5G中海量机器类型通信面临的主要技术瓶颈是前导码短缺造成的接入碰撞严重，进而影响接入效率和接入时延。两种突破该瓶颈的典型方法是基于授权(Grant-Based)的随机接入和基于免授权(Grant-Free)的随机接入。虽然Grant-Based方案通过简化MTC设备与基站之间的握手协议可降低信令开销，但与MTC设备传输的小数据包相比，现有方案的信令开销依然过大；Grant-free方案允许MTC设备直接向基站发送导频和数据，但完全Grant-Free方式会使共用资源块的MTC设备数量分布不均衡，为物理层设计带来困难。针对这些问题，本项目将研究一种基于设备分组的混合Grant-Free随机接入方案，设计适用于该方案的智能检测算法和普适多用户编码方案，分析该方案可支持的最大MTC设备达到率，设计设备分组模型和资源分配优化策略，以降低MTC设备的接入碰撞概率和接入时延，提高数据传输效率和可靠性。

Due to the shortage of preamble sequences in the random access procedure, the severe collision becomes the major bottleneck for the massive machine type communications (mMTC) in the fifth-generation (5G) communication system. This problem further results in low efficiency and high latency of the random access procedure. There are two types of solutions for this bottleneck, i.e., grant-based random access schemes and grant-free random access schemes. Although different modifications have been proposed to simplify the handshaking process in grant-based schemes, the signaling overhead in existing grant-based schemes is still prohibitively high for the small-sized data packets in mMTC applications. Alternatively, grant-free schemes reduce the signaling overhead by allowing MTC devices to transmit their pilots and data packets to the Base Station (BS) directly. However, a completely grant-free manner may lead to the unbalanced load of devices sharing the same resource block, which complicates the design of the physical layer, including the design of channel coding, the modulation scheme and so on. In order to address these problems, we propose a Grouped Hybrid-Grant Free random access (GHGF-RA) scheme. Firstly, a series of intelligent detection algorithms and robust multi-user codes are designed for this GHGF-RA scheme. Then, we analyze the performance of the proposed scheme, with emphasis on the analysis of the maximum supportable arrival rate of activated MTC devices. Based on these analytical results, the grouping model and the allocation of the resources are also optimized to reduce the collision probability and latency of the random access procedure, increase the transmission efficiency and improve the reliability.