A high-performance RACH detection scheme for random access overload in LTE-Advanced

The overload of Random Access Channel (RACH) has been always considered as one of the largest obstacles to accommodate massive Machine-to-Machine (M2M) devices. While several congestion control mechanisms have been proposed to alleviate the RACH overload, increasing the number of Random Access (RA) slots and/or RACH preamble signatures is considered as an essential solution to enlarge the RACH capacity. However, the amount of RA slots directly affects the uplink data capacity and the orthogonality between preambles deteriorates along with the steep rise of the preamble usage number (i.e., simultaneous access from M2M devices after a wide area blackout), which results in heavy interference and performance degradation at the preamble detector. In order to cope with the issue, an inter-user interference cancellation (IUIC) scheme with a low latency Parallel Interference Cancellation (PIC) architecture is proposed to guarantee the preamble detection performance in large-preamble-number scenarios. The simulation results show that the proposed scheme significantly increases the supported preamble number over the conventional matched-filter based scheme while providing satisfactory preamble detection performance. Particularly, given a target miss detection rate (MDR) of 1%, the supported preamble number increases more than 5-fold by applying IUIC.