Friday, January 1, 2016

Happy begin of 2016

2015 just passed. I don't write much here anymore as time has become a very precious resource and my job imposes tight limitations on what one can or cannot write on the web.
The yearly update will quickly cover constellation the status, some info on low cost RTK developments and some more SDR thoughts (although the most significant article in that respect will come soon in another post).

Constellation updates

As retrieved from Tomoji Takasu's popular diary, 2015 has seen the following launches:

Date/Time (UTC)     Satellite             Orbit   Launcher        Launch Site               Notes
2015/03/25 18:36    GPS Block IIF-9       MEO     Delta-IV        Cape Canaveral, US        G26
2015/03/27 21:46    Galileo FOC-3, 4      MEO     Soyuz ST-B      Kourou, French Guiana     E26, E22
2015/03/28 11:49    IRNSS-1D              IGSO    PSLV            Satish Dhawan SC, India   111.75E
2015/03/31 13:52    BeiDou-3 I1           IGSO    Long March 3C   Xichang, China            C15
2015/07/15 15:36    GPS Block IIF-10      MEO     Atlas-V         Cape Canaveral, US        G08
2015/07/25 12:28    BeiDou-3 M1-S, M2-S   MEO     Long March 3B   Xichang, China            ?
2015/09/10 02:08    Galileo FOC-5, 6      MEO     Soyuz ST-B      Kourou, French Guiana     E24, E30
2015/09/29 23:23    BeiDou-3 I2-S         IGSO    Long March 3B   Xichang, China            ?
2015/10/30 16:13    GPS Block IIF-11      MEO     Atlas-V         Cape Canaveral, US        G10
2015/11/10 21:34    GSAT-15 (GAGAN)       GEO     Ariane 5        Kourou, French Guiana     93.5E
2015/12/17 11:51    Galileo FOC-8, 9      MEO     Soyuz ST-B      Kourou, French Guiana     E??, E??


GPS replaced three IIA birds with brand new IIF, as one can see Figure 1. The number of GPS satellites transmittiing L5 raised now to 11 (as one can also verify with UNAVCO). The number of GPS with L2C is instead 18 (quite close to a nominal constellation!). The question is now how GPS will proceed in 2016 and beyond, having seen the delays that afffect OCX and in general the bad comments (see e.g. 1 and 2) on the progress of modernisation of GPS.
Figure 1: One year of GPS observations, obtained using a bespoke tool from the freely available data courtesy of the IGS network.

Stable situation here, as seen in Figure 2, with the only exception of PRN 17 going offline in mid-October (perhaps soon to be replaced according to the table of upcoming launches)
Figure 2: One year of Glonass observations

The situation has been very "dynamic" for Galileo but is indeed very promising as seen in Figure 3. The latest launch went well and we can hope for several signals in space in 2016: hopefully the year that Galileo will make its appeareance in most consumer devices. Incidentally, there are as of today 8 satellites broadcasting E5a.


Also for Beidou the situation is rapidly evolving as can be seen in Figure 4. My colleague James and I did a detailed study on the new generation satellites and published part of it on GPSWorld. Indeed 3rd generation test birds host a very versatile payload that allows them to broadcast modern navigation signals on three frequencies. Incidentally C34 and C33 (the two MEO space vehicles) also broadcast a QPSK on E5a.
Figure 4: One year of Beidou observations.

Low cost RTK

An awful lot of progress here, with NVS, Skytraq, Geostar Navigation and uBlox releasing multi-constellation single frequency products for RTK.

NVS released two products with onboard GPS+Glonass (upgradeable to Galileo) RTK engine: NV08C-RTK (for standard base-rover configuration) and NV08C-RTK-A (with added dual antenna heading determination for precision AG). Rumors say that they both run an highly reworked version of RTKLIB on a LPC32xx microcontroller (ARM926EJ-S processor with VFP unit). The price is not public, but again rumors suggest it is a few hundreds of EUR a piece (in small quantities) for the single receiver version. I got my hands on a couple of boards and build a simple adapter board to be able to use them with a standard laptop and a wireless module fitting the Xbee socket (including this one).

