multilevel coded modulation scheme is then c=分cm Design of multilevel codes: The essential point for the design of a MLC scheme is the assignment of code rates to the individual coding levels.In [Huber99]fives rules are introduce for rate design.For the capacity design rule,the individual rates are chosen to be equal to the capacities of the equivalent channels,i.e., Ro=Co,i=0,l,1-1 For the choice of FEC codes werful probabilistic coding methods such as turbo codes and LDPC codes are really necded only at the lower levels.At the higher levels.the channels become quite clean and the capacity C(AA,)approaches log(AA,).so that the desired redundancy approaches zero.For these levels,algebraic codes and decoding methods iate The state eof the art in multilevel coding is reviewed in Figures 5.10.4-5.106 depict the code rate design based on the capacity rue for 8-ASK and 8-PSK MLC schemes. -B-Co %0 Fig5.10.4采用8-ASK的MLC系统各层容量 1616 multilevel coded modulation scheme is then 1 ( ) 0 l i i C C − = = ∑ „ Design of multilevel codes: The essential point for the design of a MLC scheme is the assignment of code rates to the individual coding levels. In [Huber99], fives rules are introduced for rate design. For the capacity design rule, the individual rates are chosen to be equal to the capacities of the equivalent channels, i.e., () (), 0,1,., 1 i i Rc = Ci l = − For the choice of FEC codes, powerful probabilistic coding methods such as turbo codes and LDPC codes are really needed only at the lower levels. At the higher levels, the channels become quite clean and the capacity 1 ( /) C Λi i − Λ approaches 2 1 log ( / ) Λi i − Λ , so that the desired redundancy approaches zero. For these levels, algebraic codes and decoding methods may be more appropriate. The state of the art in multilevel coding is reviewed in [Wachsmann99]. Figures 5.10.4-5.10.6 depict the code rate design based on the capacity rule for 8-ASK and 8-PSK MLC schemes. -5 0 5 10 15 20 0 0.5 1 1.5 2 2.5 3 Es /N0 (dB) Capacity (bits/symbol) C0 C1 C2 C Fig. 5.10.4 采用 8-ASK 的 MLC 系统各层容量