# A Non-WSSUS Channel Simulator for V2X Communication Systems
## 3 Multicarrier Data Frames of the DSRC and LTE-V2X Standards
### General Overview of IEEE 802.11p and LTE-V2X Specifications  
The IEEE 802.11p standard was developed as an amendment to the specifications for WLANs to address wireless communication in vehicular environments [4; 5]. This standard presents the specifications for DSRC systems in the 5.9 GHz band. The IEEE 802.11p transceivers use OFDM as a modulation technique, in which a block of data is transmitted through equidistant subcarriers. The data transmission can be performed over three different bandwidths, which can be 5, 10, or 20 MHz. The preferred bandwidth is 10 MHz since it is more robust against the time dispersion of the transmitted signal [4]. The IEEE 802.11p standard considers a total of 64 subcarriers, among which 48 are used for data transmission and four are used as pilot subcarriers. The remaining 12 subcarriers do not transmit information to avoid interference between adjacent bands. The parameters of an IEEE 802.11p OFDM symbol for a 10 MHz bandwidth are shown in Table 1[11]. Furthermore, the frame structure considers short training symbols (STSs) with a duration of 1.6 \(\upmu\)s and long training symbols (LTSs) of 6.4 \(\upmu\)s. In addition, the specifications consider a guard interval (GI) of 1.6 \(\upmu\)s to reduce intersymbol interference. Figure 1 shows the frame structure for a typical 10 MHz bandwidth, as specified in the IEEE 802.11p. First, ten STSs (\(t_{1}\),..., \(t_{10}\)) are considered as a preamble for signal detection, automatic gain control, and diversity selection (\(t_{1}\),..., \(t_{7}\)), as well as for coarse frequency offset estimation and timing synchronization (\(t_{8}\), \(t_{9}\), and \(t_{10}\)). Next, there are two LTSs (\(T_{1}\) and \(T_{2}\)) that follow two GIs, which are placed after the tasks in the preamble. The LTSs \(T_{1}\) and \(T_{2}\) are employed for channel estimation and fine frequency offset estimation. Then, the frame considers a header that consists of a GI and a signal block where the bit rate and frame length are defined. Finally, the frame ends with the the data field, which includes one GI of 1.6 \(\upmu\)s for each information block. The IEEE 802.11 standard does not restrict the frame length, but it recommends a size between one and 4096 bytes according to the application requirements [11]. With respect to LTE-V2X, 3 GPP included a set of specifications to the LTE standard for applications in vehicular environments [14]. Two operation modes are defined in such 3 GPP specifications. The first mode allows vehicles to communicate with the cellular network for cloud-based applications, whereas the second mode enables V2X short-range communications. This latter mode is based on the PC5 interface that is considered for direct D2D communications [14]. Such a mode is referred to as sidelink transmission [9]. The PC5 interface operates in the 5.9 GHz band using SC-FDMA as the transmission scheme. The specifications of the PC5 interface consider resource blocks (RBs) that consist of 12 subcarriers. Depending on the bandwidth, the transmission scheme is scalable by carrier aggregation, which adds new resource blocks to the symbol. For a typical 10 MHz bandwidth, the specifications define 50 RBs, which occupy a total of 600 data subcarriers [14]. The main parameters of LTE-V2X employing the PC5 interface for a 10 MHz bandwidth are shown in \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **IEEE 802.11p** & **LTE-V2X** \\ \hline Data subcarriers (\(N_{pl}\)) & 48 & 600 \\ \hline Pilot (\(N_{pp}\)) & 4 subcarriers & 4 symbols \\ \hline Frequency spacing between subcarriers (\(\Delta f\)) & 156.25 kHz & 15 kHz \\ \hline Guard interval & 1.6 \(\upmu\)s & 4.69 \(\upmu\)s \\ \hline Symbol duration without Guard interval & 6.4 \(\upmu\)s & 66.31 \(\upmu\)s \\ \hline Total symbol duration (\(T_{s}\)) & 8 \(\upmu\)s & 71 \(\upmu\)s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: OFDM symbol parameters for IEEE 802.11p and LTE-V2X with a 10 MHz bandwidth [11; 14]. Figure 1: IEEE 802.11p frame structure with a 10 MHz bandwidth [11]. Table 1[14].