부산대학교 도서관

The expansion of information and communication technologies has led us to the invention of 5 th -generation (5G) communications. However, as an effort to overcome the insufficient frequency-band resource in FR1, telecommunication companies are continuously securing additional re-farming bands in FR1, and they are extending maximum throughput by applying Carrier Aggregation/E-UTRA NR Dual connectivity (CA/EN-DC) based on many fragment bands as shown in Fig. 27.5.1. For example, a major telecommunication company supports CA/EN-DC of the B1, B3, B5, B7 (1), B7 (2), and n78 bands, which require more than 20 RX paths considering the antenna diversity and 4x4 MIMO needed for maximum throughput. As the demands for spectrum re-farming increase, more fragment bands are used, and the required numbers of RX paths also increase accordingly in a conventional direct-conversion-receiver (DCR) architecture. In addition, to support the various fragment bands, multiple front-end modules (FEMs) are required and each FEM needs to be highly complexed with higher-performance multiplexers such as octaplexers or hexaplexers to maintain TX-RX isolation for TX desensitization from IIP2 as shown in Fig. 27.5.1. When B1 TX and RX are activated with B3 RX simultaneously, the isolation between the B1 TX and B3 RX path is more difficult to achieve than that between the B1 TX and RX path due to the reduced duplex spacing (i.e., 40MHz from 130MHz). Also, a local-oscillator (LO) leakage power from in-band LO frequency as well as leakage powers from the adjacent LO harmonics are added to the DC offset of receiver chains. These issues can be relaxed by a multiple-channel-processing receiver with IF conversion such as a software-defined-radio (SDR) receiver or by cognitive radio (CR) receivers that can break through the shortage of FR1 band by searching and adapting unoccupied bands in real time.