A Timing Estimation Method Based-on Skewness Analysis in Vehicular Wireless Networks
- A new cross-correlation, summing up and skewness analysis (denoted CSS) method is proposed which can be used to estimate the time offset in positioning sensors of vehicular wireless networks.
- The CSS method provides better precision than some well-known time estimation techniques, especially in low signal to noise ratio (SNR), and multi-path environments, which is very important for vehicular wireless networks.
- The CSS method can also be used in other wireless communications which use OFDM with repeated preamble symbols, such as IEEE 802.11a.
2. OFDM Preamble Structure
2.1. Modulation Technique
2.2. Preamble Symbols
3. Related Work
3.1. SC Method
3.2. RMB Method
3.3. MathWorks Method
3.4. Liu et al. Method
4. Proposed Timing Estimation Method
4.3. Skewness-Analysis and Threshold
4.3.1 Statistical Characteristics of the Summing-Up Samples
- Standard Deviation
4.3.2. Relationship between Estimation Error, Skewness and Threshold
4.3.3. Relationship between Skewness and Threshold
5. Simulation Setup and Result Analysis
5.1. Simulation Setup
5.1.1. System Model
|Number of subcarriers||52|
|Symbol duration||8 μs|
|Guard time||1.6 μs|
|FFT period||6.4 μs|
|Preamble duration||32 μs|
|Subcarrier spacing||0.15625 MHz|
|Vehicle speed||100 km/h|
5.1.2. Transmission Channel
|Tap||Channel A||Channel B||Doppler|
|Relative Delay (ns)||Average Power (dB)||Relative Delay (ns)||Average Power (dB)||Spectrum|
5.1.3. Performance Metric
5.2. Performance Results and Analysis
5.2.1. Estimation Error
5.2.2. Correct Percentage
- When Eb/N0 is high, the multipath in the ITU channel causes the peaks to move to the right, making the timing estimation incorrect. Take the SC-80 method as an example, which is illustrated in Figure 16. The percentage will be close to 0 but will not reach 0. On the other hand, Figure 17 gives the corresponding results for the CSS method. This shows that the maximum peak with the CSS method does not move in the multipath channel, and only some smaller peaks are generated, so the percentage will be nearly equal to 100% for a high Eb/N0.
- When Eb/N0 is very low (close to −10 dB), the noise levels are too high, so it is too difficult to locate the peak, so the percentage is again close to 0.
- For Eb/N0 around 0 dB, the signal energy is close to that of the noise, so it is easier to locate the peak. Now because of the randomization of noise, it’s likely that the estimated time happens to be the true time delayed.
Conflicts of Interest
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Cui, X.; Li, J.; Wu, C.; Liu, J.-H. A Timing Estimation Method Based-on Skewness Analysis in Vehicular Wireless Networks. Sensors 2015, 15, 28942-28959. https://doi.org/10.3390/s151128942
Cui X, Li J, Wu C, Liu J-H. A Timing Estimation Method Based-on Skewness Analysis in Vehicular Wireless Networks. Sensors. 2015; 15(11):28942-28959. https://doi.org/10.3390/s151128942Chicago/Turabian Style
Cui, Xuerong, Juan Li, Chunlei Wu, and Jian-Hang Liu. 2015. "A Timing Estimation Method Based-on Skewness Analysis in Vehicular Wireless Networks" Sensors 15, no. 11: 28942-28959. https://doi.org/10.3390/s151128942