Millimeter wave (mm-wave) communication using lens antenna arrays is a promising technique for realizing cost-effective large multiple-input multiple-output (MIMO) systems with only limited radio frequency chains. This paper studies a multi-user mm-wave single-sided lens MIMO system, where the base station (BS) is equipped with a full-dimensional lens antenna array and each mobile station employs the conventional antenna arrays. By exploiting the angle-dependent energy focusing property of lens antenna array and the multi-path sparsity of mm-wave channels, we propose a low-complexity single-carrier (SC)-based path-division multiple access (PDMA) scheme for the general wide-band frequency-selective channels. To this end, a new technique called path delay compensation is proposed at the BS to transform the multi-user frequency-selective MIMO channels to parallel frequency-flat small-size MIMO channels. In addition, we propose an efficient channel estimation scheme tailored for the SC-based PDMA, which requires negligible training overhead in practical mm-wave systems and yet leads to comparable performance as that with perfect channel state information. Numerical results show that the proposed design achieves comparable performance as the state-of-the-art benchmark systems in terms of spectrum efficiency, but with significantly reduced hardware/power consumption cost and signal processing complexity.
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