Lte Uplink Random Access Technology Research

Long Term Evolution aimed at achieving 100Mbps peak rate in 20MHz band downlink and 50Mbps in uplink are carried out in 3GPP. Random access procedure is very important in mobile communication system. The performance and capacity chiefly affect the whole system. In this background, this thesis analyzes random access technology in LTE uplink. Discrete Fourier Transform spread Orthogonal Frequency Division Multiplexing Access (DFT-SOFMA) is adopted in LTE uplink.Briefly introducing DFT-SOFDM technology theories, its major advantages and shortcomings are introduced firstly. DFT-SOFDMA is a multi-carrier modulation technology based (OFDM) with robustness against frequency selective fading, high spectrum efficiency and large capacity. Moreover it has low peak to average power ratio than OFDM.The random access procedure is classified into two categories: non-synchronized random access and synchronized random access in 3GPP LTE. The non-synchronized access is used for time alignment, signal detection and transmitted message at the same time. It can also request resource in uplink. A message payload of 4-8 bit is implicitly transmitted in the random access burst along with the preamble. The synchronized random access procedure may be used when the UE uplink is time synchronized by the Node B. The purpose is for the UE to request resources for uplink data transmission.This thesis mainly analyses the random access physical layer technology in LTE uplink. The message represented by CCSK sequence and the message represented by segmented RACH preambles are proposed in non-synchronized random access. Different bit message is represented by different cycle shift of CCSK signal in the former, then in the transmitter preamble sequence combined with CCSK signal is transmitted; In the latter preamble sequence is made up of different sequence which express different bit message, thereby bit message is implicitly transmitted. A method based on group is proposed in synchronized random access. In this design, some time slots make up of the time domain and the frequency domain is divided into some access bandwidths. Each user employed different preamble sequence accesses the mobile system in different time slots and bandwidths.At last, in order to test the rationality and feasibility of the system design, the performance of two modes in non-synchronized random access and synchronized random access is simulated in Matlab. As simulation shows, the proposed design modes in non-synchronized random access and synchronized random access meet the demand of 3GPP LTE.