201029403 六、發明說明： 【發明所屬之技術領域】 本發明係關於一種用於正交分頻多工系統之虛擬載波回 復系統。 【先前技術】 在習知正交分頻多工（0FDM)系統中，最常見的方式是 利用特定的子載波傳送領航符元（Pil〇t Symb〇l Assisted Modulation，PSAM)以進行通道估測（參考先前技術文獻 Π])，然而該習知方法需要浪費額外頻寬來傳送領航符 元。 另外，在習知系統中另提出使用標準中規定的循環字首 (CP)與虛擬載波造成的雜訊子空間與訊號子空間正交的特 性來進行半盲式通道估測（參考先前技術文獻[2_4])，此方 法雖然可以大幅減少所需要的領航訊號數目，然而因為訊 號在傳輸過程中，會受到雜訊以及鄰近通道的干擾，使得 接收到的虛擬載波不再是零，因此子空間半盲式通道估測 演算法的效能也會降低。 參考圖1，其顯示習知正交分頻多工系統之方塊示意 圖。習知正交分頻多工系統丨0包括：一序列並列轉換器 11、一 N點反離散傅利葉轉換器12、一並列序列轉換器 13、一脈衝整形及射頻器14、一多重路徑通道15、一匹配 濾波器16及一子空間半盲式通道估測器17 ^ 習知正交分頻多工系統1〇在傳送訊號之前，於該^^點反 離散傅利葉轉換器12輸入虛擬載波，並於該並列序列轉換 1341811.doc 201029403201029403 VI. Description of the Invention: [Technical Field] The present invention relates to a virtual carrier recovery system for an orthogonal frequency division multiplexing system. [Prior Art] In the conventional orthogonal frequency division multiplexing (OFDM) system, the most common way is to use a specific subcarrier to transmit Pil〇t Symb〇l Assisted Modulation (PSAM) for channel estimation. (Refer to the prior art document Π)), however, the conventional method requires waste of extra bandwidth to transmit pilot symbols. In addition, in the conventional system, the semi-blind channel estimation is further proposed by using the cyclic prefix (CP) specified in the standard and the orthogonality of the noise subspace and the signal subspace caused by the virtual carrier (refer to the prior art document). [2_4]), although this method can greatly reduce the number of pilot signals required, however, because the signal is interfered with by noise and adjacent channels during transmission, the received virtual carrier is no longer zero, so the subspace The performance of the semi-blind channel estimation algorithm will also be reduced. Referring to Figure 1, there is shown a block diagram of a conventional orthogonal frequency division multiplexing system. The conventional orthogonal frequency division multiplexing system 丨0 includes: a sequence parallel converter 11, an N-point inverse discrete Fourier transformer 12, a parallel sequence converter 13, a pulse shaping and RF device 14, a multipath channel 15. A matched filter 16 and a subspace semi-blind channel estimator 17 ^ A conventional orthogonal frequency division multiplexing system 1 输入 input a virtual carrier at the inverse discrete Fourier transformer 12 before transmitting the signal And in the parallel sequence conversion 1341811.doc 201029403
器13輸入循環字首，使接收訊號會產生多餘的子空問，該 子空間稱為雜訊子空間，該子空間半盲式通道估測器17係 利用雜訊子空間與訊號子空間之間互相正交的特性來估測 出通道。如上所述，習知正交分頻多工系統10雖然可以大 幅減少所需要的領航訊號數目，但訊號在傳輸過程中，會 受到鄰近通道以及雜訊的干擾，這些干擾使得接收到的虛 擬載波不再是零子載波，也破壞了雜訊子空間與訊號子空 間之間的正交性，進而降低了該子空間半盲式通道估測器 17的效能。 因此，有必要提供一種創新且具進步性的用於正交分頻 多工系統之虛擬載波回復系統，以解決上述問題。 先前技術文獻： [1] Srihari Adireddy, Lang Tong, and Harish Viswanathan, ’Optimal Placement of Training for Frequency-Selective Block-Fading Channels," IEEE Transactions on Information Theory, Vol. 48, No. 8, Aug. 2002.The first input of the cyclic prefix causes the received signal to generate redundant subspaces. The subspace is called a noise subspace. The subspace semi-blind channel estimator 17 utilizes the noise subspace and the signal subspace. The characteristics of each other are orthogonal to each other to estimate the channel. As described above, although the conventional orthogonal frequency division multiplexing system 10 can greatly reduce the number of pilot signals required, the signals are interfered by adjacent channels and noise during transmission, and the interference causes the received virtual carrier. It is no longer a zero subcarrier, and it also destroys the orthogonality between the noise subspace and the signal subspace, thereby reducing the performance of the subspace semi-blind channel estimator 17. Therefore, it is necessary to provide an innovative and progressive virtual carrier recovery system for orthogonal frequency division multiplexing systems to solve the above problems. Prior Technical Literature: [1] Srihari Adireddy, Lang Tong, and Harish Viswanathan, 'Optimal Placement of Training for Frequency-Selective Block-Fading Channels," IEEE Transactions on Information Theory, Vol. 48, No. 8, Aug. 2002 .
