MATLAB: Is the BER unreasonably high when I introduce a Multipath Rayleigh Fading Channel block into the Bluetooth Modulation and Frequency Hopping demo in Communications Blockset 4.2 (R2009a)

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I am experimenting with the Bluetooth Modulation and Frequency Hopping demol. I added a Multipath Rayleigh Fading Channel block into the demo, between the frequency hopping GFSK modulator block and the AWGN channel block. Upon simulating this system, the Bit Error Rates (BER) I obtain are unreasonably high (close to .5). I would like to understand the reason for this.

Best Answer

If you turn the Sample time colors on from the Format menu, you would notice that the Multipath Rayleigh Fading Channel block is at a different Sampling rate than the incoming signal. You will have to manually set the Sample time of this block to 1e-8, so that it matches with that of the incoming signal. The Bit Error Rates now are more reasonable. Note that this is a very high bandwidth channel (100MHz) and hence the model will be slow to initialize with a low doppler frequency. You may also get a high-interpolation rate warning.
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