Robustness of TR Scheme
3.3 TR Robustness in Realistic Channels
3.3.2 Experiments With a Changing Environment
3.3.2.1 Measurement Campaign 1 Experimental Setup
An experimental setup is established in a typical indoor environment (IETR labo-ratory) having the plan shown in Fig. 3.15. All rooms are furnished with office equipments: tables, PCs and seats. Moreover, there is a large reverberating chamber
Reverberating Chamber Tx
1 R
x
3.7m
16m
Corridor Office Office Office
10m
8.7m Tx
2
8m
Figure 3.15: Measurement environment layout
Antennax Propagation Channel
Dense Multipath
DSO 6124C
Tektronix Tektronix
AWG 7052 Network Control
Rx
Antenna T
Figure 3.16: Experimental Setup
in the laboratory, which increases the wave reflections in the environment. The exper-imental setup is shown inFig. 3.16. Two conical mono-pole antennas (CMA-118/A), are used as the transmitter and the receiver in a NLOS configuration. The distance between the transmitter and the receiver is 8.35 m. The height of the transmitting and receiving antennas is 1.8 m and 1 m from the ground respectively. The channel sounding pulse and the time reversed MCR are generated through the AWG having a maximum sampling rate of 5GS/s. The receiver is a DSO with a maximum sampling rate of 40GS/s. The DSO captures the channel response. Once the channel response is measured, the time reversed version of the MCR is created through MATLAB and is retransmitted with the AWG in the same channel to measure the TRR which is captured by the DSO. The DSO is operated in an average mode so that 1024 samples are taken and averaged together to reduce the captured noise.
Induced Variations in the Channel
In the RC, a stirrer was used to induce the variations in the channel. In realistic channel environment, the changes in the channel are induced by the movement of the
Figure 3.17: Two metallic strips used to induce variations in the channel people in the channel or by the displacement of the furniture. Therefore, experiments are performed for the following induced variations in the indoor channel environment:
1. Presence of one person near the receiving antenna
2. Presence of one metallic strip near the receiving antenna
3. Presence of one metallic strip near the receiving antenna and one near the trans-mitting antenna
The metallic strips used for the experiments are shown inFig. 3.17. The positions near the terminals are chosen because they can most affect the channel. Thus in a way, these results represent a kind of worst case channel variations in the channel.
Measurement Results
Fig. 3.18 shows for the different bandwidths, respective correlation coefficients of the original (without any change) MCR and the measured TRR with the MCRs and measured TRRs with different induced variations in the channel. The variations in the indoor channel caused by the movement of the people or by putting the metal strips in the channel (which is a sort of worst case in an indoor channel), do not de-correlate the channel completely. The correlation coefficients of the TRR is significantly higher than the correlation coefficients of the MCR for the same variation in the channel suggesting that the TR is more robust than the pulsed UWB systems.
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(a) Bandwidth = 2.0GHz
0
(b) Bandwidth = 1.5GHz
0
(c) Bandwidth = 1.0GHz
Figure 3.18: Correlation coefficient of the MCR and the TRR with different induced variations in the channel
(a) Bandwidth = 2.0GHz
FG SSR IAP NPP
(b) Bandwidth = 1.5GHz
FG SSR IAP NPP
(c) Bandwidth = 1.0GHz
Figure 3.19: Relative strength of different TR properties with different induced vari-ations in the channel
Fig. 3.19 shows the comparison of different TR properties with different induced variations in the channel for different bandwidths. FG, SSR, IAP and NPP are com-pared for different bandwidths and for different induced variations in the channel. For each bandwidth, the received peak power is normalized to the received peak power with the two metals placed in the channel because it is the lowest of all. Higher band-widths have generally higher values of different performance metrics but generally the robustness of the TR scheme is not affected a great deal with the bandwidth of the transmitted signal. The deterioration in the performance with different induced variations is of the same order for all bandwidths. A very high FG is observed with all kind of variations in the channel. SSR does not change a great deal (ascertaining the results obtained in the RC). IAP decreases with the variations in the channel especially for lower bandwidth (1.5GHz and 1.0GHz).
Fig. 3.20 shows the PDP of the TR received signal with and without induced variations in the channel for a bandwidth of 2 GHz. Although the received signal strength decreases with the variations in the channel, the received signal has a very
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Figure 3.20: PDP of the received TR signal with different variations induced in the channel or a bandwidth of 2.0 GHz
good quality. Even with two metallic strips, for which the MCR has a correlation coefficient of 0.7, the received signal has a very good quality.
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(a) Bandwidth = 1.5 GHz
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(b) Bandwidth = 1.0GHz
Figure 3.21: PDP of the received TR signal with different variations induced in the channel different bandwidths
Fig. 3.21 shows the PDP of the TR received signal with and without induced variations in the channel for a bandwidth of 1.5 GHz and 1.0 GHz. It is evident that the received signal is of very high quality and has a strong correlation with the received signal without modification in the channel. The received signal strength is however affected with the variations in the channel. This reduction in the power is strongly linked to the channel environment. In the above measurement layout, as both of the transmitter and the receiver are placed near the reverberation chamber,
Reverberating Chamber
Tx
Rx1 3.7m
16m
Corridor Office
Office Office
10m
8.7m
Rx2
Figure 3.22: Measurement environment layout for the second measurement campaign
the received signal strength is affected with a variation in the channel especially near the terminals.
3.3.2.2 Measurement Campaign 2
To include more generality in the results and ascertain the results found by the previ-ous experiment, experiments are conducted with different placement of the antennas in the environment with a bandwidth of 2GHz. This environment is relatively more typical indoor environment than the previous one (which has waveguide effects because of its layout). Fig. 3.22 shows the measurement layout of the second measurement campaign. Using the position 1, experiments are performed following the same pro-cedure followed in the measurement campaign 1. Following variations are induced in the channel.
1. One person near the receiving antenna
2. One metallic strip and one absorber near the receiving antenna 3. Two metallic strips and one absorber near the receiving antenna
Experimental Results
Fig. 3.23shows respective correlation coefficients of the original (without any change) MCR and the measured TRR with the MCRs and measured TRRs with different induced variations in the channel for second measurement campaign. TRRs have significantly higher correlation coefficients as compared to the channel responses. For experiments with one person and one metallic strip, a very high correlation coefficient for the TRR is observed. The results of all these experiments suggest that although dependent on the environment, TR scheme is generally robust in every environment.
Channel Response TR Response 0
0.2 0.4 0.6 0.8 1
Correlation coefficient
No change 1 person 1 metal 2 metals
Figure 3.23: Correlation coefficient of the MCR and the TRR with different induced variations in the channel
FG SSR IAP NPP
0 2 4 6 8 10 12
dB
No change 1 person 1 metal 2 metals
Figure 3.24: Relative strength of different TR properties with different induced vari-ations in the channel for second measurement campaign
Fig. 3.24 shows the strength of different TR performance metrics for the second measurement campaign. One thing which is different from measurement campaign 1
there is not much decrease in the focusing gain, increased average power and nor-malized peak power. SSR remains almost constant even with the induced variations in the channel. For instance, when the channel is modified by the presence of one person in the channel all TR properties experience only a minimal change although the modified and the original channel has a correlation coefficient of 0.7.
0 1 2