Inter-user interference cancellation improvements for LTE-Advanced random access detector using dynamic thresholding mechanism

In LTE-Advanced, a device which tries to connect to a basestation randomly selects one signature from predefined 64 signatures as a device ID, known as a preamble, and transmits it over Random Access Channel (RACH). Those preambles collide to each other when multiple devices transmit the same preamble over the same random access (RA) slot, which leads to a deterioration of the preamble detection rate at the basestation. This issue is often referred to as RACH overload. An essential solution can be derived by increasing the preamble number but it causes noticeable inter-user interference (IUI). This paper studies an improvement technique to the proposed IUI cancellation (IUIC) scheme by introducing a simple thresholding mechanism to ameliorate the robustness of channel estimation adopted in IUIC. The simulations indicate the interference power significantly decreases as the iteration number increases and the channel nulling threshold reduces dynamically according to the iteration number. Comparing to the fixed threshold, the proposed dynamic thresholding mechanism provides robust and satisfactory performance in both large preamble number and large Max-to-min Power Ratio (MPR) between devices.