CC BY
76
Труды Международного симпозиума «Надежность и качество», 2017, том 2
- необходимость одновременной работы по большому количеству смешанных целей;
- необходимость работы в большом секторе пространства (±70 град.);
- высокие помехозащищенность, надежность, степень интеграции и возможности конфигурации.
Все это возможно обеспечить только с использованием АФАР с твердотельным приемопередающим трактом (ППМ) делающим антенну более живучей, так при выходе из строя (в результате попадания пуль, осколков) части ППМ, антенна в целом продолжает надежно работать, с уменьшением дальности действия на несколько процентов.
ЛИТЕРАТУРА
1. Грачев В.В., Сушкевич Б.А. Бортовые радиолокационные станции. Учебное пособие.- Л.: ОЛАГА, 1986.-148 с.
2. Якимов А.Н., Неробеев А.В. Исследование влияния вибрационных воздействий на конструкцию антенной решетки// Труды международного симпозиума. Надежность и качество. - 2016. - Т. 2 - С. 46 -
48.
3. «Оса жалит метко». Вестник авиации и космонавтики, №4-2003 г.
4. «НИИП и его радары». Вестник авиации и космонавтики», №1-2002 г.
УДК 621.396 Nosrati И.
Samara National Research University, Samara, Russia
FPGA-BASED GPS RECEIVER FOR SPACE MISSION
FPGA based GPS receivers are the focus of this research and specifically the space-borne type for use in space mission. This research is undertaken to address two challenges in Global Navigation Satellite Systems (GNSS) technologies:
Consider some aspects of the problem related to Global positioning System (GPS) Linkl(Ll)Coarse/ Acquisition (C/A) processing (acquisition, tracking and decoding) algorithms for use by GPS L1 C/A receivers on-board an orbiting Cube-Sat in Low Earth Orbit (LEO)
High-expenses associated with space-borne GPS receiver design and implementation in a system-on-a-chip merges different functions and applications on a single substrate. The objective is to implement FPGA-based offline tracking system using Verilog Hardware Description Language (Verilog HDL). The program is tested and simulated by using HDL compiler. A coherent demodulation of the GPS signal is implemented. GPS receiver calculates the position based on the data collected from four satellites. Given four satellites, acquisition of the data from the signals and data extraction is performed.
The chosen GPS algorithms will be implemented in software based-on Matlab / Simulink platforms. The established schemes will serve as development platforms for the space-borne or high-dynamics GPS L1 C/A correlator and baseband processing algorithm(s) for accuracy ofposi-tion, Velocity and Time (PVT) determination computations. The designed algorithm(s) will be subjected to simulated low and possibly high-dynamics functional tests. The completed space-borne GPS receiver is expected to be used in future to autonomously and automatically determine orbiting LEO nanosatellites spacecraft position (latitude, longitude and altitude) by acquiring, tracking, decoding and processing transmitted GPS Ll C/A signals
Introduction
Global Positioning System (GPS) is a high-precision three-dimensional real time radio navigation system that used to determine accurate real time information. GPS system is widely used by land, sea and airborne users anywhere in the world and in all weather conditions. 24 hours working satellites are in orbit at 10,600 miles above the Earth. They are spaced so that from any point on the Earth, four satellites will be seen above the horizon. Each satellite sends navigation messages continuously. The GPS receivers collect and process real time information in order to obtain accurate navigation data. GPS receivers are the focus of this research and specifically the space-borne type for use in space mission. Up to now, GPS receivers, while providing an accurate and low cost means of navigation which limited to low Earth orbit (LEO) missions. The growing popularity of Cu-besat nanosatellites has delivered for the first time the opportunity to develop space missions at very low cost The Namuru Field Programmable Gate Array (FPGA) GNSS receiver has continued to develop at UNSW as research has progressed. The Namuru V3.2 FPGA based GPS receiver has been developed specifically for the Boeing Colony II 3U cube sat platform and a mission that satisfies many of these requirements. Today these innovative new receiver technology developed by NASA Goddard Space Flight Center is a leap forward for GPS technology [National Aeronautics and Space Administration Patent No:
7,548,199]. NASA Goddard Space Flight Center (GSFC) has developed a new space-borne GPS receiver called Navigator that can operate effectively in the full range of Earth orbiting missions from LEO to GEO and beyond. The Navigator is an autonomous, real-time, fully space-flight-qualified GPS receiver with exceptional capabilities for fast signal acquisition and weak signal tracking. These features enable the use of GPS navigation in high Earth orbit (HEO), geostationary orbit (GEO), and other high altitude applications. The Navigator receiver can quickly
and reliably acquire and track GPS signals at 25 dB-Hz and lower also it is a radiation-hardened GPS receiver specifically designed for use in high Earth orbits.
