數位電視地面廣播系統之通道估測與等化器設計與實現

Design and Implementation of Channel Estimation and Equalization for DVB-T Receiver

林仁傑(Ren-Jay Lin)

指導教授 ： 陳逸民

國立中央大學/資訊電機學院/通訊工程學系/碩士(2006年)

摘要

正交分頻多工（OFDM）系統具有抵抗多重路徑干擾及頻譜使用效率高等優異特性，其中抵抗多重路徑干擾是藉由循環字首（Cyclic prefix）及多載波之特性以達到免除碼字間干擾（ISI）及載波間干擾（ICI），而頻譜使用效率高則是運用多載波正交特性達到的。在循環字首的保護下，多路徑通道對各載波的影響在於其振幅與相位的失真，因此在個子載波之通道等化只需一個複數係數（One-tap）以修正其失真，而其成功要件則在於各子載波之通道頻率響應估測。
本研究中以實現複雜度許可之前提下，針對DVB-T系統進行穩定通道及快速衰落（移動）通道下之通道估測與等化演算法的模擬與硬體設計實現，其中模擬實現結果亦有助於了解OFDM傳收系統規格，如頻段、頻寬、子載波頻率間隔等與通道狀況對接收性能的影響，且針對典型的通道估測採最小平方法搭配線性內插之缺點，並提出插值濾波器之方法改善通道估測之精確度，進一步提升接收機效能。

關鍵字

通道估測 ； 數位電視地面廣播 ； 正交分頻多工 ； 通道等化

並列摘要

OFDM systems exhibit superior characteristics in terms of simplicity in combating multi-path transmission and efficiency in spectral utilization. The effects of ICI and ISI arise from the multi-path interference could be successfully eliminated by the insertion of cyclic-prefix and the use of multi-carriers. Furthermore the advantage of spectral efficiency is achieved by orthogonal property. Under the protection of cyclic-prefix, multi-path effect causes distortion of amplitude and phase only. In accordance with the exact channel estimation among each sub-carrier, the distortion could be compensated by one-tap complex coefficients.
With the consideration of hardware implementation, the algorithms of the channel estimation and equalization were investigated and simulated for static channels and fast fading channels for DVB-T system. Moreover, the dependence of the receiving performance upon relationships between channel conditions and system specifications, e.g. transmission band, bandwidth, sub-carrier spacing, etc. would be clarified from simulation results. In contrast to the least-square method with linear interpolation for conventional channel estimator, interpolation filter was proposed to estimate the channel response more accurately, and improve the performance of the receiver further.

並列關鍵字

channel equalization ； channel estimation ； OFDM ； DVB-T

參考文獻

[2] Paul H. Moose, “A Technique for Orthogonal Frequency Division Multiplexing Frequency Offset Correction”, IEEE Trans. Communications, Oct. 1994

[3] Chandranath .R.N Athaudage, “BER Sensitivity of OFDM Systems to Time Synchronization Error”, The 8th International Conference on Comm. System, November 2002

[4] Thomas Keller, Lorenzo Piazoo, Paolo Mandarini, ”Orthogonal Frequency Division Multiplex Synchronization Techniques for Frequency-Selective Fading Channels”, IEEE JNL in Comm., June 2001

[5] J-J. van de Beek, O. Edfors, M. Sandell, ”On Channel Estimation in OFDM Systems”, IEEE, 1995

[6] S. Coleri, M. Ergen, A. Puri and A. Bahai, ”Channel Estimation Techniques Based on Pilot Arrangement in OFDM Systems”, IEEE Trans. Broadcasting, September 2002