4.2 Code rate vs. background level

Using Eq. (14), a bound on the highest coding rate possible while operating at a given BER and $(M,\bar n_s,\bar n_b,T_s,$   detector$)$ was calculated. This code rate is the percentage of transmission symbols that carry information. The remainder of the transmissions carry redundancy used for coding. It can also be viewed as the fraction of the maximum data rate $\log_2M/(MT_s+T_d)$ that it is possible to achieve on the channel. Both the maximum code rate and the code rate needed by RS coding is shown in Fig.6.

Figure 6: Comparison of required RS code rate to maximum code rate implied by capacity while operating with $P_b = 10^{-6}$. Parameters: $\bar n_s=100$, $T_s=31.25$ns, and the SLiK APD detector. ($T_d$ is an irrelevant parameter.)