a single antenna.

The concept is for the low profile antenna along with the positioner motor and electronics to be enclosed in a 37 x 11 inch pancake radome. The objective weight of the antenna is approximately 100 pounds. At least four prototype antenna units are planned for test in the first quarter of FY 09. It is anticipated that this new antenna design will be ready for production in the first quarter of FY 10 with a target AUPC similar to that of the SNE terminal.

RF link conditions

To address the radio frequency link condition challenges, PM WIN-T developed and matured the Network-Centric Waveform, hosted on the MPM-1000 modem. NCW provides four receiver/demodulation chains and two transmit/ modulation chains supporting biphase shift keying and offset quadrature phase key shifting modulation, and half and three-quarter rate Forward Error Correction. NCW supports data rates from 32 kbps to 6.144 Mbps. The maximum user throughput that is achieved depends on the associated SATCOM terminal, as well as the link conditions.

Radio frequency links will suffer blockages and periodic outages due to terrain, tunnels, buildings, vehicular orientation, and weather effects. The SOTM system must be able to expediently acquire the satellite signal, and reacquire it should it be lost due to line-of-sight obstruction/blockage. NCW is designed for fast acquisition and requisition.

[FIGURE 3 OMITTED]

The modem will reacquire bursts within a second for short duration or intermittent blockages. Should the user be in extended blockage duration, such as behind a building or in a tunnel, the SOTM system will automatically reacquire and reconnect with the network within 10 seconds when the vehicle moves out of the obstruction and a clear line-of-sight is established. In addition, PM WIN-T is considering implementation of an automated persistent slot feature within WIN-T Inc 3. This feature will use Return Order Wire statistics to automatically assign and release satellite resources during OTM and intermittent blockage conditions.

The WIN-T SOTM systems will provide dynamic user throughputs nominally at 128 kbps for the SNE and 256kbps for the PoP and TCN CIs. Higher transmit user rates up to 1024 kbps will be achievable but will vary and depend on weather conditions, satellite in use, location in beam footprint, and other factors. NCW employs an advanced network scheduler that maximizes network data throughput under varying atmospheric conditions and terminal population by making optimal use of satellite power and bandwidth. The system adjusts itself dynamically and requires little operator intervention.

The data rate, modulation/ coding and power settings are dynamically scheduled for each link/burst in real time based on link conditions and satellite resource constraints. Burst scheduling recurs every 400 milliseconds. This rescheduling capability is critical, especially in OTM operations, due to the dynamic nature of radio frequency link conditions. A sample frame structure which depicts the scheduler's efficient use of spectrum while supporting multiple apertures is provided in (Figure 3.)

Networking protocol adaptations

A major challenge associated with all satellite communications is long delay times. When adding the software-based scheduling delay of the NCW waveform to the physical propagation delay of a geosynchronous satellite, it is not uncommon to see a one second round-trip time between two terminals. Standard TCP implementations will not take full advantage of available bandwidth under such long delay conditions since the TCP protocol implements a reliable sliding acknowledgement window with a limited maximum window size, and assumes data loss is the result of network congestion. WIN-T SOTM systems will make use of a Space Communications Protocol Standards TCP Performance Enhancing Proxy to alleviate many of the problems associated with TCP and long delay times over satellite.

[FIGURE 4 OMITTED]

SCPS PEPs act as a transport layer gateway essentially breaking a typical end-to-end TCP session into three separate connections. These are a standard TCP connection between local application and local PEP; a local PEP to remote PEP connection employing a SPCS-based protocol to optimize use of the satellite-based link; and lastly, another standard TCP connection between remote PEP and remote application. The PEPs work transparently through a technique known as spoofing, so no modifications need to be made to the TCP applications. PM WIN-T recently performed testing of various SCPS PEPs over a live NCW network. (Figure 4.) shows results of throughput tests from a large aperture terminal to a SOTM equipped platform, both with and without PEPs, for three types of files normally sent using the TCP protocol.

On average, throughputs increased by a range of two to six times with the PEP devices in line. An International Organization for Standardization standard SCPS-based PEP was chosen by WIN-T Increment 2 over PEPs, which implemented proprietary algorithms so that improved SATCOM TCP throughputs could be achieved in the event NCW communications are required with a non-WIN-T SOTM unit.

NCW further improves interoperability by appearing to an Ethernet/Institute of Electrical and Electronics Engineers 802.3 standard interface as a switched link-layer architecture, analogous to a Virtual Local Area Network partition in a terrestrial link-layer switch. Therefore, IP unicast, multicast, and broadcast packets are forwarded appropriately within the waveform allowing standard protocols such as Open Shortest Path First unicast routing, Protocol Independent Multicast multicast routing, and High Assurance Internet Protocol Encryptor peer discovery to work without the need for complex end-to-end tunnels to be created and maintained between wide area network routers.

