iKare / Satelles Proprietary 1

Satelles Time and Location Since the operational inception of GPS in 1995, the need for location technology has expanded beyond traditional navigation to include other applications like: geo-tagging, geo-fencing, asset tracking, location based services, timing and location based authentication. Many of these applications are significantly hindered by the poor performance of GPS and more broadly Global Navigation Satellite Signals (GNSS) within indoor environments and other occluded scenarios such as urban canyons. GNSS solutions are often unavailable in these difficult environments simply because the power of the transmitted signals are unable (even with signal processing gain) to penetrate various obstructions between the satellite sources and the user. Additionally, it is well known that GNSS signals can be readily spoofed using low cost and readily available equipment. There is a broad need for alternate methods to either: provide a widely available positioning signal when GNSS is not performing adequately or provide an authenticable (difficult to spoof) time and location solution even during cases where GNSS solutions appear to be working well. Satelles (a division of iKare Corporation) has worked in conjunction with the Boeing Company and Iridium Satellite LLC to develop Satelles Time and Location (STL). STL uses the Iridium LEO satellite constellation to transmit specially structured positioning signals that can penetrate many difficult environments including deep indoors. In 2013 Satelles closed agreements with Boeing and Iridium that enable Satelles to exclusively provide a commercial signal capability using the Iridium Satellite system. In accord with these agreements, Satelles uniquely manages all interfaces to the Iridium satellite operations center involving this technology. Additionally, Satelles has the ability to provide “commercial off the shelf” (COTS) solutions to customers in any sector of commerce including government customers. Presently, Satelles has launched pre-commercial signal service with targeted broadcast for key partners. Full continental U.S. (CONUS) coverage is planned for 2016. In addition to CONUS coverage, Satelles can deliver time and location signals from Iridium on a worldwide basis based on customer needs.

IRIDIUM BACKGROUND The Iridium Constellation consists of 66 Low Earth Orbiting (LEO) satellites, primarily used for global communications. The satellites transmit in the L-Band at carrier frequencies in the range of 1616-1626.5 MHz, using Quadrature Phase Shift Keying (QPSK) with a symbol rate of 25,000 symbols per second. Transmission is frame based, with frame length of 90 ms. Iridium satellites travel at speeds of about 7500 m/s, resulting in variations of up to +/- 40 kHz from the nominal carrier frequency due to Doppler effects. Compared to GNSS signals, Iridium signals have much higher raw signal power (300 ~ 2400x) as seen by a receiver on Earth, making them attractive for use in location applications where GNSS is obstructed, for example deep indoors.

Unlike GNSS satellites, Iridium uses spot beams to focus its transmissions on a relatively small geographic area. Each satellite supports 48 spot beams. The complex overlapping spot beams of Iridium combined with randomized broadcasts provide a unique mechanism to provide location based authentication that is extremely difficult to spoof. Additionally the fast LEO orbits of Iridium generate Doppler signatures significantly stronger than GPS which increases the utility of the STL signal for positioning applications.

STL SYSTEM

Figure 1: Example of Iridium Spot Beam Overlap

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The STL System uses the Iridium infrastructure to transmit signal bursts specifically designed to enable precision time and frequency measurements by a receiver. These measurements can be used by a receiver for a number of purposes, including 1) aiding GNSS acquisition, 2) augmenting GNSS measurements when not enough GNSS satellites are in view, or 3) computing position fixes directly, independent of GNSS.

Two main technical innovations are applied to the existing Iridium QPSK transmission scheme in order to facilitate precision measurements. First, the QPSK data at the beginning of a STL burst is manipulated to form a continuous wave (CW) marker, which can be used for burst detection and coarse measurement. Second, the remaining QPSK data in the burst is organized into pseudo-random sequences, reducing the effective information data rate while providing a mechanism for precise measurement via correlation with locally generated sequences. The processing gain associated with the sequence correlation operation also enhances the capability of the STL signal to penetrate buildings and other occlusions.

STL bursts are transmitted once every 1.4 seconds on average. If coarse time is known, such as in the case of a receiver with a network connection, then precise time can be calculated by processing a single burst. Assuming the receiver can process a burst in < 0.6 seconds, precise time and frequency can typically be acquired using STL in under 2 seconds. The precise time and frequency information derived from a single STL burst can be used to assist weak-signal GNSS acquisitions. Since the STL signal is more robust than GNSS, precise assistance is provided to acquire GNSS signals as weak as -160 dBm, assuming that the STL and GNSS signals are attenuated similarly by path occlusions. The STL system is designed such that a receiver can reliably decode the bursts and perform precise Doppler and range measurements at attenuations of up to 39 dB relative to unobstructed reception. This is sufficient to penetrate buildings and other occlusions, providing coverage in most deep indoor and urban canyon environments. STL measurements have been received in a host of difficult scenarios, including inside typical steel cargo containers. Tests performed in Tokyo at 300+ residential and commercial sites yielded successful signal reception in 98% of the cases tested. In environments where both GNSS and STL position fixes are possible, the GNSS positions will generally be more accurate. An advantage of STL is its ability to provide position fixes and random content under conditions where GNSS is not available due to occlusions, spoofing, or other issues. In this respect, GNSS and STL can be seen as complementary technologies, and it is apparent that receivers supporting both are highly desirable when practical. The complex overlapping beam pattern of STL combined with random content that changes on the order of once per second (in each beam) can be authenticated by a Satelles server to ensure users are where they claim to be. USE CASES Many positioning and timing applications can be enabled or achieve improved performance through the use of STL. In particular, applications that may be subject to spoofing or signal attenuation resulting from obstructions or jamming (either intentional or unintentional) are excellent candidates for STL or GNSS augmented by STL. Such applications include:

