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The theory of noncoherent communications was premised on the use of orthogonal multi-pulse modulation such as frequency shift keying. The main drawback of this modulation scheme has been its poor spectral efficiency (rate/bandwidth).
In FSK (if implemented as MSK) the difference between the higher and lower frequency is identical to half the bit rate. Consequently, the waveforms used to represent a 0 and a 1 bit differ by exactly half a carrier period.
A modulation index of 0.25 is the smallest FSK modulation index that can be chosen such that the waveforms for 0 and 1 are still orthogonal.
If you are thinking of implementing a new system, rather consider the more general non-orthogonal multi-pulse modulation (NMM) techniques which with the right signal sets can provide much more bandwidth that its orthogonal counterparts.
The theory of noncoherent communications was premised on the use of orthogonal multi-pulse modulation such as frequency shift keying. The main drawback of this modulation scheme has been its poor spectral efficiency (rate/bandwidth).
In FSK (if implemented as MSK) the difference between the higher and lower frequency is identical to half the bit rate. Consequently, the waveforms used to represent a 0 and a 1 bit differ by exactly half a carrier period.
A modulation index of 0.25 is the smallest FSK modulation index that can be chosen such that the waveforms for 0 and 1 are still orthogonal.
If you are thinking of implementing a new system, rather consider the more general non-orthogonal multi-pulse modulation (NMM) techniques which with the right signal sets can provide much more bandwidth that its orthogonal counterparts.
Thank you for replying. Actually, I am reading the literature on underwater acoustic communication, and it is said that coherent communication is more favorable in underwater since the channel bandwidth is severely limited.
I am curious, what is the performance loss of NMM compared to the coherent counterpart?
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