Chris Bartone

Multipath mitigation in the frequency domain

The GPS measurements can be modeled as true range plus other error sources such as orbit and clock biases, ionosphere, troposphere, multipath, and receiver noise. All of these errors have different frequency spectrum components. Ionosphere and troposphere errors are of low frequency, and the receiver noise has high frequency components. Orbit errors are typically bias terms, and multipath errors have low/medium frequency components. Since these errors have different frequency components, the methodology is presented whereby the multipath error can be mitigated through frequency domain processing. In this method, firstly, a validated multipath model provides the multipath frequency spectrum analysis, which is used to bound the frequency domain region for mitigation. Secondly, a code-minus-carrier (CmC) analysis provides the major code multipath error and its frequency spectrum; Thirdly, a code multipath correction is formed and applied to mitigate the multipath error in the GPS pseudorange measurement. Fourthly, a CmC analysis is performed on the multipath mitigated measurements to illustrate a reduction in the multipath error. Lastly, a compression ratio is defined which is used as a final metric to assess the net improvement in the standard deviation of the multipath mitigated CmC, as compared to the un-mitigated CmC, on a percentage basis. This technique does rely on an estimate of the peak frequency component of the multipath to be mitigated. Additionally, real test data shows the code multipath is mitigated without carrier phase aiding. Therefore, both the multipath mitigated pseudorange measurement and carrier phase measurement can be utilized for the user solution, which improves both accuracy and integrity.

Ranging airport pseudolite for local area augmentation

This paper discusses the integration of an airport pseudolite (APL) into a local area augmented differential GPS based precision approach system. A prototype architecture is described that is being used to develop requirements for the local area augmentation system. Key features of this prototype system are presented along with its current performance. Key features discussed include the use of a multipath limiting antenna, APL signal structure factors, a unique APL automatic gain control, and GPS blanking technique to maximize APL tracking performance, while minimizing the electromagnetic interference to nominal DGPS performance.

Flight-test results of an integrated wideband-only airport pseudolite for the category II/III local area augmentation system

The results of a flight test are presented that successfully demonstrate the integration of a wideband-only airport pseudolite (WBAPL) into a prototype local area augmentation system (LAAS). An analysis of the error performance exhibited by the prototype LAAS, with and without the inclusion of the WBAPL in the system, is presented. The inclusion of the WBAPL is shown to not only increase the availability of the system, but also to improve its error performance. The improvement in performance is seen to be most pronounced when a reduced GPS SV set is available, a state that would otherwise result in the unavailability of LAAS. This is the first demonstration of simultaneous increase in availability and accuracy from the inclusion or a WBAPL into a prototype LAAS.

Flight-test evaluation of small form-factor LiDAR and radar sensors for sUAS detect-and-avoid applications

Despite well over a decade of intensive research and development efforts, detect-and-avoid (DAA) technology remains in an immature state for medium and large unmanned aerial systems (UAS) and is in its very infancy for small UAS (sUAS). Routine Beyond Visual Line-of-Sight (BVLOS) operations will not be achieved until this technological impasse has been surpassed. Although a multi-system/multi-sensor approach is known to be the robust solution, sUAS platforms are challenged to host such an equipment suite in addition to their revenue-generating payload for commercial applications. Recent developments in small form-factor LiDAR and radar sensors may prove to be vital components in the overall DAA solution for sUAS. These types of sensors are being developed primarily for the autonomous ground vehicle market, but may be adapted for UAS applications. This paper documents a series of ground and flight tests conducted to evaluate the performance of both a small form-factor LiDAR and radar sensors. Obstacle detection range versus obstacle size is determined for both sensors in static and dynamic flight modes.

Considerations for Sensor Stabilization Using Stand-Alone GPS Velocity and Inertial Measurements

This paper explores the concept of using a high rate (i.e. 100 Hz), high accuracy integrated velocity (i.e. mm accuracy) estimate from stand-alone GPS measurement for sensor stabilization. The velocity algorithm uses GPS LI code measurements at a rate of 2 Hz and LI carrier measurements at 100 Hz. This velocity can be used for heading determination and then for inertial alignment or stabilization of other sensors. The integrated velocity vector accuracy is at the mm level and can be used to provide heading measurements better than 1 deg. This paper addresses several issues such as the velocity propagated position, relation between the velocity error and position error due to sensor lever-arms, timing accuracy of measurement association between various sensors, and a statistical technique to estimate the velocity error on a dynamic platform using two or more GPS antennas. High update rate position estimates, formed using the propagated velocity is shown to improve upon the noise performance of a triple difference technique. A velocity vector alignment technique is compared to a navigation-grade inertial heading alignment over a long lever-arm. A tradeoff discussion illustrates some measurement alignment and integration considerations for a remote sensor. Analysis of these concepts is provided using flight test data collected on April 12, 2006.

