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Re: [Discuss-gnuradio] GPS tracking on a map over mobile app software us

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] GPS tracking on a map over mobile app software using RF
Date: Mon, 14 Aug 2017 19:54:00 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

Hi Antti,

Well, it wouldn't really help you at all, because, what you're going to do?

Legally, you could only use the ISM bands (which are already congested). Or you'd need to buy a licence for licensed spectrum so that people can use that spectrum; you'd need some central station to arbitrate access to the expensive spectrum you've bought, because in a dense situation a "oh, everyone just uses this whenever they please" is not a solution. People that buy licenses for spectrum, offer infrastructure to control medium access and route data around have a name:

They are network operators. And it's unlikely you'd build a network that is better at being efficient in using spectrum to transport many people's data than LTE.

So, whilst adding another piece of (universal) radio equipment to your (fixed-purpose) radio equipment is an interesting thing, it won't solve the problem of spectral congestion. You could argue that your GPS data is "really not much data at all", and you'd be absolutely right. To transport "not much data", you can use "not much bandwidth", or a very high spreading factor, and get your data across a long distance at limited transmit power (which is a legal necessity in ISM spectrum). Now, the problem with that is, that there's really really many people that are trying to do the same, at the same time, in an uncoordinated manner. It's really hard to find sufficiently orthogonal spreading sequences so that this works out positively. Simply because "not much data" times "really many people within reach" becomes "pretty much total data", after all.

In short: if you have cake, you can distribute it. If the cake is already distributed, you either need to buy more cake (buy an LTE license and operate an LTE network) or distribute the crumbs (trying to find unused spectrum in the free-to-use ISM bands). Either way, there's no free cake.

So, if you ask me, this (sharing a few bits of position information) sounds a lot like the emerging problem field of interference modelling of IoT sensor node networks, only made harder by the fact that the network operator might not have reserved spectrum. As far as I know, there's not been a great solution to that problem.

But, to be brutally honest, sounds like you're solving a "non-problem" to me. It's been quite a while since I wasn't able to even log on to an LTE network at an event because of too many people, and not because it was in an abandoned subway station, well shielded from the LTE network. In that situation, well, you're in that hole, and whoever gets your RF signal is there, anyways. Many apps share data in the background – but they do so in blatantly inefficient ways, generating kilobytes and kilobytes of JSON or XML traffic where a simple exchange of two 32 bit numbers would have sufficed. So, I'd rather try to use the infrastructure for data transport that is given to you in a clever manner (namely, minimum amount of transferred data, make the network stack on your mobile device do actual quality of service prioritizing instead of what handwaving s*** Android does these days, disable data communication for all but important applications when getting little chance to send data – these are all software modifications to be made to a smartphone rather than additional hardware PLUS the software) than to try and build up a parallel infrastructure.


On 08/14/2017 06:31 PM, Antti Ruohonen wrote:
Thank you for your reply, Marcus. Your suggestion of an attachable device is totally fine, actually very good idea.

So, this SDR device would be the medium to the software radio (app in the mobile phone), which controls the device. How would this scenario be possible to achieve the goal? Goal is to send (GPS) data over the radio frequencies to update the app's map. :)

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