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# 6.6 Relative performance of multi-level bandpass modulation formats

## Symbol error curves for M-ary formats

#### Shown here are the BER curves for the various families of M-ary systems discussed in this chapter. The QAM formats evidently get us closest to the Shannon capacity limit when we are looking for high spectral efficiency. Care should be taken when comparing these systems in terms of their bit error probability as this will depend on whether Gray coding has been used and how many errors are restricted to adjacent Gray-coded symbols only. Assuming that only one bit error occurs per symbol, the bit error rate = symbol error rate / k (where k is the number of bits per symbol). Further information on the practical design and performance of multi-level modulation formats is available on the Wireless Systems International website. |