Most GPS receivers that are commercially available cannot be publicly upgraded and therefore be used in space due to their inability to handle high-dynamics Doppler frequency shifts which hampers GPS signal acquisition, tracking, lock, position, velocity and time accuracies. The inability in the GPS algorithms can be attributed to inefficiency due to (i) wrong mathematical models used and (ii) the computational inability of the implemented algorithmic models. The mathematical models refer to the different mathematical techniques or concepts that an algorithm is based-on. The computational inability refers to the slowness in execution speed and high memory usage of the implemented algorithms. [Nganyang Paul Bayendang: 2015]
GPS ITAR / COCOM limits embedded in commercial GPS receivers - ITAR stands for International Traffic in Arms Regulations. COCOM - discontinued, was a Coordinating Committee for Multilateral Export Controls. The GPS ITAR or previously COCOM limits, restrict operations of commercial GPS receivers to altitudes of <18km and velocities of <515m/s, (Lu, 2003: 63; Nort-ier, 2003: 20; CCII, n.d.: 2) by ensuring automatic shut-down or faulty readings if one or both limits are exceeded. This is to prevent free use of commercial GPS receivers in ballistic missiles applications. Therefore, only a handful of vendors, do design and commercialize space-borne GPS receiver units [Nganyang Paul Bayendang: 2015]
Space-borne GPS Receiver Design Considerations
This section discusses various challenges faced by a GPS receiver on-board an orbiting CubeSat. A space-borne GPS receiver design considerations can be divided into two types, namely i) physical and ii) non-physical. Both of
Twàbi Мeмдvнаvoднoгo cwnno3uvMa «Haàewnocmb u xauecmeo», 2017, moM 2
these are briefly addressed in the following sub-sections.
Physical challenges in design considerations, in the context of this document refer to those factors or space environmental conditions with a damaging effect on GPS receiver hardware and consequently leading to a malfunction or degradation of the performance of a GPS receiver in space. These factors include space radiation or ionization, extreme temperature (very hot and very cold).
Design Considerations - Physical Challenges
Radiation
This poses the most threat, which includes ionization, single event effects, upsets and latch-ups.
Appropriate hardware radiation shielding and hardening are usually the mitigation methods used.
Two types of checks are usually performed: i) total ionization dose testing and ii) single effect event testing, which involves subjecting the GPS receiver hardware to a confined radiation test chamber and checking the GPS receiver components performances
Extreme Temperatures
GPS receivers operating in space are subjected to extreme temperatures of high sun intensity and extreme coldness (during non-sunlight periods). There is also very sharp thermal cycling from extreme heat to cold and vice versa [Nganyang Paul Bayendang: 2015]
Thus, operating in such conditions could damage or cause intermittent hardware devices malfunctions. As a result, unpowered and powered temperatures cycling are performed in a controlled environment (test chamber) at both extreme temperatures and the GPS receiver operation is monitored. In extreme heat condition is mitigated by radiation heat transfer (space most ideal heat transfer means), heat-sinks and reflective structural surfaces. Extreme cold conditions can be alleviated by using micro heaters.
Oscillator
The main oscillator for a GNSS receiver needs careful attention, often requiring short term stability of better than 2.0ppm. In space the oscillator will most likely need to maintain stability over a greater range of temperatures. For instance the Namuru V3 receivers are equipped with a Temperature Controlled Crystal Oscillator (TCXO) with the option to pull the oscillator up to 5ppm either side of the nominal frequency. An option is also provided for an Oven Controlled Crystal Oscillator (OCXO) with the same frequency adjusting capability. A software algorithm drives the oscillator corrections while monitoring a precise temperature sensor.
