Re: [Discuss-gnuradio] OFDM cyclic prefix

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.

Ron

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>

    main()

  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

    self.primitive_connect(*args)

  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?

Thanks,

Simran Kaur

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