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From: | edwin |
Subject: | Re: [Discuss-gnuradio] OFDM channel tap questions |
Date: | Thu, 11 Jan 2018 13:53:15 -0700 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 |
Hi Jeff, Thanks for the reply. What you said about the noise makes sense.
However, even if I turn the noise off, I still get the weired
taps: Offset: 2112 Source: n/a Key: ofdm_sync_chan_taps Value:
#[(0,0) (0,0) (0,0) (0,0) (0,0) (0,0) (35.5567,-53.2143)
(-6.27313,-63.6921) (-45.255,-45.255) (-63.6921,-6.27313)
(-53.2143,35.5567) (-18.5783,61.2445) (24.4919,59.1286)
(56.4432,30.1695) (62.7706,-12.4858) (40.6014,-49.4729)
(2.45706e-06,-64.0003) (-40.6014,-49.4729) (-62.7706,-12.4858)
(-56.4432,30.1695) (-24.4919,59.1286) (18.5783,61.2445)
(53.2143,35.5567) (6.36922,-0.627315) (4.52551,-4.52551)
(6.27312,-63.6921) (-3.55567,-5.32143) (-6.12445,-1.85783)
(-5.91286,2.44919) (-3.01695,5.64432) (1.24858,6.27706)
(4.94729,4.06014) (0,0) (4.94729,-4.06014) (1.24858,-6.27706)
(-3.01696,-5.64433) (-5.91286,-2.44919) (-6.12445,1.85783)
(-3.55567,5.32144) (6.27312,63.6921) (4.52551,4.52551)
(6.36922,0.627312) (5.32143,-3.55567) (1.85783,-6.12445)
(-2.44919,-5.91286) (-5.64433,-3.01696) (-6.27706,1.24858)
(-4.06014,4.94729) (-1.9985e-06,6.40003) (4.06014,4.94729)
(6.27706,1.24858) (5.64432,-3.01696) (2.44918,-5.91286)
(-18.5783,-61.2445) (-5.32143,-3.55567) (-6.36922,0.62731)
(-4.52551,4.52551) (-0.627314,6.36921) (3.55567,5.32143) (0,0)
(0,0) (0,0) (0,0) (0,0)]
The piece of code you posted: for (int i = loop_start; i < loop_end; i++) { if ((d_ref_sym[i-carr_offset] != gr_complex(0, 0))) { taps[i-carr_offset] = sym[i] / d_ref_sym[i-carr_offset]; } } I believe it comes from the ofdm_chanest_vcvc_impl.cc, doesn't
it? According to my understanding, it is calculating the channel
taps by dividing the received symbol with the sync symbols, which
are known. If the channel is perfect and there is no noise, the
received symbols should be exactly the same as the sync symbols.
The channel taps should be 1.
Regards, Edwin |
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