本論文主要探討在合作式網路中有單一個來源點和終點以及多個中繼點採用放大後前送的(amplify-and-forward, AF)分散式波束賦形(distributed-beamforming)的策略。在此方法中，藉著終點少量的回授資料中繼點各自以擾動的方式微調其波束賦形係數。在[16]，作者假設通道不隨時間改變，並且個節點無法得知瞬時通道狀態(channel state information, CSI)，中繼點在每個時間裡接收到來源點(source)傳送的領航序列(pilot sequence)後，將訊號乘上兩組擾動後的波束賦形係數再將訊號放大後前送到終點，終點估測並比較兩組接收訊號的訊雜比(Signal to Noise Ratio, SNR)，最後將比較的結果以單一位元回傳給中繼點，中繼點再依收到的資訊更新下個時間的波速賦形係數，依此趨近於最佳化。但單一位元的回送在時變的通道下可能會造成中繼點波速賦形調整速率無法跟上通道變動率，而本篇論文
的貢獻在於時變通道下提出了兩位元甚至更多位元的回送，達到更好效能。我們所提出的方法主要將終點所接收到兩組的訊號對應至不同波束賦形係數，進行多種線性組合，並估測其訊雜比，找出最佳的線性組合後，告知中繼點此線性組合的編號，而以調整此組合所對應的波束賦形係數。而在第五章的模擬中，證實了多位元回傳的波束賦形的方法確實能提升平均的訊雜比並且降低傳送錯誤率。

In the thesis, we investigate transmit beamforming strategies in a wireless cooperative network consisting of one source, one destination and multi relays that adopt amplify-and-forward (AF). In our scheme, small amount of information feedback from the destination, each relays perturbs individually based beamforming coefficient. Perturbation-based beamforming have been proposed in [16], where the authors assume that the channel is time-invariant, and every relay node can not acquire channel state information (CSI) after receiving pilot sequence signals, the relays multiply the pilot sequence with two perturbed beamforming vectors, and forward
two weighted training sequence to destination. At the destination, the signal to noise ratio (SNR) of two received training sequence are evaluated and compared. Finally, the destination compare with SNRs. To indicate the result of compared SNRs,
destination feedback one-bit message to inform relays the comparison results, and then relays update beamforming vector based on one-bit message. After several iteration, the beamforming vector will approach the optimum one. However, in time-varying environment, the updating rata of beamforming vector in the method with one-bit feedback may be more slowly than rate of channel variation. The contribution of this thesis is to propose transmit beamforming scheme with two-bit or finite-bit feedback to accommodate to the time-varying environment. In our proposed scheme, the destination linearly combines two received sequence corresponding to two different beamforming vectors with various weighting factors. After evaluating and comparing the SNRs of combined signals, the destination notifies the optimum linear combining factors using a multi-bit feedback message. Based on the feedback message, relays can update the beamforming vector correspondingly. In chapter five, it shows through computer simulations that our proposed scheme can raise average SNR and reduce bit error rate effectively.

Abstract ..................................................................................................................................... i
摘要........................................................................................................................................... iii
目錄.......................................................................................................................................... iv
圖表......................................................................................................................................... vi
第一章 簡介............................................................................................................................. 1
第二章 相關背景..................................................................................................................... 5
2.1 背景............................................…………………………….……………….5
2.2 相關文獻....................................…………………………….……………….6
2.2.1 單一位元回傳的分散式波束賦形..................................... 6
2.2.2 單一位元回傳的分散式波束賦形:收斂分析..................11
第三章 系統模型................................................................................................................. 15
3.1 系統設定..................................…………………………….……………….15
3.2 傑克斯衰減通道模型..............…………………………….……………….18
第四章 多位元回授的分散式波束賦形............................................................................. 20
4.1 擾亂向量的波束賦形..............…………………………….……………….20
4.1.1 接受/拒絕(Take/Reject)擾動方法.................................... 21
4.1.2 加/減(Plus/Minus)擾動方法............................................. 23
4.2 二位元回傳的波束賦形..........…………………………….……………….23
4.2.1 二位元回傳的方法........................................................... 24
4.2.2 擾亂的集合....................................................................... 27
4.3 多位元回傳的波束賦形..........…………………………….……………….28
4.3.1 多位元回傳的係數........................................................... 31
4.4 訊雜比估測..............................…………………………….……………….32
第五章 模擬結果和比較..................................................................................................... 34
第六章 結論......................................................................................................................... 40

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