## 2 Related Works
### Existing DSRC-Based VANET
#### 2.1.2 Mathematical Model for Physical Layer OFDM  
Both uplink and downlink operations are possible with hybrid vehicular communication. Uplink DSRC to other communication networks is taken into consideration. For one OFDM transmission, DSRC required 64 FFT subcarriers, while mobile networks required 256 FFT subcarriers. With DSRC OFDM, these FFT subcarriers are matched with padding zeros, making them comparable to the mobile network subcarrier [32; 33; 34]. Each OFDM symbol associated with 1/Q signaling in this mathematical model will be:  
For DSRC 64 FFT:  
\[I_{1}(t)=\sum_{k=-26}^{k=26}I_{k}\cdot\cos(2\pi k\Delta f_{1}(t)) \tag{1}\]  
\[Q_{1}(t)=\sum_{k=-26}^{k=26}Q_{k}\cdot\sin(2\pi k\Delta f_{1}(t)) \tag{2}\]  
For 256 FFT:  
\[I_{2}(t)=\sum_{k=-100}^{k=100}I_{k}\cdot\cos(2\pi k\Delta f_{2}(t)) \tag{3}\]  
\[Q_{2}(t)=\sum_{k=-100}^{k=100}Q_{k}\cdot\sin(2\pi k\Delta f_{2}(t)) \tag{4}\]  
For example, \(I\) stands for in-phase and \(Q\) stands for quadrature phase. The employment of two sinusoids with the same frequency and a 90\({}^{\circ}\) relative phase shift is referred to as I/Q signaling. When combining two separate wireless networks, such as IEEE 802.11P vehicular communication and IEEE 802.16 WiMAX, common physical layer orthogonal frequency division multiplexing (OFDM) parameters are needed to establish communication in order to enhance the range of CR-based vehicular networks. All observed RF signals are orthogonal in nature, and that can be modulated in amplitude, phase, and frequency by summing amplitude-modulated I/Q signals. Quadrature modulation is a type of modulation that uses both I and Q signals. Quadrature phase-shift keying is achieved by adding I  
Figure 2: Different vehicular communication scenarios using OpenFlow SDN controller. and Q carriers that have each been multiplied by +1 or \(-1\) in accordance with the incoming digital data [31]. For downlink transmission, i.e., mobile network to DSRC, the 16 QAM modulation type estimates the FFT subcarrier value. The OFDM 256 FFT physical layer is modulated with 16 QAM modulation. As a result, each 256 FFT OFDM signal is modulated with 14 bits per symbol, making the DSRC 64 FFT subcarrier comparable. The 64 FFT DSRC OFDM signal = 256 \(\times\) 1/4 bits (16 QAM). The 64 FFT subcarriers are separated into 52 used data carriers, 4 pilot subcarriers, and 8 unused subcarriers for DSRC. In IQ signaling, the 52 data carrier is modulated into +26 and \(-\)26 FFT. The 256 FFT carrier is divided into 200 usable data carriers, and the remaining 56 subcarriers are utilized for pilot and unused subcarriers in IEEE 802.16. In CR-based mobile networks, OFDM is employed as a digital modulation technique. Here, \(\Delta f\) denotes the frequency separation between subcarriers, and the carrier signal \(2\pi k\Delta f\) (\(t\)) at \(f_{c}\), where \(f_{c}\) is the determining factor for which technology is employed. The sent data are represented by \(C_{k}\), where \(k\) is the frequency offset index of the subcarriers for one sample. For DSRC vehicular communication, \(f_{c}\) is the common RF frequency of 5.9 GHz. In each time domain, \(f_{1}(t)\) represents the 64 FFT DSRC carrier frequency and \(f_{2}(t)\) represents the 256 FFT WiMAX carrier frequency. After applying I and Q function values from Equations (1)-(4), \(C_{k}\) is derived as follows in Equation (5):  
Each carrier frequency \(C_{k}\) can be represented as:  
\[C_{k}=I_{k}+j\cdot Q_{k} \tag{5}\]  
\(C_{k}\) is the input data signal, which is modulated to \(I_{k}\) and \(Q_{k}\) signaling. The \"\(j\)\" operator is utilized to convert a complex number to \(\sqrt{1}\) (90\({}^{\circ}\) phase shift), so \(C_{k}=\cos(k)+j\cdot\sin(k)\) signaling. Overall, these studies show the limitations of the existing V2V model for certain futuristic scenarios. Since the future applications in VANET will include multimedia and other real-time streaming between vehicles, we need optimized and enlarged bandwidth communications.