# BER calculation - GMSK Demod block **URL:** \ **Category:** GNU Radio\ **Created:** [March 9, 2020, 9:22pm UTC](https://www.ruby-forum.com/t/ber-calculation-gmsk-demod-block/258053 "2020-03-09T21:22:30Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![Artur1988](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/3d9bf3/32.png) [@Artur1988](https://www.ruby-forum.com/u/Artur1988)\ **Post date:** [March 9, 2020, 9:22pm UTC](https://www.ruby-forum.com/t/ber-calculation-gmsk-demod-block/258053/1 "2020-03-09T21:22:30Z")
Hello, I am simulating a simple GMSK modulation/demodulation process, without any channel model, in order to evaluate the BER under normal conditions and with noise. I would like to have your opinion about the way I calculate the BER: is it correct? Is there a better way to do it? Here a brief description of the problem: I created the following input binary sequence: 1110011100 as a .bin file and I loaded it in the File Source block. Then, I fed the GMSK Mod block with this binary sequence, I added noise to it and then I sent the resulting signal to a GMSK Demod unit. Finally, I saved the output sequence in a .bin file by means of File Sink block, as summarized in the following screen capture: ![forum_1](https://www.ruby-forum.com/uploads/default/original/2X/e/e7820cfbd2c4ca2335ca5aeb764fa74a25f888e3.jpeg) Apparently, the GMSK Demod block creates 8-bit packets for each input bit, by allocating them in the LSB position. In this case, instead of calculating the BER, I am calculating the PER (Packet Error Rate), by comparing the 0’s with 00000000 and 1’s with 00000001. When I add noise to the model, the output sequence is modified (as expected). In this case, I am proceeding with the same methodology for the PER calculation so every time a non-zero bit appears between the 1st and 7th position of a byte (ex: 01000000), I suppose this is caused by noise. Does my analysis make sense? Is there a more practical or correct way of evaluating the BER/PER? Thanks. Best regards, Artur