Re: [Discuss-gnuradio] why can't use iwconfig when I run the gr-ieee802-11

[zhan siyu]

Thanks for your reply. Let me explain what I 'm doing.

I have two B210s connected with two computers. I want to measure the throughput between the two computers over the usrp connection over gr-ieee802-11. But no matter how hard I try, like tuning the parameters and turning off my own wifi card and AP, I can only get 150K B/s, which should be around 300K B/s if my theoretical calculation is right.  There are no underrun or overrun errors. The throughput measurement tool I'm using is iperf, which is an application to measure the end to end throughput.

Could you give me some hints?

Best regards.

Siyu

2017-06-07 14:02 GMT+08:00 Bastian Bloessl <address@hidden>:

Hi,

On 06/07/2017 03:04 AM, zhan siyu wrote:

Thanks. I just wonder why. Because I meet some performance problem. I thought it maybe caused by my misconfiguration of the gr-ieee802-11 code. Now, it seems not.

I'm a bit confused why the fact that the transceiver is not configured through iwconfig ruled out any configuration issues, but great that all seems to be set up now.

However, theoretically,  as my current sample rate is 10M and BPSK. So the coding rate should be 10M/2 = 5M b/s. The throughtput should be around 5M/8 = 625K B/s. Assuming the 12% head cost, so the data throughput should be 625 * 88 % = 550K B/s.  But as my experiment shows, the throughput is only 150K B/s.

I'm new to the communication. Is my calculation right ?

BPSK 1/3 is 3Mbit/s gross at 10MHz. The overhead per packet has to be subtracted, i.e. the actual maximum rate depends on the frame size.

If it were right, then what might cause the gap?

Since you don't explain what you are doing, this is very hard to tell. You would reach this theoretical throughput only if you send frames back-to-back (which probably only works if you pregenerate the sample stream). But also a WiFi card will insert inter-frame space, so that the actual throughput will not match the theoretical maximum physical layer throughput.

Best,
Bastian

One more question, I didn't run the volk_profile. Does it matter?

Best regards.

Siyu


2017-06-07 4:23 GMT+08:00 Bastian Bloessl <address@hidden <mailto:address@hidden>>:

    Hi,

    On 06/06/2017 03:55 PM, zhan siyu wrote:

        Hi all,

        I just found I can't use the iwconfig tap0 rate 20M to setup the
        bandwidth of the tap0. The error message is :

        Error for wireless request "Set Bit Rate" (8B20) :
                   SET failed on device tap0 ; Operation not supported.

        But in their video , it can be set in this way. May I know how
        to solve it ?


    The WiFi transceiver is attached to the tun/tap interface, which is
    a virtual Ethernet device. This device doesn't support WiFi-specific
    configuration through iwconfig.

    If you wanted this level of integration, you would have to write a
    kernel module that attaches the transceiver to a virtual WiFi card.

    Some group already did that, but they didn't release the source code.

    Best,
    Bastian

--
Dipl.-Inform. Bastian Bloessl
CONNECT Center
Trinity College Dublin

GitHub/Twitter: @bastibl
https://www.bastibl.net/