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channels of GNSS boards
Posted by jimantoney on August 27, 2022 at 6:22 amHi
If anybody know usage of too many channels ?
many old brands like Novatel and trimble have max 500-700 channels , but so many china brands like comnav , unicorecomm , Hemesphere have more than 800 channels also If 60sats* 5signals = 300 max channels is needed is 300 pcs.
and any body know how can realize real channels quantity for any boards ? how to calculate channels without simulator and Lab tools ?
best regarards
bill93 replied 1 year, 7 months ago 6 Members · 6 Replies- 6 Replies
Part of what I know about this is company information. As in, I work for a Topcon/Sokkia dealer so am more acquainted with their technology.
As I have been given to understand, the number of channels does define the capacity of a given receiver. Topcon’s receivers since the HiPer II & GRX1 (Sokkia version) have used GPS chips with “Universal Channels” which means that any channel can be used in the receiver to track in frequency from any satellite the receiver is authorized to track and frequency of any satellite in the constellation in view.
I was given to understand that because of this Universal channel tracking technology, a Topcon receiver had more capacity than a comparable Trimble or Leica receiver both of which were specced with a higher number of channels. The reason for this was that those competitive units had more channels, the channels were dedicated to specific satellites/frequencies. If that satellite was not in view, it was not used. But because any channel could track any frequency from any satellite, Topcon/Sokkia receivers actually gave more tracking capacity with fewer channels.
I do not know about the current competitive receivers. I have not been to a dealer training in a while and I do not know what others are doing. But if the practice of having specific channels dedicated to specific satellites/frequencies is still the norm for the other manufacturers, that would explain the apparent superabundance of receiver channels.
Years ago I got hung up trying to find out if 1-channel is needed per satellite, or if a separate channel is needed for each frequency/signal.
I still don’t know.
“Upon our arrival, guests were introduced to mockups and the magnesium skeletal frame of the Triumph-LS, Javad??s latest flagship product. The highlights of the design specifications called for an 864 channel all-in-one GNSS receiver. While an impressive feat, to be sure, I wondered, “What could the possible benefit of 864 channels be for tracking less than 30 visible satellites?” Javad??s 30 years of success suggested he deserved the benefit of the doubt. His answer: 864 channels allow the receiver to listen to each signal (GPS C/A, P1, P2, L2C , L5; GLONASS C/A, L1, L2, L3, L2C; Galileo E1, E5A, E5B, AltBoc; Beidou B1, B2; and QZSS L1C, L2C, L5 and SBAS L1, L5) with multiple independent channels (like several ears listening to the same whisper). One hundred of the 864 channels listen for in-band interference from sources such as cellular, FM, AM, TV, airport, military, civilian, etc. When I asked him about the radical departure from the conventional rover/data collector, he explained that the all-in-one is more portable, with forward pointing compass/camera sensors, a unique heads-up operation (both of which are the foundational to Visual Stakeout and pixelated angle measurement), tilt compensation and one battery pack for everything. “
https://amerisurv.com/2015/01/02/product-review-javad-triumph-ls/
To be clear, the majority of my understanding of GNSS channels is from vendor marketing. Ie. I am still completely in the dark 😉
I agree. Considering that most of the processing being done in those receivers is proprietary, it’s pretty hard to get an exact answer.
I suspect Javad is correct, and it fits with the random tidbits of info that I get from industry reps on occasion – dedicated channels are required if you need/want to perform parallel processing and evaluate a multitude of solutions in realtime.
Trimble does something very similar (although their new receivers still don’t have as many as Javad, so I’m not sure about listening for interference) with the ProPoint RTK engine on board the R12. My guess is Leica’s latest receivers do too, but I don’t think I’ve seen any white papers about the internals of their gear.
