Submitted:
07 May 2024
Posted:
08 May 2024
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Abstract
Keywords:
1. Introduction
2. FGI-GSRx Software-Define Receiver
2.1. Existing Sequential Receiver Architecture
2.2. Limitations of FGI-GSRx-v1.0.0
3. FGI-GSRx-v2.0.0: Design and Architecture
3.1. Design Strategies for Software-Defined GNSS Receivers
- Code Profiling: This refers to identifying performance bottlenecks through code profiling and optimizing critical sections of the code base. This may involve restructuring algorithms, minimizing function call overhead, and optimizing memory access patterns to improve overall processing speed. A significant effort was made in this regard for the development of v2.0.0 that included identifying the functions and processes contributing maximum processing time and removing redundant variables and computations. This effort lead to improved tracking time via v2.0.0 sequential mode as compared to v1.0.0. A more detailed insight is presented in Section 5.1 and Section 5.2.
- Memory Management and Parallelization: Parallel processing techniques and efficient memory management of the processing unit can lead to minimize memory access latency and improve overall processing speed. FGI-GSRx-v2.0.0 parallel processing mode is aimed at distributing computational tasks by invoking multiple MATLAB instances so as to utilize the maximum processing power of the processing units, such as CPU cores. This can significantly speed up signal processing algorithms, especially those that are inherently parallelizable, such as correlation and FFT (Fast Fourier Transform) operations. An analysis on performance of memory management using various versions of FGI-GSRx is shown in Section 5.3.
3.2. FGI-GSRx-v2.0.0 Receiver Architecture
- Acquisition: The acquisition block searches and acquires satellite signals one at a time. The signals are handed over to the tracking block once the search is complete. v2.0.0 also supports multiple GNSS constellations as v1.0.0. The acquisition data contains the information regarding each signal acquired (observations, duration, signal, channel) as well as statistics from the acquisition phase (e.g., peak Metric, peak value, variance, baseline, standard deviation, code phase, carrier frequency and satellite ID).
-
Tracking: The tracking block utilizes the acquisition data and correlates the incoming signal with signal replicas to generate tracking measurements from all signals and satellites. In v1.0.0, the signal tracking of each satellite is processed sequentially which was not very effective especially for the processing of longer datasets leading to higher processing time. To overcome this limitation, in v2.0.0, the user can conveniently choose between two possible options to execute the tracking process. These include:
- -
- Sequential Tracking Mode: This mode is developed on the similar lines as v1.0.0. However, v2.0.0 offers an improved sequential tracking architecture, which is carried out by code profiling, efficient handling of data variables, identifying and optimizing high complexity and time consuming processes that ultimately contributed to faster data processing.
- -
- Parallel Tracking Mode: Parallel tracking mode is aimed at maximizing the CPU utilization to speed up the processing. The parallel processing is done at the signal tracking stage only, since this is the most computationally extensive part of the receiver. The idea is to initiate multiple parallel instances of MATLAB for processing each satellite individually to achieve maximum CPU utilization from the processing platform. In this particular case, the operating system takes care of running multiple instances by allocating enough resources for these demanding parallel instances. For example, if there are altogether 17 GPS and Galileo satellites available from the acquisition stage, the new receiver architecture will open 17 MATLAB instances where each instance will process one individual tracking channel. The work flow diagram of v2.0.0 parallel tracking block is divided into three main steps as shown in Figure 3.
- Multi-GNSS Navigation: This block offers data decoding of the output generated from the tracking block and converts the processed track data into receiver observables in terms of satellite-specific pseudoranges and ephemeris for each GNSS constellation. The navigation block has four main tasks: to convert the measurements into observations, calculate each satellite’s PVT, apply satellite and environmental corrections, and finally estimate the PVT solution of the user with the corrected pseudoranges.
