随着全球移动通信的发展，人们对网络信息的需求越来越高，第三代移动通信已不能满足人们的需求，3GPP经过多年的研究和讨论，最终提出了LTE通信协议标准，其目标为实现更灵活的系统带宽、更高的传输速率以及更低的时延。随机接入作为终端接入移动通信网络的首要步骤，其性能直接影响整个通信系统的质量好坏。 目前广泛应用于LTE系统的随机接入检测算法是一种时域检测算法，该算法引用过采样技术和频域点乘等价时域卷积原理降低接收端的计算复杂度，并根据估计的噪声功率对检测门限进行调整，确保了上行同步的准确性。仿真结果表明现有算法在多径衰落信道、低信噪比下，检测概率明显优于协议规定的参考值。但是现有的PRACH检测算法也存在缺陷，它采用的过采样技术虽然可以减少实现的复杂度且提高时域分辨率，但是也会导致各个相关值点的能量分散，在高信噪比情况下，极易引起虚警；另外使用非限制集合的中低速小区，用户速度导致的多普勒频偏也会导致高信噪比下虚警的抬升。 针对此问题，本文提出了一种加大Ncs检测窗宽度联合设置二次门限抑制虚警的方法。通过加大Ncs检测窗宽度可以有效降低过采样带来的尾峰虚警，设置二次门限可以有效抑制高信噪比下多普勒频偏带来的频偏虚警。仿真证明，该方法在满足漏警概率的同时，能很好的解决高信噪比下虚警增大的问题；并对短PRACH前导格式进行了该算法下的性能仿真，仿真结果表明在没有增加漏检概率的前提下，虚警概率几乎全部抑制掉。

With the development of global mobile communication, people need more and more for network information, the third generation of mobile communication cannot unable to meet the needs of people, the 3GPP went to many years of research and discussion, proposed the LTE communication protocol finally, the goal in achieving a more flexible system bandwidth, higher transmission rate and lower delay. Random access process is the first step of UE access communication network, so it directly affects the performance of the whole communication system. Rondom access detecting algorithm widely used in the LTE system is a time domain detecting algorithm,which quot sampling techniques and frequency domain point multiplication is equivalent to the time domain convolution principle to reduce the computational complexity of the receiving end, and detection threshold to be adjusted according to the estimated noise power, which ensure the accuracy of the uplink synchronization. The simulation results show that the detection probability of the existing algorithm is superior to the reference value of the agreement under multipath fading channel and low SNR (signal to noise ratio). But existing PRACH detecting algorithm also have defectives, it uses oversampling technique can reduce the complexity of implementation and improve the time resolution, but also lead to the energy dispersion of the correlation value point, in the case of high SNR can easily cause a false alarm; in addition, the low speed resdential use of unrestricted set, Doppler frequency offset caused by the user speed will lead to the uplift of false alarm in the case of high SNR. For this problem, this paper based on the research of PRACH detection algorithm used in the LTE system, puts forward a method of increase circular shift (Ncs) detection window width joint set secondary threshold, which can achieve the purpose of suppressing false alarm. Increase the Ncs detection window width can effectively reduce the false alarm which caused by sampling, set the secondary threshold can effectively suppress the false alarm which caused by Doppler shift frequency offset in high SNR. The simulation results show that this method meet the probability of missed alarm, at the same time, can well solve the problem of false alarm increases in high SNR; and the simulation of short PRACH format under the algorithm was carried out, the simulation results show that under the premise of no increase of miss detection probability, the probability of false alarm is almost entirely suppressed.