Receiver Types

Applications
Title	Receiver Types
Author(s)	GMV
Level	Basic
Year of Publication	2011

Description

Back in the 1970s, receivers were large analogue equipments built for the military domain. Nowadays, GNSS receivers have been widely expanded to miniaturized platforms, chipsets, microprocessors, Integrated Chips (IC), DSP, FPGA, handheld units and integrated in most mobile phones.

Receiver types can be categorized following different factors such as:

Platform

GNSS receivers run in a wide variety of platforms from chipsets to microprocessors. The choice of the target platform is a trade-off of parameters such as receiver performance, cost, power consumption and autonomy. Furthermore, the increasing capabilities of microprocessors have enabled the emergence of software receivers with performances comparable to full-hardware receivers, providing the flexibility required for some user applications

Multi-constellation

In the context of the emergence of multiple satellite navigation systems (both regional and global), multi-constellation receivers are widely available. This has been encouraged at system design level by working towards interoperability and compatibility among all systems.

From the receiver perspective, multi-constellation brings a key added value on solution availability, especially in urban canyon environments.

Multi-frequency

The key benefit of multi-frequency receivers over single frequency receivers relies on the removal of the frequency-dependent errors on the signals, hence improving receiver accuracy. The most important example is the correction for ionospheric delays, since they usually represent the main contributors to the overall measurement error. The challenge, of course, relies on the higher cost of the additional RF hardware.

Code-based/Carrier-based

This aspect indicates whether the solution is computed from the pseudo-range measurements (noisier) or from the carrier measurements. Although these latter are less noisy, they present a natural ambiguity related to phase measurements, that needs to be solved at receiver level. Please refer to Solving Navigation Equations for some of the available techniques. The trade-off in this case is complexity (and processing power) versus accuracy.

Differential

Differential techniques enable improved receiver performance (namely accuracy), by providing the receiver with additional information such as measurements from receivers in the vicinities or corrections computed independently. Please refer to GNSS Augmentations for further information on DGNSS, PPP or RTK.

Aided / Assisted

Aiding the receiver operation can be achieved by providing the necessary navigation data (almanacs and ephemeris) beforehand (e.g. via Internet), rather than waiting for the message itself to be decoded by the receiver. This can reduce the time to first fix (TTFF) and improve performance on challenging environments, where signal strength and satellite visibility may be low.

Assisting information can also be provided by other technologies, such as Inertial Navigation Systems, WiFi, UWB or sending useful information over the internet. Depending on the solution envisaged, this might have an impact at several levels, such as availability or continuity.

Augmentation

GNSS receivers can benefit from corrections or measurements provided by augmentation systems (i.e. SBAS or GBAS) to improve their performances. Please refer to GNSS Augmentations for further information.

Services

Finally, GNSS Receivers may support multiple services provided by the future GNSS generation. As an example, Galileo will provide four services: Open Service (OS), Commercial Service (CS), Commercial Service (CS) and Safety of Life (SoL) services, as described in Galileo Performances.

As Many Receivers as User Applications

The design and selection of a receiver is tightly linked to the target user application: for example, a multi-constellation GNSS receiver will certainly improve solution availability (critical for example in urban environments), whereas if the user application is focused on improved accuracies, then the selected receiver will probably turn to carrier-based technologies or differential and augmented solutions. The type of assisting/aiding information to be used also focuses on the user application. On one hand, different technologies such as WiFi, UWB and INS can be used to improve solution availability and continuity, in environments where GNSS cannot guarantee the desired availability (e.g. mixed open/ indoor environments). On the other hand, this information can be used to improve indicators such as Time To First Fix (TTFF): as an example, downloading the navigation data through the internet will greatly improve this factor, since the receiver will not have to wait to demodulate the whole message to compute position.

Information Available at System Level

GNSS Receiver manufacturers rely on each system’s SIS ICD to develop their solutions. The SIS ICDs define signal properties, transmitted codes and navigation messages contents that allow the receivers to process the SIS signals. For further information please refer to GNSS Signals. Pushed by the emergence of new services aimed at professional and safety of life users, standardization activities have been launched at European level (CEN, CENELEC and ETSI), at global level (e.g. Standards and Recommended Practices (SARPS)) and at industry level (e.g. industry standards, RTCA and EUROCAE MOPS and MASPS).