8.5 Higher-Order Signal Modulation Formats
355
Fig. 8.23 The four-bit data points for a square 16QAM format
QAM formats include 32QAM, 64QAM, 128QAM, and 256QAM. The 256QAM
format can achieve a high spectral efficiency of up to 8 b/s/Hz.
8.6 Summary
The design of an optical link involves many interrelated operating characteristics of
the fiber, source, photodetector, and other components in the link. Two design analyses usually are carried out to ensure that the desired system performance can be met.
These are the link power budget and the system rise-time analysis. In the link power
budget analysis one first determines the power margin between the optical transmitter
output and the minimum receiver sensitivity needed to establish a specified BER.
This margin then can be allocated to link component losses and any additional power
margins needed to compensate for unexpected component degradations.
Then the designer makes a system rise-time analysis to ensure that the dispersion limit of the link has not been exceeded. The four basic factors that may limit
355
Fig. 8.23 The four-bit data points for a square 16QAM format
QAM formats include 32QAM, 64QAM, 128QAM, and 256QAM. The 256QAM
format can achieve a high spectral efficiency of up to 8 b/s/Hz.
8.6 Summary
The design of an optical link involves many interrelated operating characteristics of
the fiber, source, photodetector, and other components in the link. Two design analyses usually are carried out to ensure that the desired system performance can be met.
These are the link power budget and the system rise-time analysis. In the link power
budget analysis one first determines the power margin between the optical transmitter
output and the minimum receiver sensitivity needed to establish a specified BER.
This margin then can be allocated to link component losses and any additional power
margins needed to compensate for unexpected component degradations.
Then the designer makes a system rise-time analysis to ensure that the dispersion limit of the link has not been exceeded. The four basic factors that may limit