[Discuss-gnuradio] OFDM Benchmark Change Modulation

[You Lizhao]

Hi all,

 

Recently I want to implement a OFDM based multi-rate system, and I am using benchmark_ofdm_tx/benchmark_ofdm_rx programs in ofdm directory. I know I can use unlock/lock mechnism to disconenct/connect the exising blocks to change modulation block, and it indeed works. However, I also notice that the difference between all modulation, i.e. BPSK, QPSK, QAM16, QAM64, is rotated_const paramter in gr.ofdm_mapper_bcv block. So I write a new block howto.ofdm_mapper_bcv which can change rotated_const  (d_constellation in gr_ofdm_mapper_bcv.h/.cc) with a defined function call. But it does not work. When I change BPSK to QPSK by altering rotated_const, I can receive nothing but TIMEOUT in QPSK demodulator. If I still use BPSK demodulator, it works in compromised performance with some packets failed to pass CRC check. Why does it happen, since I already change rotated_const? Is there any misunderstanding on this ofdm benchmark program?

 

Furthermore, I also find that if I use QAM16, it seems that the packet reception simuation is very bad, about 50% PRR or even lower. When using QAM64, PRR~0%, almost all packets failed CRC check. I think if I use channel coding, the situation will be better. I am wondering how to add channel coding block to existing architecture. Is there any possible examples?

 

Any comments are welcomed! Thank you very much!

 

Regards,

-Lizhao