New GPS handheld receiver planned for '04: fast processors, advanced displays will simplify satellite-guided navigation in the field.

The U.S. Defense Department is preparing to test a next-generation Global Positioning System handheld receiver that will be lighter and easier to operate than current devices, officials said.

The new system, known as the Defense Advanced GPS Receiver (DAGR), will replace the so-called Precision Lightweight GPS Receiver (PLGR).

The two companies competing in the DAGR program are Raytheon Space and Airborne Systems, in El Segundo, Calif., and Rockwell Collins, of Cedar Rapids, Iowa. These firms received contracts valued at $357.1 million and $361.1 million, respectively.

Each contractor will supply the GPS Joint Program office with 250 test units by May 2003. The JPO will oversee the selection process in the fall of 2003. Operational testing and low-rate production could begin sometime in late 2004. The next phase of the program could be worth between $300 million and $400 million.

"Simply put, DAGR will reduce the logistical burden on the war fighter, enabling greater tactical situational awareness in less time, using less equipment," said Air Force Maj. Keith Hirschman, project officer for the DAGR program. "Not only will DAGR provide the soldier with ready-to-use data in one-sixth the time of PLGR, but it will do it with less than half the battery consumption, in a package less than half the weight and only two-thirds the footprint."

PLGR technology has for a decade now enabled soldiers to use coordinated position, velocity and timing data in continuously mobile, unfriendly environments. The performance of the PLGR depends on a single frequency (L1) for reception and switchover from commercial to encrypted GPS signal.

DAGR technology proposes to eliminate this reliance on one frequency by adding a second frequency (L2), enabling soldiers to obtain position information with greater accuracy, in less time, said officials.

"In essence, DAGR has twice PLGR's capability of receiving clear satellite signal transmissions," said Mike Fleenor, business director for land navigation at the Raytheon Company. "Attempts at jamming or spoofing signals, where successful against PLGR, are less likely to be effective using dual-frequency DAGR, since the bandwidth of each frequency will be available for signal acquisition."

To prevent unauthorized users from logging on a U.S. receiver, the GPS Joint Program Office implemented a security technique built around a dual-key architecture for controlling access to military encrypted P(Y) code. Color-coded, red or black, cryptographic keys represent the basic authorization levels for operating in classified P(Y) code.

The addition of a now-mandatory GPS security device called the Selective Availability Anti-Spoofing Module (SAASM) into DAGR will offer the user the guarantee that, in the event of enemy capture, the receiver encrypted architecture will be fully resistant to any attempts at reverse-engineering its components.

At the crux of military GPS security is the reliance on Precise Positioning Service-Security Module (PPS-SM) data storage and processing. Supporting a network of digitally-based receivers, PPS-SM and an Auxiliary Output Chip (AOC) produce the GPS encrypted P(Y) code, a signal requiring tight restrictions on user access in maintaining classified data security.

As a result, a complex system of red-key (classified) and black-key (unclassified) authorization codes often became a logistical burden during combat operations. "The distribution of cryptographic classified red keys to hundreds of thousands of users worldwide is a logistical nightmare," said Hirschman.

"With the arrival of SAASM-based receivers like DAGR, protecting classified GPS data will no longer be an external manual process, but an internal automated one, based on the tamper-proof construction of the units themselves."

"With PLGR, access to P(Y) code is limited, meaning certain users are cleared for classified red key access and certain are not," Hirschman said. "The introduction of DAGR with the SAASM chip will eliminate the need for strict key controls to the P(Y) code since SAASM will simply not function in the attempt of unauthorized use. This increased security will effectively decrease user authorization standards, allowing for a system based solely on unclassified black keys, enabling more soldiers in critical areas of the battlefield to have needed access to the P(Y) code."

So far, he said, the "challenge in GPS technology development has been the creation of secure, yet open architecture systems capable of being both backward compatible with existing hardware and software, as well as forward compatible with future command and control networks."

