8 ms·
It seems one of the final missing links to fully open source hardware WiFi would be the RF transceiver chip. This is, to my understanding, something similar to
by etaioinshrdlu 6y ago
It seems one of the final missing links to fully open source hardware WiFi would be the RF transceiver chip. This is, to my understanding, something similar to a high-bandwidth DAC and ADC coupled with configurable frequency mixers to access radio frequencies.
Is anyone trying to create an open source version of that chip? I understand there's not a lot in the way of open source analog chip designs out there, but with Google/Skywater's free PDK, the time may be ripe to change that.
Also, there are many SDR LTE base stations, but can we make our own SDR LTE handset as well? Can it connect to an existing cell network?
- monocasa 6y agoThe Google/Skywater PDK only allows for digital designs at the moment.
- etaioinshrdlu 6y agoThere is definite progress in bringing analog support, but I agree it is nowhere near ready yet.
- myself248 6y agoHow open does it need to be? If you're willing to take up a suitcase worth of room, you can use standard analog ICs and RF building blocks to take a quite normal DAC and upconvert it to RF, and downconvert the receive chain likewise to a very common ADC. The standard wifi channel width of 20MHz should place it within reach of quite a few off-the-shelf chips. That approach should be able to do the whole thing with no NDAs or whatever; it would be a fine capstone project for someone chasing an EE/RF degree...
- etaioinshrdlu 6y agoI think it would be cool if 100% of the digital logic was open source, and 100% of the analog was at least well-understood, and commoditized. Kind of like how you don't need an open source op-amp, they're well understood and commoditized (for most applications). Does it really take up a suitcase worth of electronics to do what the transceiver IC's are doing?
- myself248 6y agoProbably not, but it's a tradeoff between integration and modularity/testability. Take a look at slide 23: https://ntms.org/files/Jan2018/Microwave_Radio_Cowtown_2018.pdf https://ntms.org/files/Jan2018/Microwave_Radio_Cowtown_2018.... Can you build that all onto one board? Yeah sure, after it's proven and set in stone.
- exikyut 6y agoThe HackRF One can do 1MHz-6GHz, but also indicates "8-Bit I and 8-Bit Q". On the one hand I'm like, it's basically just dumping wideband spectrum into the air, right? On the other hand the OpenOFDM reference talks quite a bit about much larger I/Q values, so maybe "8-bit quadrature samples" is exactly why nobody uses it for Wi-Fi. :( (Yup, am RF noob)
- fake-name 6y agoThe HackRF One uses a series of up/down converters, plus a MAX2837 for tuning, and a MAX5864 for the actual ADC/DAC. It goes 22 MSPS, so it can theoretically look at any ~20 mhz section of the 1 MHz - 6 GHz tuning range. WiFi channels are generally 20, 40 or 80 MHz, so the latter two are not possible given the hardware, and the smallest (20 MHz) would be right at the limit of the hardware. Additionally, there may be other complications (tx/rx switching speed, tuning speed (I'm not sure if wifi would need to do frequency hopping, and if the bandwidth is sufficient to mitigate that need), etc...) And then someone would have to actually implement it.
- non-entity 6y agoSadly from my research of cheap and hobbyist SDRs, you generally aren't gonna get high bandwidth. I have a limesdr-usb sitting around which supports ~60mhz bandwidth iirc which wasn't good enough for a specific application I looked at which required a channel width up-to 192mhz. Although I'm also an absolute RF noob, do I may have misinterpreted something.
- myself248 6y agotx/rx switching speed is easy enough by just having two units. Use separate antennae so one doesn't fry the other. Also just for safety's sake, twiddle your receive preamp gain down before transmitting. That can be done very quickly. Could probably tie a line between the two and have the CPLD do that, actually.
- jxj 6y ago8bit I/Q definitely can be used for WiFi. I used HACKRF to send and capture Wifi packet without an issue (offline, use Matlab to process the captured I/Q samples). Low resolution I/Q (8bit) will impact the RX sensitivity and TX EVM, but it won't be a factor that will totally fail the WiFi implementation.
- bri3d 6y agoIf you're going down to the "fixed function chips must also be open" realm, you'd also need an open source FPGA (or to use PDK to try to tape out) for the OpenWifi design. My read is that currently OpenWifi is also tied to proprietary Xilinx IP cores like the Xilinx Viterbi Decoder.