3.2.1. FGI-GSRx-v2.0.0 Parallel Tracking Mode
3.3. Other Functional Enhancements
4. Assessment and Data Processing Strategy
4.1. Assessment Strategies
4.2. Data Processing Strategy
5. Result Analysis
5.1. Code Profiling
5.2. Data Processing
5.3. Resource Management
5.3.1. Comparison with MATLAB Parallel Processing Toolbox
5.4. Accuracy
6. Conclusions
Author Contributions
Data Availability Statement
Conflicts of Interest
References
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| Feature | Solution | Remark |
|---|---|---|
| Operating system | Windows10, LINUX | Supports any operating system that can host MATLAB or OCTAVE. |
| Programming environment | MATLAB | MATLAB 2019 or later versions and OCTAVE. |
| Input source | Raw I/Q data | Digitized raw I/Q samples after analog to digital conversion |
| Processing mode | Post-processing | Can process raw I/Q data or load previously processed and saved acquisition or tracking MATLAB data files. |
| Supported GNSS | GPS L1, Galileo E1B, BeiDou B1, GLONASS L1, NavIC L5 | Listed signals are for open-source only. In house version of FGI-GSRx can process additional signals. |
| Acquisition | FFT-based signal acquisition | The receiver searches for all the listed satellites defined by the user in the configuration file. |
| Tracking | Three stage tracking | i) Pull in ii) Coarse tracking iii) Fine tracking. |
| Navigation | Least Square Estimation (LSE) -based position computation | Possibility to select satellites based on Carrier-to-Noise density ratio () and elevation cut-off mask. |
| KPI | Remarks |
|---|---|
| Portability | It refers to the usability of the same software in different environments. Both versions can be executed on any platform supporting MATLAB e.g., LINUX and Windows). |
| Openness | This refers to the degree to which something is accessible to view, modify and use. The source codes of both versions of FGI-GSRx are publicly available and can be modified as per user requirement [1]. |
| Interoperability | This refers to the possibility to exchange information with other free and proprietary software, devices, sensors or systems. For example, the ongoing work in [44] is a good example of integration of FGI-GSRx with FGI-OSNMA. |
| Reproductibility | It describes the capacity of a whole process to be replicated either by own team or some external research group. Both versions of FGI-GSRx support this KPI and have been tested thoroughly by in-house research team while v1.0.0 has also been tested by researchers [3,8,48,49]. |
| Usability | This KPI is concerned with the availability of a (versioned) user manual, tutorials, detailed procedures. In this context, both versions are supported by datasets, release notes and user manuals which are available for download from the online repository [57]. |
| Efficiency | It refers to optimizing the speed and memory requirements or power consumption by the processor running the SDR. FGI-GSRx-v2.0.0 offers better efficiency as compared to v1.0.0. More insight into this functionality is presented in Section 5.2 and Section 5.3. |
| Accuracy | Both versions offers similar code functionalities at the navigation level. However, the minor difference in positioning accuracy can be contributed to the fewer satellites processed by v1.0.0 than v2.0.0 for the given dataset in Section 5.1 and Section 5.4. |
| Processing unit | ||
|---|---|---|
| Processor | i7-12700Hx20 | |
| RAM | 32 GB | |
| Operating System | 64 bit Ubuntu 20.04.6 LTS | |
| Reference dataset | ||
|---|---|---|
| Date | 31.10.2023 | |
| Time | ≈12:23 (UTC) | |
| Duration | 460 s | |
| Size | ≈11.4 GB | |
| Location | FGI rooftop, Espoo | |
| Receiver dynamics | Static | |