Increased Bandwidth

Aside from the added functionality of dual frequency, DAGR's increased bandwidth availability enables the receiver to process GPS position-location data more rapidly and precisely than PLGR. That helps expedite the transfer from rapid-pulse commercial-grade C/A code to slow-pulse P(Y) code. "Satellite signal acquisition and re-acquisition is achieved by the precise timing needed to go from C/A to P(Y) code," said Fleenor. "DAGR's dual-frequency coordination gives the user greater signal clarity for faster initial, post-standby, and post-power down signal acquisition."

The susceptibility of P(Y) code to enemy jamming and spoofing techniques has driven the development of GPS receivers that are able to switch from commercial to encrypted code with greater efficiency. "Signal loss or switch-out due to jamming or spoofing prior to desired code acquisition can be deadly to the war fighter who is depending on timely position-location information," said Hirschman. "If the data is not received when it is needed, it does the soldier no good."

At the heart of DAGR's ability to acquire and process GPS signals faster than PLGR is an increased number of data correlators. Representing individual translators from CIA to P(Y) code, the correlators attempt to recognize the signal patterns in each code variation, so that a bridge can be made from one code to the other. Faster code correlation means faster data acquisition.

With as many as 9,000 correlators built into it, DAGR will have 45 times the correlation capability of PLGR, which has approximately 20 correlators. This capability, made possible by DAGR's dual frequency operation, will also protect against signal interference, the contractors said.

"Resistance to signal jamming depends largely on the ability to recognize signal traits through the interference," said Fleenor. "As a jamming source gets louder, it becomes more difficult to achieve signal-to-signal correlation. The more correlators available to listen for the desired signal, the better chance that one will recognize the coded signal and link it to another."

Spoofing or swapping out of GPS signals with a false or manufactured signal is common and is also more easily overcome by DAGR's dual frequency reception. "With DAGR, there is a greater likelihood that initial GPS signal correlation will occur before any spoofing attempt can be effective," Fleenor noted.

As a purely text-based receiver, PLGR displays GPS coordinate data that must be plotted on a map, to be useful to the soldier in the field. In many cases, this procedure must be performed at night, when a light source is necessary to see the map.

"Though it may seem harmless, breaking out a map, compass and flashlight to plot coordinates when a soldier needs timely data to react to changing battlefield conditions can be quite detrimental to the soldier, let alone mission success," stressed Hirschman.

To help solve the problem of multi-tasking in order to obtain timely position information, DAGR offers a lighted text- and image-based display.

Using software pre-programmed to show the general layout of a combat zone, DAGR provides an integrated text/map interface using icons to designate user position as well as other mobile or static objects.

A keypad and pop-up windows offer various options with regard to way point classification. "In the time it rakes to deploy an accompanying map, compass or flashlight, the soldier will now be able to see his position on the battlefield relative to other objects, using only his receiver, and promptly decide what course of action to take," said Hirschman.

The DAGR would make it much easier for soldiers to navigate in unknown terrain, he added. The receiver's display presents the soldier with a pre-mapped visual of the operational zone. Continual one-second updates to the visual display map enable the soldier to stay on the move, using a laser rangefinder and other devices to input data directly into DAGR.

"Once an object is located, its coordinates are plotted by manual or electronic inputs to the DAGR receiver," said Fleenor. "Within one minute, an icon representing the object will pop up on the display screen showing the coordinates to its position. With PLGR, it can take as many as six minutes to get a fix on an object, and this does not include the time it takes the soldier to plot the received coordinates on a corresponding map."

DAGR will process data much more quickly than PLGR, officials said. Operating on one-second pulse intervals, DAGR, having achieved an initial fix, will reflect changes, in real-time, to the position or direction of a given object.

Depending on the initial clarity of DAGR's dual frequency reception, both P(Y) code and waypoint reacquisition is achieved more quickly than initial lock-on because DAGR correlators will store the initial fix data, making reacquisition of a signal or waypoint simply a matter of re-matching recognized data.

