Length tag key in ofdm_channel_allocator

GNU Radio
#1

hi,

i am trying to use the flowgraph “Core elements of an OFDM transmitter”
in
the ofdm documentation which is there at Gnuradio-3.7 API. i got the
following error.

FATAL: Missing a required length tag on port 0 at item #0
thread[thread-per-block[1]: <block ofdm_carrier_allocator_cvc (14)>]:
Missing length tag.

how to overcome this…
what to mention in length tag key in ofdm channel allocator… by default
we
have “packet_len” in that field.

thanks,
lingeswar