Millimeter-Wave Beam Multiplexing Method Using Subarray Type Hybrid Beamforming of Interleaved Configuration with Inter-subarray Coding

Two-Beam Multiplexing with Inter-Subarray Coding for Arbitrary Directions Based on Interleaved Subarray Architectures

“…In [19], the two-user case is studied, where there are two subarrays in total (M=2) and two beams are produced by an inter-subarray coding scheme with a linear combination of analogue weighting factors for two subarrays. With d = λ 2 , the antenna analogue weighting factors of the zeroth and first subarrays are given by…”

“…This interleaved-subarray beamforming system generates the first user's own beam naturally and the second user's beam in the direction of the first user's grating lobe and vice versa, and as a result, data for the first user is divided in anti-phase and data for the second user is divided in phase. Specifically, as proposed in [16], [19], the digital beamformer coefficient vector w D,i can be characterized as follows…”

“…and (8) will be transformed into the form of (9) and (10), respectively. Thus, in [19], [20], there is an important limitation to this scheme: the two user directions cannot be arbitrary and have to follow this specific relationship. Although in practice, it is difficult to find two user directions meeting exactly this relationship, it theoretically proves that it is possible to use a simple hybrid analogue and digital beamforming technique to form two beams without spatial aliasing.…”

“…Recently, a hybrid beamforming method which involves multiplexing two beams was proposed in [19]. However, as pointed out later in this paper, a limitation of the proposed method is that the directions of the two beams must satisfy a specific relationship and therefore it is not suitable for users located at arbitrary directions.…”

“…However, as pointed out later in this paper, a limitation of the proposed method is that the directions of the two beams must satisfy a specific relationship and therefore it is not suitable for users located at arbitrary directions. In this work, we focus on the interleaved subarray beamforming scheme, and investigate the inter-subarray coding technique involved in multiplexing two beams with arbitrary directions to serve two users in a userdense network, which was not considered in [19].…”