Retransmissions versus FEC plus interleaving for real-time applications: Acomparison between CDPA and MC-TDMA cellular systems

The capacity of mobile cellular systems is mainly limited by cochannel inte rference. Commonly in multiple carrier-time division multiple access (MC-TD MA) systems, like the global system for mobile (GSM) communications, the in terference noise is first reduced by means of channel clustering and slow f requency hopping. The residual interference, characterized by a level varyi ng slot by slot, causes errors in burst which are spread with bit interleav ing and fought with correcting codes for random errors. With real-time serv ices like voice, no other error control technique, such as automatic repeat request (ARQ), is usually adopted. An alternative approach is given by cap ture division packet access (CDPA) where transmissions are spread in time a dopting a dynamic slot assignment (DSA), and errors are dealt with a retran smission mechanism, In this paper, we present a comparison of this two appr oaches, and using a simple theoretic capacity analysis, we justify the bett er performance of CDPA, Moreover, by the delay performance analysis, we pro ve that in spite of its retransmission mechanism, CDPA is effective also wi th delay constrained services.