On the feasibility of full-duplex large-scale MIMO cellular systems and its applications

Abstract

This thesis concerns the feasibility of full-duplex large-scale multiple-input-multiple-output (MIMO) cellular systems, and, furthermore, its application, the feasibility of multi-hop millimeter wave (mmWave) wireless self-backhauling with full-duplex small-base stations (S-BSs) is investigated. In Chapter 1, we generally introduce the backgrounds of the thesis, large-scale MIMO or massive MIMO, full-duplex, and mmWave communication. Next, in Chapter 2 and 3, we investigate the feasibility of full-duplex large-scale MIMO system considering two multicell scenarios, non-cooperative and cooperative multicell sys-tems in detail. To elaborate, in Chapter 2, we first derive the analytic model of the ergodic achievable sum-rate for cell-boundary users by considering the non-cooperative multicell system. The model is derived by applying a simple linear filter, i.e., matched filter or zero-forcing filter, to the base-station (BS). In the analytic model, we consider large-scale fading, pilot contamination, transmitter noise and receiver distortion. In addition, to solve critical pilot overhead problem induced by self-interference channel estimation, we propose a pilot transmission scheme – the simultaneous pilot transmission (SPT) – and assess its performance, in terms of the ergodic sum-rate. Then, we obtain the ergodic achievable sum-rate. In Chapter 3, considering the cooperative multicell system, we ob-tain the ergodic achievable sum-rate by reflecting the characteristic of its scenario such as limited front-haul capacity and procedures of channel estimation, as similar as in the second chapter. With all derived results, to investigate the feasibility, we observe the trade-offs between the full- and half-duplex systems, between the SPT and conventional scheme, and between the two multicell scenarios with respect to various system param-eters and environment. In the end, we confirm the tightness of our analytic model and advantages of full-duplex, SPT, and cooperation of BSs in our system model. In Chap-ter 4, in the line with Chapter 2 and 3, we simply investigate it application, which is the multi-hop mmWave wireless self-backhauling system with full-duplex S-BSs. In this application, we investigate the frequency band, sub-6GHz and mmWave band, usage in heterogeneous network, and, furthermore, we show the possible gain of full-duplex S-BSs in multi-hop scenario by deriving the end-to-end (E2E) latency as a performance metric. By reflecting the overhead of channel estimation and data transmission, we show that multi-hop mmWave wireless self-backhauling enables to obtain more gain for certain en-vironment. Furthermore, as the S-BS operates as the full-duplex mode, it brings more gain compared with the half-duplex mode, and the gain becomes larger as the number of hops increase.

In summary, we overall investigate the feasibility of full-duplex large-scale MIMO cellular system, and its application. As a result, we show the possible gain of full-duplex operation by proposing the pilot transmission scheme and deriving the analytic model. Thus, we believe that this thesis enables to provide the guideline of many kinds of fullduplex system.