Latch-up protection and recovery
The only practical way to recover from a latch-up condition in semiconductor devices is to remove the power and restart. A special latch-up protection circuit is designed into the Na-muru V3 power supply to remove power when the current drain exceeds a set threshold. After a short programmable time the supply is restored, after which the receiver will recover as if a power failure had occurred.
Summarized in Table 2 are GPS receiver's baseband processors with their respective vendors.
Design considerations - Non-physical challenges
Doppler Frequency Shift
Doppler's shift could respectively extend in excess of ±50kHz and ±100kHz. This high Doppler's shift tremendously affects GPS signal acquisition, tracking and PVT computations - since a GPS receiver on-board a LEO satellite (Cu-beSat) has very limited time to be in contact with a GPS satellite, due to the high relative motion involved between both satellites
Hardware GPS devices utilised for space-borne GPS receivers
Institutions Mission GPS Front-end GPS Correlator GPS Baseband Researrh Par load or aim Year
Surrey Space Surrey Satellites Mitel GP2000 (GP2015. GP2021. ARM60B processor) Orbit Determination
Varions institutes iti Korea 12 Channel correlator DSP processor Tracking and Attitude Control
Standford NASA Space/Earth Science ZarlinkGP2010 Zarlint2021 Mitel GPS chip Spacecraft Fonuatiou-flving 1999
Tsinghua Surrey Tsinghua-1 MicroSat Mitel GP2010 Mitel GP2021 ARM60 Position and Velocity 1999
GSOC CHAMP. BIRD Mitel GP2000 lias built-in: (GP20I5. GP2021. ARM60B processor) Sounding Rockets and Sal 2001
Virginia Pohtech Ionosphere Research ZarlinkGP2015 ZarLink P2021 Mitel GPS Builder GPS Signal Sensor 2003
New South Wales. Svduer Colony D CubeSat Zarlink GP2015 Zarliiik P202! Cyclone H FPGA Proof Of Concept 2004
SSOOSCN Suraat 2004 Phoenix (SigTec MG5001 Orbit Determination 2004
New South Wal« Zar link GP2015 GP2021 FPGA FPGA processor Open-source GNSS Receiver 2004
Poi Hand State L ill Unmanned Satellites GP2Û10 GP4Û20 Open-source GPS 2005
GSOC X-sat. PRISMA GP2015 Plioenix-XNSHDRx (ZarJink GP4020) Orbits Determination 2006
New Brunswick CASSIOPE Nov Atel OEM4-G2L GPS receiver Multi-purpose 2007
National Cheng Kmig CKUTEX ZarliukGP20l5 Zarlink GP2Q21 ARM920T processor Experimental Payload for LEO Mission 2010
Mitigating Doppler's shifts requires implementing a robust acquisition, tracking and PVT (Position, Velocity and Time) algorithms
GPS Orbital Geometry
The higher the altitude of a GPS receiver (onboard a CubeSat), the poorer its Dilution Of Precision and position accuracy. This is due to narrow field of view and unavailability of visible orbiting GPS satellites. Efficient acquisition, tracking and PVT (Position, Velocity and Time) estimates algorithms usually compensate for poor Dilution of Precision
Multipath Effect
Multipath could have little or no effect on a GPS receiver on-board a CubeSat, due to i) the relative speed involved between GPS satellites and receiver ii) the size and shape of a CubeSat. However, space debris and other satellites could reflect GPS signals causing multipath; thus, the possibility of its occurrence and appropriate mitigation approaches have to be as well considered.
Atmospheric Effect
A GPS receiver on-board a CubeSat in LEO is subjected to ionospheric sources of error and little caused by the troposphere. The troposphere is <50km and has little effect on an orbiting CubeSat (>400 km). Therefore, only the ionosphere error model is relevant in the PVT estimates solution
Software-defined / Firmware-defined Approaches
A software-defined GPS receiver unit refers to a unit that is implemented on a computer. This approach provides a versatile/re-programmable design and development platform. With this method, the main GPS receiver functional blocks, namely the GPS correlator and baseband processor, are implemented based-on DSP or from emulating the internal circuitry of a known GPS receiver. Once the software implementation is realized, it is further fully debugged and optimized. Firmware is software embedded into hardware, such as a Field Programmable Gate Array (FPGA).
