# Reinforcement Learning Approach for Adaptive C-V2X Resource Management
## 2 C-V2X Mode 4
### C-V2X Resource Management  
The modulation coding scheme (MCS) is associated with the modulation order, which refers to the extent of modulation, such as QPSK, 16 QAM, 64 QAM, and 256 QAM. The modulation order parameter denoted as \(Q_{m}\) in 3 GPP is used to specify the modulation order. The MCS index (\(I_{MCS}\)) determines the maximum number of useful bits sent per resource element (RE). The performance of C-V2X communication is contingent upon the quality of the radio connection. The higher the MCS index, the greater the RB allocation, increasing the transmission capacity for vital data. Furthermore, it should be noted that a reciprocal relationship exists between radio conditions and the \(I_{MCS}\) used. Specifically, when radio circumstances deteriorate, the \(I_{MCS}\) is downgraded, decreasing the capacity to transmit vital data. In other terms, the performance of the MCS is contingent upon the frequency of errors occurring. In general, it is customary to establish an error probability threshold that is equivalent to 10%. The \(I_{MCS}\) is modified to ensure the error probability remains under a specified threshold, even when faced with fluctuating radio circumstances. The \(I_{MCS}\) is afterward used to ascertain the transport block size (TBS) estimation. The MCS index, TBS index (\(I_{TBS}\)), and the associated modulation order (\(Q_{m}\)) value have been standardized by the 3 GPP [34]. Upon calculating the \(I_{TBS}\) based on the \(I_{MCS}\), the value of \(N_{PRB}\), which represents the number of physical resource blocks required to transmit one unit of beacon data (in bits), is determined. The 3 GPP provided a reference table that outlines the TBS indices and the corresponding number of physical resource blocks based on the beacon data sizes expressed in bits. The combination of the TBS index, number of physical resource blocks, and beacon data size was cited by the 3 GPP. The whole beacon payload in the Mode 4 configuration consists of two components: the beacon data transport block (TB) and the sidelink control information (SCI). These two segments of the TB and SCI need an independent allocation of resources. Therefore, the total number of \(N_{PRB}\) required for a single complete data transmission equals \(N_{PRB}\) multiplied by 2. The coding rate (CR), spectral efficiency, and lowest signal-to-interference-plus-noise ratio (SINR) are computed for the chosen number of \(N_{PRB}\) in order to evaluate the data transmission process. The data transmission capacity of a certain number of physical resource blocks (PRBs) is contingent upon the modulation order and code rate. Currently, the C-V2X standard accommodates 16-QAM (Quadrature Amplitude Modulation) and QPSK (Quadrature Phase-shift Keying) modulations, which may be used with various code rate configurations. The expression for the effective coding rate (CR) is as follows:  
\[CR=\frac{TB}{N_{PRB}\times\mathcal{S}\times\mathcal{P}\times Q_{m}}, \tag{1}\]  
where \(TB\) is the transport blocks in bits, \(N_{PRB}\) is the number of physical resource blocks, \(\mathcal{S}\) is the number of symbols per subcarrier, \(\mathcal{P}\) is the number of subcarriers per PRB, and \(Q_{m}\) is the modulation order [35]. The concept of spectrum efficiency may be traced back to [PERSON]'s theorem, which mathematically defines the maximum amount of information that can be sent across a communication channel,  
\[\hat{C}=B_{c}\text{log}_{2}(1+SNR), \tag{2}\]  
where \(\hat{C}\) is the capacity in units of bits per second (bit/s), \(B_{c}\) is the channel bandwidth in Hertz, and SNR is the signal-to-noise ratio. [PERSON]'s theorem is generally acknowledged as the prevailing constraint on the maximum capacity of information that may be sent across a communication channel. Hence, an increase in signal power or a decrease in interfering signal strength directly corresponds to an amplification in the capacity of the channel to transmit information. The information-carrying capacity may be considered unlimited in the absence of noise and interference.