移動通信技術として開発されたLTE(Long Term Evolution)やLTE-Advancedは,比類ない広域無線アクセス網技術として世界各国で採用されている.しかし,LTEはH2H(Human-to-Human)の高速通信を目的としてシステム設計されているため,端末あたりのトラヒック負荷は小さいが,端末密度が極めて高いM2M(Machine-to-Machine)に特有の運用環境は想定していない.したがって,高密度に展開された端末が一斉に網にアクセスすれば,トラヒック輻輳を生じて正常な通信が阻害される.本研究では,LTEのランダムアクセス過程に注目し,LTE標準仕様の後方互換性を確保しつつ,H2HとM2M端末が共存する実環境下で,効果的なアクセス制御を実現するための検討を進めている.具体的には,RACH(Random Access Channel)容量の増大を目的とし,ランダムア クセス用のプリアンブル数が増加することによって増大する,プリアンブル間の相互相関干渉の低減技術について多角的に評価を進めている.

LTE is a wireless access system for mobile broad-band communications which is currently employed in various countries. The system was, however, originally designed to accommodate mainly H2H (Human-to-Human) terminals with high traffic density in a relatively low terminal density environment. It is obvious that normal communication will be blocked due to the traffic overload caused by the simultaneous transmission from a large number of M2M (Machine-to-Machine) terminals. This project aims to study a novel random access control method, based on the LTE framework specified in 3GPP(The 3rd Generation Partnership Project) in order to secure the backward compatibility for the past devices, which effectively works under the high device density environment. The focus of this study is to increase the number of PRACH(Physical Random Access Channel) preamble signatures as a fundamental solution to overcome random access overload issues. As an increased number of preamble signatures leads to the severe non-orthogonal preamble collisions, we are developing an inter-preamble interference cancellation scheme, and performing an intensive evaluation.