Graduate School of Global Information and Telecommunication Studies, Waseda University
Abstract of Doctoral Dissertation
Gao Nan
高 楠
Wireless communication and Satellite Communication Ⅱ
January, 2015
Performance Evaluation of Communication Schemes Based on Ultrasonic Signal
Propagation
超音波信号伝搬に基づく通信方式の性能評価
Chapter 1
This chapter introduced the background knowledge of this thesis. In recent years, wireless communications have been used more and more frequently in our life. Just like RF systems which using various kinds of technologies, including many popular commercial protocols. Therefore, in some special place electromagnetic fields waves are not allowed to be used, one classic example is in the hospital. This thesis studied the use of ultrasound for wireless communication in air, instead of using electromagnetic field wave. We select ultrasonic wave as the new transmission medium. This shows that ultrasonic wave can be used Ultrasonic wave can be used for sending data and will not cause EMC problems.
Chapter 2
In order to study a communication system, we need one simulation method first.
Therefore, in this chapter, we introduced the background of ultrasonic communication.
We dealt with the simulation method using for ultrasound wave. Because ultrasonic wireless communication is a new area, now there is few method can be used for simulation. At last, we chose FDTD method as the simulation method in my thesis. The FDTD method was first invented in 1966, by Kane Yee. The equations used in his thesis are Maxwell’s curl equations. In the aboriginal FDTD method, simulation errors are one of the major limitations. The other one is execution time. The main reasons of the errors are caused by discretizing space and time. Both of them can be calculated from numerical dispersion. And the simulation time is determined by the length of time step.
Longer time step means less execution time. However, traditional FDTD method should satisfied stability condition. Because the frequency for ultrasound is much lower than electromagnetic field wave, the traditional FDTD method may cost a long time for simulation. In order to increase the simulation speed, a method which can ignore CFL stability condition appeared. This method was introduced by Namiki and Zheng. The name of this method is Alternating-Direction Implicit(ADI) FDTD method. This is a new method for ultrasound simulation, the theoretical analysis, formula deduction and practical calculation procedures are also presented in this chapter. After we got the ADI-FDTD equations for ultrasound, a test was taken out. The result shows that this method is suit for my study very well.
Chapter 3
In the next chapter, we studied a through wall communication system using ultrasound wave. There are no useful means for sand digital information across the conductors material, such as metals, water and so on. Because we cannot make holes in this objects when we need to send data cross them, there is a need for sensor system which can communicate through them. But normal wireless communication system cannot be applied because of the shielding provided by the conductors material, however the ultrasound propagates readily through them and it also can be used to convey information. For example, the use of ultrasonic signaling to transmit digital information across metallic barriers has been demonstrated by several groups. At first we introduced the classic method for through wall communication. Most of the classic methods are one-way communication system. However, with the developments of the science and technology, it is possible to build a two-way communication system.
Therefore, in this chapter a two-way system has been studied. In the simulation part, we used the AID-FDTD method simulated the performance of ultrasound wave in the metal wall. And the modulation method for this system was also been tested. After this, experiment was carried out to test this system practically. Both of the simulation and experiment showed that ultrasound is suit for the communication in the wall.
Chapter 4
In this chapter, we introduced a wireless communication system in air using ultrasound wave. As we mentioned above, ultrasonic techniques are used in metals, waters and other materials. Most of these techniques will use coupling gel as coupling medium. But nowadays, more and more interest has been shown in air coupling medium.
A study of ultrasonic wireless communication in air has been taken. At first, we discussed the attenuation of ultrasound wave in air. After computational analysis and experiment, we proved that ultrasound wave can be used for short-range indoor wireless communication. After this, we studied the phased array method using for ultrasonic communication. Both simulation result and experiment result have been given in this chapter. These result show that theory can also been used in ultrasonic communication.
It can increase the available range and communication quality of this system. At last, we test the modulation method using for ultrasound. Compared with other method, QPSK is better suited for this system.
Chapter 5
In closing, all of these analyses in this chapter proved that ultrasound wave can be used for building a short-range indoor communication system. Modulated ultrasonic wave can send signals through walls and air. In some special cases, it is a good instead of the traditional electromagnetic fields waves. However, this is still an elementary study of ultrasonic communication. Much still remains to be done. For example, how does the environment element affect the ultrasonic wave transmit. Transmission channel model is a direction of research. Some other technology, just like smart antenna technology, also can be used in ultrasonic system. So in the future, we will go on with this study and build a complete ultrasonic communication system.
