# An Improved Channel Estimation Technique for IEEE 802.11p Standard in Vehicular Communications
## 5 Simulation Results and Analysis
The RMSE values obtained at SNR equal to 8 dB for LS, DFT, CDP, STA, and iCDP are: 0.2111, 0.2046, 0.209, 0.1865, and 0.1860 respectively. If we go on further at the point where SNR is 26 dB, then the STA and CDP schemes have roughly similar RMSE value of 0.1227 and the iCDP scheme has a value of 0.1071. The RMSE values of DFT and LS schemes are 0.1916 and 0.1943 respectively. Finally, at an SNR of 40 dB, the RSME value of iCDP is 0.0899 and corresponding RMSE values for CDP and STA are 0.9796 and 0.1112 respectively. The RMSE for LS and DFT seems saturated at roughly 0.1916 with no further improvement in performance. This result demonstrates the performance improvement of the proposed scheme over DFT/LS, STA, and CDP schemes with the RMSE percentage differences of 72.3%, 21.1%, and 8.5% respectively at SNR of 40 dB. Figure 8: HIPERLAN-E channel model with Data Symbols = 100. It is equally important to visualize the 3-dimensional image of the actual HIPERLAN-E channel and its estimation by the proposed iCDP scheme to show that it tracks the channel in time and frequency domain for the different SNR values. Figure 10 shows the effect of lower and higher SNR on the HIPERLAN-E channel model. Figure 10a shows the actual channel conditions at under \(f_{d}=1200\), data symbols = 200, and SNR = 15 dB. Figure 10b shows the estimation of the actual channel in Figure 10a through the proposed scheme. On the other hand, Figure 10c shows another channel conditions at SNR = 35 dB and Figure 10d shows its estimation through the proposed scheme. It is evident from Figure 9 that at lower SNR, the correlation among the data symbols and frequency subcarriers suffers due to the randomness of the noise. The proposed scheme performs relatively better than CDP under lower SNRs because it constructs the data pilots after taking into consideration the front and previous data symbol in time domain and front and previous frequency carrier in the frequency domain. Figure 11 shows the multipath components of the HIPERLAN-E channel used in the simulation of the proposed scheme. The bandlimited impulse response in Figure 11a shows 18 different paths that are arriving at the receiver vehicle with different amplitudes and delays. Figure 11b shows the contribution of these components with the passage of time up to 850 \(\upmu\)s. The delay of the first path is set to 0 \(\upmu\)s. For subsequent paths, a 1 \(\upmu\)s delay corresponds to a 300 m difference in path length. In vehicular communication, the multipath environments have reflected paths that can be up to several kilometers longer than the shortest path. With the path delays specified above, the last path is 528 m longer than the shortest path, and thus arrives 1.76 \(\upmu\)s later which is also obvious from the specifications in Table 2. The path delays and path gains specify the channel's average delay profile. Typically, the average path gains decay exponentially with delay (i.e., the dB values decay linearly), but the specific delay profile depends on the propagation environment. In the delay profile specified in Figure 11, we assumed the specifications of Table 2 HIPERLAN-E channel model. Figure 9: Root-mean-square error (RMSE) comparison for HIPERLAN-E channel model with Data Symbols = 200. Figure 11: Multipath components of the HIPERLAN-E channel: **(a)** Bandlimited impulse response. **(b)** Multipath fading components after 850 \(\upmu\)s.  
Figure 10: Actual and Estimated HIPERLAN-E channels: **(a)** Actual channel at SNR = 15 dB. **(b)** Estimated channel at SNR = 15 dB. **(c)** Actual channel at SNR = 35 dB. **(d)** Estimated channel at Signal-to-Noise Ratio (SNR) = 35 dB.