Re: [Discuss-gnuradio] Use gnu-radio & usrp to make a wireless relay node

[Marcus Müller]

Hello Shilei Tian,

I'm pretty sure that the cited gr-ieee-802-11 module is the most
developed IEEE802.11 (wifi) implementation for GNU Radio in existence.
> Wow, a new idea occurs to me, could the USRP only amplify the Wi-Fi signal of 
> the selected base station? For example, I have a base station, whose SSID is 
> "Base_Station", "my relay" (USRP + GNU Radio) receives the signal from the 
> base station and amplify it. If the mobile devices connect to my "replay" 
> want to send data, it sends to "my relay", my relay receive it and then send 
> to the base station, transmission done. In this way, the assignments of IP 
> address and NAT service are still finished by the base station. In this way, 
> "my relay" don't need to implement protocols. Can this way work?
Sadly, I don't think so. The USRP you have has only one RX and one TX
port, so you can only have one full-duplex operation: You can only
forward signal from your client to your Access Point, or from your
Access point to your client, but not simultaneously. You'd have to be
very clever to detect when to switch between forwarding in one and the
other direction. I think it might not even be possible at all --
802.11a/b/g/n, as far as I know, uses CSMA/CA as access scheme, which
means that there's no "fixed" time at which you can be sure only one
party uses the medium.

Also, most WiFi devices already have adjustable TX power. My home
router, for example, supports a lot of nominal TX power settings from
+0dBm to +20dBm; I don't trust these numbers the least, but I guess you
could calibrate them with a calibrated spectrum analyzer and use them.

An idea: you really don't want to do any processing on the signal. Now,
as much as I like GNU Radio and USRPs, you really don't need to use
either if you just want an adjustable amplifier. You can probably just
use the tools that exist on Linux for the wifi devices to adjus the TX
power.

Also, what you want is really something that basically is analog in
nature; maybe two antennas, a circulator at each one of them and an LNA
in RX and an adjustable amplifier in TX direction would serve you better?

> By the way, I want to ask, is there any relay that suits for me on the market?
So: Many (most, probably) Access Points and repeaters are actually Linux
boxes that run the drivers for the WiFi chipset and Access Point
software (such as HostAPd). Did you already set up an Access Point on
your PC and experiment with it? It might very well be worth the time, as
you might be able to adjust quite a lot of the parameters.

Best regards,
Marcus
On 13.12.2015 16:29, Shilei Tian wrote:
> Dear all,
>
> Recently, I'm working on a subject about wireless relay network energy 
> efficiency, and I want to do do some experiments, so I need a wireless relay 
> whose wireless signal power is adjustable. The client nodes are mobile 
> devices, like Android phones, iPhones, and iPads.
>
> My idea now is to use USRP(I own N210 now) and GNU Radio. The USRP implements 
> the RF side of Wi-Fi, and GNU Radio implements all protocols, like MAC, NAT 
> and DHCP Server, just make it a wireless router. But the work is so huge, so 
> I'm afraid that I cannot make it. Besides, I've read the paper "An IEEE 
> 802.11a/g/p OFDM Receiver for GNU Radio", but it could only work on the pure 
> OFDM mode, which my clients don't support.
>
> So I want to ask whether there are existing 3rd party GNU Radio modules that 
> could do this job.
>
> Wow, a new idea occurs to me, could the USRP only amplify the Wi-Fi signal of 
> the selected base station? For example, I have a base station, whose SSID is 
> "Base_Station", "my relay" (USRP + GNU Radio) receives the signal from the 
> base station and amplify it. If the mobile devices connect to my "replay" 
> want to send data, it sends to "my relay", my relay receive it and then send 
> to the base station, transmission done. In this way, the assignments of IP 
> address and NAT service are still finished by the base station. In this way, 
> "my relay" don't need to implement protocols. Can this way work?
>
> By the way, I want to ask, is there any relay that suits for me on the market?
>
> ----------
>
> Sincerely yours,
>
> Shilei Tian（田世磊）
> Postgraduate Student
> Department of Computer Science and Engineering
> Shanghai Jiao Tong University
>
>
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio