This exercise applies basic capacity results to analyze the IS-856 system. You should use the parameters of IS-865 given in the text.
1. The table in the IS-865 example in the text gives the SINR thresholds for using the various rates. What would the thresholds have been if capacity-achieving codes were used? Are the codes used in IS-856 close to optimal? (You can assume that the interference plus noise is Gaussian and that the channel is time-invariant over the time-scale of the coding.)
2. At low rates, the coding is performed by a turbo code followed by a repetition code to reduce the complexity. How much is the sub- optimality of the IS-865 codes due to the repetition structure? In particular, at the lowest rate of 38.4 kbits/s, coded symbols are repeated 16 times. With only this constraint on the code, find the minimum SINR needed for reliable communication. Comparing this to the corresponding threshold calculated in part (1), can you conclude whether one loses a lot from the repetition?