Code Detection in a CDMA-Based Common Channel

A CDMA-based common channel is a shared uplink channel that multiple users may send their event- specific CDMA codes to indicate their status. In such a channel, the base station may fail to detect a transmitted CDMA code due to the channel fading effect and the multiple access interference (MAI) resulting from the simultaneous transmission of the other CDMA codes. This paper presents system architecture to detect the transmitted CDMA codes in a CDMA-based common channel. A dynamic-threshold- setting method is presented to reduce the detection time and maximize the detection probability. A selective-retransmission method is further proposed to enhance the detection probability by exploring the time-diversity gain. Simulations results showed the proposed method may reduce the number of required radio resource units and achieve a low detection error probability than conventional methods. Hence, it could be a potential solution to reduce huge uplink singling overhead resulted from the simultaneous feedbacks from all multicast/broadcast subscribers.