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Fixed satellite services (FSS) were once used in conjunction with tactical radios to provide the entire chain of communications between the tactical edge of the battlefield and the Department of Defense (DoD) enterprise. The tactical edge can now use technologies such as mobile ad hoc networks (MANETs) to establish data and communications links, distribute situational awareness information, and integrate new and existing technologies on the battlefield (see the MANETS sidebar on p. 14). In addition, mobile satellite services (MSS) and associated platforms can connect remote warfighters, unmanned vehicles, and MANETs to other parts of the tactical edge or to the enterprise.

However, there is still demand for the development of comprehensive end-to-end communications solutions. To address this shortcoming, the DoD has envisioned and is currently implementing the global information grid (GIG). The GIG is using a standards-driven approach to create interoperable solutions across its global infrastructure. Standards, such as IPv6, created by the Internet Engineering Task Force (IETF), will enable data from a set of tactical-edge wireless sensors in a networked IPv6 tactical sensor system to be aggregated, transported, fused with satellite imagery or force tracking data, processed, and then presented to anyone on the GIG, regardless of their location.

Our enemy's tactics in the global war on terror skew heavily toward infiltration, deception, and misdirection. There is an ever-widening array of technology that today's warfighter can bring to bear against these enemy threats, but frontline elements still have problems accessing that technology from the austere environments where they are most frequently deployed. In these environments, communications infrastructures are typically unreliable, untrusted or non-existent, yet the need for real-time information is high. Robust communications and situational awareness are more important than ever, and warfighters need mobile communications solutions that can keep pace with those needs.

The DoD net-centric warfare (NCW) doctrine envisions our military forces as a network of connected nodes. The GIG will be the means by which everyone from theater-level commanders to the squad leader on patrol out at the tactical edge are connected. At present, there are several challenges to providing this level of connectivity. Highly mobile combat elements, often referred to as disadvantaged units, do not enjoy the same connectivity or access to information services that higher-level command elements receive from their fixed or semi-fixed locations.

Given their missions, however, these highly mobile combat units need the same level of access as their commanders. Modern command, control, communications, computers, intelligence, surveillance and reconnaissance (C4ISR) solutions can enable the delivery of real-time data to these warfighters. By leveraging commercial-off-the-shelf (COTS) technology at the tactical edge, C4ISR solutions can bring advanced technology from industry to provide state-of-the-art capabilities on the battlefield. Reliable mobile communications that greatly increase the bandwidth available to the warfighter are the key enabler.

Mobile communications on the battlefield have played a significant role in supporting the vast new array of C4ISR technologies and applications used by the warfighter. To provide tactical users with flexible communications and the ability to share information, the tactical edge has become dynamic, integrating various transport architectures into a common networking environment. The transport architectures can include any combination of terrestrial wired, fixed wireless, satellite, mobile wireless, and mobile ad hoc networks. However, with the advancement of new C4ISR technology for the battlefield, tactical users have developed a critical requirement for rapidly deployable communications.

Mobile ad hoc networks and mobile satellite services (MSS) have emerged to fill the void for rapidly deployable, tactical communications. Although FSS provide a valuable capability, they represent a second- or third-phase satellite backhaul solution that is deployed as part of a static tactical command. Warfighters at the tactical edge require their communications to travel with them. As a result, there has recently been a surge in the development of mobile communications solutions that are small, lightweight, power efficient, and easy to use for all warfighters.

Mobile satellite services are global satellite solutions that can connect a remote tactical user, unit, or device back to the tactical edge or the enterprise. With support for voice, video and data they can provide the same types of services as FSS. MSS are fundamentally different from FSS in that they use L and S bands, which operate in the 1 GHz to 4 GHz frequency range, while FSS use C, X, K, Ku and Ka bands, which operate in the 4 GHz to 40 GHz range (Figure 1). Support for a higher-frequency range enables FSS to provide high bandwidth links on the order of tens of megabits per second, but this comes with a trade off to mobility.

