TDD-CDMAセルラーネットワークにおける遠方基地局間干渉の検討

摘要

TDD-CDMA uses same frequency band in downlink and uplink in order to adopt TDD, so that TDD-CDMA has high frequency efficiency. However TDD has the interference problem between base stations by propagation delay. Although TDD adopted in the cellular network gives no interference between near base stations because of small delay between them, it gives possibility of the interference between distant base stations because of large delay between them. The interference possibility depends on the type of propagation between them. If the base stations have propagation type with small attenuation such as line of sight propagation in spite of far distance, it is high. If they have propagation with higher attenuation, it is low. We discuss the interference possibility. In addition we propose a system which combines adaptive tilting and resource allocation in order to avoid the interference and examine its performance.%TDD-CDMAはアップリンクとダウンリンクにTDDを使用するため周波数効率が高い．しかし，セルラーシステムにTDDを採用すると，伝般遅延による基地局間干渉が問題になる．基地局間の離礁が近ければ伝般茸廷は小さいので，基地局間干渉は発生しない．しかし，基地局間の郎離が大きくなれば，伝般遅延も大きくなるので，基地局間干渉が発生する．また，その干渉は基地局問の伝搬状況にも依存する．基地局間の郎離が大きく，基地局間が見通せるような環境であれば，遠方基地局からの信号電力の減衰は小さい．よって，基地局間干渉が発生する可能性が高い．しかし，基地局間の郎離がさらに大きくなれば，遠方基地局からの侶号電力の温裏も大きくなり，基地局間干渉の発生の可能性は低い．本研究ではまず，基地局間干渉について議論する．そしてこの基地局間干渉を回避するためのアダプティブチルティングとリソース割り当てを組み合わせた方式の提案，評価を行う．