| Antenna | Septentrio’s PolaNt Choke Ring | |
| GNSS front-end | NSL Stereo dual band | |
| Signal configurations | ||
|---|---|---|
| Center frequency | 1569 MHz | |
| Bandwidth | 4.2 MHz | |
| Sampling frequency | 26 MHz | |
| Quantization | 8 bits | |
| I/Q | Complex | |
| GNSS constellations | GPS | Galileo |
| Acquisition | ||
| Visible Satellites | PRN 5, 7, 8, 9, 13, 14, 18, 20, 22, 27, 30 | PRN 4, 9, 21, 31, 34, 36 |
| Replica modulation | BPSK | CBOC |
| Max. search freq. | 7000 Hz | 6000 Hz |
| Coherent Integration | 5 ms | 4 ms |
| Non-coherent Integration number | 5 | 3 |
| Threshold | 9 | 9 |
| Tracking | ||
| DLL | ||
| Discriminator | NNEML | NNEML |
| Correlator Spacing | 0.1 | 0.1 |
| Damping ratio | 0.7 | 0.7 |
| Noise bandwidth | 1 | 1 |
| FLL | ||
| Discriminator | atan | atan2 |
| Wide bandwidth (Hz) | 100 | 75 |
| Narrow bandwidth (Hz) | 50 | 45 |
| Very-narrow bandwidth (Hz) | 10 | 5 |
| Damping ratio | 1.8 | 1.5 |
| Loop gain | 0.7 | 0.7 |
| PLL | ||
| Wide bandwidth | 15 | 15 |
| Narrow bandwidth | 15 | 15 |
| Very-narrow bandwidth | 10 | 10 |
| Damping ratio | 0.5 | 0.7 |
| Loop gain | 0.2 | 0.2 |
| Function Name | Function Description | Run Time (v1.0.0) (hh:mm:ss) |
Run Time (v2.0.0) (hh:mm:ss) |
Improvement (%) |
|---|---|---|---|---|
| ’gsrx’ | Main function to execute the whole process chain of FGI-GSRx. |
14:00:10 | 08:24:14 | 40 |
| ’doTracking’ | Main tracking function to do code and carrier tracking. |
13:56:20 | 08:19:00 | 40 |
| ’GNSSTracking’ | Performs state-based tracking for the received signal. |
06:25:10 | 03:16:21 | 49 |
| ’GNSSCorrelation’ | Performs code and carrier correlation. | 07:26:33 | 04:46:12 | 36 |
| ’carrierMixing’ | Performs carrier and code mixing. | 04:09:03 | 01:53:03 | 55 |
| ’CN0fromSNR’ | Function for estimating CN0 values using SNR. |
01:31:05 | 01:07:56 | 25 |
| ’phaseFreqFilter’ | Loop filter to do carrier tracking. | 01:06:12 | 00:44:41 | 32 |
| ’getDataForCorrelation’ | Read data for processing. | 00:51:16 | 00:29:25 | 43 |
| Function | FGI-GSRx-v1.0.0 | FGI-GSRx-v2.0.0 Sequential | FGI-GSRx-v2.0.0 Parallel | ||
|---|---|---|---|---|---|
|
Processing Time (hh:mm:ss) |
Processing Time (hh:mm:ss) |
Improvement (%) |
Processing Time (hh:mm:ss) |
Improvement (%) |
|
| Acquisition | 00:02:09 | 00:02:14 | -1.8 | 00:02:14 | -1.9 |
| Tracking | 13:56:20 | 08:19:00 | 40.31 | 05:42:44 | 59.2 |
| Navigation | 00:01:40 | 00:02:00 | -16.6 | 00:02:00 | -16.6 |
| Total Run Time | 14:00:10 | 08:24:14 | 39.98 | 05:47:53 | 59.13 |
| Constellation | No. of Satellites | FGI-GSRx-v2.0.0 Parallel | FGI-GSRx-v2.0.0 with MATLAB PCT | |||
|---|---|---|---|---|---|---|
|
Processing Time (hh:mm:ss) |
CPU Average (%) |
Processing Time (hh:mm:ss) |
CPU Average (%) |
Improvement w.r.t v2.0.0 Parallel (%) |
||
| Galileo only | 6 | 00:37:56 | 69 | 00:37:48 | 38 | 0.35 |
| GPS only | 11 | 04:07:25 | 90 | 02:51:24 | 58 | 30 |
| GPS + Galileo | 17 | 05:42:44 | 89 | 03:14:36 | 60 | 43 |
| FGI-GSRx-v1.0.0 | FGI-GSRx-v2.0.0 | |
|---|---|---|
| Available Satellites for Position Solution | ||
| GPS | 10 Ephemeris for GPS PRN 27 is not found. |
11 |
| Galileo | 5 Ephemeris for Galileo PRN 21 is not found. |
6 |
| Horizontal Position | ||
| Error50 | 1.74 | 1.62 |
| Error95 | 3.06 | 2.65 |
| Max | 4.39 | 3.83 |
| Std. Dev. | 0.76 | 0.62 |
| RMS | 2.09 | 1.95 |
| Mean | 1.76 | 1.62 |
| Vertical Position | ||
| Error50 | 1.04 | 1.11 |
| Error95 | 3.19 | 3.19 |
| Max | 4.7 | 4.65 |
| Std. Dev. | 0.98 | 0.99 |
| RMS | 1.37 | 1.39 |
| Mean | 1.25 | 1.32 |
| DOP | ||
| Pdop | 1.20 | 1.13 |
| 3DRMS | 2.49 | 2.40 |
| No. of Positioning Epochs | 451 | 451 |
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