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#1 2020-May-31 07:23:49

Lavender
Member
Registered: 2020-Apr-07
Posts: 20

why channel 6 can receive the channel 1 signal?

When I use warp v3 to do the experiment, the sender is set to channel 1 and the receiver is set to channel 6, but on the channel 6 , it  can receive the channel 1 signal, I wonder why it can be received.
The center frequency of channel 1 is 2.412G, and the center frequency of channel 6 is 2.437, which is theoretically unacceptable.

    wl_interfaceCmd(node_tx, TX_RF_ALL, 'channel', 2.4, 1);
    wl_interfaceCmd(node_rx, RX_RF_ALL, 'channel', 2.4, 6);


Thanks for your answer!

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#2 2020-Jun-01 08:45:04

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 5159

Re: why channel 6 can receive the channel 1 signal?

Are you certain the nodes are tuned to different channels? Do you observe a stronger received signal if you change your code so both nodes are tuned to the same channel? How much attenuation is present between the Tx and Rx nodes? For very low attenuation it is possible for off-band signals to be captured by the receiver, due to aliasing and imperfect filter responses.

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#3 2020-Jun-02 08:28:22

Lavender
Member
Registered: 2020-Apr-07
Posts: 20

Re: why channel 6 can receive the channel 1 signal?

murphpo wrote:

Are you certain the nodes are tuned to different channels? Do you observe a stronger received signal if you change your code so both nodes are tuned to the same channel? How much attenuation is present between the Tx and Rx nodes? For very low attenuation it is possible for off-band signals to be captured by the receiver, due to aliasing and imperfect filter responses.

Thank you very much for your reply ^_^

1. I am sure that the node has been tuned to different channels:
     wl_interfaceCmd (node_tx, TX_RF_ALL,'channel', 2.4, 1);
     wl_interfaceCmd (node_rx, RX_RF_ALL,'channel', 2.4, 6);
2. If both TX and RX are tuned to channel 1, a stronger received signal will be observed.
3. The distance between TX and RX is 10m.Is it because of the short distancethe and small attenuation, causing channel 6 to receive an out-of-band signal.

So, can this phenomenon be solved? If we do not want to capture the out-of-band signal on channel 6 or reduce the energy of the out-of-band signal, do we need to make some hardware modifications to the warp; or design a low-pass filter at TX and so on.

Thank you.

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#4 2020-Jun-02 08:39:45

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 5159

Re: why channel 6 can receive the channel 1 signal?

You will need to investigate further. All filters and mixers are imperfect - with low enough attenuation / high enough gain, observing spectral repeats is expected. I would guess you're observing a harmonic of your transmitted signal, possibly due to saturation in the Tx device or from aliasing.

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#5 2020-Jun-06 13:40:33

Lavender
Member
Registered: 2020-Apr-07
Posts: 20

Re: why channel 6 can receive the channel 1 signal?

I see. Thank you very much for your reply. This harmonic will have a certain impact on my experiment. I will study it based on your analysis.

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#6 2020-Jun-07 01:31:34

Lavender
Member
Registered: 2020-Apr-07
Posts: 20

Re: why channel 6 can receive the channel 1 signal?

murphpo wrote:

You will need to investigate further. All filters and mixers are imperfect - with low enough attenuation / high enough gain, observing spectral repeats is expected. I would guess you're observing a harmonic of your transmitted signal, possibly due to saturation in the Tx device or from aliasing.

hi, I have another question to consult you.

In the example code wl_example_siso_ofdm_txrx.m on the official website, we can see that the indices of pilot subcarriers and data subcarriers are shown below. What should I do when I need to send an empty subcarrier, such as #38 subcarrier.
(In other words, out of 64 subcarriers, only the subcarrier with index 38 is sent, and the remaining subcarriers are not sent instead of the data being 0.)

SC_IND_PILOTS=[8 22 44 58];% Pilot subcarrier indices
SC_IND_DATA=[2:7 9:21 23:27 39:43 45:57 59:64];% Data subcarrier indices

I tried setting SC_IND_DATA=[38], but found that this method actually sent 64 subcarriers, the data subcarrier is 0.

Thanks.

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