Skytraq has built on its Navspark initiative and came out with two groundbreaking products S2525F8-RTK
and S2525F8-BD-RTK. The -I shall say- provocative price of 50 and 150 USD respectively sets a new threshold very hard to beat. Skytraq has also done extensive analysis on the performance of GPS only versus GPS+Beidou single frequency RTK, e.g. here and here. In Asia the dual constellation (2x CDMA) single frequency (1540x and 1526x f0)  RTK shows incredibly promising results, mainly due to the impressive number of birds in view. I got my hands on a couple of plug&play evaluation kits and already verified the sub-minute convergence time to fix in zero baseline and good visibility conditions.

Geostar Navigation has also recently released the GeoS-3MR which is practically identical in terms of capability to the GeoS-3 and GeoS-3M, but has a factory setting such that the most recent firmware provides carrier phase for both GPS and Glonass. Although Glonass phase is not calibrated, last month statements from Tomoji suggest that this feature could be incorporated in v2.4.3 anyway.
A few years ago I had designed and produced some carrier boards for GeoS-3M so I could just place an order for a few raw-capable chips (at 25 USD each) and test them out. The software provided by the manufacturer (Demo3 and toRNX) allows to extract Rinex observations from the binary logs. At the time I had also developed some parser code for RTKLIB but I now found out that it has a small issue.. I don't feel like reinstalling C++ Builder just to fix it but anyone please feel free to take that code and push it to v2.4.3.

uBlox released the M8T module with raw data support for two simultaneous constellations.. very interesting chip but I have the feeling that some big change is going to happen there since the Company is focussing much more on comms than nav lately.

ComNav offers the K500 OEM board also for less than 300 EUR in small quantities.

In view of all the above, one could expect that initiatives like Reach® and Piksi® will surely have to reconsider their approach. In particular, things based on Edison® are facing the competition of ARM-based modules which are perfectly capable of RTK and are accessible at a much lower price (e.g. see Raspberry Pi Zero and C.H.I.P.  SwiftNav has recently release an update but unless they go multi-frequency rapidly the competition will give them very hard times.

Finally, low cost dual frequency cards such as Precis-L1L2 have started to appear. Apparently based on a Chinese Unicorecomm OEM board it offers multi-constellation multi-frequency RTK at 800 USD.


Over the holydays I assembled the test-bench for the NT1065, the latest multi-constellation front-end from NTLAB. The setup again is very clean and builds on lessons learnt with the NT1036: I will present the first results soon, in the next post.

Since the chip has the native capability of streaming about 60 MBytes/sec (4 channels ~15 MHz IF output at 2-bit per sample) a USB2.0 transceiver is sub-optimal as limited to about 40 Mbytes/sec.
I started investigating the FT601 USB3.0 trasceiver from FTDI and the KSZ9031RNX GigETH transceiver from Micrel, as seen in the beautiful development from Peter Monta. Also, the availability of the FX3 Explorer Kit is tempting as easy mid-step solution. There are many SDR boards, but I would just need a cheap programmable FPGA+GigETH/USBSS and I cannot find it... Parallella seems the best candidate with its Porcupine to use and some software to develop of course (I am surprised nobody published a GPIO-GigEth streamer software with Parallella yet). Ettus and Avnet are much ahead with powerful SDR platforms (e.g. the B210 and the picoZed SDR SOM) but there is what feels a steep lerning curve to use them. Perhaps it is time again to go design something?
In the meantime, I am watching the pcDuino3 Nano Lite and the Odroid XU4 as cheap NAS solutions to efficiently store long snapshots of IF data.


Unknown said...

Do the new Sirf V modules provide carrier phase outputs?

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