Operational challenges

Communication architectures vary among the Army echelons and among different brigade combat teams. Users require reliable but flexible communications network structures to accommodate separate units with different loading traffic profiles. When deploying a SOTM-based solution to enable wideband BLOS communications, operational planning must be addressed. Network size or the number of nodes in a network, expected traffic duty cycle of nodes, number of distinct networks, interconnection between networks, and quality of service must all be considered. The NCW system is highly flexible and can be adapted to many diverse user network scenarios.

Automated devolution

A typical NCW network consists of satellite earth terminals with one terminal operating as the network controller and the other terminals operating as network members. The NC serves as the source for network time synchronization and as the focal point for network control and network resource management. It is also used to establish priority-driven band-width-on-demand traffic communications. The NC also provides the heartbeat for the entire network. NCW provides a critical and flexible NC devolution capability to maintain network reliability and survivability. In order to avoid a single point of failure scenario, certain terminals, designated as NC-Capable, are capable of assuming the NC function, via seamless planned and unplanned handover protocols.

Mesh architecture

NCW supports a heterogeneous network of terminal types with varying antenna sizes and power characteristics, ranging from large-aperture strategic terminals to small-aperture tactical mobile terminals. In a fully mesh network configuration setup, NCW always initially tries to establish a peer-to-peer communications between all terminals.

Technically, peer-to-peer communications will reduce the satellite resources required to relay the data to the destination terminal and will also significantly reduce the delays associated with two-hop communications associated with a hub-based architecture. Operationally, a mesh architecture is crucial for transport of time critical data, but may also be required to support certain types of communications such as duplex voice.

Depending on the frequency band used (Ku-band), mesh communications may not be possible for small terminal to small terminal communications. Small tactical mobile SOTM terminals typically have reduced aperture antennas and may require more power than is available from the satellite to close a one hop link.

In these instances, the NCW Hub-Assist mode will dynamically route packets through the Net Control terminal or alternative NC to reliably maintain communications. The NC and alternate NCs serve as store and forward hubs to assist NMs and route traffic to the destination node when the link cannot be directly closed in a single-hop link.

NCW will not be new to the field when it will be introduced under the WIN-T Increment 2 program in FY 11. Early NCW releases are in use today in the Mounted Battle Command on-the-Move program and a quick reaction program called Triton. The integration, small scale fielding, and operational lessons learned have been invaluable in identifying technical and operational issues early and provide improvements to the system as the WIN-T program moves forward. Periodic technical and field tests continue at the C4ISR OTM Test Bed, Fort Dix, N.J., to mature the system into a high performance and reliable WIN-T communications network.

Statutory challenges

The WIN-T design will capitalize on ubiquitous commercial Kuband satellites and military Ka-band aboard Wideband Global SATCOM satellites to provide high bandwidth SOTM capabilities. From a regulatory perspective, both Ku and Ka bands present unique challenges to the Army.

Commercial Ku-band

Within the Fix Satellite Service Ku-band, there are approximately 220 geosynchronous satellites listed as operational. This density of satellites makes adjacent satellite interference a very significant issue, especially when using small aperture SOTM terminals. The current criteria established for SOTM by both the FCC (continental United States) and ITU (outside of the continental United States), however, were principally adapted for shipborne applications and do not consider ground mobile environments. PM WIN-T has formally proposed that the regulatory limits be changed from the rigid go/no-go off-axis power spectral density profile to an approach using a statistical model. The statistical model approach would require a very low probability of exceeding the off-axis power spectral density profile caused by momentary pointing errors due to movement of the vehicle or ground mobile platform on which the antenna is mounted. These proposals are currently being evaluated at ITU working groups.

Regardless of changes to the FCC/ITU criteria, dynamic spreading of the radio frequency signal will be required when using Ku-Band. The WIN-T NCW design has implemented seven unique spreading factors which range from 0 to +12 dB and which are computed based on the power required to close the link and the aperture parameters. NCW optimizes the available satellite bandwidth by spreading the signal the minimum amount needed to avoid ASI.

These changes are distributed, every 400 milliseconds, to each node in the network, from the network controller via the Forward Order Wire channel. Each of the SOTM terminals planned for WIN-T Increment 2 will comply with the current criteria established by the FCC and ITU.

Military Ka-band

For military Ka-band, the interference environment is not as severe. The performance criterion for all earth terminals for military Ka-band is codified in MIL-STD-188164A. Currently, Ka-Band off-axis limits have not been established in MIL-STD-188-164A. However, there is an ITU Radio Regulation that imposes the requirements for coordination between geostationary-satellite networks sharing the same frequency bands.

Currently, the Army is analyzing the ITU Radio Regulation and will propose to the MIL-STD community a maximum permissible off-axis power spectral density from SOTM earth stations. This will promote quasi-free interference satellite operations while maintaining reasonable SOTM spectral efficiency.