- etaioinshrdlu 6y agoYes, I agree. But perhaps the design that is implemented on the FGPA could just be turned into a regular ASIC as well, once it is known to work well.
- Lramseyer 6y agoThe challenge of doing that, is that there are apparently a lot of proprietary IP blocks (both analog and digital) that are in the FPGA (like the Viterbi decoder as the parent comment suggests) that would need to be redesigned before you could tape it out into your own chip. I am not sure what other IP blocks are being used in these FPGAs, but a viterbi decoder can be pretty area and power heavy (relatively speaking.) I'm not sure if you would be able to get enough performance [speed] with modern WiFi protocols by implementing it in normal FPGA fabric hence why those blocks are woven into the FPGA. All that said, this is still a very good thing, because it marks a step forward towards a more open source hardware ecosystem.
- jxj 6y agoIndeed, not only the viterbi but also many basic building blocks in the Xilinx and Analog Devices reference design which is the starting point of our openwifi project. Viterbi won't be an issue, we know how to write our own viterbi decoder on FPGA. It just need some time. A Thorough and comprehensive IP block analysis will be needed and we will also evaluate how big the effort will be to replace all (almost) the big company owned blocks. We have to do this analysis and invest effort in the future, because we really want to tape out a real opensource WiFi baseband chip! As the first step, RF won't be integrated.
- deleted 6y ago
- jacquesm 6y agoIsn't that a patent minefield?
- mschuster91 6y agoIf one is selling it yes indeed. For merely publishing the source? I'm not sure.
- otterley 6y agoAt least in the U.S., patents forbid making, using, selling, or importing a patent-encumbered device without the inventor or assignee's consent. So no, not just selling.
- throwaway2048 6y agoAnd source code is none of those things
- otterley 6y agoDo you have a legal citation for this assertion? I don’t think the law is clear on this either way.
- throwaway2048 6y agoDo you have a legal citation that it does? You are the one putting forward that its illegal.
- otterley 6y agoI did not claim that source code constitutes an "invention" for the purpose of patent law or that the act of copying source code constitutes "making" an invention--the law is unclear on that. I was only stating that "selling" an invention was not the only act forbidden by patent law. Here is the relevant law that supports my claim: https://www.law.cornell.edu/uscode/text/35/271 https://www.law.cornell.edu/uscode/text/35/271 (a) Except as otherwise provided in this title, whoever without authority makes, uses, offers to sell, or sells any patented invention, within the United States or imports into the United States any patented invention during the term of the patent therefor, infringes the patent. (b) Whoever actively induces infringement of a patent shall be liable as an infringer. Title 35 of the U.S. Code is the full text of U.S. Patent legislation. Then there are the volumes of case law interpreting it, if you'd care to read it.
- sasaf5 6y ago> can we make our own SDR LTE handset To achieve the same data rates as a usual LTE handset, but using SDR instead of an ASIC, would make it extremely power hungry. Power is not much of an issue for the base station, but for the handset it is essential.
- apcragg 6y agoYou're right. It's trite, but given design flexibility, low power, or cost you only get to pick two.
- teleforce 6y agoI'd say it is very unlikely and close to impossible unless it's sponsored by a government fund or a very big IC design company that's as big as Intel. But I'm glad if someone can proof me wrong :-) Nowadays if you want an RF transceiver chip you either go with direct synthesis of ADC/DAC or homodyne architecture. The companies that have both of these design capabilities are ADI and TI, and both them are happy with their monopoly. But if any R&D company that probably can pull it off it will be IMEC, and coincidentally it is the employer of some of Openwifi engineers. FYI, IMEC are both funded by Belgium government and a well established IC design company.
- floatingatoll 6y ago"Is anyone being funded to create an open source version of that chip?" might be a more pragmatic question.
- jxj 6y agoGood and tough question. So far, we are not very successful to find enough funding to bring the design to the next mature level and tape out it. Working on it, but difficult. No one can decide to pay 200~300k euro in a minute with very uncertain return (like charity), because no one can 100% answer the question of how many openwifi chips can be sold per year.
- forgot_account 6y ago>>>but can we make our own SDR LTE handset as well? Maybe if you put one these in a kinda-large handheld: https://tinysdr.org/ https://tinysdr.org/ https://limemicro.com/products/boards/limesdr-mini/ https://limemicro.com/products/boards/limesdr-mini/ https://xtrx.io/about/ https://xtrx.io/about/