Can we break the Shannon capacity?

Can we break the Shannon capacity?

• I have a friend working in wireless communications research. He told me that we can transmit more than one symbol in a given slot using one frequency (of course we can decode them at the receiver). The technique as he said uses a new modulation scheme. Therefore if one transmitting node transmits to one receiving node over a wireless channel and using one antenna at each node, the technique can transmit two symbols at one slot over one frequency. I am not asking about this technique and I do not know whether it is correct or not but I want to know if one can do this or not? Is this even possible? Can the Shannon limit be broken? Can we prove the impossibility of such technique mathematically? Other thing I want to know, if this technique is correct what are the consequences? For example what would such technique imply for the famous open problem of the interference channel? Please cite references, if possible.

• Answer:

  No, we can't. What we can do, with better modulation, is approach the shannon limit more closely. Otherwise, if you need more bandwidth (in megabits), either increase the bandwidth (in (mega)Hertz), or increase the signal/lower the nose to get better SNR.