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 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 (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 below shows an assessment of the advantages and disadvantages of each approach.

Table 1: GNSS technology comparison, from (++) major advantage to (--) major disadvantage.

Technology	Development Costs	Performance	Power Consumption	Single Unit Costs	Flexibility
ASIC	--	++	++	++	--
FPGA	-	++	+	-	+
DSP / CPU	++	+ / ++	+ / --	+ / -	++
Hybrid FPGA / CPU	+	++	+	-	+

Table 1 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.

Table 1: Comparative 95% three-dimensional position/time errors across various receivers.

	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

• GNSS Receivers General Introduction
• Generic Receiver Description