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Abstract
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In Massive MIMO, for transferring information in downlink, directional and omnidirectional precoding schemes are used. Omnidirectional precoding is used to broadcast the common signals such as synchronization or control signals to all users. The main purpose of omnidirectional precoding is to design the precoding matrix so the signals sent on downlink are emitted with equal and maximum energy in all directions. In the existing method, the omnidirectional precoding is designed for 180-degree broad coverage. In practice, there are some states in which the users in the cell are placed at limited angles, which leads to necessary need of broad coverage less than 180-degree. In this paper, we propose a flexible quasi-omnidirectional precoding method which allows the space coverage range less than 180-degree for full-dimensional massive MIMO. For designing the precoding matrix of the proposed method, quasi-omnidirectional, equal transmitting power of the all antennas and maximum transmitting rate constraints were used. In the proposed method, by changing the distance between adjacent antennas in the antenna array, the space coverage range of the antenna arrays is changed. The performance of the proposed method is evaluated in term of the space coverage range, HPSC, and SLL.
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