Fast and Flexible Initial Uplink Synchronization for Long-Term Evolution

Abstract

Orthogonal frequency-division multiple access has been widely adopted by the modern wireless networking standards. These use initial uplink synchronization (IUS) process to detect and uplink-synchronize with new user equipments (UEs) (3rd Generation Partnership Project; technical specification group radio access network; evolved universal terrestrial radio access (E-UTRA); physical channels and modulation (release 10), (2011) [1]). IUS is a random access process where a UE intending to start communication transmits a code during an “IUS opportunity”. The code is chosen uniformly at random from a predefined codebook. The eNodeB uses the received signal to detect the codes, and estimate the uplink channel parameters associated with each detected code. This detection and estimation problem is known to be quite challenging, particularly when the number of UEs transmitting during an IUS opportunity is not small. We discuss some recent sparse signal processing methods to address this problem in the context of long-term evolution (LTE) standards. This research does not only give some new directions to solve the detection and estimation problem but also provides guidelines for designing the codebook. In addition, the key ideas are applicable to other OFDMA systems.