Gnss Required

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Giuliana

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Aug 3, 2024, 5:55:16 PM8/3/24

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RNP - Required Navigation Performance: It's a PBN navigation method/specification in which the airplane achieves an specified accuracy (RNP 1, RNP 2, etc) the a 95 % of the flight time. It has an onboard monitoring system that alerts the pilot when the integrity is loss. Examples of Equipments that are able to perform RNP 1, RNP2, etc are IFR GPS receivers with RAIM or WAAS (integrity monitor).

RNAV - Area Navigation: As we know, FAA uses RNAV in chart tittles only to determine Area Navigation. But RNAV it is also a PBN method/specification in which the airplane achieves an specified accuracy (RNAV 1, RNAV 2, etc) the a 95 % of the flight time. The only difference is that the aircraft won't alert the pilot when the integrity of the system is loss. I've never used an RNAV system without integrity monitor, I guess that DME/DME/IRU is wan of those. Is an IFR GPS with RAIM capability lost considered an RNAV system without integrity monitor?

The final and most important question is: On SIDs and STARs, Why is it not required to have a system that monitors the integrity of the equipment and alert the pilot if the accuracy can't be determined? Are pilots supposed to monitor the integrity of the systems by themselves? How?

"For procedures requiring GPS and/or aircraft approvals requiring GPS, if the navigation systemdoes not automatically alert the flightcrew of a loss of GPS, the operator must develop procedures to verify correct GPS operation"

First of all, an RNP 1 procedure requires a GPS/ GNSS. And as you have said, it requires an inbuilt navigation monitoring and an alerting system. On the other hand, an RNAV 1 procedure does not. In RNAV 1 you can get navigational aid from the IRS/ VOR/ DME or IRS/ DME/ DME.

The SIDs and STARs can either be RNAV 1 or RNP 1. RNAV 1 is the system introduced at the start of performance based navigation to cater for smaller air spaces (terminal area procedures) and it is a step towards changing over to RNP 1. Many countries these days require an aircraft with RNP 1 capability to fly their SIDs and STARs. They sometimes tend to name it unambiguously on the chart. Like a chart might state, RNAV 1 and then state that you require a GNSS. This essentially makes the procedure an RNP 1 procedure. Others state specifically that you need to be RNP 1 complaint. This means that you need to have a GPS and a monitoring and alerting system. This is mainly seen in China, where most of the airports require the aircraft to be able to fly RNP 1 procedures so that they can pack airplanes together, with minimal ATS surveillance. This is done to accommodate the ever increasing air traffic in the region.

It has been quite a while, since I have not been to Wuhan, China for obvious reasons. Wuhan airport is one those example airports which allow only aircraft that can fly RNP 1 for their SIDs and STARs.

I think the advantage of keeping the charts and procedures RNAV is that it allows operation of older aircraft, which does not comply with RNP operations. This is I believe quite important in a place like the United States where airlines still tend to operate older aircraft and has a big general aviation sector. In other places, airlines tend to have newer aircraft, which easily fits into the current navigation standards. This makes it easy for the regulators to change their procedures to RNP.

For the question regarding losing RAIM (Receiver autonomous integrity monitoring). If you lose RAIM, you probably cannot do a GPS/ RNAV (GNSS)/ RNP approach (same type of approach, just different names). But the aircraft can still be used for RNAV navigation, as RNAV does not require the monitoring and alerting.

The reason for using RNAV1 as opposed to RNP1 is simply because it would have been considered quite adequate for the STAR or SID in question. Adding superfluous requirements could mean that an aircraft would have to abort the procedure if they temporarily lose RAIM capability (or get an alert), costing money for no added safety benefit.

GNSS-SDR will process incoming raw samples as fast as the computing platformexecuting it allows. It will automatically take advantage of multi-corearchitectures, and it will select the fastest SIMD implementation available inyour machine (covering technologies such asSSE2,SSE3,SSE4.1,AVX,AVX2,and NEON). It can even offloadsome of the computing work to the Graphics Processing Unit. If there iscomputational power enough, GNSS-SDR can be used in real-time, reading rawsamples from a radio frequency front-end. In slower machines, GNSS-SDR willexecute exactly the same code, for instance reading raw samples from a filestored in a hard drive.

