5G massive MIMO with digital beamforming and two-stage channel estimation for low SHF band

Transmit Beam Selection Scheme for Massive MIMO Using Expected Beam Responses

“…The assumed frame structure in a downlink is shown in Fig. 1 [6]. Beam selection is carried out by receiving the discovery signals (DSs) that are transmitted towards different directions on different subcarriers of a orthogonal frequency division multiplexing (OFDM) signal.…”

“…Suppose that a two-dimensional planar array antenna shown in Fig. 2 is implemented in a BS and the intervals between the antenna elements are ∆x and ∆z in the horizontal and vertical directions, the weighting coefficient vector, W(ϕ, θ), for the horizontal angle of ϕ and the vertical angle of θ is expressed as follows [6]:…”

“…The total number of beams is then L = N ϕ N θ . The signal with the direction of (n ϕ , n θ ) is transmitted on the l-th subcarrier where l = (n θ − 1)N ϕ + n ϕ + ∆l (6) and ∆l is the number of null subcarriers assigned at the lower edge of a channel as a guard band. The BF coefficient vector on the l-th subcarrier is given by…”

“…In the conventional scheme, the MS returns the subcarrier index, k max , that corresponds to the received signal with the maximum power [6] k max = argmax In the proposed scheme, the correlations between the received signals and the expected response sequences are calculated. The expected response sequence is calculated in advance as follows.…”

“…The directivity of a beam is required to be selected prior to data transmission. In the conventional beam selection scheme for massive MIMO, a transmit beam is selected based on the power of received signals over subcarriers [5] [6]. The signal on a different subcarrier is transmitted to- † The author is with the Dept.…”