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Coherence Time Measurement in NTT Lab.

Coherence Time Measurement in NTT Lab. Date: 2009-7-14. Authors:. Purpose and content of this measurement. Doppler frequency is T.B.D. in the current channel model document [1]. We showed that Doppler frequency is small compared to the value which is suggested in TGn channel model [2] [3].

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Coherence Time Measurement in NTT Lab.

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  1. Coherence Time Measurement in NTT Lab. Date: 2009-7-14 Authors: W. Yamada, K. Nishimori and Y. Takatori (NTT)

  2. Purpose and content of this measurement • Doppler frequency is T.B.D. in the current channel model document [1]. • We showed that Doppler frequency is small compared to the value which is suggested in TGn channel model [2] [3]. • Coherence time / Doppler frequency is one of the key parameters to evaluate MU-MIMO. • We conducted coherence time measurements in a typical office room to suggest typical coherence time / Doppler frequency in an office environment. W. Yamada, K. Nishimori and Y. Takatori (NTT)

  3. Measurement equipment Sleeve antenna (Omni-directional) Sleeve antenna (Omni-directional) Wireless Communication Analyzer (Base band real-time spectrum analyzer) LNA 10MHz L.O. Signal Generator (CW) Receiver site Transmitter site W. Yamada, K. Nishimori and Y. Takatori (NTT)

  4. Measurement parameter • Frequency 4.85GHz • Signal CW • Transmit power 0 dBm • Number of FFT 1024 • Frequency span 100 Hz • Antenna height (LOS) 2.7m (Tx), 0.85m (Rx) • Antenna height (NLOS) 0.85m (Tx), 0.85m (Rx) W. Yamada, K. Nishimori and Y. Takatori (NTT)

  5. Measurement place ﾄﾞｱ ﾄﾞｱ 円卓 円卓 ﾄﾞｱ 円卓 P P P P P 第3会議室 第1会議室 男子更衣室 -12m +4m ﾄﾞｱ ﾄﾞｱ Tx 紙置場 ﾄﾞｱ ﾄﾞｱ 書庫/倉庫ｽﾍﾟｰｽ Rx Rx 女子更衣室 0 m COPY ﾄﾞｱ 第2会議室 P ＋専用FAX P 円卓 円卓 円卓 たな　たな しょが しょが 冷・ﾚﾝｼﾞ TV FAX FAX COPY COPY しょが ﾄﾞｱ ﾄﾞｱ Window Coherence time is measured at 9 points (2m interval) 富士山側 W. Yamada, K. Nishimori and Y. Takatori (NTT)

  6. Photo of measurement place 2.7m (for LOS) 0.85m (for NLOS) Transmit antenna Receive antenna Tx2(1.2m)-Rx1(0.75m) 0.85m Sometimes, people walk between the transmitter and receiver. Real-time Spectrum analyzer W. Yamada, K. Nishimori and Y. Takatori (NTT)

  7. Method to obtain coherence time (1) FFT is employed for received data after A/D conversion. (2) Power spectrum is obtained using the data in Step (1). (3) Time auto-correlation function is obtained by IFFT for the power spectrum obtained in (2). (4) Coherence time Tc is calculated which the time auto-correlation function is 0.5. (5) Doppler frequency fd is calculated using the following relationship [3]. W. Yamada, K. Nishimori and Y. Takatori (NTT)

  8. Measured coherence time • We confirmed that the coherence time becomes almost the same between LoS and NLoS scenarios. • If we consider that the coherence time is 1.2 s, we can see that the Doppler • frequency becomes 0.3 Hz in TGn channel model. Coherence time 0.062s (1.2km/h) at 4.85GHz in TGn model [3]. Coherence time 1.2s (0.3 Hz) in TGn model. W. Yamada, K. Nishimori and Y. Takatori (NTT)

  9. Examples of Doppler spectrum in this measurement Height :2.7m Height :2.7m Tx LoS Height :0.85m Height :0.85m Height :0.85m Tx NLoS Rx 0.9m 0.9m - - 2m 2m +4m +4m - - 12m 12m - - 0m 0m +2m +2m - - 4m 4m Receiving points Receiving points LoS NLoS W. Yamada, K. Nishimori and Y. Takatori (NTT)

  10. Summary and Conclusion (1) Results Coherence time becomes 1.2s at the CDF=10% for LoS and NLoS.  Coherence time is 20 times than the value (0.062s) which is shown in TGn model [3]. Doppler frequency is estimated by coherence time and its value is approximately 0.3 Hz. (2) Conclusion Doppler frequency should be changed to approximately 0.3 Hz, in order that the coherence time is 1.2 s. W. Yamada, K. Nishimori and Y. Takatori (NTT)

  11. References [1] Greg Breit et al., TGac Channel Model Addendum Document, IEEE802.11-09/308r5, May , 2009. [2] W. Yamada, K. Nishimori, and Y. Takatori, Measured Doppler Frequency in Indoor Office Environment , IEEE 802.11-09/537r0, May 11, 2009. [3] Erceg, V. et al., TGn Channel Models, IEEE 802.11-03/940r4, May 10, 2004. W. Yamada, K. Nishimori and Y. Takatori (NTT)

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