Why 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)?

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.

Answer 1

[MathWorks Support Team]

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.