System for providing stream based and packet based services

DETAILED DESCRIPTION One aspect of the invention provides a novel common packet data channel (CPDC) system structure and method to efficiently provide variable-rate packet data services in a CDMA system.
This system uses CPDC channels to serve packet data calls for a plurality of packet data users within a cell or sector.
CPDC channels are defined for forward link (base station-to-terminal) communications and reverse link (terminal-to-base station) communications.
Preferably, on the forward link (FL), an ATM-type multiplexing scheme is employed on a CPDC channel, while a spread ALOHA-type random access scheme is used on the reverse link (RL).
Advantageously, the overhead and delays due to call setup and channel assignment in a conventional circuit-switched system is reduced for packets in this system.
Overhead of idle transmissions for inactive terminals is also reduced.
The preferred embodiment allows ATM cells to be directly transmitted over the air interface.
One advantage of CDMA systems compared to other types of digital cellular systems is that several terminals can communicate using the same frequency simultaneously.
It is well known for CDMA systems that several virtual channels can be used by having each communication unit code their transmissions with a distinct spreading code sequence.
Furthermore, only a communication unit with the appropriate code can decode such a coded message.
This provides security against eavesdropping and also provides a multiple access scheme.
These aspects of CDMA are well known in the art.
It is also known that several communication units can communicate using the same spreading code as long as they are offset in time.
This is currently utilized in the access channel, which is shared by a plurality of terminals in a cell/sector.
Thus if, for example, three terminals send requests on the access channel using the same spreading sequence, the first received request can be successfully decoded, even if they overlap, provided they are offset in time.
Of course in conventional systems, the subsequent requests are discarded