In software-defined GPS receivers based-on Matlab have gained tremendous popularity over the years and can be regarded as the de facto approach. Thus, majority of the GPS research
In this part we want highlight on Primary of Easy Suite and some of their application.
The first version of easy suit was published in 2003 by Professor Kai Borre. The GPS Easy Suite is a collection of ten Matlab scripts or m-files, which can be used for any anyone.
Twdbi Мeмдvнаvoднoгo cuMno3uVMa «HadewHocmt u xauecmeo», 2017, moM 2
Software-defined GPS receiver architecture Software-defined GPS Receivers Based-on Matlab Only
The Easy Suite Open Source in Matlab
Software-defined GPS Receivers Based-on Sim-ulink Only
In Hamza et al. (2009), Simulink - a graphical computing software tool in Matlab, was used as a software development platform to design and implement a GPS receiver unit. Similar to Matlab approach, GPS signal data is acquired by a GPS front-end with ADC and processed on a PC.
Software-defined GPS Receivers Based-on Both Matlab and Simulink
This approach utilizes a combination of both Matlab and Simulink software's from Math Works to design and implement a GPS receiver. This approach seems suitable, especially as Matlab and Simulink are integrated together as a single package and supports designs inter-conversion. With this method, both software's complement each other in scenarios where GPS receiver algorithms cannot efficiently and / or easily be designed or implemented using either Matlab or Simulink.
In Gleason and Gebre-Egziabher (2009); C/C++, Octave and Python PC languages can be used. In all, a GPS front-end and any suitable PC software with DSP and math's libraries can be used.
Firmware-defined GPS Receivers
Contrary to software-defined GPS receivers that are designed to run on a PC by utilizing the PC's Central Processing Unit (CPU), Random Access Memory (RAM), Read Only Memory (ROM), Operating System (OS) and other resources; a firmware-defined GPS receiver is designed to run on standalone System-On-Chip (SOC) devices such as microcontrollers. Akin to software GPS receivers, they are easily modifiable although with embedded proprietary toolkits.
The design and implementation often follows a similar procedure as that of software-defined GPS receivers; however, the final software is transformed to firmware (small tokenized embedded software for a specific hardware) to run on a particular microcontroller (e.g. Virtex-5QV) in one of two ways: (i) direct adaptation to firmware for a suitable microcontroller or (ii) first converted to software in another language and finally to firmware in an embedded language.
Matlab SDR Plots"2011 by Kai Borre"
Conversion of Software to Firmware in a Similar Language
This approach is applicable in instances where the software development platform and GPS receiver software have been written in a language that can easily be tailored for direct programming into a suitable microcontroller, without any conversion from one language to another. In other words, the same programming language is utilized within the software development platform and the microcontroller. For instance, a software GPS receiver can be developed in ANSI-C or HDL which is then easily adapted to firmware for direct programming to a suitable C or VHDL based ARM or FPGA microcontroller (Ra-makrishna et al., 2008).
Conversion of Software to Firmware in a Different Language
This approach lends itself to scenarios where the software GPS receiver has been written in a language that cannot directly be used to program a microcontroller but has to be converted to a suitable embedded language using multiple software languages and toolkits (e.g. Matlab with Altera or Xilinx) 6. This can be performed in two stages as follows: (i) the final GPS receiver software (e.g. developed in Matlab / Simulink) is converted to firmware in another language (e.g. to tokenize code in VHDL or C or C++) using a suitable workflow (e.g. Matlab HDL coder) and (ii) it is further developed and programmed into a suitable microcontroller (e.g. Altera FPGA). Contrary to software which is directly modifiable, a firmware (software embedded in hardware) cannot be directly modified and can only be upgraded and as a whole. The research objectives / available resources, necessitate the software and firmware approaches to be the preferred choice.
Conclusion
In this paper we consider some receiver problems of inefficient some space-borne GPS receiver algorithms and high-cost with design and implementation The problems were addressed by developing open-source GPS algorithms, using Matlab HDL coder workflow and Altera software,
Труды Международного симпозиума «Надежность и качество», 2017, том 2
with focus on the Xilinx low-cost space-grade FPGA.
