Towards Massive Connectivity Support for Scalable mMTC Communications in 5G Networks

“This observation was the motivation for the use of Bloom filters – a data structure based on the OR operation for testing set membership [25] – for the construction of the access signatures.”

“…MAC and PHY numerical simulation was conducted over 10 4 trails including the full physical layer processing (encoding, modulation, channel estimation, multi-user detection, demodulation, decoding) with BPSK, a [5 ; 7] 8 convolutional code, least squares multi-user equalization and BCJR decoding.”

“This property led to the so-called compute-and-forward [39], [40], which proved achievable gains, from an information-theory point of view.”

“We follow the common simulation assumptions described in Table I. Note that the pilot-to-data ratio is only 13% so the overhead compared to LTE-4G has significantly reduced (reported to be up to 2000% in [48]).”

“Thus, enhancement of the access reservation procedure for mMTC traffic has been in the focus of both the research community [3] and standardization [4].”

“Focusing on a one-stage protocol early works on sporadic access in combination with Code Division Multiple Access (CDMA) already noted that intermittent user activity leads to a multi-user detection (MUD) problem with sparsity that required novel algorithmic solutions [31].”

“The presented Slotted Compute-and-Forward (SCF) approach is a random access extension of the Compute-and-Forward (CF) relaying scheme introduced in [49].”

“tage protocols by allowing more than one packet transmission per radio resource block and resolving collisions through advanced receivers. The solution falls under the category of coded random access [36], where features of channel coding are exploited both at the slot and frame level. In particular, the scheme partia…”

“The main focus of the NB-IoT is on providing extreme coverage, with supported number of users similar to LTE-M [18].”

“…related to GF access either discusses the performance of standardized GF schemes or proposes new schemes attuned towards collision detection/reduction methods or discusses them in conjunction with URLLC and physical layer (PHY) technologies [4], [6], [7], [8], [9], [10], [12], [13], [14].”

“With the development of the Internet of Things (IoT), billions of devices are expected to be connected, such as smartphones, sensors and tracking devices [1].”

“…to support unprecedented user connectivity with a certain quality of experience met evenly, to enable services such as live sports and video game broadcasting [1], or to deliver massive machine-to-machine communications (mMTC), e.g., large-scale software updates for IoT devices [2], [3], [4], [5].”

“In accordance with this trend, massive machine-type communications (mMTC) have received a great deal of attention in recent years as a means to support the access of variety of things [1].”

“A related comprehensive study with focus on the MAC layer solutions can be found in [19].”

“In NB-IoT uplink, the DMRS (Demodulated Reference Signal) is multiplexed with the data so that it is only transmitted in Resource Unit (RU) which contains data transmission.”

“In recent years, mMTC has gained a lot of attention due to applications such as smart grid and metering, smart factories, autonomous driving, and public health [1], [2].”

“…communication (mMTC) has been treated as one of the most indispensable services in the next generation networks [1], [2], [3], due to its wide applications with Internet of Things (IoT), e.g., environment and structure monitoring, smart-grid, autonomous driving, and health monitoring [4], [5], [6].”

“We consider grant-free uplink transmission protocol, which is generally accepted as one of the most suitable MAC layer solutions for massive connectivity [4], [7], [9], [10], [27] and is also being considered for standardization in Release 16 of NB-IoT.”

“Massive machine-type communications (mMTC), where a massive number of sensors, autonomous systems and edge computing devices are connected to the Internet, is a major Internet of things (IoT) category supported by the fifth generation (5G) wireless communication technologies [1].”

“[3].”

“In mMTC services, the following requirements need to be satisfied [5]: (i) Low throughput (ii) Low power (iii) Low cost (iv) Massive connectivity (v) Wider coverage.”

“Provided that messages transmitted from devices are short, to improve efficiency, 4-step random access can be replaced with 2-step random access [10], which is also referred to as grant-free random access or compressive random access (CRA) [11] [12] [13] [14] [15].”

“In [18], the MAC and PHY layer enhancement of RA was studied to consider the QoS requirements of the various service types of mMTC.”

“For instance, a strong interest is given to the the impact of massive access, short packets and capacity evaluation [3, 4, 5].”

“In particular, massive Machine Type Communications (mMTC) require extensive connectivity with the number of users in the system being more than 106 [2].”

“Of course, new challenges will appear when the massive IoT becomes a reality [42,43] due to scaling issues, but 5G communications have been conceived of to deal with these from the onset [44].”

