The random access procedure in cellular networks suffers from a congestion problem caused by massive access requests from a large number of devices. Since this congestion problem causes inefficient energy consumption and increases the random access delay, an efficient random access procedure is required for various types of devices. In this paper, we propose a new access control scheme to reduce the access delay and the energy consumption by mining hidden random access resources. The proposed scheme consists of the random access procedure and the resource allocation algorithm. The proposed random access procedure utilizes the multiple access class barring (ACB) procedure to mine and utilize the hidden random access opportunities (RAOs) in order to increase the number of successfully admitted devices. The proposed algorithm optimizes the resource allocation parameters according to the estimated number of devices. We provide an analytical model for the proposed scheme by using an embedded Markov chain. The proposed scheme is shown to reduce the random access delay and the energy consumption for green communications by achieving 53 % maximum efficiency compared to 37 % in the conventional schemes with the ACB and random access procedure.

Since massive number of User Equipment (UE)s will cause more collisions and increase delay, improved Random Access (RA) methods have been researched and proposed. With the introduction of the new two step RA procedure in 3rd Generation Partnership Project (3GPP) Release 16, the average RA delay of UE could be further reduced. To further enhance two step RA in association with four step RA, we propose a new RA method that integrates four step RA and two step RA for heterogeneous IoT devices, so that UEs can perform two types of RA methods in parallel. With the proposed method, we aim to minimize the UE conflicts with the available RA resources, increasing the efficiency of RA and decreasing the average RA delay. We optimize the probability of two step RA in the proposed method and present algorithm to provide the optimal resource configuration and parameter settings in the RA procedure according to the RA status of UEs. A Markov chain model is formulated to analyze and confirm the effectiveness of the proposed RA method. As a result of extensive simulations, we present that the proposed RA method can enhance the property of the RA procedure for massive and heterogeneous devices access scenarios in 5G and 6G communications.

In the massive Machine Type Communications (mMTC) scenario of the 5G network, a huge number of devices communicate with each other. The massive access requests will cause frequent access collisions, which will reduce the efficiency of Random Access (RA) procedure. In this paper, we propose the random power back-off scheme that utilizes power domain Non-orthogonal Multiple Access (NOMA) scheme to solve the RA collision problem in 5G networks. In the proposed method, we attempt to mitigate the RA conflict situation when devices send the same preamble even if the Base Station (BS) does not detect the preamble collision. The proposed method is shown to improve the RA efficiency and average delay.

In dense indoor Internet of Things (IoT) environments, simultaneously transmitting and reflecting intelligent surfaces (STAR-IRS) can provide full-space coverage by steering energy to both sides of the surface. However, most STAR-IRS works focus on the physical layer and overlook medium access control (MAC) challenges, such as how to collect channel state information (CSI), dynamically assign each STAR-IRS element to either the reflection or transmission mode, and coordinate concurrent users. We propose a two-stage MAC protocol that couples carrier sense multiple access with collision avoidance (CSMA/CA) for contention and time division multiple access (TDMA) for scheduled data transmission. During contention, devices send extended request-to-send (eRTS) frames to enable CSI acquisition; during transmission, the access point (AP) configures the STAR-IRS, allocates TDMA slots, and pairs one reflection-region device (RD) with one transmission-region device (TD) for non-orthogonal multiple access (NOMA) with successive interference cancellation (SIC). Analysis and simulations show that the proposed scheme increases throughput and reduces delay compared with reflective-only IRS baselines without NOMA, while remaining practical for dynamic indoor IoT.