Summary

Substantial progress has been realized with respect to addressing the technical, operational and statutory challenges associated with deploying a SOTM based solution to enable BLOS communications on warfighting platforms. The initial widescale deployment of this capability will occur with the WIN-T Increment 2 fieldings of PoP and SNE CIs in FY11. The TCN CI, which will be owned and operated by Signal Corps personnel, will also use the SOTM technology to enable the entire WIN-T WAN to operate on the move. During the course of FY 08-10, PM WIN-T will continue to mature each of the SOTM components, integrate them into functional B-kit configurations, and subject them to both developmental and operational tests.

In addition, several new advanced NCW features are being considered for implementation. Many of these features are being implemented to take advantage of new WGS capabilities, including variable size bandwidth segments and gain states, not available on many commercial satellites. Other features include improvements related to ease of use and maintain ability. Although much work remains to be done, the vision of improved warfighter situational understanding, lethality, survivability, and overall combat effectiveness via high capacity BLOS communications is closer than ever to reality.

ACRONYM QUICKSCAN

ADAPT--Affordable Directional Antenna and Pointing Technologies

APUC--Average Procurement Unit Cost

ASI--Adjacent Satellite Interference

ATO-D--Army Technology Objective-Demonstration

BLOS--Beyond Line-of-Sight

BPSK--Biphase Shift Keying

C4ISR--Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance

CERDEC--Communications-Electronics Research, Development & Engineering Center

CIs--Configuration Items

COTS--Commercial Off-The-Shelf

EDMs--Engineering Development Models

FCC--Federal Communications Commission

FEC--Forward Error Correction

FOW--Forward Order Wire

FSS--Fix Satellite Service

FY--fiscal year

GSO--Geosynchronous

HAIPE--High Assurance Internet Protocol Encryptor

HMMWV--Highly Mobility Multipurpose Wheeled Vehicle

IEEE--Institute of Electrical and Electronics Engineers

INU--Inertial Navigation Unit

ISO--International Organization for Standardization

ITU--International Telecommunications Union

LOS--Line-of-Sight

MBCOTM--Mounted Battle Command on-the-Move

MRAP--Mine Resistant Ambush Protected

NC--Network Controller

NCW--Network Centric Waveform

NM--Network Members

OQPSK--Offset Quadrature Phase Key Shifting

OSPF--Open Shortest Path First

OTM--On-the-Move

PEP--Performance Enhancing Proxy

PIM--Protocol Independent Multicast

PoP--Point-of-Presence

ROW--Return Order Wire

SCPS--Space Communications Protocol Standards

SNE--Soldier Network Extension

SOTM--SATCOM On-the-Move

SWAP--Size, Weight, and Power

TCN--Tactical Communication Node

WAN--Wide Area Network

WGS--Wideband Global SATCOM

WIN-T--Warfighter Information Network Tactical

Mr. Swenarton is serving as the TMD chief for PM Warfigher Information Network-Tactical.

Mr. Levchenko, P.E., serves as a senior systems engineer for SATCOM on-the-Move development, test and integration for Warfighter Information Network-Tactical Increment 2 and associated Army Team C4ISR programs.

Mr. Gonzalez has provided direct system engineering support to the U.S. Army Program Executive Office; Project Manager, Military Strategic, Tactical and Relay , PM Military Satellite Communications and PM Warfighter Information Network-Tactical for the past 16 years. His area of expertise is in Military satellite communication systems such as MILSTAR, UFO, GBS and GAPFILLER. Before joining the LinQuest Corporation he worked at the Johns Hopkins University Applied Physics Laboratory, Bendix Corporation, and BAE Systems.

Mr. Lange is a systems engineer at Project Manager, Warfighter Information Network-Tactical. He holds an M.E. degree in systems engineering from Stevens Institute of Technology and a B.S. degree in computer science from the New Jersey Institute of Technology.

Mr. Pedoto is an independent consultant supporting the Program Executive Office for Command, Control and Communications-Tactical, Project Manager, Warfighter Information Network-Tactical in the areas of test and evaluation of Satellite Communications terminals and tactical communications, including the development of SATCOM on-the-move terminals. He holds an M.S. degree in management science and a B.S.E.E.
COPYRIGHT 2008 U.S. Army Signal Center
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2008 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:satellite communications
Author:Swenarton, Chris; Levchenko, Eugene; Gonzalez, Lino; Lange, Mark; Pedoto, Eugene
Publication:Army Communicator
Article Type:Report
Geographic Code:1USA
Date:Jun 22, 2008
Words:3418
Previous Article:Advancing the army through an innovative process.
Next Article:Satellite communications for company level warfighter.
Topics:

Terms of use | Privacy policy | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters