Conclusion

6.1 Summary of Preceding Chapters

This thesis has revised and proposed improved attenuation mitigation methods to support the next generation of satellite communications operating in the Ka-band and above. The main results are summarized as follows.

Chapter 1 presented the roadmap of satellite communication and overall rain attenuation mitigation technologies.

Chapter 2 revised the cross-polarization effects due to rain from 10-100 GHz and discussed the relation between rainfall rate, attenuation and XPD.

Moreover, homogeneous and inhomogeneous rain models were considered.

According to the conventional raindrop size distribution of MP model it may overestimate small diameter raindrop number, on the other hand the latest Gamma model has convex shape distribution. Then, it is expected that the propagation parameter such as attenuation and XPD difference between MP

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and Gamma models becomes apparent in higher frequency are such as 100 GHz which as short wave. This speculation is theoretically proved by attenuation and XPD relations.

Chapter 3 proposed that the most effective method is time diversity for non-real time satellite communication services. Regarding the time diversity strategy is to transmit the broadcasting contents twice with certain time difference. More specifically, if the exact real-time transmission is not needed such as broadcasting type transmission, the contents are transmitted in advance with certain time to the formal transmission time. This time advance contents are largely compressed to save frequency resource. In this research work, it is found that even several minutes time diversity, it is equivalent to double the transmission power or antenna area. The results were expressed well as a rain intensity map, a cumulative time percentage and a diversity gain. In addition, significant parameters that can improve the accuracy of the prediction system were found.

Chapter 4 proposed the adaptive satellite power control method for locations in Japan to preliminarily investigate the power consumption. The results revealed that boosted areas can be increased by increasing the beam number, beam size or even the boost power. More specifically, if the summation of boosted areas are the same, it is efficient to use many small boosted beams rather than one large boost beam because of rain confinement to small areas as rain intensity increases.

Chapter 5 described improvement of the site diversity method by using the Thai rain gauge network. Three factors, which are spatial correlation,

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Chapter 6. Conclusion

distance and direction, were taken into account to enhance the prediction of the site diversity gain formula. Regarding the spatial correlation pattern in Thailand look like no large correlated areas, it is due to rain behavior in the tropical areas as convective rain is happened in the short period of time with small areas. It is expected that the site diversity method in more effective in tropical areas than middle latitude areas because at the same distance difference rain spatial correlation in tropical areas may be much smaller than middle latitude. It is speculated from the fact that space correlation property derived in Thailand which use the 3 hour integrated time is nearly the same as Japan using several minutes integration time. It is well known that the integration time decreases as space correlation of rain decreases. That is why it becomes important to realize transformation method from correlation with longer integration time to shorter one. This becomes important for future work.

Note: 1.) To realize high-speed wireless network, one example is to use dual polarization link which uses orthogonal polarization with the same frequency. In the design for such dual-polarized link, it is important to consider the both effect of attenuation and XPD. For digital communication link, it is known that the effect of attenuation is larger than depolarization.

Then, the following Chapter 3-6, author emphasize the analysis on attenuation mitigation technologies.

2.) For the tropical regions high speed satellite links, some attenuation mitigation technologies should be combined.

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Chapter 6. Concl usion

6.2 Comparison of attenuation mitigation technologies

The comparison of rain attenuation mitigation technologies in this research are shown in Table 6.1 to summarize the advantage and disadvantage among three methods. These methods are not exclusive and may be realize more effective attenuation countermeasure.

Table 6.1: Advantage and disadvantage of 3 mitigation methods.

Method Advantage Disadvantage

Time diversity

The most effective method Ground technologies

- Non-real time communication

Adaptive satellite power control

Specific areas needed Real time communication

Limited power resource Ineffective for large attenuation

Site diversity

Good for large attenuation Real time communication

- Cost expensive

6.3 Future Work

Specific rainfall rate information for Japan is very useful to improve the performance of rain attenuation mitigation technologies. It will be more useful if we can establish the following systems to obtain valuable information in tropical areas, especially Thailand. Our planned work is listed below:

> A collection system of the raindrop size distribution in Thailand

should be established.

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Chapter 6. Concl usion

> It is very important to improve the rain gauge network in Thailand

from a long duration (3 hours) to a suitable duration (1 minute). A shorter duration can be used to evaluate time diversity and site

diversity performances.

> By using above additional valuable data, more detailed evaluation of attenuation mitigation technologies should be done.

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Appendix List of Pu

A

blications

Journals

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2.

3.

4.

P. Chodkaveekityada and H. Fukuchi, "Prediction Model of Time Diversity Using Rain Radar Data," International journal of satellite communications and networking, 2016, DOI: 10.1002/sat. 1182.

P. Chodkaveekityada and H. Fukuchi, "Time Diversity Evaluation for Attenuation Mitigation Method Using Attenuation Data in Thailand and Japan," International journal of satellite communications and networking, 2016, DOI: 10.1002/sat. 1184.

P. Chodkaveekityada and H. Fukuchi, "Evaluation of Adaptive Satellite Power Control Method Using Rain Radar Data," IEICE Transaction on Communication, Vol. E99-B, pp.-, No. 11, Nov. 2016.

P. Chodkaveekityada and H. Fukuchi, "Effect of Raindrop Size Distribution and Rain Rate Inhomogeneity on the Relationship between Attenuation and Depolarization," International journal of satellite communications and networking. (Major revision)

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List of Publications

5. P. Chodkaveekityada and H. Fukuchi, "Differences in the Dynamic Properties of Rain Fade between Temperate and Tropical Regions,"

Advances in Space Research. (Major revision)

International Conferences

1.

2.

3.

4.

5.

P. Chodkaveekityada and H. Fukuchi, "On-board Adaptive Attenuation Compensation Technique for Future Satellite Communication", International Symposium on Antennas and Propagation (ISAP), Kaohsiung, Taiwan, December, 2nd — 5th, 2014.

H. Fukuchi, Y. Inose and P. Chodkaveekityada, "Spatial Correlation Property Derived from Radar Rain Map and Site-Diversity Effect Evaluation", International Symposium on Antennas and Propagation (ISAP), Kaohsiung, Taiwan, December, 2nd — 5th, 2014.

P. Chodkaveekityada and H. Fukuchi, "Improvement of Depolarization Formula Using Gamma Raindrop Size Distribution Up to 100GHz", Asia-Pacific Conference on Antennas and Propagation (APCAP), Bali Island, Indonesia, June 30th — July 3rd, 2015.

H. Fukuchi and P. Chodkaveekityada, "Propagation Impairments Along Satellite-To-Earth Path and Their Mitigation Technologies", Asia-Pacific Conference on Antennas and Propagation (APCAP), Bali Island, Indonesia, June 30th — July 3rd, 2015.

P. Chodkaveekityada, H. Fukuchi, T. Limpiti and P. Supnithi , "Time Diversity Evaluation for Attenuation Mitigation Method Using Attenuation Data in Thailand and Japan", International Symposium on Space Technology and Science (ISTS), Kobe-Hyogo, Japan, July, 4th —

10th, 2015.

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