“To serve for the soaring access requests of these MTDs, the centralized access, i.e., the AP coordinates transmissions and allocates resource to each MTD, leads to intolerable overhead of scheduling, especially for small-packet and low-rate transmissions [3].”

“In the ongoing 5G transformation of wireless communication, massive machine type communication (mMTC), where a large number of users are expected to be served, provides a core use case [1]–[3].”

“INTRODUCTION The fifth-generation (5G) mobile network might be applied to four different scenarios [1]-[5]: massive machine-type communications (mMTC); extreme mobile broadband (eMBB); ultra-reliable low latency (URLL) communications; long-range communications for remote area access.”

“To circumvent the restriction of the synchronization, GF asynchronous multiple-access (GF-AMA) schemes are proposed with the orthogonal frequency division multiplexing (OFDM) waveform [18]–[20], and developed with the code division multiple-access (CDMA) [21].”

“To simulate the network environment of the low power wide area network (LPWAN) [18] for massive IoT devices, we set the transmission rate to vary from 0 Mbps to 10 Mpbs.”

“Thus, the future mMTC networks will be required to support multiple service communications with highly heterogeneous requirements [40], [41], [42], [43].”

“Since the required number of iterations is not known in advance, iterative algorithms might not be suitable for use in lowlatency applications such as 5G ultra reliable low-latency communication (URLLC) [4], [5], where an (approximate) solution within a very low latency budget must be provided.”

“ayer cell identities [4]. Since there is no specific collision avoidance procedure, a massive number of access attempts can cause severe congestions that accompany the increase in transmission latency [3]. Even assuming congestion-free scenarios, the sumrate growth in a large-user regime K˛Mhas slowed because the sum-r…”

“Therefore, planned scheduling and allocation of radio resources may result in a huge waste of resources [9].”

“This multiplicity of services and applications will fundamentally redefine the value framework in 5G networks and beyond, especially as machine-centric communications will be supported in 5G [7] and vertical industries start playing a bigger role in 5G.”

“Various applications of the IoT, such as smart cities, connected vehicles, smart agriculture, public safety, and asset tracking, require different levels of coverage area, battery life, and connection capability [102].”

“Technologies such as Narrowband IoT (NB-IoT) and enhanced Machine-Type Communication (eMTC) provide extended coverage, deep indoor penetration, and low power consumption, making mMTC ideal for smart cities, agriculture, and environmental monitoring [49].”

“Ideally, a direct transmission would be preferred for small data, especially in the case of Ultra Reliable Low Latency Communications (URLLC) [5], [6], as any additional signalling message makes the overhead much larger than the transmitted data and consequently extends the latency as well.”

“In contention-based, IIoT mobile devices access the channel in a random way, thus if multiple IIoT mobile devices simultaneously choose the same channel to offload their computation tasks, high interference and collision may occur leading to low efficient task offloading performance [3], [4].”

“In [7], the author lists various approaches to improve the cellular IoT systems both at PHY and MAC layer but not really consider alternative to this basic repetition scheme.”

“This is quite similar to machine-type communication (MTC) [17] where devices have sporadic traffic and become active to transmit data packets at random times in a number of IoT applications [18].”

“Thus, several years after the NB-IoT, the LTE Cat M1 has been rolled out in the Czech Republic to cover the white spot of the data-hungry data transmissions [7]–[9].”

“Digital Object Identifier 10.1109/TWC.2024.3354956 property; (4) the users are very sensitive to energy consumption [1].”

“This might come in form of transmitting the same message concurrently over independent channel realizations using different resources (time or frequency) [10].”

“The solutions for massive connectivity mainly fall into two categories: solutions based on protocol designs and solutions based on receiver signal processing [9].”

“These aspects have been addressed for massive machine-type communication, which shares some of the practical hurdles like initially unknown users and channels [13], [14], [15].”

“Unlike traditional communication systems, mMTC is characterized by high device density and sporadic transmission patterns, where only a small subset of devices is active at any given time, typically triggered by external events [2], [3], [4].”

“It is characterized by a massive number of devices that sporadically and unpredictably transmit short data packets to a central base station (BS), typically under stringent constraints on energy consumption and signaling overhead, and often mild latency and reliability constraints [1], [2], [3].”

“Coleman in [4] highlights some physical and medium access techniques to address the problem of a massive number of access attempts mMTC devices in the 5G network.”

“In this article, using the weighted average peak AoI 1 as the performance metric, we revisit the IRSA protocol with heterogeneous types of users in order to address the heterogeneity nature in mMTC usage scenarios [21], [22].”

