## 1 Introduction  
Current fifth-generation (5G) technology is capable, efficient and flexible, but can be further improved. With the densification of cellular networks, where each cell has an identical capacity, covering the same area with smaller cells allows us to support more traffic. As a result, 5G supports higher traffic per cell than fourth-generation (4G) technology; this is also due to higher available bandwidths and more efficient transmission modes that allow us to send more bits per frequency unit. The use of network densification is a key player in 5G, requiring a wide deployment of small cells and thus increasing infrastructure cost and reducing energy efficiency (EE). Reconfigurable intelligent surfaces (RISs) are also capable of increasing throughput and coverage performance with high EE. Therefore, they can potentially be the right replacement for sites with BS as they do not increase the infrastructure cost and increase the EE. Orthogonal frequency division multiplexing(OFDM), and mMIMO systems [1] are two of several pillars of 5G technology that works in both bands, below 6 GHz and above 24 GHz (mmWave), according to 5G New Radio (5G NR) [2], accommodating more users than the fourth generation. The use of the mMIMO approach allows for 100\(\times\) higher efficiency without requiring additional base stations (BSs). Non-orthogonal multiple access (NOMA) [3] is used in wideband networks and can accommodate an higher number of users and streams, but fails to achieve a higher EE that is required to meet the challenges and requirements of beyond 5G (B5G) and future generations (6G). Another 5G technology is carrier aggregation, which started in 4G and allows users to be served by carriers from 5G NR and LTE-Advanced at the same time [4]. This requires the terminals' support to work at different frequency bands, namely, sub-6 GHz and beyond 24 GHz. The cloud or centralized radio access network (C-RAN) is another primary component of 5G used to mitigate the effects of users located at cell borders. As networks exponentially grow in size, the cloud alone is not enough, and edge computing is essential. Security is also part of 5G technology, and is deployed on a large scale such as in software-defined networks (SDNs) and network function virtualization (NFV), where software-level components can be attacked [5]. Another use case of 5G is massive Internet of Things (mIoT) or massive machine-type communications (mMTC) supporting 5G IoT use cases with billions of connected IoT devices and sensors. The use case covers both low-data-rate/low-bandwidth IoT devices with infrequent bursts of data requiring long battery life as well as very-high-bandwidth/data-rate IoT devices. These billions of IoT devices represent a real challenge in current 5G wireless networks [6; 7]. To support the massive connectivity of IoT devices, powerful and versatile BSs are required close to the data centers. mMIMO has the capability to vastly increase spectral efficiency (SE) and EE. Moreover, mMIMO has the capacity to support the massive connectivity of IoT devices, as has already been shown in the literature [8; 9]. In general, a single cell can be used to support IoT networks, such as a smart factory. However, for a smart city scenario, there is a need for a cellular network and a C-RAN. In this article, we assume that the number of IoT devices is greater than the number of service antennas in mMIMO. Orthogonal reference signals (RS) are reused in each sector of a cell with a transmission and reception point (TRP) consisting of a mMIMO. Our objective is to serve as many low-rate IoT devices as possible, given the time and bandwidth of coherence of the channel characteristic of the smart city scenario. RISs can be synthesized as \"intelligent\" surfaces comprising a large set of periodic elements that can change the phase (and also the amplitude) of incident waves [10]. RIS may be attached to practically any surface, including walls, furniture, building panels, and clothes.