適用於LTE與LTE-Advanced系統之雙模低複雜度碼簿搜尋演算法及硬體架構設計

LTE與LTE-Advanced系統具有頻譜使用率高、傳送頻帶大以及網絡部署與管理成本低廉等優勢，並採用多輸入多輸出（Multiple-Input Multiple-Output, MIMO）和正交分頻多工（Orthogonal Frequency Division Multiplexing, OFDM）兩項關鍵技術，可以提供大頻寬、成本低的無線通訊傳輸，為未來第四代行動通訊的主要規範。在MIMO系統中，接收端的天線會接收到每個傳送天線的訊號，天線之間會互相干擾，接收端需要透過複雜的檢測技術來恢復數據。然而，在行動通訊系統的下行傳輸中，由於受限於接收端手機的尺寸與功耗等，各種複雜的檢測技術難以實用，因此會利用預前編碼（Precoding）技術，使傳送端可以預先知道通道狀態資訊(Channel State Information, CSI)，再依據通道狀態來調整訊號發射策略，能夠有效抑制多天線之間的干擾，在相同錯誤率的情況下可提升4dB左右的效能，並能簡化接收端手機處理的複雜度。在行動通訊系統中，通道環境變化較快，一般是採用僅需回傳少量碼字的碼簿(Codebook)機制為預前編碼技術。雖然碼簿機制可以大大節省回傳的資訊量，但是主要問題在於需要搜尋碼簿裡最佳的預前編碼器作為回饋的指標。在碼簿搜尋方面已有多篇論文討論與研究[13][14][22]-[24]，但其提出的方法複雜度過高，無法適用於通道快速變化的行動通訊系統，並且實作於手機所需硬體成本過高，因此如何有效率且快速地從碼簿中選出適當的預前編碼矩陣來做預編碼為重要的議題。針對上述議題，本論文將開發出同時支援LTE與LTE-Advanced雙模低複雜度碼簿搜尋器。我們利用碼簿之間的關聯性與巢狀特性來提出一個低複雜度分群以快速傅利葉轉換(Fast Fourier Transform; FFT)為基準的演算法。根據複雜度分析，本論文提出的方法相對於目前文獻可減少約56%的運算複雜度並且沒有任何系統效能的損失。最後，本論文利用TSMC 90 nm製程來實現出雙模低複雜度碼簿搜尋器，此碼簿搜尋器的面積為2.2 mm2，等效邏輯閘數目為547.6K，操作頻率為125MHz。

關鍵字

碼簿；第四代行動通訊

並列摘要

LTE (Long Term Evolution) and LTE-A (LTE-Advanced) systems are dominant standards in future mobile communication systems. LTE and LTE-A systems utilize multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) technique, which can resist multipath interference and improve the spectrum efficiency. The main concern is the interferences among all transmit and receive antennas. The closed-loop scheme, i.e. precoding, is proved to be about 4dB better performance [28] compared with the open-loop solution, which also reduces the overall power consumption. Codebook is a useful precoding technique for limited feedback systems because only few bits are required to feedback. Several codebook selection criteria for linear receivers have been proposed in [13][14][22]-[24]; nevertheless, these selection criteria are computationally intensive and most of them are not feasible for aperiodic feedback reporting in LTE and LTE-A systems. On account of the limited processing hardware and feedback delay constraints, low-complexity transceivers with efficient codebook selection scheme should be considered. In this thesis, the low-complexity codebook searching engine is proposed for LTE and LTE-A systems. The properties and mutual correlations of the LTE and LTE-A codebooks are analyzed and then a low-complexity grouping FFT-based codebook searching algorithm is proposed. Since the proposed algorithm is an algorithmic transformation, there is no performance loss. The proposed schemes have significant effect of reducing the number of multiplications by 56%, compared with the low-complexity cofactor scheme [26]. At last, a dual-mode low-complexity codebook searching engine with TSMC 90 nm is implemented. The IP size is 2.2 mm2 and the equivalent gate count is 547.6K. The operating frequency is 125MHz.

並列關鍵字

Codebook ； LTE ； LTE-A

參考文獻

[3] 3GPP, TS 36.213, “ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 9),” Sept. 2010.

[5] 3GPP, TS 36.211, “ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 10),” Sept. 2011.

[6] 3GPP, TS 36.213, “ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 10),” Sept. 2011.

[8] F. Akyildiz, D. M. Gutierrez-Estevez and E. Chavarria Reyes, “The evolution to 4G cellular systems: LTE-Advanced,” in Physical Communication, vol. 3, pp. 217-24, December 2010

[9] D. Martin-Sacristan et.al., “On the way towards fourth-generation mobile: 3GPP LTE and LTE-Advanced,” EURASIP J. Wireless Commun. Netw., vol. 2009, p. 10, Sep. 2009.

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適用於LTE與LTE-Advanced系統之雙模低複雜度碼簿搜尋演算法及硬體架構設計

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