Channel Capacity

Conclusions

This chapter presents asymptotically exact capacity bounds for the optical intensity channel with average optical power and bandwidth constraints in Gaussian noise. These results are complementary to previous work on Poisson photon counting channels, since we consider the case of high intensity optical channels in which the noise can be modelled as being Gaussian and signal independent. The derived capacity bounds demonstrate that optical intensity signalling schemes based on rectangular basis sets have significantly lower achievable maximum spectral efficiencies than bandwidth efficient techniques. In particular, significant rate gains can be obtained by using raised-QAM or prolate spheroidal wave function pulse set over rectangular PAM at high optical signal-to-noise ratios.

This chapter has addressed the use of spectrally efficient modulation to achieve high dimensional efficiency, however, the use of spatial dimensions are not considered. The following chapter considers the use of spatial dimensions to provide a degree of diversity at the receiver and proposes a novel wireless optical channel architecture, the pixelated wireless optical channel, in which spatial dimensions are exploited to yield gains in spectral efficiency.