Title: Device Activity Detection for Massive Grant-Free Access Under Frequency-Selective Rayleigh Fading Show Chinese title

Title: 设备活动检测在频率选择性瑞利衰落下的大规模无许可接入中

Abstract: Device activity detection and channel estimation for massive grant-free access under frequency-selective fading have unfortunately been an outstanding problem. This paper aims to address the challenge. Specifically, we present an orthogonal frequency division multiplexing (OFDM)-based massive grant-free access scheme for a wideband system with one M-antenna base station (BS), N single-antenna Internet of Things (IoT) devices, and P channel taps. We obtain two different but equivalent models for the received pilot signals under frequency-selective Rayleigh fading. Based on each model, we formulate device activity detection as a non-convex maximum likelihood estimation (MLE) problem and propose an iterative algorithm to obtain a stationary point using optimal techniques. The two proposed MLE-based methods have the identical computational complexity order O(NPL^2), irrespective of M, and degrade to the existing MLE-based device activity detection method when P=1. Conventional channel estimation methods can be readily applied for channel estimation of detected active devices under frequency-selective Rayleigh fading, based on one of the derived models for the received pilot signals. Numerical results show that the two proposed methods have different preferable system parameters and complement each other to offer promising device activity detection design for grant-free massive access under frequency-selective Rayleigh fading. Show Chinese abstract

Abstract: 设备活动检测和在频率选择性衰落下的大规模无授权接入中的信道估计不幸仍然是一个悬而未决的问题。 本文旨在解决这一挑战。 具体而言，我们提出了一种基于正交频分复用（OFDM）的大规模无授权接入方案，适用于具有一个M天线基站（BS）、N个单天线物联网（IoT）设备和P个信道抽头的宽带系统。 我们在频率选择性瑞利衰落下获得了接收导频信号的两个不同但等效的模型。 基于每个模型，我们将设备活动检测建模为非凸最大似然估计（MLE）问题，并提出一种迭代算法，使用最优技术获得平稳点。 两种提出的基于MLE的方法具有相同的计算复杂度阶O(NPL^2)，与M无关，并且当P=1时退化为现有的基于MLE的设备活动检测方法。 基于接收导频信号的两个推导模型之一，传统信道估计方法可以方便地用于检测到的活跃设备的信道估计。 数值结果表明，这两种方法具有不同的优选系统参数，并相互补充，为在频率选择性瑞利衰落下的无授权大规模接入提供了有前景的设备活动检测设计。