| dc.description.abstract | 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.
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