Joint Optimization of Preamble Selection and Access Barring for MTC with Correlated Device Activities

Abstract

Most existing works on random access for machinetype communication (MTC) assume independent device activities. However, in several Internet-of-Things (IoT) applications, device activities are driven by events and hence may be correlated. This paper investigates the joint optimization of preamble selection and access barring for correlated device activities. We adopt a random access scheme with general random preamble selection parameterized by the preamble selection distributions of all devices and an access barring scheme parameterized by the access barring factor, to maximally exploit correlated device activities for improving the average throughput. First, we formulate the average throughput maximization problem with respect to the preamble selection distributions and the access barring factor. It is a challenging nonconvex problem. We characterize an optimality property of the problem. Then, we develop two iterative algorithms to obtain a stationary point and a low-complexity solution respectively by using the block coordinate descend (BCD) method. Numerical results show that the two proposed solutions achieve significant gains over existing schemes, demonstrating the significance of exploiting correlation of device activities in improving the average throughput. Numerical results also show that compared to the stationary point, the low-complexity solution achieves a similar average throughput with much lower computational complexity, demonstrating the effectiveness of the low-complexity solution. I. INTRODUCTIONInternet-of-Things (IoT) has had broad applications in several areas, such as home automation, smart grids, healthcare systems, and industrial monitoring, and has received increasing attention in recent years. The number of IoT devices is expected to grow up to 30 billion by 2030, and more and more new IoT applications are emerging. There is a need to design a robust, scalable, and efficient sixth-generation (6G) wireless network that can effectively realize machine-type communications (MTC) to support future IoT applications. This paper aims to provide a promising solution for random access for MTC in 6G.In random access for MTC, devices compete in a random access channel (RACH) to access a base station (BS) through the random access procedure [1]. Specifically, each active device randomly selects a preamble from a pool of available preambles according to a preamble selection distribution and transmits it during the RACH. The BS acknowledges the