Research On The Key Technology Of LTE TDD Physical Layer Process

To encounter the challenge of the wimax, the Long Term Evolution system is the fourth generation for the wireless cellular network, especially after the HSPA (High Speed Packet Access) network. Currently, the first version for the LTE is achieved; moreover, the prototype is released by many manufacturing company, furthermore, to providing the QoS for the user has gained more attention. As an evaluation technology of the TD-SCDMA technology, the LTE is viewed as the focus for the mechanism of OFDM, MIMO adopted to enhance the capability of the wireless transmission.Considering about the state of our country, the TD-LTE system is determined to be an important technology in the future. As the evaluation procedure for the LTE, Physical layer technology is the key to improving system performance, to achieve lower latency and improve the user's data rate, increasing the system capacity and coverage and reduce costs. The uplink synchronization process,power control process,random access procedure,physical downlink shared channel related processes and physical process of shared control channel is main course of the LTE system physical layer process. By through random access procedure UE establish the initial uplink synchronization with base stations, through using the synchronization tracking it can track the uplink user channel and adjust the uplink signal transmission time. Effective control can track the change of users channel response better and make better convergence of the main peak position of the cyclic prefix in the appropriate position. Through the cell search UE can search for an available cell, a well-designed test program can get more information in this district and the neighboring cell information accurately. Random Access is the beginning of the process before UE and network communications. The detection method of receiver must meet the performance requirements of LTE systems when corrected probability false alarm and false detection. For high bit rate and higher order modulation data transmission, the symbol timing offset affects greater impact on system performance. The more offset the more affect on system performance, so it need a algorithm of downlink symbol timing to minimize the scope of the symbol timing offset.Considering about the problems above, the interface of Uu is studied in detail, and upstream synchro control, cellular searching, random access and downstream symbol timing mechanism is proposed.1. In according with the analysis on the procedure of upstream synchronous, a novel data transmitting method is proposed. To adjusting the offset of the packet sending, the threshold detecting method is designed reasonable.2. Base on the reach of the cellular downstream link and the initial synchronous of the carriers, the predicting on the timing, sector ID and frequency offset is introduced; moreover, the simplified method based on the FFT theory is proposed to reduce the complexity of the algorithms.3. With the analysis on the random access for the LTE-TDD system, the frame structure and corresponding resources mapping is studied. A novel algorithm for the receiver based on the PRACH is proposed; moreover, the detecting threshold is designed; finally, the simulation results show that the proposed algorithm is actually enough.4. The timing problem in the LTE TDD system is researched deeply, and based on the downstream symbols; the function of timing synchronous is achieved effectively. Results show that the accuracy of following can be guaranteed; furthermore, the complexity and the influence on the SNR can be reduced dramatically.From the researches on the above directions, the available of TD-LTE system can be enhanced; moreover, the evaluation from TD-SCDMA to the LTE system is smoother.