## 3 Simulation Results and Discussion  
In this section, the performance of CID and AoD estimation in an mmWave cellular system is evaluated by simulation when the proposed beam weight generation method is used. Simulation is performed with a simple mmWave cellular model in a LOS dominant condition. It is assumed that an MS is located at the cell boundary of three cells. The distance between the MS and three BSs are the same. AoAs at the MS are set to \(-30^{\circ}\), \(0^{\circ}\), and \(30^{\circ}\) for three neighboring cells. AoDs at three BSs are randomly selected from a value ranging from \(-90^{\circ}\) to \(90^{\circ}\). Also, ULA antennas with \(N_{Tx}\) and \(N_{Rx}\) are used at the BS and MS, respectively. \(N_{Rx}\) is set to 16 and the number of available CIDs (maximum number of CIDs) \(M\) is set to \(N_{SA}-1\). The channel between each BS and MS is assumed to experience Rician fading, consisting of a LoS path and a non-line-of-sight (NLOS) path. The non-line-of-sight (NLOS) path is generated by the spatial channel model (SCM), and composed of 20 rays with \(2^{\circ}\) azimuth spread. The power of NLoS path is 15 dB less than the power of LoS path [21]. In the simulation, the proposed method is compared with the conventional method in terms of performance and overhead. In the conventional methods, the DFT-based beamforming weight is used for Tx beamformer at the BS and the OMP algorithm is used for AoD estimation at the MS [8,9]. In the proposed method, the signals generated by the beam weights with CID information (BSs) are simultaneously transmitted since the proposed method allows an MS to distinguish neighboring BSs. In the conventional beam training method, the BS transmits single Tx beams generated by the DFT-based orthonormal RF precoder until all the Tx beams are transmitted. Here, BSs are distinguished by the time slots assigned differently depending on their CIDs. The MS sweeps the Rx beam. The beam sweeping operation is performed for all neighboring BSs to select a serving BS. The MS estimates the signal quality and AoD of the serving BS by applying the OMP algorithm. Figures 3 and 4 show the performance of CID detection and AoD estimation when the conventional and proposed methods are used, respectively. The following combinations of \((N_{SA},B)\) are used for the proposed method in the simulation: (17,1), (17,2), (31,1), and (31,2). The large (\(\mathcal{X}\),\(\mathcal{D}\)) and small (\(\odot\),\(\Diamond\),\(\triangle\)) markers in the figure represent the conventional and proposed methods, respectively. In the proposed method, \(N_{F}\) is set to 256, implying that the angle resolution in the AoD estimation is approximately given by \(180^{\circ}\) divided by 256. For the conventional method, \(N_{Tx}\) is set to 17 (\(B\)=1), and the angle resolution of the OMP technique is set to be the same as that of the proposed method. The Tx power at the BS is set to 1 regardless of the value of \(B\). From Figure 3, it can be seen that the performances of CID detection decrease as \(N_{SA}\) decreases, as indicated by the numbers 31 (\(\square\),\(\triangle\),\(\triangleright\)) and 17 (\(\odot\),\(\Diamond\),\(\mathcal{H}\)), because the SNR gain decreases as the number of antenna elements decreases. For example, the CID detection performance of the proposed method, (17,1) (\(\Circle\)), is degraded by about 2.5 dB, compared with that of (31,1) (\(\Box\)), in a low SNR region. From this figure, it can be also seen that the CID detection probability of \(B=2\) is degraded by about 0.5 dB compared to that of \(B=1\) due to the effect of subarrays in the combining process. In Figure 4, the mean absolute error of AoD is measured only when the CID detection is performed successfully. From this figure, it can be seen that the AoD estimation performance is degraded as \(N_{Tx}\) decreases, because the correlation peak becomes smoother as \(N_{Tx}\) decreases. From Figures 3 and 4, one can conclude that the conventional and proposed methods have similar performance in CID detection and AoD estimation.