Research Of Random Access Algorithm For LTE High-speed Scene

LTE is the evolution of3.9G to4G mobile communications which is proposed by the3GPP, through the use of OFDMA, MIMO and other advanced technology its data transmission rate have been greatly improved, which is higher than3G mobile systems.The theoretical rate of downlink is up to100Mbit/s and uplink theoretical rate is up to50Mbit/s, at the same time it can provide access services to350km/h high-speed mobile users at a data rate of greater than100kbps.A UE can be scheduled to transmit Uplink data only when its uplink time synchronization be obtained. Therefore PRACH plays a key role in the LTE system uplink synchronization. When the mobile speed is greater than250km/h, the channel model is a special scene, such as high-speed rail environment, so you need to propose a new channel models and solutions.The main subject of the research work to improve the access performance of the LTE random access channel in high-speed environment:(1) Achieve the PRACH physical layer link simulation, including the transmission sequence generation, the conversion of the length, frequency domain offset and time-domain resources scheduling in the UE transmission terminal, and sequence of extraction, delay power spectrum calculation and threshold settings, the last window of detection, parameter calculation in the receiving end.(2) Described LTE high-speed rail channel simulation and analysis,o n the basis of the PRACH link model and the model of high-speed rail, in-depth study the impact of high-speed channel model on random access performance,(3) Then for these impacts this paper proposed a new threshold setting algorithm against the fast fading, as well as limited cycle shift collection algorithm to eliminate the effects of frequency offset.