Multiuser Full-Duplex Communication

The inevitable high bandwidth requirement in the future cellular network has made researchers to come up with revolutionary ideas in recent times. One such idea is the introduction of full-duplex (FD) communication. A FD systems make the simultaneous in-band transceiving feasible, i.e, simultaneous uplink and downlink operation using the same spectrum resources. In recent years, extensive work has been done in the area of self-interference cancellation (SIC) design, including for compact devices like laptops and smart phones, enabling FD communication for both single and multiple antenna transceiver units. The designs aim in optimal cancellation of interference from the receiver chains introduced by the transmitter chains of the transceiver unit. While this is far from true today for cellular networks, sufficient progress is being made in this direction to start considering the FD model and its implications, especially in case of small cells. In this work, multiple user equipments (UEs) are considered operating in an FD mode on the same set of spectrum resources simultaneously. However, the use of the same spectrum resources (or subcarriers) for both uplink and downlink results in co-channel interference (CCI) at the downlink of a UE from uplink signals of other co-existing UEs. Two techniques have been proposed to mitigate the CCI in case of multiuser full-duplex communication. The first technique involves deployment of the smart antenna technique at the UEs with highly spatially correlated multiple antennas. The second technique involves the use of diversity gain at the UEs, acquired by using multiple antennas at eNB and UEs in a rich scattering environment. However, the dynamical nature of operating conditions can make the CCI large enough for these solutions to tackle. Hence, a dynamic resource block allocation (DRBA) algorithm is proposed which shifts the operation of co-existing UEs to different spectrum resources. The deployment of multiuser FD communication is shown to have a significant gain in terms of the capacity of the communication system. Further, an analysis is carried out for a method to mitigate the path loss through the dynamic spectrum access method. In a small cell scenario which has an operating frequency in the sub-3 or sub-6 GHz bands, the operating environment can change rapidly with sudden degradation of operating conditions or arrival of obstruction between transmitter and receiver, resulting in possible link failure. The method analyzed includes dynamically allocating spectrum at a lower frequency band for a link suffering from high path loss. For the analysis, a wireless link was set up using Universal Software Radio Peripherals (USRPs). The received power is observed to increase by dynamically decreasing the operating frequency from 1.9 GHz to 830 MHz.