“A S ONE of the three generic scenarios in the fifth-generation (5G) mobile networks, massive machine-type communication (mMTC) plays an important role in supporting massive connectivity of the Internet of Things (IoT) networks [1].”

“However, in wireless networks where bandwidth is limited and multipath fading exists, it is still a challenge to provide reliable massive access for mMTC [3].”

“Coleman and colleagues, in [28], highlight some physical-and medium-access techniques to address the problem of massive access attempts from mMTC devices in the B5G network.”

“One important application area is to connect a large number of objects, such as sensors and machines, to the Internet of Things (IoT) [2].”

“However, the support of low-latency massive access for massive connectivity is still challenging in current wireless networks [2].”

“Massive machine-type communications (mMTC) is one of the three generic scenarios in the fifth-generation (5G) mobile networks and will also play the important role in the future sixth-generation (6G) systems [1].”

“Although existing communication systems can support small scale MTC, the characteristics of mMTC, such as the huge number of machine-type devices and the small data payloads, drive the demands for new massive access schemes [3].”

“For them, 2-step random access approaches are preferable [15] [16] [17] [18].”

“However, actual networks are not prepared to support such traffic, and even less the case of mMTC, which require simultaneous connections of a massive number of low-data-rate devices [1], [2].”

“Moreover, the need for retransmissions in case of transmission failure could exacerbate complexity, latency, and power consumption, which are the most critical factors in the majority of MTC networks [2].”

“The term massive machine-type communication (mMTC) was coined with reference to a very large number of IoT devices located in the same area and operating in an uncoordinated manner, each sending short data packets intermittently to a central base station (BS) [3]– [5].”

“Moreover, the introduction of the fifth-generation (5G) wireless network has greatly impacted IoT and enabled the realization of massive machine-type communications (mMTC) [1], [2], [3].”

“Several papers were produced in the recent years, such as [4] which is providing a good overview of various possible improvements.”

“The fifth generation (5G) of wireless communication aims to support Internet of things (IoT) through massive machine type communication (mMTC), where a large number of devices (close to 10(6) devices per km(2)) will be served with a tolerable latency and good energy efficiency [1].”

“…of Internet of Things (IoT), massive machine-type communications (mMTC) which has been defined as one of the three major application scenarios in the fifth generation (5G) wireless communications, is supposed to providing robust connectivity for a vast number of user equipments (UEs) [2], [3], [4].”

“Nonorthogonal multiple access (NOMA) is proposed to enhance the system throughput and accommodate massive communication connections [1].”

“The terminology of onestage and two-stage access protocols is borrowed from [1], which introduced the nomenclature to help classify recent work towards the design of more agile protocols in terms of signaling, and better support for massive connectivity.”

“The new wireless standard will support applications in enhanced mobile broadband (eMBB), ultra-reliable and lowlatency communications (URLLC) and massive machine type communications (mMTC) [2], [3], [4].”

“It enables Internet of Things (IoT) [1] which connects massive number of objects like computers, services and devices like sensors and mobile phones together.”

“The mMTC service has its particular features: (1) compared with human-to-human (H2H) communications, the number of potential users (devices) in mMTC scenario could reach up to millions [1]; (2) the user activity patterns are very sporadic; (3) mMTC demonstrates a salient short-packettransmission property [2]; (4) the…”

“With this drive comes with a number of challenges in the field of designing communication technologies in terms of, e.g., service provisioning, reliability, Quality of Service (QoS), or security [1]–[3].”

“[1]. mMTC has the connectivity characteristics of large-scale devices using sensing, computing, and communication functions [2].”

“I N 5TH generation (5G) systems, there are three main connectivity types, namely enhanced mobile broadband (eMBB), massive machine-type communication (MTC), and ultra-reliable low-latency communication (URLLC) [1], [2], [3].”

“Effectively, we consider that the device has x bits to transmit in the 10 ms time-frame, giving it a data rate of x/ 10 kbps. Starting with 80 bits, we go up to 390 bits per frame, which is typical for status update packets [11], [20].”

“In such applications, the system is typically uplink-dominant where the number of active users is uncertain, and the transmission is sporadic [1].”

“…resource utilization provided by different access technologies and configured at the user equipment The benefits of multi-connectivity in terms of throughput increase and reliability improvement, as well as issues like energy efficiency and energy consumption are studied in [3], [4], [5], [6], [7].”