The LTE Access Procedure Brian Katumba 1 , Johannes Lindgren 1 and Kateryna Mariushkina 2 1 Department of Computer Science and Engineering and 2 Department of Signals and Systems Chalmers University of Technology Gothenburg, Sweden {katumba, johlinb, katmar}@student.chalmers.se Abstract—This paper describes the LTE access procedure with a main focus on the cell search procedures. The cell search is carried out by two synchronization signals i.e. the primary synchronization signal which is needed when a user equipment (UE) connects for the first time to a cell or is looking for a new one to make a cell handover, and secondary synchronization signal which is needed to provide the terminal with information about the cell ID, frame timing properties and the cyclic prefix (CP) length. The report goes through the different synchronization methods in the cell search discussing their advantages and disadvantages in synchronization. We propose an algorithm that aims for improving the cell search procedure in terms of lower complexity and increased detection probability while maintaining a robust connection. KEYWORDS: LTE, Access procedure, Cell search, Synchronization signals, Cell search algorithms I. I NTRODUCTION The driving forces behind the evolution of 3G is that the carriers need to stay competitive by providing better services at lower cost. It is this competitiveness that drives the technology advancement. Since the fundamental goal of any mobile communication system is to deliver services to the end users, the engineers need to build systems that can adapt to the changing environment i.e. predict which services that could become popular in a period of five to ten years [1]. To be able to solve these challenges the third generation partnership project (3GPP) group came up with a standard consisting of two parts. One part is the high speed packet access (HSPA) Evolution which is built on existing specifica- tions and can use already installed equipment that uses the 5 MHz spectrum. However, one drawback is that HSPA must be backward compatible with older terminals [1]. The other part is the long term evolution (LTE) which is based on orthogonal frequency-division multiple access (OFDMA) in down-link and single-carrier frequency-division multiple access (SC-FDMA) in up-link. It offers favorable features such as high spectral efficiency, robust performance in frequency selective channel conditions, simple receiver architecture and lower latencies [2]. It also uses the same spectrum bands as most of the other 3G technologies. In LTE there is the possibility to use new designs and LTE does not need to be backward compatible with the older terminals. This made it possible to design the radio interface to be completely based on packet-switched network technology and the designers did not need to care about the circuit-switched part [1]. All in all, the main reasons of developing LTE was to sustain packet switched traffic (IP traffic), voice traffic e.g. voice over IP. In addition it permits both frequency-division duplexing (FDD) and time-division duplexing (TDD) communication. Its support for multiple input multiple output (MIMO) technology gives it an advantage in the communication arena [3]. As a starting point, in LTE, before a terminal can start to use the network there must be some connection associated with the network and that is what is called the access procedure. This procedure consists of the following parts: finding and acquiring synchronization to a cell within the network, receive and decode the information (cell system information), request a connection setup (random access) and network-initiated connection setup (paging) [1]. The cell search in 3GPP LTE is complex and computation- ally expensive. It is also power and time consuming since it is computing correlation between transmitted and received signals. The fundamental issues in cell search synchronization are rotated on cell detection, complexity, channel fading and robustness. Although many algorithms are in place to solve the fore mentioned issues, still we have not found one that capture them at once hence making the cell search even more complex with even higher power consumption by applying different algorithms to solve the issue. This research is focused on the cell search and synchro- nization with a main objective of increasing the detection probability of the cell ID and reducing complexity while maintaining robustness. In this, the report explains how the user equipment (UE) behaves depending on if it is an initial synchronization procedure or new cell identification. The different synchronization methods and algorithms are used as a basis for a proposed algorithm for cell search synchronization. This algorithm tries to increase detection probability, reduce complexity, and handle channel fading yet leaving the access procedure robust and yet in a single algorithm. Together with this introduction, the paper is organized as follows; section II describes the general view of the access procedure steps i.e. the cell search, the system information, the random access and paging. Section III covers the different, already existing cell search algorithms, Section IV covers the proposed algorithm, and section V covers the conclusion of the paper.