A new slotted ALOHA based random access method for CDMA systems

This paper describes a new S-ALOHA based random access (RA) method for CDMA systems. The method consists of two principal stages: a slot (frame)-based RA by a mobile and the subsequent acknowledgment from a base station. It dispenses with a number of steps which characterise other CDMA RA procedures, namely, power ramp and power control. Furthermore, there exists no requirement for a busy-idle flag. The proposed method is capable of significantly reducing the required time for the RA stage at call set-up. It can also receive and process simultaneous multiple access attempts. Analytical and simulation results show that the system is capable of receiving simultaneous RA attempts with very high success rate, and small total average delay (including re-transmissions.) One case study shows that a traffic of 100 random accesses per second can be successfully processed with a probability of 90% first attempt success rate and with an average delay of only 6 msec using one matched filter.