Multiuser access capacity of packet switched CDMA systems

We consider packet DS-CDMA systems with a connectionless architecture where no dedicated connection is kept between users and the system. Users have to access the system using the same signature sequence and have to be acquired each time they need to send packets. Due to the asynchronous nature of the system, multiple users can be accommodated even when a single signature is available. However, we observe that even under optimistic assumptions, the capacity of such a system is less than that of G orthogonal ALOHA channels that can be accommodated in the same bandwidth of this CDMA system with processing gain G.