Wireless Data Transmission for High-Speed Train Control 指導教授：黃文傑 老師 指導教授：黃文傑 老師 學 生：曾凱霖 學 生：曾凱霖 學 號： M 學 號： M 無線通訊實驗室 無線通訊實驗室

Outline Multipath fading characterization Multipath fading characterization Delay Spread Delay Spread Doppler Shift Spread Doppler Shift Spread Channel Model Channel Model Realizable Analysis Realizable Analysis Conclusion Conclusion

Multipath fading characterization (1/2) Time Dispersion ： Time variations of the channel are caused by motion of the antenna. Time variations of the channel are caused by motion of the antenna. Moving antenna gives Doppler spread. Moving antenna gives Doppler spread. Fast fading requires short packet durations ， thus high bit rates. Fast fading requires short packet durations ， thus high bit rates. Interleaving may help to avoid burst errors. Interleaving may help to avoid burst errors.

Multipath fading characterization (2/2) Frequency Dispersion ： Delay reflections cause ISI. Delay reflections cause ISI. Channel equalization may be needed. Channel equalization may be needed. Frequency selective fading. Frequency selective fading. Multipath delay spreads require long symbol times. Multipath delay spreads require long symbol times. Frequency diversity or spread spectrum may help. Frequency diversity or spread spectrum may help.

Dealy Spread (1/4) Caused by multipath reflections. Caused by multipath reflections. In time dispersive medium. In time dispersive medium. Delay spread can result in ISI. Delay spread can result in ISI. Delay spread limits transmission rates. Delay spread limits transmission rates. Ex ： Ex ： Environment Avg. Delay Spread In-building In-building Suburban Suburban Urban Urban

Dealy Spread (2/4) Excess delay spread is the overall span of path delay Excess delay spread is the overall span of path delay RMS delay spread is a weighted measure RMS delay spread is a weighted measure Mean excess delay Mean excess delay

Delay Spread (3/4)

Delay Spread (4/4)

Doppler Shift(1/5) portable transmits a tone at f c portable transmits a tone at f c for fixed transmitter, the received signal is for fixed transmitter, the received signal is where where but if the transmitter moves, the propagation time changes with times, but if the transmitter moves, the propagation time changes with times, the received signal is the received signal is where is the original phase shift where is the original phase shift vmvm d0d0

Doppler Shift (2/5)

Doppler Shift (3/5) Doppler shift ： Doppler shift ： The frequency of received signal ： The frequency of received signal ： From (1), if v= 3 miles/hr, f D = 4 Hz at 910 MHz From (1), if v= 3 miles/hr, f D = 4 Hz at 910 MHz if v= 60 miles/hr, f D = 80 Hz if v= 60 miles/hr, f D = 80 Hz

Doppler Shift (4/5) Power spectra of multiplicative disturbance Power spectra of multiplicative disturbance <- Theoretical spectra for an omni-directional sinusoidal

Doppler Shift (5/5)

400MH z 2GHz5.2GHz25GHz45GHz 傳輸頻 寛 很小小中大大 都卜勒位移133Hz666Hz1.7KHz8.3KHz15KHz 細胞覆 蓋範圍 半徑 大 (>10k m) 中 ( 數 公里 ) 小 ( 數公 里 ) 小 (<1km) 時間 約 5s 約 2s <1s <1s<30s<30s 接收端大中中小 註：火車車速 360km/hr ，細胞覆蓋範圍半徑以衰減 100dB 推算

Channel Model (1/2) Line-coverage. Line-coverage. The rails of high-speed railway become more smooth. The rails of high-speed railway become more smooth. The received signal has a dominant LOS. The received signal has a dominant LOS. The movement of trains brings Doppler frequency shift. The movement of trains brings Doppler frequency shift. An empty tunnel can be compared with a hollow waveguide. An empty tunnel can be compared with a hollow waveguide.

Channel Model (2/2) Received signal ： Received signal ： 其中 其中 ： band limited zero-mean Gaussian noise ： band limited zero-mean Gaussian noise

Realizable Analysis FER & BER FER & BER Undetected errors Undetected errors ISI & Doppler shift ISI & Doppler shift

Conclusion Diversity tech. Diversity tech. Increase data rate Increase data rate Adaptive equalizer. Adaptive equalizer.