Is it possible to associate single wireless network interface controller (WNIC) with multiple Wireless Access Points (WAP) at a time? If not: why?
I've never heard about such a feature, so I assume it's technically impossible or fairly difficult and rarely implemented. Is it really that difficult/impossible to implement driver providing such a feature? Is it software or hardware difficulty?
I assume that TCP/IP protocols' specifications doesn't limit us at all because if I attach multiple WNICs to my computer, I can easily connect to multiple APs.
If it's software difficulty, than what's the actual problem? Does Linux/Windows kernel or WNIC's drivers limits it? Or maybe system libraries (like libc on GNU/Linux systems)?
If it's hardware difficulty, what actually limits us? Antennas? Using single radio frequency at a time? If yes, than why can't we implement frequency hopping (like Kismet does)? Because of lost packets during time spent on other channels? If yes, than can we associate WNIC with multiple routers working on the same channel (I know that channel overlapping is bad)?
Note: I'm not talking about dual band routers. I assume that we consider most common WNIC and AP which both work on 2.4GHz channels. If I have to put my question into OS context, than I choose GNU/Linux context.
Yes. The basic technique is that the client tells AP 'A' that it is going to sleep and then talks to AP 'B' while A is buffering frames for it.
Microsoft research worked this out a while ago:
http://research.microsoft.com/en-us/um/redmond/projects/virtualwifi/
Many low-level drivers support Wi-Fi interface virtualization (e.g. the BRCM wl command has options which support this).
Apple's AirDrop and MultiPeer features for OS X and iOS use a similar technique, but instead of talking to a 2nd AP they talk to a peer device.
Related
Background
I'm very new to electronics/IoT dev. I'm trying to create a solution to be able to read my wife's Car's CAN Bus signal (messages) and store it to an SD card. I hope to analyze the data and build a dashboard based on the car's telemetry.
This specific question is in relation to a chip (STM32F1) on an IoT board (MXChip AZ3166) I already own, which I hope to incorporate into my overall solution as the data acquisition layer.
For reference the:
Chips is the: STMicroelectronics STM32F103C8T6, 32bit ARM Cortex M3 Microcontroller
and the IoT board is the: (MXChip AZ3166 IoT DevKit)
Reading the MXChip AZ3166 board's spec and after doing some research, I have found out that the MXChip AZ3166 comprises two main chipsets:
Vendor
Part Number
Ref Link
STMicroelectronics
STM32F103C8T6
https://uk.rs-online.com/web/p/microcontrollers/1023545
MXChip
EMW3166
https://www.mxchip.com/en/products/module/54
Main Question
The product specification mentions the STM32F1 features Comprising of motor control peripherals plus CAN and USB full speed interfaces, it also states it has 1x CAN Channel. Does that mean I can interface the MXChip AZ3166 board featuring this chip via the GPIO pins to the CAB bus in my wife's car and receive the CAN Bus signals (I presume adhering to the
ISO 11898-1 CAN data communication protocol).
How would I find out which pins to connect to the CAN Hi & CAN low connections on the cars CAN Bus?
Concerning power, how would I determine that the CAN signal received doesn't fry the MXChip Board with a stated max Operation voltage of 3.3v?
Yes you'll want an MCU with a built-in CAN controller for communicating on a CAN bus. However, the CAN standard only covers the physical and data link layers. You need to know the application layer in order to meaningfully interact with a bus.
The application layer on a car may or may not be proprietary. It may even be encrypted. If you don't know what protocol is uses, then no can do. Reverse-engineering CAN protocols is hackish, hard and dangerous. Plugging into a CAN bus where you have no clue about timing considerations etc is also very dangerous.
But cars usually have an "on-board diagnostics" (OBD) port used for service purposes, with standardized application layers, through which you may have access to various parts of the car. There's lots of different standards for OBD and older ones didn't even use CAN. It depends on the car model.
