Grant-Free Non-Orthogonal Multiple Access for IoT: A Survey
Grant-Free Non-Orthogonal Multiple Access for IoT: A Survey
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DOI：
10.1109/comst.2020.2996032
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发表时间：
2020-01-01
影响因子：
35.6
通讯作者：
Johnson, Sarah J.
中科院分区：
文献类型：
--
作者：
Shahab, Muhammad Basit;Abbas, Rana;Johnson, Sarah J.
大规模机器类型通信（mMTC）是第五代（5G）无线通信技术中的三个主要关注领域之一，以在很少或没有人为干预的情况下实现大量物联网（IoT）设备的连接。在传统的人型通信（HTC）中，由于可用信道资源的有限数量和正交资源分配技术，用户通过进行调度/连接请求来获得传输时隙。所涉及的控制信道信令（相对于巨大的发送数据可以忽略）不是主要问题。然而，这可能变成mMTC中的潜在性能瓶颈，其中大量设备以零星的方式发送短分组数据。为了解决有限的无线电资源和大规模的连接性挑战，非正交多址接入（NOMA）已经成为一种有前途的技术，其允许多个用户在相同的信道资源上同时发送他们的数据。这是通过在发送设备处采用用户特定的签名序列来实现的，接收器利用该签名序列进行多用户数据检测。由于其巨大的连接潜力，NOMA也被认为能够实现免授权传输，特别是在mMTC中，其中设备可以在需要时发送数据而无需调度请求。现有的调查主要讨论不同的NOMA方案，并利用它们的潜力，在典型的基于授权的HTC场景中，用户与基站连接，并且在调度阶段预定义各种系统参数。与这些工作不同的是，本调查从免赠款连接的角度全面回顾了NOMA的最新进展。各种赠款免费NOMA计划，其潜力和相关的实际挑战突出，并在最后彻底讨论了未来可能的方向。
Massive machine-type communications (mMTC) is one of the main three focus areas in the 5th generation (5G) of wireless communications technologies to enable connectivity of a massive number of Internet of things (IoT) devices with little or no human intervention. In conventional human-type communications (HTC), due to the limited number of available channel resources and orthogonal resource allocation techniques, users get a transmission slot by making scheduling/connection requests. The involved control channel signaling, negligible with respect to the huge transmit data, is not a major issue. However, this may turn into a potential performance bottleneck in mMTC, where huge number of devices transmit short packet data in a sporadic way. To tackle the limited radio resources and massive connectivity challenges, non-orthogonal multiple access (NOMA) has emerged as a promising technology that allows multiple users to simultaneously transmit their data over the same channel resource. This is achieved by employing user-specific signature sequences at the transmitting devices, which are exploited by the receiver for multi-user data detection. Due to its massive connectivity potential, NOMA has also been considered to enable grant-free transmissions especially in mMTC, where devices can transmit their data whenever they need without the scheduling requests. The existing surveys majorly discuss different NOMA schemes, and exploit their potential, in typical grant-based HTC scenarios, where users are connected with the base station, and various system parameters are pre-defined in the scheduling phase. Different from these works, this survey provides a comprehensive review of the recent advances in NOMA from a grant-free connectivity perspective. Various grant-free NOMA schemes are presented, their potential and related practical challenges are highlighted, and possible future directions are thoroughly discussed at the end.