Study on Wireless Multimedia Communication using Adaptive Modulation Techniques

本课题的目标是开发自适应调制系统的关键技术，并研究其在实际无线多媒体通信系统中的应用。在自适应调制系统中，调制方案和码率等调制参数是根据传输路径条件进行控制的。因此，如何在时变传播路径条件下准确估计传输信号的信道条件是自适应调制系统的关键。1995财年，我们开发了信道状态监测技术等自适应调制系统所必需的关键技术，并证实了根据信道状态估计进行调制参数控制和以突发为单位进行调制参数估计是可行的，具有较高的精度。此外，还验证了自适应调制调制解调器在硬件相对简单的情况下是可行的。在1996财年，我们对自适应调制调制解调器进行了计算机模拟，证实了自适应调制在实现比传统QPSK系统更高质量和更高比特率的传输方面非常有效，特别是在频率选择性衰落条件下。此外，我们还研究了它在实际无线多媒体通信系统中的应用，如电路交换系统和分组交换系统。计算机仿真结果表明，该自适应调制系统的系统容量是传统QPSK系统的3.5倍。在分组监视系统中，由于自适应调制技术，吞吐量性能的提高被证实是传统QPSK系统的两倍。这些结果表明，所开发的自适应调制技术对于实现灵活可靠的未来无线多媒体通信系统是非常有效的。

This project targets the development of key technologies for the adaptive modulation systems as well as to study its applications to some practical wireless multimedia communication systems. In the adaptive modulation systems, modulation parameters, such as the modulatio scheme and sysmbol rate are controlled according to the propagation path conditions. Therefere, key for the adaptive modulation system is how to precisely estimate channel conditions for the transmitted signals under time varying propagation path conditions.In 1995 fiscal year, we have developed key techniques necessary for the adaptive modulation system, such as the channel condition monitoring techniques and confirmed that modulation parameter control according to theestimated channel condition and modulation parameter estimation on the burst by burst basis are feasible with high accuracy. Moreover, it is confirmed that the adaptive modulation modem is feasible with relatively a simple hardware.In 1996 fiscal year, we have conducted computer simulation of the adaptive modulation modem and confirmed that the adaptive modulation is very effective in achieving higher quality and higher bit rate transmission than the conventional QPSK systems, especially unde frequency selective fading conditions. Moreover, we have studied its applications to the practical wireless multimedia comunication systems, such as the circuit switching system and packet switching systems. As a result of computer simulation, system capacity for the adaptive modulation system was confirmed to be 3.5 times higher than the conventional QPSK systems. In the case of packet wsitching systems, throughput performance improvement due to the adaptive modulation technique was confirmed to be two times higher than the conventional QPSK systems.With these results, we have concluded that the developed adaptive modulation techniques are very effective in achieving flexible and reliable future wireless multimedia communication systems.