In case of the OBD port the pinouts are standardized and you can find them on the Internet. Otherwise it is very simple to find out which signal that's CANH and CANL with an oscilloscope. CANH goes 2.5V +1V and CANL 2.5V -1V. A more hacky solution is to measure this with a multimeter, but it's perfectly possible since one signal with be slightly above 2.5V and the other slightly below.
CAN is standardized so if you have a CAN bus on the board, you connect there. In some cases there may be 12V supply wired together with the signal and that's the only one which could fry something.
Overall, please note that the project you describe here is very difficult and not a beginner task. It sounds as you have next to no experience of electronics/embedded systems, so I would recommend picking a far simpler project.
Furthermore, modifying car electronics or installing your own electronics in a car is illegal in most parts of the world. Third party type approvals with EMC tests are mandatory (and very expensive). If your car is involved in an accident and they find custom electronics without type approval in it, you could be facing serious legal consequences.
I live in a building where the laundry machine is a bit far away from my suite. There is only one machine there so only one person can use it at a time. Quite often I take my laundry there just to realize that the machine is in use so I have to go back defeated and try again later. I want to build a doodad that can detect when the machine is in use and broadcast that information throughout the building so that I know that the machine will be available before I go there.
This question is not about how to build the detector. I am planning on using a raspberry pi somehow. This question is about what do I do when I detect that the machine is in use. How do I broadcast that information mainly to myself or potentially to anyone in the building?
I need a cheap solution (< $100). It has to be wireless. The signal has to travel approximately 30 meters in one direction. The broadcast should be readable on any laptop or cell phone (not a requirement but nice to have).
I was considering making an android app using WiFi direct. I'm sure others in the building would be interested in this app and I can use them as peers to extend the range of the broadcast. But I don't like this solution because I know that wifi direct doesn't work with iOS devices. Also this solution will require others to side-load an apk which they might not know how to do.
Please let me know if you can come up with something a bit less reliant on p2p and more platform independent.
I have seen several projects now which derive novel spatial information from radio data collected from a typical wireless router:
http://wisee.cs.washington.edu/
http://www.extremetech.com/extreme/133936-using-wifi-to-see-through-walls
The idea of using a wireless router as a sort of passive radar is fantastic.
I am very interested in experimenting with data collected from a wireless router myself, but there is little information on how to go about actually interfacing with a wireless router and getting a raw stream of information collected by the device. Similar questions have been asked on here before, but I am yet to see a satisfactory answer.
I don't have the rep points necessary to link to the other questions but see:
'Capture Raw Signal from WiFi card as You Would a Sound Card'
'raw wifi “signal data” access'
I am looking for a solution that would let me use a low-cost device such as the oh so common WRT54G wireless router. If your answer involves custom radio hardware, you needn't bother posting.
As far as I know, the only option using a commodity hardware is to use Intel 5300 Wifi card. You can get the complex CSI (amplitude and phase info therein) from the three antenna on it from a sample of subcarriers (OFDM). You can take a look at this site:
http://dhalperi.github.io/linux-80211n-csitool/
If you read the wisee research paper you will find the platform they use for the system, it is USRP N210 from Ettus plus GNU radio software.
So it is not your usual WiFi AP they are using but the SDR solution this question also hints about.
WiFi devices are build to handle physical layer in silicon and the monitor mode is the best thing you can get without going the SDR path. You can get quite a lot of information from it - the radiotap header contains for example received signal strength and receiving antenna information. But if you really want to explore physical layer of WiFi then commodity hardware is not going to cut it.
I'd like to have an iPhone and an Arduino-based device talk to each other. Here are the requirements:
I want to fully rely on iPhone's built-in components without any peripherals (for example, HiJack).
The less configuration before the two can communicate, the better. This means a WiFi-based is not desirable, because we'll need to set up Wi-Fi credentials for the Arduino beforehand.
Bitrate is not important. Only a few bytes are exchanged.
