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[Discuss-gnuradio] Try to improve E100's performance at high sample rate

From: ziyang
Subject: [Discuss-gnuradio] Try to improve E100's performance at high sample rate
Date: Fri, 13 Jan 2012 18:19:42 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110419 Thunderbird/3.1.9

Dear all,

I have been trying to transmit data between usrp e100 (with RFX2400 daughter board) and a non-usrp device, which has a fixed 4M sample rate. On e100 side (running in half duplex mode), although data from the uhd_source will go through a gr.pwr_squelch_cc block before being demodulated, the device will still continuously overflow at this sample rate, and judging from the output of the packet_sink, only less than half of the data is correctly demodulated.

To reduce the computation load of the processor, I tried two methods:
1) modify the gr.quadrature_demod_cf block, replace some multiplication operations with volk-based operations (gr.multiply and gr.multiply_const modules in gr_blocks); 2) use complex_int16 type instead of complex_float32 at uhd interfaces and modulation / demodulation blocks.

But I got unexpected results after the changes. If I adopt method 1), the amount of correctly demodulated data is roughly the same as when using the original demodulation block. And for method 2), the result is even worse - less data is correctly demodulated.

Could someone please tell me if I did something wrong, or there are other solutions to this overflow-at-high-sample-rate problem?

On e100, I burned the latest console file system, use UHD_003.004.000-6795022, and Josh's next branch of GNU radio,
uhd setup: center frequency 2.416 GHz, sample rate 4M.

BTW, it took almost twice the amount of time to build both uhd and GNU radio after burning the latest console file system, and the initialization process of uhd (when device information is printed out) took a lot longer time than before as well. But what I concerned more is that much fewer packets could be received, compared with another e100 which has the same flow graph setup but installed previous versions of tools: file system, UHD_003.004.000-1a25e48, GNU radio 3.5.0. Could it be caused by some hardware problems? I will greatly appreciate it if someone could give me a hint on this.

Thanks in advance,


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