因為在毫米波頻段的傳輸中，電波會有很嚴重的能量衰減，而透過大型天線提供的大型天線增益節合波束成形技術來做指向性傳輸被廣泛的用來彌補此缺點，並增加訊號的覆蓋率，因此近幾年，波束追蹤在第五代無線通訊系統擔任了一個十分重要的角色。而對於在毫米波上的波束成形，為了最大化方向性傳輸增益，追蹤使用者設備的方向也變的十分的重要。因此，波束追蹤的各種方法陸續被提出。有些方法利用預測的方式來追蹤使用者設備。使用者設備移動模式是已知的情況下，這些方法可以利用過去的資訊追蹤使用者。然而，預測方式的追蹤很容易受到初始值錯誤的影響，此外，因為移動模式實際上很少是固定的，因此預測方式的追蹤較不容易實現在實際系統中。更重要的是，在現在的系統中都假設系統只存在單一使用者設備，或只能逐個追蹤使用者。因此我們提出一個更有效的方法可以用更有效率的方式同時追蹤多個使用者。我們提出的架構利用波束空間多重輸入輸出通道的空間解析度不斷的追蹤擁有最強能量的波束。因此，我們不必透過通道估計且不需要關於移動模式的資訊就可以追蹤最強能量的波束。為了同時追蹤多個使用者，使用者設備被區分成數個組別，而每個組別都會被分配到一組正交的領航序列。透過允許在不同組別的使用者設備可以在相同時間資源傳送領航序列，基地台就可以同時追蹤多個使用者設備。最後，我們用模擬來比較並驗證提出方法與現有方法在移動場景下的效能優劣。

In recent year, beam tracking plays a big role in 5G mmWave wireless communications. Because of severe power attenuation of mmWave transmission, the exploitation of antenna gain provided by a large antenna array and directional transmission through beamforming have been extensively considered to enhance the transmission rate of coverage of mmWave. For mmWave communication based on beamforming, tracking the direction of individual user equipment(UE) is of vital importance to maximize the directional transmission gain. Numerous beam tracking schemes have been developed. Some of them track UEs by prediction. According to historical tracking results, the UE’s spatial direction can be tracked following a known movement pattern. However, prediction-based tracking is sensitive to the error due to the inaccurate knowledge of the initial location. In addition, the movement pattern is seldom fixed and thus the prediction-based tracking can hardly implemented in practice. More importantly, all the existing tracking schemes either consider a single UE only or need to track multiple UEs one by one. We propose a beam tracking scheme that can track multiple UEs more efficiently. The proposed scheme keeps tracking the strongest beam for each UE by leveraging the spatial resolution inherent in the beamspace MIMO channel. Consequently, the strongest beam can be tracked without resorting to channel estimation and does not require any knowledge on the movement pattern. To track multiple UEs simultaneously, UEs are partitioned into groups and each group is assigned with an orthogonal pilot sequence. By allowing UEs of different groups to send pilot sequences using the same time resource, the base station (BS) is able to track them simultaneously. Simulation is performed to study the performance of the proposed beam tracking scheme in comparison with existing methods under the mobile scenario.

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