As cheap as possible.
I see that Bluetooth 4.0 LE (for example, Stack Overflow question iPhone - Any examples of communicating with an Arduino board using Bluetooth?) meets my requirements, but are there any cheaper solutions?
One thing that came into my mind is sound - the way Chirp used to share data between two iOS devices, but I don't know if is feasible on Arduino and, if it is, how much it would be. Any other solutions?
I can think of a few options:
Bluetooth, you can get a cheap one from eBay for about $10
Wi-Fi using Electric Imp (cost around $30), which is very easy to setup using the brilliant BlinkUp technique. See the project ElectricImp, control central heating via iPhone for an example.
Chirp is a brilliant idea as well. From a hardware prospective I see it is feasible to do in Arduino; you just need a MIC circuit ($8) and speaker.
However, the real challenge is the software side, i.e., the algorithm that you will use to encode data as sound and vice versa. If such algorithm requires intensive calculation, you might not be able to do it in Arduino, and you can consider using an ARM-based microcontroller.
Do you know a SDR (Software Defined Radio) kit with a 2.4GHz ISM band (2400MHz - 2483.5MHz) transceiver?
I need to perform some software defined radio including customised modulation. Also the price for one kit should be at maximum $1000. I know there are some extremely expensive solutions out there, but that is unfortunately not an option.
Also a low delay from reception to transmission is necessary, thus the GNU Radio + USRP solution is not usable.
Update:
I have taken a closer look at the USRP solution. From previous experience with the USRP + GNU Radio software I initially completely dismissed it as a solution in this case. I did that because I need to implement a packet radio protocol, thus I need precise bit synchronisation between input and output, and I need low delay that would allow me to transmit the next symbol following a received symbol, with a rate of 1000 kBaud.
From experience I know that the GNU Radio framework as default uses streaming chains of blocks, with very little synchronisation between TX and RX. Thus I suspect that using the USRP I would probably have to work directly with libusrp, and avoid most of the GNU Radio software. Am I mistaken in this?
I would suggest taking a look at the GNU Radio (gnuradio.org) SDR toolkit. Several projects (such as this one) have successfully used it for Bluetooth research.
There also exists development hardware designed for use with GNU Radio called the Universal Software Radio Peripheral which, with a suitable daughterboard for 2.4GHz development, costs around $1000.
I'd like to second GNU Radio. Specifically you are looking for the USRP not the USRP2. The USRP2 is still in heavy development(and out of stock) while the USRP is a stable platform for GNU Radio. The USRP motherboard cost $700. The daughterboard transceiver you want is the RX2400(2.4-2.9GHz, TX=50mW). You can find both of these boards at Ettus Research
Update six years later: USRPs come in the sub-1000$ range (B200/B210), they have very strict synchronization (ADC-rate accurate timed commands can control sampling) and coherency. GNU Radio supports these features through the gr-uhd interface.
Describing latency is quite a bit more complex, because it depends much more on how you deal with the data coming from any SDR frontend -- really, frontend latency isn't usually the problem when you try to do your processing on a general purpose OS, which makes no hard real-time guarantees. However, many just "hide" the latencies elegantly by employing timed commands and letting the frontend get the data early enough.
I recommend HackRF One wich is a half-duplex tranceiver form 1MHz to 6GHz and also has huge comunity support but is half the price of USRP.
EDIT
You now also have LimeSDR. It has 2 Rx and 2 Tx MIMO full-duplex channels and it's cheaper than tje HackRF. The only drawback may be the shipping time because at this moment there's no stock so you will have to pre-order.
We have successfully been using a professional development platform from Sundance Multiprocessor Technology (www.sundance.com). They do have some very affordable 2.4GHz/5GHz RF front-end solutions with integrated ADC/DAC and multiple DSP/FPGA processors.
University offers: http://www.sundance.com/docs/mimo_lte_booklet.pdf