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[Discuss-gnuradio] GLFSR transmission with BPSK Mod

From: Nazmul Islam
Subject: [Discuss-gnuradio] GLFSR transmission with BPSK Mod
Date: Mon, 28 May 2012 13:39:34 -0400


I am trying to transmit a GLFSR sequence using bpsk (non-differential modulation). I am using gnuradio-companion to construct the blocks. My transmit path is is simply the following: GLFSR source -> BPSK Mod (Non-differential) -> USRP Sink. I am currently simulating the output of the GLFSR source and BPSK Mod source before connecting the blocks to USRP. I have attached the screenshot of the blocks and the corresponding grc file with the email.

I have two questions:

1. How can I control the bit transmission rate of the GLFSR source?  I want to transmit the GLFSR source at 3.5 Mbits/sec (500 kilo sequence per second with degree 3). The GLFSR block does not have any option for transmission rate. The UHD USRP sink has a option of sample rate. But I don't see how that will control the bit transmission rate of the GLFSR source.

2. I can't understand the relation between the output of the GLFSR source with that of the PSK Mod. The GLFSR source is producing an expected output: 1110110..(repeat). But the BPSK Mod output is producing strange output in the following two ways:

a) The length of the PSK Mod output is almost 8 times with respect to that of the GLFSR output. I am using 2 samples/symbol. Why is the PSK Mod creating so many output?

b) The PSK Mod is producing output with different complex values, e.g., 1.2, 0.95, 1.05, -0.2, -1.2, etc. I have 2 samples/symbol in the PSK mod block. Since the PSK Mod output length is not twice the output length of the GLSR block, how can I find which two samples correspond to which GLFSR bit?

Feedback on any of these questions and the overall GRC block will be highly appreciated.



Muhammad Nazmul Islam

Graduate Student
Electrical & Computer Engineering
Wireless Information & Networking Laboratory
Rutgers, USA.

Attachment: GLFSR_transmission.png
Description: PNG image

Attachment: sample_galois_pn.grc
Description: application/gnuradio-grc

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