Prize-Winning Ohio University Students Present Their Work on an Antenna for Body Area Networks [Education Corner]

This article provides details on the OU BAN system that was submitted to the 2015 IEEE Antennas and Propagation Society (AP-S) Student Design Contest: Antenna for Body Area Networks. The team completed this project as its undergraduate senior capstone design sequence. The system senses heart rate with a chest-mounted heart rate monitor and transmits these data to a bodymounted receiver using a 5.5-kHz data link; the low frequency of this link helps minimize body effects. Additionally, temperature and provisions for fall detection using an IMU are incorporated. Sensor data are provided to an Arduino microcontroller and interfaced with a BLE transceiver to transmit data via a specifically designed inset-fed patch antenna. The torso-mounted BLE patch antenna provided good match efficiency and good radiation coverage in the forward and downward directions. Sensor data were transmitted from the torso-mounted BLE antenna to a Nexus 5 smartphone running a custom-built Android application on the smartphone. Various subsystem and anechoic chamber system-level tests were performed. The data indicate satisfactory performance of the demonstrated OU BAN system with the Bluetooth antenna mounted to the users torso and the smartphone in three test locations: held in the hand 1 m in front of the torso, in the front pocket, and in the back pocket. The OU BAN configuration could be improved by miniaturizing the system to be more easily worn by the user.

An e-textile antenna for body area network

This paper provides details on an e-textile spiral antenna used in a Body Area Network application. The system senses heart rate, has provisions for fall detection using an inertial measurement unit, and measures ambient temperature. An Arduino microcontroller collects and processes the data and interfaces with a low-energy Bluetooth (BLE) transceiver to transmit data via an e-textile antenna. Data is received via BLE on a custom built Android application running on a Nexus 5 Smartphone. Power received measurements were performed to compare the e-textile spiral antenna with a traditional inset-fed patch antenna.

An e-textile edge-fed spiral antenna for flexible wearable applications

This paper presents an e-textile embroidered Archimedean spiral antenna using conductive silver thread on polyester fabric for wearable applications. The two-arm spiral antenna has 5 turns with an extension of 180 deg of one arm to enable an edge-feed. The edge-feed enables a planar feed suitable for a wearable planar fabric configuration. The spiral is feed at the edge with coaxial cable. The spiral was designed to cover the wireless bands from 2.4 to 6 GHz. An initial design was done with a high-fidelity computational electromagnetic mode, and then the antenna was fabricated and tested.

A terrestrial positioning and timing system (TPTS)

This paper investigates the concepts of a Terrestrial Position and Timing System (TPTS) that could be used within the National Airspace System (NAS) in the event of a GPS outage to provide a positioning, navigation, and timing (PNT) service to aviation users. Concepts for a TPTS are presented for an L-band based system to be integrated/compatible with the distance measuring equipment (DME) system. The TPTS will be based upon a CDMA and TDMA signal structure. Three main operational modes are presented for a TPTS: 1) Autonomous Broadcast Mode, and 2) Active Interrogation/Response (IR/XP) Mode, and 3) a Hybrid solution. With a fully operational TPTS, an active TPTS aviation user could calculate a position, velocity, and time (PVT) solution from a single TPTS Site. The passive TPTS aviation user could calculate a PVT solution using the signals broadcast by two TPTS ground sites. With three TPTS sites in view, the passive TPTS aviation user equipment can calculate an “all-in-view” PVT solution using a subset of the signals transmitted from the TPTS ground sites. Additional studies will be needed to further explore the concepts of a TPTS for refinement, investigate compatibility with current systems, and validate these concepts, parameters, and techniques.

Improvement of high accuracy DGPS with real-time WaveSmooth/spl trade/ multipath mitigation technique

The reduction of multipath has become an essential part of any high precise system architecture using satellite navigation. A recently proposed hybrid domain real-time WaveSmoothtrade multipath mitigation technique using wavelets is a simple and effective technique to offer reliable 50-90% multipath mitigation in a real-time high fidelity fashion. The improvement of high accuracy (cm level) differential Global Positioning System (DGPS) with WaveSmoothtrade multipath mitigation technique is studied in this paper. Two types of user solution approaches are compared: type I uses both code and carrier phase measurements; type II uses only carrier phase measurements. Analysis and simulation results indicate that type I approach results in better performance solution in terms of faster convergence in the fixed solution and overall accuracy. Field data test results show that the utilization of WaveSmoothtrade mitigated code measurements using the type I solution approach reduces the ambiguity resolution convergence time from about 380s to 90s and increases the ambiguity resolution success rate from 27% to 87%, for a 250km baseline. The conclusion is drawn that the WaveSmoothtrade technique improves DGPS positioning performance in terms of accuracy and ambiguity resolution convergence, as well as, implementation complexity/cost and real-time capability