長程演進(LTE)是目前最合乎第四代行動通訊標準的網路技術。有賴於正交分頻多工(OFDMA)技術的發展，無線承載可一次載送更多資訊，高效率的傳輸能力將是新一代無線網路不可或缺的特徵，因此，先進長程演進(LTE-Advanced)所提出的目的，即是在現有的基礎上更精進，以求此技術可以更靠近未來行動網路；先進國際行動電信(IMT-Advanced)定義：定點傳輸達1Gbps、高速行動傳輸達100Mbps的通訊標準。為了達成上述技術規格，LTE-A與LTE的系統都必須擁有更大的傳輸頻帶與更強的傳輸功率，在第三代合作夥伴計畫(3GPP)所公布的第十版(Release 10)文件中，載波聚合(Carrier Aggregation)被加入LTE-A的標準之中，這也代表著，此技術將會讓演進型基地台(eNB: Evolved Node B)擁有更高的傳輸速率與更多的載波單元(Component Carriers)運用於排程之中。在早先的研究當中，使用較大功率傳輸的LTE將會使共存在同一地的分碼多工(CDMA)系統遭受鄰近通道干擾(ACI)的影響；換言之，在由LTE-A與LTE共同組成的網路當中，使用較大功率的LTE-A系統也會使環境中的LTE系統感受到明顯的ACI。首先，在研究當中，我們建立了六角形網路模型模擬現實環境中的基地台布建，並且提出於LTE-A與LTE共存網路的下行連線(Downlink)中，保護LTE用戶免於ACI影響的載波單元使用門檻值；另外，我們再進一步將使用門檻值改良為動態，使其在減少不同系統間產生的ACI同時，也能減少同系統間傳輸干擾。研究使用吞吐量與容量衰減作為評估指標，結果將說明本次研究在降低共存網路中ACI於LTE下行連線影響的同時，也讓LTE-A網路保持相當的網路效能。LTE (Long-term evolution) is the most compatible network with the standard of 4th generation mobile network. Owing to the OFDMA technology, the radio bearer can carry more information at the same time. There is no doubt that high efficiency transmission is the feature of the future, hence, LTE-Advanced (LTE-A) is aiming at closer the gap of next generation mobile network, which was promised to have about 1Gbps for local access and 100Mbps for high speed mobility by IMT-A (International Mobile Telecommunications Advanced). To meet the standard, system need to transmitted with wide spectral bandwidth, and more transmission power is needed in both LTE and LTE-A. In the 3GPP document-release 10, carrier aggregation, added to LTE-A standard, was proposed to supply high data rate for single user and more component carriers for one eNB (Evolved Node B) during scheduling. It is well known that LTE, using higher power during transmission, brought ACI (adjacent channel interference) in coexistence network with CDMA systems. On the other hand, LTE-A can also make a considerable ACI in the coexistence network, assembled by LTE and LTE-A systems. In this research, we built a hexagonal grid model to estimate the influence of ACI in the coexistence between LTE and LTE-A, and proposed a threshold for the usage of carrier aggregation in the downlink LTE-A network that is applied to protect the existing LTE users. Moreover, we also modified a dynamic threshold to reduce the interference in both inter-network and intra-network cases. The performance indicators are throughput loss and capacity loss. This research grants that the low affect in the downlink of LTE network by ACI as well as the decent performance of LTE-A network.
