A Multiuser Detection Algorithm for Random Access Procedure With the Presence of Carrier Frequency Offsets in LTE Systems

In the LTE system, uplink synchronization can be established through the random access channel, by which timing and frequency offsets between transceivers can be estimated and adjusted. As the single carrier frequency division multiple access (SC-FDMA) structure is utilized in LTE uplink, preambles for the random access channel should be generated and detected in the transform-domain at user equipments and the base station, respectively. However, in available literature, an explicit transform-domain signal model with respect to timing and frequency offsets has not been provided, and the impact of frequency offsets on the transform-domain signal is not analyzed either. Therefore, suffering from unknown interference among multiple user equipments, existing multiuser detection algorithms provide unsatisfied multiuser detection and estimation performance. In this paper, an explicit transform-domain signal model is first derived with respect to both timing and frequency offsets. The characteristic of transform-domain frequency offsets is then analyzed, which indicates that transform-domain frequency offsets behave differently with time-domain frequency offsets. After that, a multi-steps hybrid multiuser detection algorithm is proposed to improve the multiuser detection and estimation performance, and the Cramër-Rao bound to the accuracy of parameters estimation for the random access procedure is finally obtained. Simulation results show that the proposed algorithm is able to significantly improve the multiuser detection and estimation performance compared to existing ones.