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I was going through a Bluetooth LE tutorial in which it was mentioned that by increasing the modulation index of GFSK scheme, the peak power was reduced & range & robustness was enhanced over Bluetooth Classic. I would like to know how has this been achieved?

Thanks ,

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2 Answers 2

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Consider case-a with modulation index 0.32 and case-b with moduation index 0.5

In case-a, each bit contributes a phase change of +/-0.32 pi based on the bit being +/-1 and +/-0.5pi in case-b

Since the phase deviation is more in case b (pi) compared to case a (0.64pi) more rapid changes in the waveform are expected and so contribute to higher frequencies in frequency domain.

When same power is used in both cases, the peak power is less in case-b compared to case-a as the contribution of higher frequencies (away from DC) are more in case b compared to case a.

As frequency deviation is also more in case-b compared to case-a, distance between symbols is more in case-b. So case-b can have more range compare to case-a.

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With more modulation, you get wider separation of the datapoints (there are 4, if I recall, in the GSM mag-phase constellation) and thus higher SNR and lower BER. However, at some point you violate the conditions for MSK Minimum Shift Keying, and your output waveform no longer is constant amplitude.

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