Omnidirectional Precoding for Massive MIMO With Uniform Rectangular Array-Part I: Complementary Codes-Based Schemes

In the public channels, it is desirable to transmit the common signals omnidirectionally to ensure cell-wide coverage. In Part I of this two-part paper, we develop low-cost closed-form omnidirectional precoding designs for a massive multiple-input multiple-output (MIMO) system equipped with a uniform rectangular array (URA). By formulating the omnidirectional transmission design for a general URA as a feasibility optimization problem, we derive an optimal solution based on the complementary set (CS) or the complete complementary codes (CCC). We prove that the precoding vectors based on the CS or CCC sequences can generate a perfectly omnidirectional power radiation pattern. Since both CS and CCC sequences are binary and constant-modulus, the proposed schemes are well suited to be implemented in the radio frequency analog domain with low hardware cost and suppressed peak-to-average power ratio. The numerical results validate the superior performance of the proposed schemes over the existing alternatives.