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Comment by jokoon | Hacker News Reader

I really wish that I could do some basic sdr with android.

People talk about decentralization and privacy and net neutrality, but sdr on handheld would sound very exciting. I'm sure ISPs would argue against it, but communicating small segments of data wirelessly between terminals would open a lot of gates for new kinds of software.

Dht is already at the core of Bitcoin, yet it's not talked a lot about. Dht, to me, is the most important networked algorithm. Implementing the concepts of dht over sdr sounds new and unexplored, but it should be the internet of the future...

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The problem is that interactions between radio systems can be highly unpredictable. LTE-U, for example, was specifically designed to co-exist with coexist with Wi-Fi, but doesn't do it very well: https://pdfs.semanticscholar.org/presentation/a4ac/9af05963e.... When designing wireless protocols, there are real benefits to homogeneity.

> LTE has been modified by a few companies so that it can operate in the same unlicensed spectrum that Wi-Fi uses (called LTE-U)

It looks like to me that the problem is they decided to use the same bands of wifi. If you're going to be using the unlicensed spectrum expect interference.

But that's what you'd be doing if you permitted user-controlled transmissions from ordinary cell phones. The analog hardware in a cell phone is tied to specific frequency bands. So you'd have user-controlled transmissions, not mediated by the cell towers, on the LTE bands.

Also, LTE-U was interfering with Wi-Fi. In general, the unlicensed bands would be a lot more useful if they weren't quite so unlicensed and every radio had to follow certain basic rules.

Actually there are rules, at least in Germany, and I assume the same is true for the US. You can use a microwave heating gun, i.e., a device that shoots a beam of microwave energy to serve similar to a leaf-blower sized hair dryer, in the ISM band(s), which might be able to saturate the LNA in 2.4 GHz radios (depending on where it is placed relative to the band-pass), but you are not allowed to use a broad-band, not-caring-about-others telecommunications radio on the same frequency. For some lower frequencies I could use them to transmit power via a resonant, one-wire transmission line to a quadrocopter to save on the weight of insulation, possibly by using aluminium-clad single mode fibers to get data capacity at the same time, so I can reduce the weight of the tether reducing overall power usage, weight and size, but if I were to use the same frequency for a direct-sequence-spread-spectrum (GPS-style) radio-location-beacon network, that would not be allowed, or only within certain restrictions usually based on both EIRP/PEP/PA-in power and techniques that allow for friendly coexistence between users of the same spectrum, i.e. with CSMA/CA or restrictions to send only 1% of the time, averaged over e.g. 24h or so.

Yup, just because it's an unlicensed band doesn't mean there aren't other restrictions on it.

Pretty sure OP was talking about using the 2.4Ghz/5Ghz unlicensed spectrum. Obviously allowing user transmissions on licensed bands is a bad idea.

So you think instead people should be playing around with SDR on licensed spectrum?

If you've got a license for the bands, sure. I can blast IQ on 14.025Mhz if I feel like it assuming I stay within baud limits. Pretty cheap and easy to get a ham license these days.

Cell phones have multiple radio chips, I don't see issues with allowing SDRs on the unlicensed bands.

No need to dip down to DSP. You can do this with Android over AP-less ("peer-to-peer") Wi-Fi, so you're coding against a nicer API and Android will speak the protocol for you [1][2].

[1] https://developer.android.com/guide/topics/connectivity/wifi... [2] https://developer.android.com/guide/topics/connectivity/wifi...

For anyone working with P2P WiFi I highly recommend the Salut Library.

https://github.com/markrjr/Salut

Thé Android P2P API is pretty difficult to use in general.

> communicating small segments of data wirelessly between terminals

Packet radio? Or, if you're content with short range, what do you need that isn't provided by wifi?

It's not the ISPs you have to worry about, it's the FCC or other local radio authorities. Because radio is a locally-shared medium, bad implementations can jam it very easily.

> Dht is already at the core of Bitcoin

No, it's bittorrent that uses DHT.

have you seen this: https://www.rtl-sdr.com/questasdr-new-rtl-sdr-software-for-a...

You could take something like a NooElec (http://www.nooelec.com/) and connect it to your phone. Though you'll need a rooted device.

I tried it and it wasn't the fastest thing out there but let me do some basic scanning.

I've tried a few of the apps on the Play store (non-rooted) and they did work, but they were crashy and when they did work, clunky to the point of being unusable

GNU Radio has a guide of how to compile it for Android. Having said that, if you're just trying to run it on your phone, it doesn't (usually) have enough power to do anything "fun". You need more capability than your average Android device. The other option is to have something a little more powerful running GNU Radio stack and then control that via your phone :)

Needs tx. LimeSDR Mini or similar would let you test the concepts but obviously embedding it into the device would be best.

Rtl-sdr driver[0] -- Port of rtl-sdr's rtl_tcp.

Allows you to use I/Q packet source in your Android applications.

All you need is to launch an intent in the form "iqsrc://rtl_tcp_arguments" where you replace rtl_tcp_arguments with the arguments that you want your application to run rtl_tcp with and the magic will be done behind the scenes.

This driver could be used by third party applications to implement Software Defined Radio.

It does not require root for Android 3.1 and above.

[0] https://f-droid.org/en/packages/marto.rtl_tcp_andro/

Certainly this is possible with a raspberry pi and a handheld radio.

At my last company I had a friend and coworker who used a pi to communicate with his Android phone for GPS data to then broadcast APRS packets to track his morning bikeride in to the office.

Not exactly handheld but there is room for miniaturization.

https://wiki.gnuradio.org/index.php/Android

> People talk about decentralization and privacy and net neutrality, but sdr on handheld would sound very exciting

"but"?

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