My question is related to the performance of 2-FSK modulation scheme against M-FSK (M > 2). From the SNR vs BER curve it seems that as the number of tones (frequencies) increases the BER decrease for the same SNR compared to 2-FSK(pics attached). (I assume maintaining the same symbol duration)
As the number of tones increases the bandwidth increases but i can't figure out why the performance of MFSK also increases. At first glance i would say that the resilience to the noise should be the same as the 2-FSK.
Which is the benefit of using 2-FSK instead of M-FSK (M>2) given a fixed available bandwidth?