The maximum bit rate that can be transmitted over a channel with bandwidth B is determined by Shannon C=B log(1+S/N)
Are there any techniques that could break this limit?
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2$\begingroup$ It's sorta like asking if there is a technique that can break the Conservation of Energy principle. $\endgroup$– robert bristow-johnsonMar 19, 2022 at 20:18
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No, but the capacity formula you mentioned assumes a very specific channel. Other channels may have larger capacities (see "faster than Nyquist signaling", for example in this question).
Also, nitpicking but this is important: the bit rate over a given channel is unbounded; you can transmit as fast as you want. The capacity is the limit at which you can transmit with vanishing probability of error.
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$\begingroup$ Some of the faster than nyquist (FTN) papers seem to imply that since the shannon capacity assumes the use of orthogonal sinc pulses, that FTN signaling will actually have a higher capacity. Perhaps this is just a misunderstanding on my part, but it seems to me the shannon capacity will always hold (for the AWGN channel w/ bandwidth B) and that FTN 'gains' are actually the result of re-gaining the BW thrown away in typical communication systems that use for example RRC filtering w/ excess BW. In other words - IF we could use nyquist pulses in the real world easily then we wouldn't need FTN. $\endgroup$ Mar 19, 2022 at 23:19
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1$\begingroup$ It is correct to say that FTN exploits the excess bandwidth; FTN is impossible with sinc pulses. However, note that the formula C = B log(1+SNR) is not the Shannon capacity -- it's the capacity of a very specific channel. It is possible to calculate the Shannon capacity of other channels, for example a channel with excess bandwidth when using a given pulse shape. There's a paper by Anderson that shows this. $\endgroup$– MBazMar 19, 2022 at 23:50