# Channel Estimation Based on Statistical Frames and Confidence Level in OFDM Systems
## 6 Simulation Results  
### The Performance in Static Multipath Channels  
The profiles for the China digital television (DTV) Test 1 st (CDT1) [18], Brazil A, Brazil B and Brazil D channel models are shown in Tables 1 and 2, respectively. The Brazil A, Brazil B and Brazil D channels were developed from the Brazilian field test on digital terrestrial television broadcasting (DTTB). The main simulation parameters based on the CP-OFDM system are represented in Table 3. Table 4 proposes a computational complexity comparison of the five channel estimation methods. A simplified radix-two IFFT/FFT approach whose implementation cost is much lower is adopted to process the cyclic convolution operation, and the IFFT/FFT is taken based on \(2N\) points. The five channel estimation methods are based on \(2N\) points division, and \(N=300\) is utilized in the proposed CP-OFDM  
to be 5, 7, 9, 11 and 13 in the CP-OFDM receivers to calculate the confidence level. The modulation mode 16 QAM is chosen to equalize the constellation signals in the receiver of the CP-OFDM system. The length of CP is 180 OFDM subcarriers, and the OFDM symbol consists of 300 subcarriers. In the five channel estimation methods, block-type pilots are inserted in all the subcarriers of the OFDM symbols in the frequency domain. In the simulation, the Doppler spread is chosen to be 20 Hz, 60 Hz and 80 Hz in Brazil A, Brazil B and Brazil D, respectively.  
Figures 3 and 4 present the SER performance in the 16 QAM-modulated CP-OFDM system over static CDT1 and Brazil A, respectively. As shown in Figure 3, the gap of the SNR gain among \(T_{1}=5\), \(T_{2}=7\), \(T_{3}=9\) and \(T_{4}=11\) is about 1.5 dB, 0.5 dB and 0.3 dB at the SER of  
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In Figure 4, the gap of the SNR gain among \(T_{1}=5\), \(T_{2}=7\), \(T_{3}=9\) and \(T_{4}=11\) is about 1.4 dB, 0.8 dB and 0.7 dB at the SER of \(10^{-2}\), respectively. Therefore, the SER curves of \(T_{1}=5\) have the best SER gain under the CDT1 and Brazil A multipath fading channels.  
Figure 5 presents the SER performance of the proposed confidence level channel estimation method over static CDT1. Compared with the threshold value method, the ideal channel estimation method outperforms the threshold value estimation method with the SNR gains by only about 0.1 dB SNR gains at the target SER of \(10^{-2}\). The proposed confidence level method outperforms the conventional LS method by about a 1.6 dB SNR gap at the target SER of \(10^{-3}\). It could be seen that AWGN is the main factor that impacts the accuracy of channel estimation [16].  
Under the static CDT1 multipath channel, the threshold value method has the best channel estimation performance since CDT1 belongs to the light frequency selective fading channel. In the static multipath fading condition, the interference caused by noise is relatively small. Therefore, selecting a suitable threshold can remove most of the noise interference in the OFDM receivers. The CDT1 channel has a small amount of side paths. The IMMSE method suppresses the noise while not restraining the energy of the main path; thereby, the IMMSE method has a good channel estimation effect. The SER curve of the confidence level is similar to that of the Chi-square distribution method under static CDT1 since the false alarms obey the Chi-square distribution strictly. Therefore, the SER curves of the proposed confidence level method and Chi-square distribution method can suppress the noise effectively.