Link-level simulation of W-CDMA satellite-UMTS random access channel

In this paper, link level simulation for the W-CDMA Satellite-UMTS RACH (radio access channel) has been presented. Simulation results show improvements in detection using a longer preamble with differential accumulation. For a longer preamble, coherent processing suffers large losses in the presence of Doppler. Efficient channel estimation algorithms and pre-Doppler compensation are required if a coherent approach is used. The reduced sensitivity of coherent detection in the presence of Doppler could be compensated by adopting a differential approach even though this solution increases the complexity at the receiver. It can be seen that the modified ETSI proposal does not degrade the performance compared to the ETSI proposal in terms of detection probability. Hence, we can expect improvements in the RACH throughput efficiency and delay since there are more available signatures and so the probability that more than one user chooses the same signature that results in collision is lower. Also, to achieve a one-shot-acquisition for the random access burst, the performance of preamble detection and message detection must be aligned, i.e. at an E_c/N₀, where the preamble detection is likely, the RACH message BLER (block error rate) must be adequately low. The alignment is done by adjusting the preamble detection performance setting the threshold of the received energy of the matched filter at the receiver. From the simulation results, it was shown that with the used threshold, the probability of detection corresponds to more than 0.9 at the required E_b/N₀ for a BLER of 10^-1 for the message part.