[2] B. Muquet, M. de Courville, and P. Duhamel, "Subspace-based blind andsemi-blind channel estimation for OFDM systems," IEEE Trans. «SVgwa/Praceshvol. 50, no. 7, pp. 1699-1712, Jul. 2002.[2] B. Muquet, M. de Courville, and P. Duhamel, "Subspace-based blind and semi-blind channel estimation for OFDM systems," IEEE Trans. «SVgwa/Praceshvol. 50, no. 7, pp. 1699-1712, Jul. 2002.
[3] C. Li and S. Roy, "Subspace-based blind channel estimation for OFDM by exploiting virtual carriers," IEEE Trans. Wireless Commun., vol. 2, no. 1, pp. 141-150, Jan. 2003.[3] C. Li and S. Roy, "Subspace-based blind channel estimation for OFDM by exploiting virtual carriers," IEEE Trans. Wireless Commun., vol. 2, no. 1, pp. 141-150, Jan 2003.
[4] C. Shin, R. W. Heath, Jr., and E. J. Powers, "Blind channel estimation for MIMO-OFDM systems," IEEE Trans. Veh. Technol., vol. 56, no. 1341811.doc 201029403 2, pp. 670-685, Mar. 2007. 【發明内容】 本發明提供一種用於正交分頻多工系統之虛擬載波回復 系統’其包括：一序列並列轉換器、一 N點離散傅利葉轉 換器、一虛擬載波歸零裝置、一 N點反離散傅利葉轉換器 及一並列序列轉換器。該序列並列轉換器用以接收一序列 輸入訊號，並轉換輸出一並列輸入訊號。該N點離散傅利 葉轉換器用以將具複數點之該並列輸入訊號，進行離散傅 利葉轉換，以產生一 N點頻域訊號。該虛擬載波歸零裝置 用以將該N點頻域訊號之虛擬載波歸零，以產生一已回復 N點頻域訊號。該n點反離散傅利葉轉換器用以將該已回 復N點頻域訊號，進行反離散傅利葉轉換，以產生一時域 訊號。該並列序列轉換器用以將該並列之時域訊號，轉換 輸出一序列輸出訊號。 利用本發明用於正交分頻多工系統之虛擬載波回復系 統’可大幅改善虛擬載波受到雜訊干擾的影響，有效提升 估測效能。 【實施方式】 參考圖2’其顯示本發明用於正交分頻多工系統之虛擬 載波回復系統之方塊示意圖。本發明用於正交分頻多工系 統之虛擬載波回復系統20包括：一序列並列轉換器21、一 N點離散傅利葉轉換器22、一虛擬載波歸零裝置23、一 N 點反離散傅利葉轉換器24及一並列序列轉換器25。 該序列並列轉換器2 1用以接收一序列輸入訊號，並轉換 1341811.doc 201029403 輸出一並列輸入訊號。在本實施例中，該並列輪入訊號包 括符元訊號及循環字首。其中，r*為％xl的向量，表示時 域上第灸個接收的OFDM符元，而义，#為一個〇FDM 符元的載波數，\為循環字首之長度。 該N點離散傅利葉轉換器22用以將具複數點之該並列輸 入訊號，進行離散傅利葉轉換，以產生一N點頻域訊號。 在本實施例中，該N點離散傅利葉轉換器22用以將符元訊 號，進行離散傅利葉轉換，不將循環字首（&(0)至1^(^-1)) 進行離散傅利葉轉換。 該虛擬載波歸零裝置23用以將該N點頻域訊號之虛擬載 波歸零，以產生一已回復N點頻域訊號。該N點反離散傅 利葉轉換器24用以將該已回復>^點頻域訊號，進行反離散 傅利葉轉換’以產生一時域訊號。 該並列序列轉換器25用以將該並列之時域訊號，轉換輸 出一序列輸出訊號。在本實施例中，該循環字首輸入至該 ❹ 並列序列轉換器25，該並列序列轉換器用以將該並列之時 域訊號及該循環字首，轉換輸出該序列輸出訊號6。 利用本發明用於正交分頻多工系統之虛擬載波回復系統 之該虛擬載波歸零裝置23,將虛擬載波強制回復為零該 序列輸出訊號所含之雜訊會比習知系統未經該虛擬载波歸 零裝置的訊號還少，故本發明用於正交分頻多工系統之虚 擬載波回復系統可大幅改善虛擬載波受到雜訊干擾的影 響’有效提升估測效能。 本發明利用下列之推導來證明之K表示第W固不包 1341811.doc 201029403 含循環字首部份的㈣Μ接收符元之雜訊、表示第請不 包含循環子首部f”且經過該虛擬載波歸零裝置23的〇FDM 接收符元之雜訊，接著定義一個矩陣： F=忐 /；2 /n /2π/Ν (^-1) /； 再定義一個的矩陣f，其K+1忡到行和F相對 應的位置相同’而其它的元素均為零，而^。為第—個傳資 料的載波所在的位置；^的平均功率為< =(1/Λ^问， 而圮的平均功率可以如下式所示：[4] C. Shin, RW Heath, Jr., and EJ Powers, "Blind channel estimation for MIMO-OFDM systems," IEEE Trans. Veh. Technol., vol. 56, no. 1341811.doc 201029403 2, Pp. 670-685, Mar. 2007. SUMMARY OF THE INVENTION The present invention provides a virtual carrier recovery system for an orthogonal frequency division multiplexing system, which includes: a sequence parallel converter, an N-point discrete Fourier converter, A virtual carrier zeroing device, an N-point inverse discrete Fourier transformer, and a parallel sequence converter. The serial parallel converter is configured to receive a sequence of input signals and convert the output to a parallel input signal. The N-point discrete Fourier converter is used to input the parallel input signal with a complex point for discrete Fourier transform to generate an N-point frequency domain signal. The virtual carrier zeroing device is configured to zero the virtual carrier of the N-point frequency domain signal to generate a recovered N-point frequency domain signal. The n-point inverse discrete Fourier transform is used to perform the inverse discrete Fourier transform on the recovered N-point frequency domain signal to generate a time domain signal. The parallel sequence converter is configured to convert the parallel time domain signal to output a sequence of output signals. The virtual carrier recovery system for the orthogonal frequency division multiplexing system of the present invention can greatly improve the influence of the virtual carrier on the noise interference, and effectively improve the estimation performance. [Embodiment] Referring to Figure 2', there is shown a block diagram of a virtual carrier recovery system for an orthogonal frequency division multiplexing system of the present invention. The virtual carrier recovery system 20 for the orthogonal frequency division multiplexing system of the present invention comprises: a sequence parallel converter 21, an N-point discrete Fourier transformer 22, a virtual carrier zeroing device 23, and an N-point inverse discrete Fourier transform. The device 24 and a parallel sequence converter 25. The serial parallel converter 2 1 is configured to receive a sequence of input signals and convert 1341811.doc 201029403 to output a parallel input signal. In this embodiment, the parallel rounding signal includes a symbol signal and a cyclic prefix. Where r* is a vector of %xl, representing the OFDM symbol received by the moxibustion in the time domain, and meaning, # is the number of carriers of a 〇FDM symbol, and \ is the length of the cyclic prefix. The N-point discrete Fourier transformer 22 is configured to input the parallel input signal with the complex point and perform discrete Fourier transform to generate an N-point frequency domain signal. In this embodiment, the N-point discrete Fourier transform 22 is used to perform discrete Fourier transform on the symbol signal, and does not perform the discrete Fourier transform on the cyclic prefix (&(0) to 1^(^-1)). . The virtual carrier zeroing device 23 is configured to zero the virtual carrier of the N-point frequency domain signal to generate a recovered N-point frequency domain signal. The N-point inverse discrete Fourier transformer 24 is configured to perform an inverse discrete Fourier transform on the recovered >^ point frequency domain signal to generate a time domain signal. The parallel sequence converter 25 is configured to convert the parallel time domain signals to output a sequence of output signals. In this embodiment, the cyclic prefix is input to the parallel sequence converter 25, and the parallel sequence converter is configured to convert and output the parallel time domain signal and the cyclic prefix to the sequence output signal 6. The virtual carrier zeroing device 23 of the virtual carrier recovery system for the orthogonal frequency division multiplexing system of the present invention forcibly returns the virtual carrier to zero. The noise contained in the sequence output signal is not higher than that of the conventional system. The virtual carrier zeroing device has fewer signals, so the virtual carrier recovery system for the orthogonal frequency division multiplexing system of the present invention can greatly improve the influence of the virtual carrier on the noise interference' effectively improving the estimation performance. The present invention uses the following derivation to prove that K represents the first and second unencrypted 1341811.doc 201029403 contains the (four) Μ received symbol of the first part of the cyclic word, indicating that the first sub-part f is not included and passes through the virtual carrier. The 〇FDM of the zeroing device 23 receives the noise of the symbol, and then defines a matrix: F=忐/;2 /n /2π/Ν (^-1) /; and then define a matrix f, which is K+1忡The corresponding position of the line and F is the same 'the other elements are zero, and ^ is the position of the carrier of the first transmission data; the average power of ^ is < = (1/Λ^问, and 圮The average power can be as follows:
