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#1 2016-Aug-29 11:07:05

sbock
Member
Registered: 2016-Aug-29
Posts: 3

OFDM Signal field

Hello,
I am trying to parse OFDM packets with the output of the "Detect & Decode" block in the 802.11 Reference Design v1.5.3.
Therefore I used every available tx_output in the rx_sigs folder for the simulation.
When analysing the scope of the simulation with wlan_tx_NONHT_MCS0_52B.mat as the input file, the first byte has the value 139.
In binary representation, this is equal to 1000 1011.
After the IEEE 802.11-2012 standard, the first 4 bits are not a valid.

I tried this with all three example inputs, but all failed to match a valid Signal field in some sort of way.
Even using a test file created by myself with the tx simulation failed.

Do I miss something, or am I looking at the wrong bytes?

Thank you very much,
Sebastian

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#2 2016-Aug-29 12:05:51

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

Re: OFDM Signal field

There's an endian swap between the standard's bit order and the MATLAB bit order. In that example the 4-bit RATE field has value 1101 (6 Mbps = BSPK 1/2 rate code) using the standard's bit order.

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#3 2016-Aug-30 12:18:56

sbock
Member
Registered: 2016-Aug-29
Posts: 3

Re: OFDM Signal field

Thank you very much for your quick reply.
With this information, everything works as expected.

Does this mean I have to implement a Matlab version and a real world version of my VHDL code because of number representation?

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#4 2016-Aug-30 22:19:56

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

Re: OFDM Signal field

Does this mean I have to implement a Matlab version and a real world version of my VHDL code because of number representation?

I'm not sure what you mean. If you're using System Generator to design an FPGA core the Sysgen model directly represents the HDL. The Sysgen simulation is bit and cycle accurate to the final HDL. You can design your HDL with whatever endianness you choose. Our PHY models use the 802.11 standard's bit order where required and implement bit-order swapping where necessary to adapt the C code (where 0x1 means LSB) to the PHY logic.

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#5 2016-Sep-02 07:23:18

sbock
Member
Registered: 2016-Aug-29
Posts: 3

Re: OFDM Signal field

Okay, this clarifies a lot .

Thank you for help!
Sebastian

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