## Extracting narrow-band ZigBee signals from a wide-band WiFi signal?

Started by 6 years ago10 replieslatest reply 6 years ago227 views

Hello,

I am planning the following.

First sample the 20 MHz WiFi channel (WiFi channel-1 in figure).

Put band pass filters (5 MHz wide) around each of the ZigBee center frequencies (11, 12, 13, 14).

Re-sample the chunks to 4 MHz.

Is there anything wrong with this approach ?

[ - ]

Presumably you're trying to do a dual WiFi/Zigbee receiver?

I don't see anything wrong with it in principle; the devil is always in the details, however.

[ - ]

Yes, I am trying to do ZigBee and WiFi simultaneously in real-time.

So far I found successive interference cancellation the most suitable one.

[ - ]

There's nothing "wrong" with it, given what you're asking is fairly vague. If you're wanting to keep the WiFi data for future processing then there would be some differences in design. If you're purely looking for the ZigBee channels then something like a polyphase filter (think channelizer) given your sampling may introduce aliasing of the wifi into the Zigbee channels which you'll have to account for.

Again, if you're purely keeping the zigbee channels, couldn't you narrow your filters at the time of collect and then collect each channel separately? I don't believe zigbee spreads its data across multiple channels.

[ - ]

No actually I have to decode both WiFi and ZigBee at the same time.

So during interference, assuming most of the time WiFi will be strong, I can detect the WiFi and decode it first.

Now from the decoded WiFi data(bits) and channel estimates, I can recreate the estimated WiFi signal and subtract it from the mixed signal(ZigBee + WiFi).

This will give me a signal which will be relatively clean from WiFi interference and hence making ZigBee easy to detect/decode.

"If you're wanting to keep the WiFi data for future processing then there would be some differences in design. "

[ - ]

Wow.  10 years ago I'd say "that's wacky enough to be a good thesis topic", but I have this sad feeling that technology has progressed to the point where it may actually be practical in the real world.

Even if it isn't practical, there should be some papers or even a thesis in there someplace.

[ - ]
Hahaha, I agree with you Tim.

But this is more than that :D (Devil is in the details :D)

Following to this, I have to generalize it for other standards where there are re-usable blocks during the transmission and reception chain(WiFi + LTE).

Development of an architecture for simultaneous operation of different wireless standards using GPU based SDR.

The difficulty is there in the RF part where same RF front end has to be used for all the standards :)

[ - ]

And yes, at least a good part of the challenge will be sampling the RF cleanly enough and fast enough.

[ - ]

As of now my WiFi and ZigBee Rx are working in real time independently.

Yes I will try your suggestion also, to make them working independently in vicinity of each other.

Yes the sampling and AGC requirements are still a challenge and we are working on it.

Just for info, I am developing with Openairinterface and USRP B210.

[ - ]

Hi Tim,

I realize that you used the term gut feeling, but I would like to know why your gut believes that 20 dB is the best you could get?

David

[ - ]
In general, it's a problem that involves saying that $$y = x - \hat{x}$$.  It's only going to work as good as the estimate $$\hat{x}$$.  To make it work you must generate $$\hat{x}$$ from the message, the carrier frequency, the carrier phase, the bit timing of the message, and the amplitude of the message.  I count five different ways that it can go horribly wrong right there.