# Resource Allocation in 5G Cellular IoT Systems with Early Transmissions at the Random Access Phase
###### Abstract  
While the market for massive machine type communications (mMTC) is evolving at an unprecedented pace, the standardization bodies, including 3 GPP, are lagging behind with standardization of truly 5G-grade cellular Internet-of-Things (CIoT) systems. As an intermediate solution, an early data transmission mechanisms encapsulating the data into the preambles has been recently proposed for 4G/5G Narrowband IoT (NB-IoT) technology. This mechanism is also expected to become a part of future CIoT systems. The aim of this paper is to propose a model for CIoT systems with and without early transmission functionality and assess the optimal distribution of resources at the random access and data transmission phases. To this end, the developed model captures both phases explicitly as well as different traffic composition in downlink and uplink directions. Our numerical results demonstrate that the use of early transmission functionality allows one to drastically decrease the delay of uplink packets by up to 20-40%, even in presence of downlink traffic sharing the same set of resources. However, it also affects the optimal share of resources allocated for random access and data transmission phases. As a result, the optimal performance of 5G mMTC technologies with or without early transmission mode can only be attained if the dynamic resource allocation is implemented. 5G; mMTC; CIoT; random access; early transmissions; delay; optimal resource allocation +
Footnote †: journal: Sensors  
0000-0002-4001-5000]E. A. S.  
EDs. To enable such versatility, 6G mMTC systems have to employ flexible frame structures with different and dynamically changeable allocations in uplink and downlink directions. To enable a long-lasting lifetime for mMTC EDs that would still constitute the major traffic load in modern and future mMTC systems, they have to rely upon the random access (RA) phase followed by the data transmission (DT) phase. The RA phase is conventionally organized by utilizing the multichannel slotted ALOHA-type algorithms [5]. The DT phase relied upon multiplexing of uplink and downlink traffic over the orthogonal-frequency division multiple access (OFDMA) scheme. Depending on the traffic type and direction, ED is required to be served at both phases or only at the DT phase. The use of RA and DT phases consecutively for small data transmissions brings significant signaling overhead to the system design. To this end, a number of optimizations have been proposed by 3 GPP in the recent releases. One of the principal enhancements introduced in Release 16 is the use of early data transmissions (EDT) for small data [6]. This feature allows to transmission small data already at the RA phase. As highlighted in [7], under specific conditions, the use of EDT allows one to maximize the system's capacity. The aim of this paper is to propose a model of the service process in 5G/6G mMTC systems by explicitly accounting for design specifics of RA and DT phases, including the EDT operational regime and traffic service specifics in uplink and downlink directions. To this end, we formulate the system model as a multi-stage queuing system with multichannel ALOHA at the RA phase and a queuing system with batch arrivals at the DT phase. The latter allows us to explicitly account for traffic impact consisting of asynchronous transmissions in the uplink direction and software updates in the downlink one. We establish the stability conditions and then proceed to investigate user- and system-centric performance metrics including delay and system throughput.