# A Systematic Review of Perception System and Simulators for Autonomous Vehicles Research  
[PERSON]  
1 Division de Sistemas e Ingenieria Electronica (DSIE), Universidad Politecnica de Cartagena, Campus Muralla del Mar, s/n, 30202 Cartagena, Spain; [EMAIL_ADDRESS] (C.F.); [EMAIL_ADDRESS] (A.P.)  
[PERSON]  
1 Correspondence: [EMAIL_ADDRESS] (F.R.); [EMAIL_ADDRESS] (P.J.N.); Tel.: +34-968-32-6589 (F.R.)1  
[PERSON] and [PERSON]  
1 Division de Sistemas e Ingenieria Electronica (DSIE), Universidad Politecnica de Cartagena, Campus Muralla del Mar, s/n, 30202 Cartagena, Spain; [EMAIL_ADDRESS] (C.F.); [EMAIL_ADDRESS] (A.P.)1  
Footnote 1: email: {dred  
Systematic testing of autonomous vehicles can be performed in simulation or in the physical world. Physical tests offer real testing scenarios, and engineers can use actual vehicles instead of models. However, regulations restrict the use of these vehicles in cities; thus, to perform tests with real AVs, one needs access to expensive hardware and field tests, which consume a considerable amount of time. According to recently published reports [5; 6], it is impossible to perform empirical field tests that verify the safety of autonomous cars in a reasonable timeframe. In this context, simulation, modelling and testing has the potential to fill the gap and enable rigorous, controlled, and timely evaluation AV systems.  
The research community recognizes three types of simulations [7]: live, virtual, and constructive (LVC). A live simulation is simply an operational test, with sensors used to identify which systems have been damaged by simulated firings, using real forces and real equipment. It is the closest exercise to real use. A virtual simulation (\"X-in-the-loop\") might test a complete system prototype with stimuli produced either by a computer or otherwise artificially generated. This sort of exercise is typical of a developmental test. A constructive simulation is a computer-only representation of a system or systems. Therefore, a simulation can vary from operational tests to a fully computer-generated representation (i.e., no system components involved) of how a system will react to multiple inputs. It can be used for several purposes: (1) The design and evaluation of operational and development tests; (2) simulation, taking into account the levels of system aggregation, modeling level of the individual components of a system (for example, the system software), or modeling level of the system as a whole--to model a complete prototype and model multiple system interactions (i.e., a RADAR component with the rest of the system).  
However, as is exposed in [8], the first thing that must be taken into account is the type of characteristics or systems that can be tested through simulation (see Figure 1). In this work, we focus on the perception of autonomous vehicles as offering greater autonomy and complexity, emphasizing on their subsystems [9]: Environmental perception, and localization.  
In this paper, we present a systematic literature review on simulators applied to system perception in autonomous vehicles. For this, the technological and legacy aspects involved in the development of AVs are presented in detail, specifying the different alternatives available to simulate and test each of the subsystems.  
The paper is organized as follows: Sections 2 and 3 detail the technologies habitually engaged to capture information from the environment and to estimate position of the autonomous vehicles. Section 4 discusses the current fusion technics used to combined information from the perception systems. Section 5 carries out an exhaustive collection of tools and platforms capable of performing simulation tasks in the AV ambit. Section 6 shows the current state of legislation with regard to the  
Figure 1: Typical autonomous vehicle system.  
legal aspects of autonomous driving and testing possibilities of AV in different countries. Section 7 presents our conclusions.