Return Link RACH Code Acquisition Based on Combining Techniques for Future S-DMB Systems

This paper tackles the problem of code synchronization for the return link random access channel (RACH) in future satellite-digital mobile broadcasting (S-DMB) systems. The design of the code acquisition procedure is based on the selection of a novel preamble structure, and introduces combining techniques to allow compatibility with the terrestrial W-CDMA standard. To this aim, the preamble is composed by the juxtaposition of N terrestrial preamble words, where N has to be optimized to meet the performance target limiting at most the overhead. Both hard and soft combining techniques are investigated, yielding different performance/complexity/overhead trade-offs. Numerical results show that in-spec performance can be achieved through soft combining of two terrestrial preambles, if a smart detector structure is employed, introducing only limited hardware modifications in the receiver with respect to the terrestrial case. On the other hand, hard combining needs to extend the repetition to four terrestrial preambles, but requires only software modifications in the receiver