Very small aperture terminals (VSATs) used for FSS are bulky and can end up weighing hundreds of pounds, which places obvious limits on mobility. In addition, the low beam-pointing accuracy tolerance of VSATs negatively impacts setup time. For a Ku-band VSAT, which has less than one degree of steering accuracy tolerance, setup could take 45 minutes or more.

In contrast, MSS use a lower-frequency range to support enhanced mobility. MSS terminals are small, portable devices that provide a short setup time. The short setup time is due to the fact that MSS terminals have a high beam-pointing accuracy tolerance. An L-band MSS terminal, which has 12 of steering accuracy tolerance, commonly takes less than five minutes to setup. In addition, MSS frequencies are largely unaffected by rain or dust attenuation, and are not affected by co-site interference. This makes them suitable for use in a broad range of environments, even if devices are co-located with one another.

Man-portable MSS terminals are no larger than the size of a laptop, and weigh less than five pounds. Mounted MSS terminals for ships, vehicles, and aircraft are larger, but usually weigh less than 100 pounds. The mounted MSS terminals are larger and heavier due to their additional requirements, such as support for aircraft mobility and quality of service (QoS), but pale in comparison to the size and weight of VSATs in similar situations. Unlike FSS, MSS capabilities can also be offered as part of an integrated system, such as a satellite phone or smart sensor with an integrated MSS antenna.

Another benefit of MSS is a significantly lower cost of ownership. Besides being smaller and lighter than VSATs, MSS terminals are also much cheaper. While VSATs average in the hundreds of thousands of dollars, a man-portable MSS terminal is on the order of a few thousand dollars. Mounted MSS terminals are usually more expensive, perhaps a few hundred thousand dollars, but still have lower cost than comparable FSS VSATs. Having a relatively inexpensive terminal is important at the tactical edge or on the battlefield, where loss or damage becomes more likely. As new FSS and MSS technologies become available, it will be much less expensive to upgrade legacy MSS systems than to upgrade comparable FSS systems. A wide range of MSS solutions are available, including popular services such as Inmarsat's BGAN, Iridium, and the hybrid satellite-cellular solution offered by Mobile Satellite Ventures (MSV).

In addition to supporting basic communications, MSS can serve as enablers on the battlefield for situational awareness and the incorporation of C4ISR technology. Although a MANET can provide situational awareness for the nodes within its network, it may still require backhaul communications capabilities to distribute that information along the tactical edge or across the GIG. MSS provide a great complement for MANETs because they provide a mobile backhaul solution. Since MANETs can support a heterogeneous community of nodes, a node equipped with MSS can share its capabilities with the rest of the MANET. Because the MANET and MSS architectures are so versatile, they are becoming key components in facilitating tactical end-to-end connectivity solutions on the battlefield.

MSS is a key enabler for global asset tracking, a capability that is especially useful given the nature of emerging military threats. MANETs may also come to play an equally crucial role in asset tracking. For example, radio frequency identification (RFID) tracking solutions may be tailored to work within MANETs to monitor the supply chain on the battlefield. Logistics information can be collected locally within the MANET, then transported via MSS and aggregated to provide an overview of all supplies at the tactical edge. That data could then be used to locate and proactively replenish the tactical supply line.

Sensor networks can operate in a similar fashion to provide comprehensive situational awareness of the tactical edge. Currently, a number of solutions for sensors use MSS or MANET as their sole network architectures. All of these various clusters of sensors could be interconnected to leverage MSS and MANET to distribute situational awareness information while ensuring the precise distribution of data to where it is most needed. For example, it would not be necessary for each sensor within a cluster to transmit information over MSS if the sensor information from each member of the cluster is first aggregated within a MANET before transmitting it over a satellite infrastructure. Similarly, sensor nodes within a remote MANET could increase situational awareness by directly distributing data over a mobile satellite backhaul solution to other users on the tactical edge.

To support all of the capabilities necessary at the tactical edge, there is an ever-growing need to develop comprehensive end-to-end connectivity solutions. As new capabilities are extended to users, sensors, and devices at the tactical edge, scalability, performance, and information assurance become even greater concerns to the enterprise. Technology standards, such as IPv6, have aided in addressing a few of these concerns. Since IPv6 has a larger address space and provides enhanced quality of service, IPv6 solutions are more scalable and can provide better performance.

