1. Coherence Time Measurement in NTT Lab.
Month Year
doc.: IEEE yy/xxxxr0
July 2009
Coherence Time Measurement in NTT Lab.
Date:
Authors:
W. Yamada, K. Nishimori and Y. Takatori (NTT)
John Doe, Some Company

2. Purpose and content of this measurement
July 2009
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
July 2009
Measurement equipment
Sleeve antenna
(Omni-directional)
Sleeve antenna
(Omni-directional)
Wireless Communication Analyzer
(Base band real-time
spectrum analyzer)
10MHz
L.O.
Signal
Generator
(CW)
LNA
Receiver site
Transmitter site
W. Yamada, K. Nishimori and Y. Takatori (NTT)

4. Measurement parameter
July 2009
Measurement parameter
Frequency GHz
Signal CW
Transmit power dBm
Number of FFT
Frequency span Hz
Antenna height (LOS) m (Tx), 0.85m (Rx)
Antenna height (NLOS) m (Tx), 0.85m (Rx)
W. Yamada, K. Nishimori and Y. Takatori (NTT)

5. Measurement place Coherence time is measured at 9 points (2m interval)
July 2009
Measurement place
ﾄﾞｱ
ﾄﾞｱ 円卓
ﾄﾞｱ 円卓
P P P 円卓
P P
男子更衣室
第1会議室
第3会議室
-12m
+4m
ﾄﾞｱ
ﾄﾞｱ Tx
紙置場
書庫/倉庫ｽﾍﾟｰｽ
ﾄﾞｱ
ﾄﾞｱ Rx Rx
0 m
女子更衣室
ﾄﾞｱ
COPY
第2会議室 P
＋専用FAX P 円卓 円卓 円卓
たな　たな
COPY
COPY
FAX
FAX
しょが
冷・ﾚﾝｼﾞ TV
しょが
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
July 2009
Photo of measurement place
Transmit antenna
2.7m (for LOS)
0.85m (for NLOS)
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
July 2009
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
July 2009
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
July 2009
Examples of Doppler spectrum in this measurement Tx
Height :2.7m
Height :2.7m
LoS
Height :0.85m Tx
Height :0.85m
Height :0.85m
NLoS Rx
0.9m
0.9m - -
12m
12m - - 4m 4m - - 2m 2m - - 0m 0m
+2m
+2m
+4m
+4m
Receiving points
Receiving points
LoS
NLoS
W. Yamada, K. Nishimori and Y. Takatori (NTT)

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