## 4 Simulation Model  
The system model shown in Figure 2 represents the details of the transmitter, receiver and propagation channel (only for a single LED unit in detail for simplicity). The analysis is performed by both SISO and MISO configurations. For the simulation work, the system modeling is performed in MATLAB, based on the analytical model presented in the previous section. MATLAB provides a comprehensive set of tools for signal processing and is considered to perform numerical computations in the most efficient way. Apart from the ease of RF domain component modeling using its available library of toolboxes, MATLAB's inbuilt set of commands allows the implementation of large and complex equations of optical components. Firstly, the stream of bits is generated using a Pseudo Random Binary Sequence (PRBS) generator. The bit series is passed through an OOK modulator and pulse shaping is performed to band limit the information signal. A bias control is required to ensure linear operation of the LED unit and it also provides the required amplification to the signal before optical modulation. The data-modulated signal is transmitted using an LED unit into the free space, where different channel effects are considered to model a practical VLC system for an ITS. A reflector is used to simulate a diffused form of the LOS signal, with reduced strength and a delay which is higher than the coherent wavelength of the LED. In addition to that, an interference is introduced by a different source which imparts its visible light intensity on to the photo-receiver. In a real-world ITS, the unwanted signal can originate from a number of possible sources, such as a traffic light, billboard or a near-by vehicle. The simulations are performed using MATLAB, which provides a high performance and integrated environment for modeling and analysis of engineering problems. It provides a large set of tools and a library for signal processing and data visualization, which are required for the presented VLC model.  
The receiver consists of an optical filter which aligns the incident light for the photodetector. The composite received signal, consisting of a LOS path signal, an interferer and a non-LOS reflected form of the transmitted signal, is converted to electrical form by a bandwidth-limited photodetector. The field of view (_FOV_) and responsivity (_R_) of the photodiode are the major parameters affecting the performance of the photodetector, which have been improving with the advancements in this area. After opto-electric conversion, the RF signal is filtered through an RF bandpass filter to exclude any out-of-band noise from the photodetector. The recovered signal is amplified and demodulated using an envelope detector for BER analysis. A simple Zero Forcing (ZF) equalizer is used to decode the received signal for the case of MISO transmission. The performance of the received signal is further  
Figure 2: System model consisting of the transmitter, channel and receiver modules to realize the SISO or MISO transmission.  
improved using a blind-adaptive time domain equalizer, as presented in [41]. The set of parameters used for the simulation work is shown briefly in Table 1. For a realistic approach, the experimental set of values for the optical components [12; 28] and \(4\times 1\) MISO channel [41] are used. A training sequence of 10 k length is used to optimize the equalizer weights at the start of the transmission. Afterwards, the channel state information from the MISO processing is used to change the equalizer weights. For practical V2V communication where channel conditions are constantly changing, the frequent transmission of the training sequence will considerably reduce the effective data rate. Therefore, the use of MISO processing at the receiver becomes more useful in such scenarios.