Try the software on your own computer: GNSS-SDR can be executed in a widerange of processor architectures, from the newest ones to those that have beenaround for a while. Your own computer will probably be among the listed above.The software receiver processes data as fast as it can, taking advantage ofthe particularities of your processor and dumping messages to the terminaloutput in case it is not able to perform the required computation in real-time.If your processor is not fast enough to process GNSS signals in real-time, youcan still use files and use the software, performing exactly the same processingbut at a slower pace, and thus without processing time constraints.

The input of GNSS-SDR is a sequence of raw digital samples of GNSS signals. TheSignal Source abstraction wraps all kind of sources, regardless of theirnature: it can be a file containing a sequence of samples (which can besynthetically generated by a computer program, or real GNSS signals grabbed byan actual antenna and radio frequency front-end, and then translated into thedigital domain and stored in a hard disk), or an actual device delivering livesignal in real-time. In GNSS-SDR, whatever source delivering GNSS signal samplesis a Signal Source.

GNSS-SDR consumes data as fast as it can, regardless of the original samplerate in which the signal was captured. Hence, the processing of a filecontaining captured samples can take less time than the actual recording length.

On the contrary, in multi-system, multi-band configurations using a high numberof parallel channels or highly complex algorithms, the host computer could notbe able to perform the required processing in due time. While this is an issuein real-time configurations (that would cause buffer overflows and servicediscontinuity), it is not a problem when processing samples from a file. Thesoftware receiver will process samples at its own pace, applying exactly thesame processing as it were real-time, and delivering the corresponding outputsas soon as they are available. This is very useful for algorithm prototypingsince its functional performance can be checked before code optimization anddoes not require a powerful computer.

Ettus Research USRP family is designedfor RF applications from DC to 6 GHz, and provides a wide range of devices. TheUSRP product line spans from affordable hobbyist SDRs to high-end high-bandwidthradios. All USRPs can be used by GNSS-SDR through the USRP Hardware Driver(UHD).

Fairwaves UmTRX is anopen hardware dual-channel wideband transceiver that covers from 300 MHz to 3.8GHz with a maximum RF bandwidth of 28 MHz, delivering 12-bit quadrature samplesup to 40 MS/s, and it is able to operate at industrial temperature ranges. Hostconnection is via Gigabit Ethernet, and a special version of UHD provides a hostdriver, along with the firmware.

Great Scott Gadgets HackRF Oneis an open-source hardware platform for Software Defined Radio that can operatefrom 1 MHz to 6 GHz, with a maximum quadrature sample rate of 20 MS/s with 8-bitquadrature samples (8-bit I and 8-bit Q). It features a software-controlled portto feed an active antenna and a Hi-Speed USB 2.0 connection. GNSS-SDRintegration is provided viagr-osmosdr.

Nuand BladeRF is a wideband transceiver that coversfrom 300 MHz to 3.8 GHz, delivering 12-bit quadrature sampling at a rate of up to40 MS/s. The host connection is via USB 3.0 Superspeed, and GNSS-SDR integrationis provided viagr-osmosdr.

For testing purposes, the antenna can be replaced by a radio frequency GNSSsignal generator, which can directly feed the front-end and thus providecontrolled inputs to the software-defined receiver. In such a case, you mightneed an attenuator between the signal generator and the antenna input in orderto protect the RF circuitry.

The term GNSS is given to a worldwide position, velocity, and time determination system, that includes one or more satellite constellations, receivers, and system integrity monitoring, augmented as necessary to support the required navigation performance for the actual phase of operation. (EUROCONTROL)

Currently, the USA-operated GPS and the Russian GLONASS systems are operational. The Galileo system is currently expected to be operational in 2015. The BeiDou system is partially operational and is anticipated to be fully functional by 2020.

GNSS is often generically referred to as GPS (Global Positioning System) but that acronym actually refers specifically to the United States constellation. There are several GNSS constellations provided by governments around the world, including:

In addition, there are some other systems that are engineered to service specific regions only, rather than offering a global service. These are known as RNSS (regional navigation satellite systems) including:

Today, most GNSS receivers can receive and decode signals simultaneously from more than just a single satellite constellation. This means that they can be used globally for immediate deployment and can provide wider use than receivers that are limited to a single GNSS constellation.

A full 24-satellite constellation that offered global coverage became operational in 1993. Since this time, the use of GPS and other GNSS constellations has become synonymous with a vast array of commercial, defence and civilian applications and services that continue to shape many aspects of our lives.