Using IPv6, a networked tactical sensor system can aggregate its data at the tactical edge and transport it to a desired location (or locations) where it can be processed and fused with other information (such as satellite imagery and force-tracking data). A common operational picture (COP) could then be distributed as part of another end-to-end connectivity solution to any authorized user, anywhere in the GIG.

Although IPv6 can be used as a network enhancement, there will be additional challenges incorporating information assurance into a tactical end-to-end connectivity solution. The warfighter must already contend for limited bandwidth on the battlefield. Since the devices in these networks must share RF spectrum and are usually restricted in terms of the size, weight, and power (SWAP), only a limited amount of bandwidth is available on any given link. When leveraging IPv6 with an IPsec secured VPN in tunnel mode, each packet that traverses the tactical network may have greater than 120 bytes of overhead.

These 120 bytes of per-packet overhead may not seem significant. However, consider a situation in which three tactical users are required to share a 256 kilobits-per-second (kbps) bandwidth-constrained satellite link for voice communications. Even if a low-bit-rate VoIP codec (G.729, for example) were used, each tactical user would require approximately 112 kbps of bandwidth for a two-way VoIP call (Figure 2). With three users, the link would congest quickly, and calls that were not dropped would suffer from poor voice quality. Header compression (HC) could provide an appropriate solution in this case by compressing RTP/VDP/IPv6 overhead by as much as 50%, which would support the required number of users for this mission requirement.

To satisfy the emerging requirements of the warfighter and the GIG, the tactical edge must encompass end-to-end connectivity solutions. MANETs and MSS architectures support solutions at the tactical edge because they are flexible, mobile, scalable, and support rapid deployment. The incorporation of C4ISR technology and situational awareness into these architectures represents part of an optimal solution for the tactical edge. However, for these end-to-end connectivity solutions to operate effectively and seamlessly, a number of technical challenges, several of which were mentioned briefly, must be resolved.

Note that DoD programs and agencies have initiatives and programs under way to incorporate advanced information technologies into their systems (e.g., Army's Warfighter Information Network — Tactical (WIN-T) and LandWarnet). The process is complex and, therefore, time consuming. This article expresses a few of the challenges being addressed along the way, but recognizes that technology insertion is a continuing effort that will require coordination within the DoD and industry.

Mobile ad hoc networks (MANETs) are autonomous, self-healing networks that can connect anyone or anything on the battlefield (Figure 3). Unlike legacy radios that can support only direct, in-range voice communications, networked tactical radios can provide a variety of communications over a much larger range with support for voice, video and data. Networked devices in MANETs are capable of supporting voice, video and data. A MANET's ability to create autonomous networks allows it to leverage networked devices as routable nodes to distribute the flow of information. It can also leverage existing network infrastructures such as terrestrial wired and fixed satellite networks to provide a backhaul solution, resulting not only in a highly mobile network, but also in a highly flexible network well suited for tactical edge users.

By creating dynamic communities with nodes on the ground, at sea, or in the air, MANETs are an ideal tool for facilitating joint force operations and integrating various C4ISR technologies. When joint forces use interoperable C4ISR systems within a MANET, they can quickly carry out a plan of attack to shorten the kill chain. To provide in-theater support in response to a threat, other types of C4ISR technologies, such as an unmanned aerial vehicle (UAV) or unmanned terrestrial vehicles (UTV), can be deployed, controlled, and monitored within the MANET. As joint forces work together, they can also share valuable situational awareness information over the MANET. This information can be fused with other relevant information to create a common operational picture (COP) illustrating the current state of affairs to help determine the best course of action for a soldier, a company, or an entire battalion.

Etzel C. Brower Jr., senior network engineer with Trace Systems, has extensive experience supporting GIG engineering efforts surrounding technologies such as IPv6, header compression, and MANET within the JTEO, TSAT, JTRS, NSA HAIPE, and DISA programs. He earned his MS and BS in electrical and computer engineering from Carnegie Mellon University. Any inquiries relating to this article may be addressed to ebrower@tracesystems.com.