The bandwidth and noise trade-off

Having briefly considered the question of 'how fast can we send data', it is immediately apparent that there are two fundamental factors affecting the information transfer rate on a channel, namely:

  • The maximum possible detectable rate of change of waveform or symbol state

– The bandwidth of the channel (and any bandwidth limits imposed by the transmitting and receiving devices) will determine how quickly the signalling states on the channel can be changed.

  • The ability to resolve any number of discrete symbol states

– The level of noise in the channel will impose an upper limit on the number of different unique symbol states that can be correctly resolved (decoded) at a receiver.

– The degree of distortion introduced by the channel will also limit the number and rate of change of symbol states that can be accommodated with acceptable performance.

So, if we had a channel with infinite bandwidth, or no noise and distortion, it would be possible to send the 1000000 bits of information 'instantaneously' – well, at the speed of light anyway.