A 5G network must be heterogeneous and support the co-existence of multilayer cells, multiple standards, and multiple application systems. This greatly improves link performance and increases link capacity. A network with co-existing macro and pico cells can alleviate traffic congestion caused by multicast or unicast subscribers, help satisfy huge traffic demands, and further extend converge. In order to practically implement advanced 5G technology, a number of technical problems have to be solved, one of which is inter-cell interference. A method called Almost Blank Subframe (ABS) has been proposed to mitigate interference; however, the reference signal in ABS still causes interference. This paper describes how interference can be cancelled by using the information in the ABS. First, the interference-signal model, which takes into account channel effect, time and frequency error, is presented. Then, an interference-cancellation scheme based on this model is studied. The timing and carrier frequency offset of the interference signal is compensated. Afterwards, the reference signal of the interfering cell is generated locally and the channel response is estimated using channel statistics. Then, the interference signal is reconstructed according to previous estimation of channel, timing, and carrier frequency offset. The interference is mitigated by subtracting the estimated interference signal. Computer simulation shows that this interference-cancellation algorithm significantly improves performance under different channel conditions.

In recent years, much attention has been paid to software-defined radio (SDR) technologies for multimode wireless systems. SDR can be defined as a radio communication system that uses software to modulate and demodulate radio signals. This article describes concepts, theory, and design principles for SDR down-conversion and up-conversion. Design issues in SDR down-conversion are discussed, and two different architectures, super-heterodyne and direct-conversion, are proposed. Design issues in SDR up-conversion are also discussed, and trade-offs in the design of filters, mixers, NCO, DAC, and signal processing are highlighted.