• Network security • Financial transaction security • Urban canyon positioning • Indoor positioning • Network router location authentication • Femtocell location • Shipping container tracking

• Power grid timing synchronization • Blue Force Tracking • Parolee tracking • Nuclear material tracking • Software license geofencing • Digital media playback geofencing • E911

Figure 2: Unique Features of the Iridium Based Satelles Signal

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For hybrid GNSS/STL systems, a consistency check between STL and GNSS may be performed. An inconsistency between the GNSS measurements and STL measurements can be handled appropriately for the application. For example, a financial transaction may be declined when an inconsistency is detected. For applications that have accuracy requirements that can be achieved by STL without GNSS, disabling GNSS processing can decrease power consumption.

SYSTEM INTEGRATION AND RECEIVER TECHNOLOGY

LNABTL Measurements

SiRFstarVxp™ UART/USB Bridge

FlashROM

Iridium Signal

SiRFstarVxp™ EVK

Figure 3: STL Prototype Block Diagram Leveraging the SiRFstarVxp™ Chip STL user equipment can be implemented in various ways depending on the application. Two methods are especially compelling. The first is to utilize existing equipment that already supports Iridium communications and to upgrade the software in those systems. A number of candidate Iridium radio solutions have been identified that in principle can be upgraded to support STL with a software upgrade. The second integration method of interest is to incorporate STL on one or more high quality GNSS chip sets. To that end, Satelles has worked closely with CSR SiRF to implement STL on a state-of-the-art GNSS device: the SiRFstarVxp™. The STL receiver architecture utilizing the SiRFstarVxp™ is illustrated in Figure 3. It consists of a standard SiRFstarVxp™ Evaluation Kit (EVK), with the inclusion of an on-board Low Noise Amplifier (LNA) in front of the Sniffer Radio input to optimize Noise Figure. The EVK includes on-board Flash memory to store the prototype version of firmware. The SiRFstarVxp™ chip outputs STL measurements, including Doppler and range, over a standard UART port. The EVK includes an on-board UART/USB bridge for connection to a host computer via USB. The measurements can be logged for offline processing, or processed in real time by STL Navigation Software running on an embedded computing device.

STL NAVIGATION SOFTWARE

The STL navigation processing software is implemented as an Extended Kalman Filter (EKF). The measurement updates to the EKF are composed of a Doppler measurement and a range measurement. The range measurement provides observability of position along the line of sight to the satellite. The Doppler measurement provides observability of position in the direction of the change in line of sight to the satellite. A single satellite pass can provide 3D position observability with the 2 directions in the orbit plane of the satellite being more observable than the direction perpendicular to the orbit plane. Measurements from multiple satellites can provide good 3D position observability. For some applications, the user vertical position can be constrained to provide faster horizontal position convergence. For dynamic users, there is a version of the EKF with 3 additional states to model user velocity. That version can accept measurements from an inertial measurement unit (IMU).

PERFORMANCE RESULTS Doppler and range measurement performance results reported here are based on measurements collected simultaneously from a STL prototype and a reference receiver. The STL prototype was located in a lab environment with indoor antenna, while the reference receiver was located at a base station with outdoor antenna. Figure 4 shows range measurement error vs. penetration attenuation, and Figure 5 shows Doppler measurement error vs. penetration attenuation. Measurement error is defined as the standard deviation of the differential measurement error between the two receivers. For geolocation performance results in this section, a configuration of the STL Navigation Software that assumed a static user with differential corrections was used. All data assumes a “cold start”. Figure 6 shows geolocation performance for an indoor scenario where the STL prototype and the reference receiver were co-located, used the same indoor antenna, and used measurement clocks derived from the same disciplined source. Figure 7 shows geolocation performance for a scenario where

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the STL prototype’s measurement clock was derived from a low cost Temperature-Controlled Crystal Oscillator (TCXO), and the STL prototype was located several miles from the reference receiver. For Figure 6, the STL prototype used an indoor antenna, while the reference receiver used an outdoor antenna with open sky view. For both Figures 6 and 7, geolocation performance is shown in terms of horizontal position error vs. time, for 50%, 67%, and 90% certainty.

Figure 4: Range Measurement Error

Figure 5: Doppler Measurement Error

Figure 6: Geolocation Performance (GPS-disciplined clock)

Figure 7: Geolocation Performance (TCXO)

STL also performs in a completely unconnected user mode where no differential corrections are applied. Typically converged performance yields 20m-50m accuracy subject to conditions. The stand-alone mode can accommodate users in remote conditions, while the connected modes are intended to leverage the benefits of available networked information. Additionally STL has been successfully integrated with other signals and sensors such as WiFi and has achieved remarkable performance less than 10m 1σ accuracy in some augmentation scenarios. CLOSING Satelles offers a worldwide Position Navigation and Time solution that provides a unique capability to perform in GPS/GNSS denied environments. Additionally the STL signal structure and system design (combined with the unique capabilities of Iridium) is very difficult to spoof and can be used to not only calculate user location but prove that location in applications where position and time assurance is critical. The Satelles operations infrastructure is located in the Iridium operations center in Tempe Arizona and were developed with Iridium to provide reliable and secure operations 24/7.