I seem to remember an article not too long ago where a Trimble rep implied that increased onboard processing power was a factor in adding more and more channels for the engine to work with.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil PostmanDunno if this helps or just makes more mud:
“Tracking Loops, Channels and the Microprocessor
GPS for Land SurveyorsWe’re not talking about just receiving one signal from one satellite but rather a minimum of four, and perhaps many more, from four to more satellites and the antenna itself does not sort the information it gathers. The signals from several satellites enter the receiver simultaneously. But in the channels of the RF section, the undifferentiated signals are identified and segregated from one another. There are usually several IF stages before the copies are sent into the separate channels, each of which extract the code and carrier information from a particular satellite. A channel in a continuous tracking GPS receiver is not unlike a channel in a television set. It is hardware, or a combination of hardware and software, designed to separate one signal from all the others. A receiver may have 6 channels, 12 channels, or hundreds of channels. At any given moment, one frequency from one satellite can have its own dedicated channel, and the channels operate in parallel. This approach allows the receiver to maintain accuracy when it is on a moving platform; it provides anti-jamming capability and shortens the time to first fix (TTFF). Each channel typically operates in one of two ways; working to acquire the signal or to track it. Once the signal is acquired, it is continuously tracked unless lock is lost. If that happens, the channel goes back to acquisition mode and the process is repeated.
While a parallel receiver has dedicated separate channels to receive the signals from each satellite that it needs for a solution, a multiplexing (aka muxing) receiver gathers some data from one satellite and then switches to another satellite and gathers more data and so on. Such a receiver can usually perform this switching quickly enough that it appears to be tracking all of the satellites simultaneously. A multiplexing receiver must still dedicate one frequency from one satellite to one channel at a time; it just makes that time very short. It typically switches at a rapid pace, i.e., 50 Hz. Even though multiplexing is generally less expensive, this strategy of switching channels is now little used. There are several reasons. While a parallel receiver does not necessarily offer more accurate results, parallel receivers with dedicated channels are faster; a parallel receiver has a more certain phase lock; and there is redundancy if a channel fails and they possess a superior signal-to-noise ratio (SNR). A multiplexing receiver also has a lower resistance to jamming and interference compared to continuous tracking receivers. Whether continuous or switching channels are used, a receiver must be able to discriminate between the incoming signals. They may be differentiated by their unique C/A codes on L1, their Doppler shifts, or some other method, but, in the end, each signal is assigned to its own channel.”
https://www.e-education.psu.edu/geog862/book/export/html/1659
“If we look at the major developments over the last few years, then it is the continuous addition of systems to the satellite constellation such as Beidou and Galileo as well as the longer existing GPS and Galileo. But even within the existing systems developments are ongoing, with new frequencies such as L1C, L2C and L5 being added to the spectrum of available signals. Most receivers are ahead of actual GNSS operations and will supply their receivers prepared to receive all GNSS and the maximum number of satellites and signals available.
As a result, a modern receiver may boast over 400 channels with an average of around 200 channels in a receiver. A single channel will receive a single frequency from a single satellite for a single GNSS. Thus, current high-end receivers can track over 125 satellites at the same time! Be aware however that not all systems are currently at full operational capability (FOC). GPS and Galileo are at FOC whereas both Beidou and Galileo have limited coverage. Those working in the far East will benefit from Chinese Beidou, the Japanese QZSS and the Indian IRNSS as the local coverage is very stable. However, elsewhere in the world Beidou coverage is still marginal and QZSS and IRNSS coverage non-existent due to their regional character.”
https://www.hydro-international.com/content/article/technology-in-focus-gnss-receivers
GPSWorld (my usual go-to for new GNSS info) had this Javad article which basically mirrors what I posted earlier:
https://www.gpsworld.com/new-javad-triumph-ls-receiver-features-864-channels/
The GNSS side of the business changes so quickly anymore it seems hard to keep up at times. Well, that, and I’m likely becoming more of a curmudgeon 😉
From my engineering background, I would expect each signal L1, L2, etc. of each satellite to occupy one channel. Besides, that lets them advertise the biggest number.
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