# 3 GPP 5G V2X Scenarios: Performance of QoS Parameters Using Turbo Codes
## 1 Introduction and Related Work
The authors propose a scheme which incorporates the QoS parameter that reflects the latency required in both user equipment and the base station and the aim is to maximize the throughput of all vehicle-to-infrastructure (V2I) links, while meeting the latency constraints of vehicle-to-vehicle (V2V) links. Reference [16] presents the novel Multi Level QoS (MLQ) feature, a candidate enhancement for 3 GPP Release 16 specifications. MLQ feature aims at improving service availability and continuity, specifically targeting safety critical V2X services. In [17] the authors mention that in V2V communication, link reliability has been regarded as an important QoS performance metric and they analyze link reliability of the centralized mode (Mode 3) for LTE\(-\)based V2V from the physical and medium access control (MAC) layers perspectives. The authors also propose a resource size control (RSC) method for improving link reliability. The enhancements in Release 14 of LTE\(-\)V2X support advanced automated driving services and adapt it to the high mobility environment of vehicular networks guaranteeing backward compatibility [18; 19]. The 5G\(-\)V2X NR modifications designed to enhance side\(-\)link PC5 interface will include low density parity check (LDPC) and polar codes designed to offer higher robustness without increasing encoding and decoding complexity. The drawback of this channel coding technique is the channel overloading by hybrid automatic repeat request (ARQ) retransmission using incremental redundancy, where the network can retransmit erroneously received data and the device combines the soft information from multiple transmission attempts [14]. However, the coding gain from turbo codes lead to longer transmission range and a better V2V transmission efficiency especially for security\(-\)related autonomous driving applications. However, none of the above works includes channel coding optimizations at physical layer so that the required QoS levels are met. Specifically, some papers focus on RSCmethods [17], whereas other papers focus on radio resource management [15] and the last subcategory of papers optimize the QoS papers triggered by dynamic radio conditions [16]. The idea of focusing on physical layer channel coding process and particularly using turbo coding in 5G V2X systems has been initially discussed in [20; 21; 22; 23] without, however, the channel coding parameters being optimized for realistic QoS indicators. Turbo decoding adds significant complexity to the system and the most popular algorithms to be used are log maximum a\(-\)posteriori (log-MAP), max-log-MAP and soft output Viterbi algorithm (SOVA). Turbo codes compensate complexity with BER performance and for large frame lengths complexity and latency are remarkable [24]. Considering 3 GPP 5G V2X Release 16 implementation scenarios, the motivation of this work is to investigate LTE turbo coding performance for V2V transmission and small frame lengths. Particularly, we examine which of these scenarios can be implemented considering different QoS parameters. For this purpose, we simulate nine V2V simulation scenarios with LTE turbo coding at the physical layer and a geometry\(-\)based stochastic mobile channel (GEMV) appropriate for realistic urban scenarios. An initial approach has been investigated in [20], where only a small frame length of 128 bits is examined without the message size to be investigated in the simulation results. Additionally, not many vehicle density values are considered. In the present work we establish the nine V2V simulation scenarios in a way that they give a clear picture of QoS issues considering different vehicle speeds, density and data rates. The general idea, according to [21], is to use the specific simulation results in a future system with real--time coding parameters dynamic prediction, which is based on the conditions of the external environment. In this case the specific QoS parameters of the specified scenarios have to be satisfied.