用於多輸入多輸出正交分頻多工系統之波束形成輔助多用戶適應性無線電資源管理技術

Abstract

多輸入多輸出(Multiple-Input Multiple-Output, MIMO)為使用多天線於傳送和接收端的可靠通訊技術，並被認為是符合第四代高速通訊需求的最佳方案之一，透過空間多工的方式，多輸入多輸出技術可在空間中的獨立平行通道傳送不同資料串流，藉以提昇系統的整體傳輸速率。另一方面，正交分頻多工（Orthogonal Frequency Division Multiplexing, OFDM）為一種具高頻譜效益，並能有效克服多路徑衰落效應的調變技術。在本論文中，吾人將探討結合多輸入多輸出技術與多用戶正交分頻多工系統的通訊系統架構。基於相同副載波對於不同用戶會展現不同通道條件的現象，吾人將針對多用戶正交分頻多工系統提出一種動態副載波配置演算法，此演算法考慮個別用戶對於服務品質與傳輸速率不同的需求，配置一組最適當的副載波給每一用戶，藉以提昇系統的整體傳輸速率，並藉由波束形成技術，使用多用戶能在不干擾彼此的情況下，同時在相同的副載波傳送。此外，吾人更進一步針對多用戶多輸入多輸出正交分頻多工系統提出一種適應性傳收架構及位元負載演算法，使系統能夠隨時間動態地在頻率與空間通道上調整傳輸參數—例如，調變階數與傳輸能量—以便充分地利用空間、時間以及頻率通道上的特性以維持系統的目標錯誤率和各用戶的傳輸速率要求，同時更進一步有效降低系統所需要傳送能量。最後，吾人藉由電腦模擬驗證上述架構在多用戶無線通訊環境中具有優異的傳輸表現。

Multiple-input multiple-output (MIMO) is a promising technique suited to the increasing demand for high-speed 4G broadband wireless communications. Through spatial multiplexing, the MIMO technology can transmit multiple data streams in independent parallel spatial channels, hence increase the total transmission rate of the system. On the other hand, orthogonal frequency division multiplexing (OFDM) is a high spectral efficiency modulation technique that can efficiently deal with multipath fading effects especially suited to multiuser systems. In this thesis, a new wireless communication system called the multiuser MIMO-OFDM system is considered. Based on the fact that the same subcarrier experiencing different channel conditions for different users, a dynamic subcarrier allocation algorithm is proposed. This algorithm enhances the overall transmission rate of the system by allocating the most appropriate subcarriers to each user under the constraints of user-specific quality of service (QoS). In addition, by using beamforming techniques, we also allow users to occupy the same subcarrier at the same time without interfering each other. It results in system performance enhancement. Then, an adaptive multiuser MIMO-OFDM transceiver architecture along with a bit loading algorithm is proposed, which dynamically adjusts the transmission parameters such as modulation order and transmit power over spatial and frequency channels, to fully exploit the properties of the space-time-frequency channels to meet the target bit error rate (BER) and each user’s rate requirement and further reduce the overall transmission power of the system. Finally, the performance of the proposed systems is evaluated by computer simulations, confirming that they work well in multiuser wireless communication environments.