Enabling the co-existence of contention based random access (CBRA) and contention free random access (CFRA) is an effective technique to improve network flexibility and usage of network resources. In some embodiments, all available communication opportunities in the CBRA schedule and all available communication opportunities in the CFRA schedule may be used to generate a final schedule Different subsets of preamble indices are employed to ensure that both CBRA and CFRA communications can co-exist. In other embodiments, all available communication opportunities in the CBRA schedule, but only the dedicated communication opportunities in the CFRA schedule, may be used to generate a final schedule. As a result, a smaller subset of preamble indices is used.