# Cluster-Based Transmission Diversity Optimization in Ultra Reliable Low Latency Communication
## 2 Related Work  
Current industries emphasize sensor-based wireless application networks to guarantee speedy data transfer in mission-critical applications. Many researchers aim at achieving a very high data transmission reliability in the intra-vehicular network within short latency. Previously, the Controller Area Network (CAN) [13] serves as the foremost way out for intra-vehicular communication which was developed in the 1980s by Robert Bosch GmbH. CAN has always been welcomed due to its low cost and higher reliability. In the last two decades, CAN-C [14] became more reliable for its low latency feature. The network protocol has been widely used for vehicle body electronics, chassis, and power-drain related issues. Without any external interference, the data transfer rate can vary from 125 kb/s to 1 MB/s. However, having low bandwidth and usage of a shared medium in data communication makes the data rate slower [15]. Alongside CAN network, Local Interconnect Network (LIN) [16] was also in the market, but due to the link speed of 20 kb/s [17], it has not stayed in a more extended period. Another x-by-wire application-driven network FlexRay was being developed from 2000 to 2009 [18]. In the task involving safety measurement, FlexRay outperforms the market with a link speed of 10 MB/s [15]. TSN+AVB Ethernet is used in an intra-vehicular environment, and the dashcam unit sends data of 46 Bytes with a uniform distribution of 0.5 ms within to the receiver [19]. However, all of these widely used sensor-based networks have brought a slew of issues: having wired architecture, complex structure, an increase in weight, and a large number of sensor placements. This renders these networks unsuitable for intra-vehicular data transmission scenarios as stringent latency is often required with high reliability. The wireless network is popular and has replaced the wired architecture. In this consequence, CDMA and OFDM have been taken into consideration in [17], but they did not reveal any experimental procedure. Bluetooth and WiFi have always been acceptable, but there are only some primary tasks to deal with, such as infotainment and multimedia. An IoT enabled Intra-Vehicle Wireless Sensor Networks to increase data communication reliability has been accepted in [20], but they consider a transmission period of 60-120 ms. Another wireless mesh topology named ZigBee has been analyzed the reliability and link speed in [21] for intra-vehicular sensor networks. However, the packet transmission latency for the ZigBee network is 16 ms [22, 23] which is still high. The mentioned networks provide high reliability as they can handle high link speeds. However, these schemes caused network instability, interference, momentary failure, and high transmission latency. Table 1 summarizes the comparison of existing protocols. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**System** & **Latency** & **Data Rate** & **Channel Bandwidth** & **Transmission Power** \\ \hline CAN [13] & 5 ms & 2.5 Mb/s & 50\(\sim\)95 MHz & \(-\)50 dBm \\ Bluetooth LE [23] & 3 ms & 305 kb/s & 2 MHz & \(-\)20\(\sim\)10 dBm \\ Ultra Wideband & & & & \\ (UWB) [24] & Evolving & 53\(\sim\)480 Mb/s & \(\geq\)500 MHz & \(-\)41.3 dBm \\ ZigBee [25] & 16 ms & 20\(\sim\)250 kb/s & 2 MHz & \(-\)32 dBm \\ OFSMA [11] & 0.1 ms & 1 Mb/s & 10 KHz & \(-\)20 dBm \\ C-OFSMA & 0.2 ms & 1 Mb/s & 10 KHz & \(-\)20\(\sim\)\(-\)5 dBm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of existing protocols with different matrices. At the end of 2015, researchers predicted that the usages of wireless sensors for intra-vehicular communication would increase significantly in the near future [26, 27]. After that, smart vehicles were designed with many sensors, installed in various positions and performing distinct activities, e.g., engine battery, temperature, the battery or fuel level, the pressure of the tire, interior temperature, speed, seat belt, door locks, passengers positions, back-light, or retrofit rain sensor.