= -itr{E[FF«wtwfFF]} _D 2 ~ nGw· 由於虛擬載波的存在’因此；^>£)，由上式我們可以觀察 出’訊號在通過該虛擬載波歸零裝置23後，不含猶環字首 部份的雜訊有效地被減少了，而且當虛擬載波數目越多 時，改善效果會更明顯。 參考圖3，其顯示本發明之系統與習知系統之效能比較 圖。在本發明實施例中，在循環字首長度义d，子載波數 目# = 64，其中52個資料子載波，12個虛擬载波的情況下估 測通道長度為4的通道時，本發明該虛擬載波歸零裝置^ 1341811.doc 201029403 對子空間半盲式通道估測效能的改善程度與訊雜比 (Signa卜to-Noise Ration, SNR)之間的關係，其中，曲線31 為本發明系統之效能與訊雜比之關係’曲線3 2為習知系統 之效能與訊雜比之關係。由圖可知，本發明之誤差低於習 知系統’且當SNR比較低時，改善程度會比snr高還明 顯。= -itr{E[FF«wtwfFF]} _D 2 ~ nGw· Due to the existence of the virtual carrier 'hence; ^> £), we can observe from the above equation that after the signal is passed through the virtual carrier zeroing device 23, The noise that does not contain the first part of the Uyghur word is effectively reduced, and the more the number of virtual carriers, the more effective the improvement will be. Referring to Figure 3, there is shown a comparison of the performance of the system of the present invention with conventional systems. In the embodiment of the present invention, when the channel prefix length d, the number of subcarriers #=64, 52 data subcarriers, and 12 virtual carriers, the channel length 4 is estimated, the virtual Carrier zeroing device ^ 1341811.doc 201029403 The relationship between the improvement degree of subspace blind semi-channel estimation performance and the signal-to-noise ratio (Signa), where curve 31 is the system of the present invention. The relationship between performance and signal-to-noise ratio curve 3 2 is the relationship between the performance of the conventional system and the signal-to-noise ratio. As can be seen from the figure, the error of the present invention is lower than that of the conventional system' and when the SNR is relatively low, the degree of improvement is also higher than that of snr.
因此’利用本發明用於正交分頻多工系統之虛擬载波回 復系統’可大幅改善虛擬載波受到雜訊干棱的影響，有效 提升估測效能。 上述實施例僅為說明本發明之原理及其功效，並非限制 本發明。因此習於此技術之人士對上述實施例進行修改及 變化仍不脫本發明之精神。本發明之權利範圍應如後述之 申請專利範圍所列。 【圖式簡單說明】 圖1顯示習知正交分頻多工系統之方塊示意圖； 圖2顯示本發明用於正交分頻多工系統之虛擬載波回復 系統之方塊示意圖；及 圖3顯示本發明之系統與習知系統之效能比較圖。 【主要元件符號說明】 10 11 12 13 14 習知正交分頻多工系統 序列並列轉換器 N點反離散傅利葉轉換器 並列序列轉換器 脈衝整形及射頻器 1341Sll.doc 201029403 15 多重路徑通道 16 匹配濾波器 17 子空間半盲式通道估測器 20 本發明之虚擬載波回復系統 21 序列並列轉換器 22 N點離散傅利葉轉換器 23 虛擬載波歸零裝置 24 N點反離散傅利葉轉換器 25 並列序列轉換器Therefore, the use of the virtual carrier recovery system for the orthogonal frequency division multiplexing system of the present invention can greatly improve the influence of the virtual carrier on the noise edge and effectively improve the estimation performance. The above embodiments are merely illustrative of the principles and effects of the invention and are not intended to limit the invention. Therefore, those skilled in the art can make modifications and changes to the above embodiments without departing from the spirit of the invention. The scope of the invention should be as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a conventional orthogonal frequency division multiplexing system; FIG. 2 is a block diagram showing a virtual carrier recovery system for an orthogonal frequency division multiplexing system according to the present invention; A comparison of the performance of the inventive system and the conventional system. [Major component symbol description] 10 11 12 13 14 Conventional Orthogonal Frequency Division Multiplexing System Sequence Parallel Converter N-Point Inverse Discrete Fourier Transformer Parallel Sequence Converter Pulse Shaping and RFr 1341Sll.doc 201029403 15 Multipath Channel 16 Matching Filter 17 Subspace Semi-Blind Channel Estimator 20 Virtual Carrier Recovery System 21 of the Invention Sequence Parallel Converter 22 N-Point Discrete Fourier Transformer 23 Virtual Carrier Zeroing Device 24 N-Point Inverse Discrete Fourier Transformer 25 Parallel Sequence Conversion Device
1341811.doc1341811.doc