It is our great pleasure to welcome you to APCC 2015, the 21st Asia- Pacific Conference on Communications, which will be held October 14-15, 2015, in Kyoto, the ancient capital of Japan a city of rich Japanese traditions combined with modern culture. APCC 2015 is sponsored by the IEICE (Institute of Electronics, Information and Communication Engineers) Communications Society and technically sponsored by IEEE ComSoc, KICS (Korea Information and Communications Society), and CIC (China Institute of Communications). Since 1993, APCC has been the forum for researchers and engineers in the Asia-Pacific region to present and discuss advanced information, communication technologies, and services, while opening the door to the world at the same time. The theme of APCC 2015 is "Innovating Communications Networks toward a Sustainable and Smart Society." Communications networks are now indispensable in our daily lives and are being used in various ways everywhere to make our lives convenient and comfortable, and communication traffic is increasing at a very fast pace. In addition, we need to pay attention to the sustainability of our society and communications networks. Thus, continuing the innovation of communications networks with advanced technologies is strongly required. All papers for APCC 2015 will be included in IEICE I-Scover as well as IEEE Xplore and indexed by EI and Scopus. Furthermore, an opportunity will be provided for submitting papers to a special issue of IEICE Transactions on Communications. Prospective authors are invited to submit original technical papers for presentation at the conference and publication in the conference proceedings. We believe that APCC 2015 will provide you with a valuable opportunity to share ideas on an international basis with other participating researchers and engineers from around the world.