changes for MSK to GMSK in MATLAB example

Hi, In this example, what all changes we need to make for recovering a GMSK signal. openExample('comm/MSKSignalRecoveryInSimulinkExample')

Im getting a high BER value. despite changing the GMSK modulator and demodulator, and GMSK tsignal timing recovery block.

Answer 1

[akshatsood]

Dear Rezim,

I understand that you are keen to convet the MSK Signal Recovery example to be compatible with GMSK. While changing the "GMSK Modulator", "GMSK Demodulator" and "Timing Recovery" block are essential steps, there may be several other adjustments needed to achieve successful signal recovery.

To provide more specific advice, I would appreciate it if you could share your updated model.

Furthermore, if you are interested in comparing GMSK modulation with "MSK Type A" and "MSK Type B" modulations, I recommend referring to the following File Exchange submission:

https://www.mathworks.com/matlabcentral/fileexchange/26083-gmsk_msk

This submission models these three modulation schemes and provides a comparison of their BER, Eye Diagrams and Constellation Diagrams. Analyzing the model accopanied with this submission could be beneficial in identifying the correct locations and parameters for modeling signal recovery in GMSK.

I hope this helps.

[Rezim]

Hi @akshatsood

Although this fileexchange model use basic blocks, the BER obtained is too large to compare the difference. around 0.5 is what the BER in case of GMSK.

[akshatsood]

Dear @Rezim

Please clarify whether the submission itself contains this large difference, or if you attempted to model GMSK in your own model and are observing such a significant discrepancy?

[Rezim]

Hi @akshatsood submission it self contains this difference.

[akshatsood]

Dear @Rezim,

I understand that since the submission dates back to 2009 and has not been updated since, the author would be best equipped to address this discrepancy. You can contact the author directly using the "Message" button on their profile page to highlight this significant difference:

https://in.mathworks.com/matlabcentral/profile/authors/1408272

Based on my understanding, here are some changes you might need to consider:

Replace Modulator and Demodulator Blocks: Substitute the existing blocks with ones compatible with GMSK.

Include Gaussian Filtering: You may need to specify the bandwidth-time product (BT) parameter, which influences the Gaussian filter's bandwidth. A typical "BT" value is 0.3.

Adjust Timing Recovery: You need to reconfigure the MSK-Type Signal Timing Recovery block to accommodate GMSK signals. Ensure that the timing recovery mechanism aligns with GMSK's characteristics.

Carrier Synchronization: The settings of the Carrier Synchronizer block might require adjustments to handle GMSK's distinct phase characteristics. Verify that block manages GMSK phase transitions.

Reconfigure the Channel Model: If required, modify the Channel Model subsystem to reflect GMSK's unique spectral characteristics. This involve changes to noise levels, frequency offsets or phase noise.