本論文主要探討放大後傳輸(Ampfily-and-Forward) 的合作式通訊系統(CooperativeCommunication Systems) , 透過目的端接收的資訊經過檢測後進行通道估測。在以往的研究中, 中繼點(Relay) 會在合作的前提之下進行傳送, 此時目的端可以接收到完整的資訊, 讓經過中繼點的通道估測更加準確。不幸地, 實際情況並不是如此, 目前也尚未有一種機制來保證中繼點要進行合作, 而此異常中繼點會導致通道的估測能力下降, 為解決此現象, 本論文將考慮有直接傳輸(With Direct Path) 的模型, 並提出檢測的機制。在此機制下, 目的端將考慮經過中繼點的資訊以及直接傳輸的資訊, 利用不同的機率密度以及概似比(Likelihood Ratio) 來檢測異常的資訊, 使得目的端得到更完整的資訊, 讓通道估測更加精準。此外, 本論文使用均方差(Mean Square Error) 作為通道估測能力的指標,並經由數學推導及電腦模擬驗證我們提出的檢測方法確實能夠達到強健通道估測的效果。

In this thesis, we investigate the problem of channel estimation in the amplify-and-forward cooperative communication systems when the networks could be in the presence of selfish relays. The information received at the destination will be detected and then used to estimate the channel. In previous studies, the relays will deliver the information under the prerequisite for cooperation and the destination
can receive the information sent from the source without any possible selfish relay. Therefore, the channel will be estimated under this over idealistic assumption. Unfortunately, the assumption does not make sense in real applications. Currently, we
don’t have a mechanism to guarantee the relays will always be cooperative. The performance of channel estimation will be significantly degraded when the selfish relays present in the network. Therefore, this thesis considers an amplify-and-forward cooperative communication system with direct transmission and proposes a detection mechanism to overcome the misbehaving relay problem. The detection mechanism
employed estimation is based on likelihood ratio test using both direct transmission and relayed information. The detection result will then be used to reconstruct the codeword used for estimating product channel gain of the source-to-relay and relay-
to-destination links. The mathematical derivation for the considered problem is developed and numerical simulations for illustration is also carried out in the thesis. The numerical simulation results verify that the proposed method is indeed able to achieve robust channel estimation.

摘要 i
Abstract ii
目錄 iii
圖目錄 iv
表目錄 v
1 序論 1
2 系統模型 5
2.1 放大後傳輸合作式通訊系統模型 5
2.2 中繼點之異常模式 8
3 合作式通訊系統發生異常中繼點之強健通道估測 9
3.1 中繼點隨機發生異常之檢測 9
3.2 中繼點隨機發生異常之線性最小均方差估測 13
4 數值模擬結果和分析 16
5 結論 25

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