Abstract
heMIMO-OFDMtechnologyandthemulti-modeQC-LDPCcodehavebeenappliedforthenewcommunicationsystemssuchasIEEE802.16eandIEEE802.11ntoachieveabetterperformanceinthewirelessdataaccess.Combiningwiththemulti-modeQC-LDPCcodeinthechanneldecoderwiththeMIMOreceiver,thereceivingsignalqualityisimprovedevenatthehighspeedmobilechannel.ButtheMIMOsymboldetectionisnoteasyforimple-mentationbecauseoftheoptimaldetectionmessagesearchingatthemulti-dimensionalchannelresponses.Intheotherway,themulti-modeQC-LDPCdecoderisso°exiblethatthegeneraldecodingarchitectureisnotsuitableforthisapplication.

FortheMIMOsymboldetectorapplication,theK-bestspheredecodingestimatestheEuclideandistancesbetweenthereceivedsymbolsandexpectedconstellationmappingnodesusingthedecomposedchannelresponsesinfor-mation.TheswitchnetworkisimplementedtosortthesmallerEuclideandistanceforthesymbolvaluedecision.Themaximalsortingsizebecomeshuge,e.g.512.Asaresult,thetraditionalbutter°y-basedswitchnetworkcannotexecutethelargesizesorting.Wethereforeproposeaprogrammabledistortion-freeswitchnetworktoperformthelargesizesorting.Resultshowsthattheproposedswitchnetworkcanachievelesscomplexityinthehardwareimplementation.

Inthemulti-modeQC-LDPCdecoder,thesub-matrixsizesaresovariable,andtheprogrammablemessagepassingnetwork(PMPN)isthekeycompo-nentforthe°exibledecoder.Basedonasinglebarrelshifterstructure,weproposethreecost-e®ectivePMPNsfortheIEEE802.16eandIEEE802.11nstandards.ThesignalroutingcongestionbetweenthePMPNsandthemem-orycanbereduced.Themulti-modeLDPCdecoderbasedontheproposedPMPNscanachieveahigherthroughputwithbetterhardwaree±ciency.

摘要

MIMO-OFDM的技術已經被大量應用在新的無線通訊系統規格中，例如IEEE802.16e與IEEE802.11n都採用了這項技術。使用多天線接收器的技術，可以大幅度改進接收器的性能，為了在移動的通道中獲取更佳的性能，目前在這兩種高速的通訊規格中，都採用多模的QC-LDPC做為通道解碼器，以搭配MIMO-OFDM信號偵測接收器。但在硬體實現方面，對於MIMO-OFDM的輸出速度，要求到非常高的吞吐率，而且會切換到不同的操作模式，因此實現MIMO的信號偵測或是多模的QC-LDPC解碼器，設計出高速且有彈性的架構都將會是一項很大的挑戰。

在MIMO-OFDM的信號偵測的研究方向上，K-Best球型解碼器是目前較容易實現的演算法，此法會跟據QR分解後的多維度通道資訊，去計算收到的信號與預期對應的星座圖上節點的歐幾里得距離，並且使用網路交換器去搜尋出其中較小的歐幾里得距離所對應的節點，限制要搜尋的節點數目到K這樣的固定值，使得信號偵測實現的難度降低不少，具有將球型解碼器吞吐率固定的好處。但是在MIMO-OFDM中，這樣搜尋交換器的尺寸非常大，由其是要支援64-QAM高調變模式，在K的數值等於64的時後，有可能大到512這樣的尺寸，以至於傳統的butterfly-based的搜尋交換器很難被應用在這方面，在本文中，我們提出一種可程式化且無失真的搜尋交換器(programmable distortion-free switch network)，採用新開發的搜尋演算法，希望用較小的硬體代價去實現這樣大尺寸的搜尋電路。

在多模QC-LDPC通道解碼器方面，重點是如何設計出足夠彈性的電路去執行多種尺寸的解碼訊息交換，因為QC-LDPC規律的解碼矩陣特性，其矩陣是由位移後的對角矩陣與零矩陣組成，因此在內部子矩陣內的訊息交換，可以不採用複雜的cross-bar 網路交換器，僅使用一般的barrel位移器即可完成，我們提出三種基於單一尺寸的barrel位移器電路結構設計的可程式化訊息交換器(programmable message passing network)，來搭配具有彈性的LDPC解碼器架構，以實現多種尺寸的訊息交換，這樣的電路已經被實現在IEEE802.16e與IEEE802.11n 的QC-LDPC解碼器晶片中，可同時支援此兩種規格，共22種不同的訊息尺寸，並且操作在較高的頻率，以增加整體解碼器的吞吐率，也解決因為支援多種尺寸訊息交換而造成的訊號繞線擁擠問題，使得晶片的後段設計與收斂更為容易，這樣的可程式化的訊息交換器架構可用最少的硬體成本去執行高速交換QC-LDPC 解碼器的資訊。

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