If you wish to contribute or participate in the discussions about articles you are invited to contact the Editor
Receiver Characteristics
| Receivers | |
|---|---|
| Title | Receiver Characteristics |
| Author(s) | GMV |
| Level | Advanced |
| Year of Publication | 2011 |
Receiver characteristics and design (link to system design) are strongly related to the application at hand. In fact, the target application requirements are actually the main driver to a given receiver architecture and design decisions and therefore the selection of an adequate receiver usually underlies a large set of trade-offs.
Design considerations
From a system design perspective, there isn't a real set of "rules of thumb" to chose a given approach for a GNSS receiver design. In fact, the requirements are strongly influenced by the application itself, whether in terms of architecture or performance. Below are a few examples[1] of the requirements, analysis and tradeoffs involved:
- Environmental Constraints: Factors such as temperature, humidity, water resistance, shock and vibration ranges depend on the application. Furthermore, the surrounding environment can also impact the design in terms of performance, e.g. urban environments can originate several multipath signals, where the reflection of GNSS signals on surrounding surfaces generates a non-line-of-sight ray. In the latter case, multipath mitigation signal-processing techniques may be required.
- Precision and Accuracy: Higher precision is required, for instance, in survey or military operations, whereas automotive or mobile applications may not require centimeter-level precision. As another example, the solution accuracy, precision, and rate are surely different for aircraft precision approach, than for marine or automotive navigation.
- Single/Multi Frequency/Constellation: An increasing range of GNSS frequencies, bands, modulations and constellations enable a multitude of possibilities in receiver design, from single frequency / single constellation (e.g. the common GPS L1 C/A devices on current PND's or smartphones) to multi-frequency / multi-constellation (e.g. L-band GPS/Galileo/GLONASS capable high-end survey receivers).
- Assisting Sources: Several external or assistance information sources can be taken into account at system design, since there is a straightforward impact on resources and solution computation. If the use of augmentation (SBAS) or differential (DGPS) data is envisaged, the receiver must be prepared to interface and use the information provided from such systems. Other external interfaces and aiding sensors can be coupled to a receiver, such as inertial sensors[2] (IMU and INS), or even the means to get external aiding information (e.g. accessing the internet through WiFi or GPRS/UMTS).
- Hardware Platform: On a physical platform point of view, several design considerations are made in terms of the hardware host platform, user interface design, storage capability, power/battery consumption, electromagnetic compatibility, or portability. The underlying platform for a GNSS receiver can be an ASIC, FPGA, DSP, CPU, hardware/software defined, or a combination of these and other technologies. Table 1[3] below shows an assessment of the advantages and disadvantages of each approach.
| Technology | Development Costs | Performance | Power Consumption | Single Unit Costs | Flexibility |
|---|---|---|---|---|---|
| ASIC | -- | ++ | ++ | ++ | -- |
| FPGA | - | ++ | + | - | + |
| DSP / CPU | ++ | + / ++ | + / -- | + / - | ++ |
| Hybrid FPGA / CPU | + | ++ | + | - | + |
Table 1[4] presents an order of magnitude of the 3-D position/time errors achieved with different types of receivers, both for Standard Positioning Service (SPS) and Precise Positioning Service (PPS) using legacy GPS. Note that this table is valid for GPS only and it is provided here for illustrative purposes[5].
| SPS | PPS | |||||
|---|---|---|---|---|---|---|
| Best Location | Median Location | Worst Location | Best Location | Median Location | Worst Location | |
| Handhelp (best 4-SV solution) | 16m | 32m | 72m | 10m | 30m | 71m |
| Handhelp (AIV solution) | 11m | 25m | 54m | 8m | 23m | 53m |
| Mobile (land/marine vehicle) | 7m | 23m | 53m | N/A | N/A | N/A |
| Aviation receiver (AIV, RAIM, tightly coupled with INS) | 7m | 24m | 55m | 4m | 5m | 6m |
| Survey receiver (dual-frequency, real-time performance) | 3m | 4m | 5m | 3m | 4m | 5m |
| Aviation receiver dynamic time transfer performance | 14ns | 45ns | 105ns | 12ns | 13ns | 14ns |
| Time transfer receiver static time transfer performance | 10ns | 19ns | 35ns | 10ns | 10ns | 11ns |
Related articles
References
- ^ For another example on receiver design considerations, see Kaplan, E.D. et al, "Understanding GPS: Principles and Applications", second edition, chapter 3, section 3.4.
- ^ wikipedia:Inertial measurement unit
- ^ Hein, G., Pany, T., Wallner, S., Won, J., "Platforms for a future GNSS receiver - A discussion of ASIC, FPGA, and DSP technologies", Working Papers, InsideGNSS, March 2006.
- ^ Kaplan, E.D. et al, "Understanding GPS: Principles and Applications", second edition, chapter 7, section 7.7.
- ^ For further information on the accuracy of each of the GNSS, please refer to the applicable sections.