Performance Evaluation of the Enhanced Access Channel in cdma2000

The existing access scheme used in the Reverse Access Channel (R-ACH) in IS95A/B is based on a Slotted Aloha protocol. The mobile sends a probe and waits for an acknowledgement from the base station. If no acknowledgement is received, the mobile increases power and tries again. This type of access scheme requires a large probe power to guarantee detection and presents high delays. Data applications require a connectionless packet service capability and a low latency access protocol. The bursty nature of data communications requires many more transitions from idle state to active state than voice communications. In order to improve call set-up reliability, the cdma2000 proposal introduces a new physical channel called Reverse Enhanced Access Channel. This channel is used not only to originate a call or to respond to a page message but also to send short messages to the base station, without the need to set-up a traffic channel. The access protocol used in the Reversed Enhanced Access Channel is studied here. The protocol was implemented using the OPNET simulator, and access delay and comparative performance results were obtained.