In this paper, we propose an improved CDMA/PRMA protocol named CDMA/CAC (Code Assignment Control). In the proposed protocol, each terminal can be assigned spreading code by simple control before packet transmission. We introduce the permission probability for code request. The permission probability for code request restricts the number of terminals requesting code in order to avoid the collision of request signal adaptively to traffic load. In the proposed protocol with enhanced mode, the voice terminals have priority in initial access by setting the permission probability to 1. Also in this protocol, the data terminals can transmit packets continuously if necessary. We carry out the performance evaluation of the protocols by computer simulation and confirm their validity.

CDMA is considered a suitable access control for wireless multimedia communication systems. In this paper, we present an access scheme for packet-typed wireless networks, called PRMA/URN (Packet Reservation Multiple Access/URN) for the CDMA environment. This protocol combines URN algorithm with PRMA, instead of slotted-ALOHA. Also, we introduce enhanced access control into PRMA/URN for effective transmission of multimedia information, i.e. voice and data information. The enhanced access control has two characteristics. First, voice mobile terminals have priority in the initial access. Second, data mobile terminals can transmit packets continuously if necessary. We carry out the performance comparisons for CDMA environments between PRMA, PRMA/URN and PRMA/URN with enhanced access control, and show numerically the effectiveness of PRMA/URN with enhanced access control.