Validation of TR Scheme
2.5 Effect of Different Antennas on TR
3
x 10−4
tpk
Time (ns)
PDP
tpk+2 tpk−2
Figure 2.24: PDP of the measured TR received signal in the RC
Fig. 2.24 shows the measured PDP of the TRR in a RC. The received signal is time compressed and has a very short effective length. A delay spread of only 0.65ns is observed. Large number of multi-paths combines to give a very strong main lobe.
The secondary lobes are significantly weaker than the main lobe. Table 2.4 gives the values of different TR properties in the RC. As expected, by using the multi-path diversity, a very good TR performance is achieved in the RC. A FG of approximately 23.4 dB is observed whereas it was at most 13.3 dB in the indoor environment. It shows the extent to which the RC environment is conducive for the TR technique.
The TR received signal has a very high SSR of 4.42 dB. Furthermore, the IAP of 3.66 dB is calculated with the TR scheme. All these TR properties show that the received signal with the TR scheme in the RC is of very good quality.
2.5 Effect of Different Antennas on TR
The performance of the TR scheme is studied for different types of antennas. To analyze how different types of antennas affect the performance of the TR scheme,
Figure 2.25: A snapshot of horn, log-periodic and CMA
experiments are conducted under similar conditions with different types of antennas.
Conical monopole antenna (CMA), double ridged waveguide horn antenna and log periodic antenna are used for the experiments. The choice of the antennas is carried out so that these include both quasi omni-directional antenna (CMA) and directive antennas (horn and log periodic). The CMA provides good impedance matching (return loss<−10 dB) for the frequency range 0.7−8 GHz. The radiation pattern of the antenna is approximately omni-directional with a constant phase center. The horn antenna is a double ridged waveguide antenna covering a frequency range of 1 GHz to 18 GHz. It has a directive pattern and acts as a spatial filter which captures most of the signal energy from the main lobe. Log-periodic antenna is also a directive antenna. The phase center and the radiation pattern are variable with the operated frequency and the impulse response has significant ringing effect that causes the spread of the transmitted input short pulse in the time delay. A snapshot of all these antennas is presented in theFig. 2.25. The data sheets of these three antennas can be found in their data sheets.
To compare the performance of the TR scheme with different antennas, similar conditions are chosen. The RC allows examining different characteristics of the TR scheme with different antennas by providing the same channel model. Experiments are also conducted in the indoor environment with NLOS co-polar configuration.
2.5.1 Experimental Results in RC
Experimental setup in the RC is the same as presented in Fig. 2.22 for all type of antennas. Fig. 2.26 shows the PDP of the TR received signal in the RC. RC is an environment which has a uniform multi-path floor. As all the walls of the RC are metallic and have a very high reflective index, multi-path components can be received from every direction. Therefore, in this case the CMA whose radiation pattern is close to the radiation pattern of an omni directional antenna performs a little better than the directive antennas. Nevertheless, the directive antennas perform at a good level.
A comparison of different TR properties are tabulated in Table 2.5. It can be seen that for the horn and log periodic antennas, the performance is comparable to CMA.
The received peak power is normalized to the received peak power of the CMA. The NPP of the other two antennas is slightly lesser than NPP of CMA. A very high FG is observed with all types of antennas. It was expected that the SSR will be worse
0 1 2 3
tpk
Time (ns)
PDP
tpk+1 tpk−1
CMA Horn
Log−periodic
Figure 2.26: PDP of the TR received signal with CMA, horn and log-periodic antennas in the RC
TR Property CMA Horn Log-periodic σM CRτ (µs) 2.20 2.02 2.04 PL (dB) 19.93 21.51 21.02
NPP (dB) 0 -1.67 -0.47
FG (dB) 25.41 24.67 25.69
SSR (dB) 4.49 3.93 3.67
IAP (dB) 3.51 4.05 4.67
σT Rτ (ns) 0.53 0.68 0.91
Table 2.5: Time Reversal characteristics with different types of antennas in a RC for log-periodic antenna because of the ringing effects inherent to the antenna. SSR with the log-periodic antenna is 0.82 dB lesser than that of the CMA. The IAP is however greater for the directive antennas than CMA. The RMS delay spread of the TR received signal with the log periodic antenna is greater than the delay spread with the other two antennas.
2.5.2 Experimental Results in the Indoor Environment
Experiments are also performed in the indoor environment in NLOS co-polar configu-ration for all antennas. The experimental setup is the same as presented inFig. 2.18.
Now, as most of the multi-paths are expected to come from one particular direction, the directive antennas are expected to perform far better than the omni directional antenna if they are placed such that the main lobe of the radiation pattern coincides with the angle of arrival of the multi-path components.
0 2 4 6
x 10−4
Time (ns)
PDP
tpk t
pk+2 tpk−2
CMA Horn
Log−periodic
Figure 2.27: PDP of the TR received signal with CMA, horn and log-periodic antennas in an indoor environment
TR Property CMA Horn Log-periodic σM CRτ (ns) 24.96 18.54 17.19 PL (dB) 19.93 22.37 19.23
NPP (dB) 0 5.39 8.41
FG (dB) 13.41 10.39 12.32
SSR (dB) 4.19 5.09 2.75
IAP (dB) 7.18 5.13 7.90
σT Rτ (ns) 19.63 9.43 14.64
Table 2.6: Time Reversal characteristics with different type of antennas in an indoor environment
Fig. 2.27 shows the PDP of the TR received signal with the three antennas in the given indoor environment. As expected, the received signal power is far greater with the directive antennas than the omni directional antenna as directive antenna has significantly greater gain in the direction from where the multi-path components are arriving. The log periodic antenna gives significantly better TR peak performance than the other two antennas. The horn antenna also has quite large received peak power as compared to the CMA. Table 2.6 compares different TR properties with different antennas in the indoor environment. The received peak power is normalized to the received peak power of the CMA. Horn antenna has almost 5.39 dB better NPP than the CMA. All other TR properties with the horn antenna are comparable with the CMA. The log-periodic antenna has a NPP of 8.4dB better than the CMA, but it has a significantly lower SSR compared to the other two antenna types. All other properties are comparable to with the CMA. Therefore, the TR performance
στ (µs) 2.09 2.12 2.14
PL (dB) 21.52 20.98 20.28
NPP (dB) 0 3.77 6.67
FG (dB) 23.36 24.32 23.40
SSR (dB) 1.07 2.61 4.42
IAP (dB) 2.89 3.26 3.66
στT R(ns) 0.77 0.64 0.65
Table 2.7: Time Reversal characteristics with different bandwidths in a RC with different antennas depends upon the environment. An omni-directional antenna is expected to perform better in the environments with a constant multi path floor or where the direction of arrival for majority of the multi-paths is uniformly spread, whereas a directive antenna is expected to perform significantly better than the omni-directional antenna if the direction of arrival for most of the multi-paths is with in the main lobe of the radiation pattern of the antenna.