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Re: [Discuss-gnuradio] OFDM cyclic prefix

From: Ron Economos
Subject: Re: [Discuss-gnuradio] OFDM cyclic prefix
Date: Sat, 13 Apr 2019 15:46:52 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

It's telling you there's a mismatch in the vector size (based on the FFT length) between the FFT block and the Cyclic Prefixer block. It appears you have the FFT block set to 512/8 = 64 and the Cyclic Prefixer block set to 8/8 = 1.

Unless you're just writing this block as an exercise, if you set the rolloff to 0 in the built-in Cyclic Prefixer block, the rolloff is disabled completely.


On 4/13/19 14:27, Simran Kaur wrote:
Hi Team,
I am trying to make own cyclic prefix block in C++ in GNU Radio(removing roll-off part and keeping all other parameters same). After connecting my cyclic_prefix block to the already present FFT block in tx_ofdm.grc, i am getting the following error:

Executing: /usr/bin/python2 -u /home/labuser/workarea-gnuradio/gnuradio/gr-digital/examples/ofdm/tx_ofdm.py

Traceback (most recent call last):
  File "/home/labuser/workarea-gnuradio/gnuradio/gr-digital/examples/ofdm/tx_ofdm.py", line 352, in <module>
  File "/home/labuser/workarea-gnuradio/gnuradio/gr-digital/examples/ofdm/tx_ofdm.py", line 340, in main
    tb = top_block_cls()
  File "/home/labuser/workarea-gnuradio/gnuradio/gr-digital/examples/ofdm/tx_ofdm.py", line 239, in __init__
    self.connect((self.fft_vxx_0, 0), (self.cyclicprefix_CP_cc_0, 0))
  File "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/hier_block2.py", line 47, in wrapped
    func(self, src, src_port, dst, dst_port)
  File "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/hier_block2.py", line 110, in connect
  File "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/runtime_swig.py", line 5334, in primitive_connect
    return _runtime_swig.top_block_sptr_primitive_connect(self, *args)
ValueError: itemsize mismatch: fft_vcc_fftw0:0 using 512, CP_cc0:0 using 8

NOTE: CP_cc is the block name that i gave when creating my own cyclic_prefix block.
Can anyone help with your suggestions?

Simran Kaur

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