WiFi Successive Interference Cancellation : Channel Estimate for Unused Carriers ?

Started by cogwsn 7 years ago3 replieslatest reply 7 years ago220 views


I am working on SIC between WiFi(802.11g) and ZigBee(802.15.4). First I am decoding the #WiFi signal. Once decoded I have to regenerate the WiFi signal with the decoded bits and channel estimates. However the channel estimates are available only for 52 sub carriers (using LTS). How shall I put channel effects for the unused sub carriers i.e. -32 to -27 and 27 to 31 as well as the DC. Because for these sub carriers, I don't have nay channel estimate ? Am I doing something wrong ? 



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Reply by SlartibartfastJanuary 17, 2017

There is no signal in the unused subcarriers, ever, so any channel effects in the unused spectrum will be inconsequential to the signals in the occupied subcarriers.

It's the same as not caring about adjacent channels.   Unless adjacent energy bleeds into the used part of the spectrum it is generally inconsequential.

Is there some other aspect of this that is causing confusion?

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Reply by cogwsnJanuary 17, 2017

Hello, thanks for your reply. 

Yes, I have a confusion because for Successive Interference Cancellation, I have to recreate the entire OFDM symbol. 

ZigBee signal (4 MHz wide)  gets interference from all the 64 sub-carriers of WiFi. So in order to subtract that effect, I am supposed to regenerate an estimate of all the 64 sub-carriers even though some of them are unused. After estimating, I will have to subtract it from the mixed signal i.e. ZigBee + WiFi in order to get a relatively clean signal. From this signal I will extract the ZigBee signal.

As of now, after detecting and decoding the WiFi signal, I generate one clean OFDM symbol (64 samples) plus I already have the channel estimates for 52 subcarriers. Now I have to insert channel effects in the clean OFDM symbol in order to subtract it. 

Let me know if I am not able to put my query clearly. 


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Reply by SlartibartfastJanuary 17, 2017

The unused subcarriers are the easiest to regenerate because they're always zero.   So when you recreate the OFDM symbol, there is no energy in those subcarriers.   The Zigbee signal cannot receive interference from the unused WiFi subcarriers because there is no energy in them, ever.

Subtracting zero is always easy.