Massive MIMO in Spectrum Sharing Networks: Achievable Rate and Power Efficiency

Massive multiple input multiple output (MIMO) is one of the key technologies for fifth generation and can substantially improve energy and spectrum efficiencies. This paper explores the potential benefits of massive MIMO in spectrum sharing networks. We consider a multiuser MIMO primary network, with <inline-formula><tex-math notation="LaTeX">$N_\texttt{P}$</tex-math></inline-formula>-antenna primary base station (PBS) and <inline-formula><tex-math notation="LaTeX">$K$</tex-math></inline-formula> single-antenna primary users (PUs), and a multiple-input–single-output secondary network, with <inline-formula><tex-math notation="LaTeX">$N_\texttt{S}$</tex-math></inline-formula>-antenna secondary base station and a single-antenna secondary user. Using the proposed model, we derive a tight closed-form expression for the lower bound on the average achievable rate, which is applicable to arbitrary system parameters. By performing large-system analysis, we examine the impact of large number of PBS antennas and large number of PUs on the secondary network. It is shown that, when <inline-formula><tex-math notation="LaTeX">$N_\texttt{P}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$K$</tex-math></inline-formula> grow large, <inline-formula><tex-math notation="LaTeX">$N_\texttt{S}$</tex-math></inline-formula> must be proportional to <inline-formula><tex-math notation="LaTeX">$\ln K$</tex-math></inline-formula> or larger, to enable successful secondary transmission. In addition, we examine the impact of imperfect channel state information on the secondary network. It is shown that the detrimental effect of channel estimation errors is significantly mitigated as <inline-formula><tex-math notation="LaTeX">$N_\texttt{S}$</tex-math></inline-formula> grows large.