Plotting Coordinates

Tracking mobile objects will be easier with DAGR, contractors claim. Unlike acquiring fixes on static objects, obtaining and reobtaining information on moving ones involves regular surveillance.

Using PLGR, a soldier must continually re-plot new coordinates on a separate map based on changing target course and velocity. With DAGR, initial-fix data is automatically updated on the visual display map for targets with constant speed and direction and with inputs for targets with changing speed and direction.

"DAGR does in one step what PLGR does in two," said Steve Jones, marketing manager for land navigation systems at Rockwell Collins. "The act of plotting new coordinates can now be accomplished by the receiver itself, reducing the total time-to-fix."

DAGR also addresses the need for data sharing during operations. In situations where a common picture of the battle-space is required for objective coordination, soldiers can link PLGR with DAGR or DAGR with DAGR to update information where necessary. Using PLGR, data is transferred textually and then must be plotted by hand. DAGR will allow the instant transfer of visual displays with waypoints already designated.

"This will eliminate the time it takes for one soldier to re-plot objects that are already plotted on another soldier's map," Jones said.

One key difference between PLGR and DAGR is the latter's ability to alert a soldier to danger zones not depicted on an operational map. As a function of DAGR's visual display, threats such as the presence of enemy units or terrain irregularities are designated by icons that differentiate them from friendly or neutral waypoints.

"By not having to go from receiver to map and back to receiver again, as is the case with PLGR, DAGR users can keep their eyes on the receiver to show them objects and areas to be aware of," Jones noted.

"Assuming these obstacles have a static location or constant course, DAGR will continue to update their positions by the second. If the objects are moving with continually changing courses and speeds, inputs from the user, either visually or electronically, will result in updated positioning on the DAGR display."

Program officials also predict that DAGR will help synchronize battlefield communications systems, such as the single-channel ground and airborne radio system and the joint tactical radio system. Using its dual frequency capability, DAGR would establish optimal radio frequencies for soldier-to-soldier voice transmissions.

"In situations where standard frequency hopping is being used, the synchronization of GPS equipment to a particular radio network requires precise timing," said Jones. "With DAGR's dual frequency operation, faster GPS signal lock-on will in turn enable faster radio connectivity, giving soldiers quicker access to the data they to need for performing their mission."

As far as the development of DAGR goes, both contractors said that there is a big push by the Defense Department to incorporate as much commercial technology as possible.

"Providing user-friendly functionality within technologically advanced packaging to the war fighter continues to be a top priority," Hirschman said. "DAGR's visual display, ability to acquire a quick position fix, and easy-to-manage platform are perhaps the aspects best demonstrative of this trend toward the commercial."

An example of a commercial-like capability is the integration of satellite photography and the receiver's visual display. DAGR software will enable users to geo-reference a satellite image to specific GPS coordinates on the display map.

"By downloading satellite views of a battle-space taken prior to a mission into DAGR, a soldier can carry an accurate picture of the operational theater and continually update that picture with inputs accordingly," said Fleenor. "In situations where a soldier is not line-of-sight to a moving object, but has communication on an approximate location, speed and direction of that object, DAGR's visual display software will return instant position data, once the waypoint has been entered."

Efforts by the U.S. Army to digitize battlefield systems and improve interoperability also have shaped the DAGR program. "Where PLGR has provided positioning and timing functionality as part of larger integrated systems, DAGR will now extend that functionality to a greater number of systems, maintaining backward compatibility while simultaneously raising the standard of GPS receiver operation," Hirschman said. "DAGR's presence should aid in transforming the very manner in which operational commanders view the challenges in maintaining control of mission situational awareness."

Initial fielding of DAGR is slated for fall 2004. So far, only the U.S. Army and U.S. Air Force have signed up for the new receiver. The Navy and Marine Corps have expressed interest in integrating DAGR technology into their existing GPS-capable platforms.

The JPO currently is conducting an international cooperative test with several allied nations, including Norway, Germany, France, Australia and the United Kingdom, which have expressed interest in purchasing the receiver for their military forces.