# Cluster-Based Transmission Diversity Optimization in Ultra Reliable Low Latency Communication
###### Abstract  
Intra-vehicular communication is an emerging technology explored spontaneously due to higher wireless sensor-based application demands. To meet the upcoming market demands, the current intra-vehicular communication transmission reliability and latency should be improved significantly to fit with the existing 5G and upcoming 6G communication domains. Ultra-Reliable Low-Latency Communication (URLLC) can be widely used to enhance the quality of communication and services of 5G and beyond. The 5G URLLC service is highly dependable for transmission reliability and minimizing data transmission latency. In this paper, a multiple-access scheme named Cluster-based Orthogonal Frequency Subcarrier-based Multiple Access (C-OFSMA) is proposed with 5G URLLC's high requirement adaptation for intra-vehicular data transmission. The URLLC demanded high reliability of approximately 99.999% of the data transmission within the extremely short latency of less than 1 ms. C-OFSMA enhanced the transmission diversity, which secured more successful data transmission to fulfill these high requirements and adapt to such a network environment. In C-OFSMA, the available sensors transmit data over specific frequency channels where frequency selection is random and special sensors (audio and video) transmit data over dedicated frequency channels. The minimum number of subcarrier channels was evaluated for different arrival rates and different packet duplication conditions in order to achieve 99.999% reliability within an air-interface latency of 0.2 ms. For the fixed frequency channel condition, C-OFSMA and OFSMA were compared in terms of reliability response and other packet duplication. Moreover, the optimal number of clusters was also evaluated in the aspects of the reliability response for the C-OFSMA system. 1 2022 20  
and Low-Latency Communication (URLLC), and massive Machine-Type Communication (mMTC) [5]. URLLC strictly maintains higher reliability within a stringent latency for time-critical application such as modern intra-vehicular communication. A modern vehicle has around 60\(\sim\)100 numerous wireless sensors such as the fuel sensor, ultrasonic sensor, exhaust gas sensor, and video-audio sensor, for real-time safety applications, monitoring traffic conditions, and environmental conditions, etc. [6, 7]. A metaphorical wireless sensor-equipped vehicle is presented in Figure 1. Three different types of sensors (general, audio, and video sensors) are placed in different locations of the vehicle, which ensures the expected reliability and latency. Relying on the latency requirement, URLLC comes in two forms: long-term Ultra-Reliable Communication (URC), and short-term URC [8]. The long-term URC applications demand a latency of \(>\)10 ms, and short-term URC ensuring demands a latency of \(\leq\)10 ms. Long-term URC is appealing for use in cases that require resilient wireless connectivity, such as disasters or emergency scenarios. There are remote interactions with a higher latency budget, such as adjusting the flight route of a drone. Short-term URC maintains a very stringent latency in applications, such as communication among machines and robots [9]. Latency and reliability are completely contradictory concepts. The latency requirement significantly increases to attain a high transmission reliability. In mission-critical environments such as intra-vehicular sensor communication, it is extremely challenging to achieve high reliability within a stringent latency of \(\leq\)1 ms. However, in our survey, an intra-vehicular communication environment, a WSN scheme with low latency and high transmission reliability has not been implemented yet. All the previous works were based on more than 5 ms latency. To overcome this constraint, we devised a scheme that effectively addresses short-term URC. The main focus of this article was not only to ensure short-term URC, but also to maintain higher reliability for intra-vehicular communication.