Re: [Discuss-gnuradio] IEEE 802.11 a/g/p Transceiver module - Making changes in WiFi PHY Hier Block

[Qurat-Ul-Ann Akbar]

How is a particular polarity picked for the pilot tones in each symbol with 52 subcarriers in GNU Radio? I can see the list in the OFDM Carrier Allocator block but where is this exactly happening in the code?

On Mon, Mar 20, 2017 at 3:37 PM, Bastian Bloessl <address@hidden> wrote:

Hi,

On 03/20/2017 09:17 PM, Qurat-Ul-Ann Akbar wrote:
> Hi,
>
> Thank you. I got it! I have another question. In the OFDM Carrier
> Allocator block, there are 127 values for pilot symbols each of them
> either (1,1,1,-1) or (-1,-1,-1,1). The pilot frequencies are
> (-27,-7,7,21) according to IEEE 802.11 standard. But I do not understand
> why are there 127 symbol values. Can you kindly explain that ?

The four values indicate the four pilot symbols (on subcarriers -21, -7,
7, 21). With 802.11, the pilots change polarity based on a predefined
sequence (of length 127). It is in this exact format also in the
standard (Section 18.3.5.10 of the 2012 version).

Best,
Bastian



>
> On Mon, Mar 20, 2017 at 12:09 PM, Bastian Bloessl <address@hidden
> <mailto:address@hidden>> wrote:
>
>     Hi,
>
>
>     > On 20 Mar 2017, at 17:50, Qurat-Ul-Ann Akbar <address@hiddennorthwestern.edu

>     <mailto:address@hiddennorthwestern.edu>> wrote:
>     >
>     > If I want to make changes in the PHY hierarchical block, can I just make changes in the grc file available in the examples folder and then recompile ? Because I cant file a .cc file in the lib folder in IEEE_802.11 module and the source code for most blocks is in there.
>     >
>
>     I’m afraid I don’t get the question, but if you don’t see any .cc
>     files in the lib folder, you might want to clone the repository
>     again, because actually there are some
>
>     https://github.com/bastibl/gr-ieee802-11/tree/next/lib
>     <https://github.com/bastibl/gr-ieee802-11/tree/next/lib>
>
>     If you only change the flow graph in GRC, you don’t have to
>     recompile the module (i.e., recompile c++ code). Just click on the
>     “generate” button (or press F5) this will rebuild the PHY. Then the
>     other flow graphs will automatically use the new version of the PHY.
>
>     Best,
>     Bastian
>
>