The primary or main objective was to implement a software-defined GPS receiver. This was achieved using Matlab. The secondary objective was to improve the primary objective. This was reasonably attained using the Matlab HDL Coder workflow and some of the GPS receiver algorithms could be improve from Matlab floating to fixed-point implementations which making them more
compact, efficient and implementable into a low-cost microcontroller.
The tertiary objective was to implement a firmware and to propose a low-cost space-borne GPS receiver roadmap. Tracking spacecraft can be done by radar stations from the ground, but it's much more expensive and takes longer than an in flight system I think there's a good chance we'll end up being able to use FPGA-Base GPS and save us some of the expense of using ground observations.
REFERENCES
1. Strang G, Borre K (1997) Linear Algebra, Geodesy, and GPS. Wellesley Cambridge Press, Wellesley.
2. Borre, Kai (2003). The GPS easy suite-Matlab code for the GPS newcomer.
3. Kai Borre ,GNSS and positioning for the future
4. K J Parkinson, A G Dempster, P Mumford, C Rizos,FPGA based GPS receiver design considerations
5. Peter J Mumford 1, Nagaraj Shivaramaiah 1, Eamonn Glennon 1, Kevin Parkinson 1 ,The Namuru V3.2A Space GNSS receiver
6. Nganyang Paul Bayendang (2015) , Nano-satellite GPS Receiver Design and Implementation A Software-to-Firmware Approach
7. Yong Li, Eamonn Glennon, Rui Li, Yuanyuan Jiao, Andrew G Dempster ,
8. K J Parkinson , P J Mumford , E P Glennon , N C Shivaramaiah , A G Dempster , C Rizos
9. Eamonn P. Glennon, Joseph P. Gauthier, Mazher Choudhury ,Kevin Parkinson , Andrew G. Dempster,Project Biarri and the Namuru V3.2 Spaceborne GPS Receiver
10. National Aeronautics and Space Administration, Patent No: 7,548,199
УДК 621.396
Fonseca Norena L. A., Cari Siles J.
Samara National Research University, Samara, Russia
ANALYSIS OF THE IMPACT OF BEIDOU NAVIGATION SYSTEM ON VOLGA REGION
This paper analyzes the positioning capability of BEIDOU Navigation Satellite System by visibility of satellites and DOP values. We show the use of BEIDOU system in Volga region and we give a glimpse oof its possible positioning accuracy and its service range. The paper also proves the positioning capability enhancement of the western high attitude area by improved constellation. Also we give a short review of the constellation of BDS and its coverage through the pf. K. Borre's Easy Suite. Thus we give conclusion and possible uses for
Introduction
China has completed the construction of the BeiDou-2 system that consists of 14 BeiDou satellites and 32 ground stations. China is ready to continue the upgrade of the system with the launch of 18 satellites to create global coverage constellation that will be completed by 2020, 35 BeiDou-3 satellites will be sent into the space, providing service to users around the Earth[1].
Nowadays, Beidou-3 or the third phase of the project has been started. It will contain 2 satellites which have already been launched and are operable at the moment, and 18 more satellites which are expected to be launched in July of this year (2017)[1]. The BeiDou system (BDS) currently consists of 7 GEO, 8 IGSO and 7 MEO satellites [2,3]. The figure 1 shows a screenshot of BeiDou satellites by Orbitron 3.71 (FREE tracking software). It is visible that the major concentration of satellites is in the Asia-Oceanic region.
Figure 1 - Screenshot of Orbitron tracking at 18th of April of 2017
The preliminary results of analysis of accuracy for BDS presented in [4,5,6] by the means of simulations show that finished BDS-3 will become a superior navigation system in Asian region and around the globe. In a standalone case or using only BDS, the performance of BDS-3 would be a little better than using GPS on a global scale, whereas the most effective performance is definitely in the Asian region. In fact, the
performance of BDS in Asia is improved significantly compared to GPS alone in terms of visibility, DOP values, and robustness to urban canyon effect. Our goal is to test the current performance of the BDS worldwide and on Volga region using a standalone case.
We analyze what the current performance of the BDS is. We do an analysis that allows us to observe accuracy of the received data of this
