多天線普遍出現在各種無線通訊系統中，除了形成波束增加通訊品質外，也可以分空間多工。多重進接數量跟天線數量成正比，然而基地臺端的天線數量沒辦法無限增加，所以經由選擇部分使用者進行同時傳輸是另一種改善通道容量的方法。此外，分空間多工的精神是基於使用者位於不一樣的空間，也就是對於基地臺來說，使用者的訊號是從不一樣的方向入射。為了知道使用者的訊號入射角度，引入毫米波所使用的波束空間通道，基地台只需要知道各個使用者的通道響應，就可以轉換到訊號的入射角。因此，波束空間通道輔助選擇使用者能夠提供較好的分空間多工通訊品質。為了驗證波束空間通道用於輔助選擇使用者的效能，本論文建立了多用戶多輸入多輸出波束空間通道之軟體無線電原型。這個原型支持中心頻率介於五十百萬赫茲至六吉赫茲，並可傳送任何預先定義的訊號，以及最高支援到十六隻天線。除此之外，在這個軟體無線電原型中，包含了空中同步，所以基地台所儲存的訊號不需要尋找實體層封包訊號的開頭。為了要量測出所有通道狀態信息，使用了兩種不同型態的封包格式，並應用在實際的測量中。在實驗中，可以看到在視距傳播環境下，波束空間通道跟使用者相對於基地台的位置確實有著密切相關性，並且波束空間通道比起通道矩陣的秩，更有助解析用戶的空間位置，進而提收用戶選擇的效能。

Wireless systems with multiple antennas, known as Multi-Input Multi-Output (MIMO), has been shown to tremendously improve the system capacity and reliability compared to the single-antenna systems. Generally, the number of parallel data streams that a MIMO system can support is limited by the number of transmit or receive antennas, whichever is less. As the number of users increases, more antennas at the Base Station (BS) is required to ful- fill the user demands, leading to increased capital cost to the operators. An alternative is to select a subset of users to serve simultaneously based on the Channel State Information (CSI). In this context, the beamspace provides the required spatial information for user se- lection. While the beamspace theory is well known, its practical application to addressing the user selection problem has not been explored. In this thesis, a versatile prototype based on Software Defined Radio (SDR) is developed to study the user selection problem based on the beamspace MIMO channel. The implemented prototype operates at the sub-6 GHz band with the capability to support a wide range of antenna configurations and user-defined signals. Besides, the over-the-air synchronization is achieved by considering two types of frame structures. A filed measurement campaign is conducted in an indoor environment and the measurement results confirm the superiority of the beamspace MIMO channel over the antenna space MIMO channel in identifying an appropriate subset of spatially distributed users.

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