## 1 Introduction
[12] proposed that the channel estimation can be used to subsequently discover the quality of MU-MIMO systems as a refreshing channel assessment approach which employs reliable soft symbols. They collect reliable data tones from both desired and interfering users related to the conclusion and apply them as pilots for re-evaluation of the channel. The channel assessment and data decoding are obtained iteratively when the channel and data symbols become joined. These two processes utilize the familiar expectation maximization algorithm. [PERSON] et al. [13] considered the problem of CE for a mm-wave system with one RF chain used at the BS and mobile station (MS). Being different from most existing studies that examined narrowband channels, they considered the estimation of wideband mm-wave channels with frequency selectivity, including the angles of arrival/departure, time delays and fading coefficients. In their proposed method, the two stages compressed the sensing algorithm with the low-rank matrix, which allows the sampling process to be performed. After this, the sparse recovering stage occurs, which allows us to estimate the mm-wave channel. Hence, their proposed method has the potential to achieve lower sample complexity and overhead reduction. [PERSON] et al. [14] considered multiple access and broadcast channels to examine the error performance of multidimensional constellations. Specifically, the closed-form expression for the pairwise error probability (PEP) in the joint maximum likelihood detection was provided for multiuser signaling. The arbitrary numbers of users and multidimensional signal sets were assumed, while the simulation results show the importance of the multidimensional constellation. Furthermore, a useful average symbol error probability was also obtained through the upper bound with the results from the analysis being more accurate. [PERSON] and [PERSON] [15] considered IoT-based on 5G or machine type communication (MTC), in which the low-power transmitter communicates with the high-quality receiver. However, they combine the joint maximum-likelihood estimation of the channel and the multi-path fading OFDM systems to investigate the probability of the receiver-side compensating for the transmitter RF impairments. In particular, they proposed an alternative optimization algorithm, which uses frequency-domain block-type training symbols to prove that their algorithm is able to solve the two alternate algorithms. After this, they calculated the Cramer-Rao lower boundary, which showed that the proposed estimator provides a high signal-to-noise ratio. Fixing the packet collision impairment in both the Advocates of Linux Open-source Hawaii Association (ALOHA)-based networks and the random access networks is the main aim for reducing performance degradation. [PERSON] et al. [16] proposed a novel MUD scheme, which is used to separate the collided signals to enable multiple packet reception capabilities in random access schemes. The performance of Markov chain approach is analytically derived and optimized in terms of network throughput, before being compared with that of different alternatives. At BS, each user's uplink pilots are also transmitted due to the absence of CSI during the estimation of the channel [17; 18; 19]. One of the optimal detectors in the MUD is the maximum likelihood (ML) method, although it is difficult to use this to achieve the exponential complexity. The zero-forcing or null steering detector [20], the minimum mean square error (MMSE) detector in M2M [21] and the maximum a posteriori (MAP) or marginal likelihood detector [22] are some of the sub-optimal MUD detectors that can be used for situations with less complexity. The main objective of the multiuser detection involves the study of strategies to demodulate the digital information sent simultaneously by several transmitters, which share a multiple-access channel. Common channels that are encompassed by this general model include up-link satellite channels, local area networks and radio networks.