FTW 80211 OFDM frame encoder with USRP2 N210

Hi, I used Gnuradio and USRP2 on Ubuntu. (Ubuntu 12.04, Gnuradio 3.6,
USRP2 N210, UHD, Python 2.7)

I’m trying to use IEEE802.11a or IEEE802.11g with Gnuradio and USRP2.
So, I downloaded the file named “ftw_80211_ofdmtx” by
https://www.cgran.org/wiki/ftw80211ofdmtx”.

I rewrite “ftw_ofdm.py” and “ftw_ofdm_tx.py” with reference to
http://www.ruby-forum.com/topic/4031911#new”, because these files don’t
support newest USRP2(UHD) version.

However, it output the following Error when i tried “ftw_ofdm_tx.py”.

linux; GNU C++ version 4.6.3; Boost_104601;
UHD_003.004.003-228-ge5570d10

Traceback (most recent call last):
File “./ftw_ofdm_tx.py”, line 49, in
from ftw_ofdm import ftw_transmit_path
File “/home/…/src/examples/ftw_ofdm_py”, line 28 in
import ftw
File “/home/…/src/ftw/ftw.py”, line 26, in
_ftw = swif_import_helper()
File “/home/…/src/ftw/ftw.py”, line 18, in swig_iport_helper
import _ftw

ImportError : No module named _ftw

“ftw.py” is automatically made by “Makefile.swig.gen”
But, I can’t find module “_ftw.py” in other files or directory.
What’s the module named “_ftw” ?

Please tell me about this error.