16-QAM,64-QAM Modulation

By Vikas Bagwe -

16-QAM,64-QAM

  • The number before QAM (for example 16QAM) refers directly to the number of decision points in the constellation. Meaning, 256QAM has 192 more decision points than 64QAM. The number before QAM is also always a power of two. (EG. 2^6=64QAM) 
  • There are several trade offs to this: 
  • The more Decision points, the more throughput per channel. 
  • The more Decision points, the more susceptible the channel is to noise (as the decision boundaries get smaller to accommodate more decision points, it becomes harder to distinguish which boundary the point was intended to lie in). 
  • More Decision points=More Bandwidth=Higher susceptibility to noise or poor signal (the same applies inversely as well). 
  • At best, it'll enable either to: 
  • Deliver the same number of customers incrementally faster speeds.-or- 
  • Deliver a larger number of customers the same speeds as before.

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