lte的多址接入技術(shù)外文翻譯-資料下載頁(yè)
【導(dǎo)讀】它的特點(diǎn)是在一個(gè)頻域內(nèi)分布著許多帶有間隔的子載波△。如圖2-1所示，“OFDM子載。每個(gè)OFDM符號(hào)間隔之間，調(diào)制符號(hào)是并行發(fā)。調(diào)制符號(hào)可以通過(guò)調(diào)制字母表得到，如QPSK，16QAM或64QAM，對(duì)于。3GPP組織LTE，子載波間隔是相等的為15kHz。于傳輸帶寬，在一個(gè)10MHZ的頻譜分配下，600個(gè)子載波可以有序傳輸。帶寬減小了，子載波數(shù)目也相應(yīng)減少，帶寬增加了，子載波數(shù)目也相應(yīng)增加。在OFDM傳輸時(shí)，物理資源經(jīng)常被描述成一個(gè)時(shí)域—頻域的網(wǎng)格坐標(biāo)圖。在這個(gè)坐標(biāo)圖里一列對(duì)應(yīng)一個(gè)OFDM子載波，一行對(duì)應(yīng)一個(gè)OFDM子載波。這是因?yàn)椋庹{(diào)器相關(guān)區(qū)間的一條。況下，就意味著在吞吐量方面有相應(yīng)的損失。在接收端，解調(diào)后允許發(fā)送的信息準(zhǔn)確解碼。一個(gè)OFDM需要10%的保護(hù)間隔。選擇一個(gè)15KHZ的子載波間隔，那么，在5MHZ內(nèi)應(yīng)對(duì)應(yīng)于300個(gè)子載波。顯然，DFTS-OFDM可以看作是OFDM調(diào)制之前的DFT運(yùn)算。時(shí)發(fā)射功率，對(duì)提高功率放大器效率是可能的。定義為在峰值功率一個(gè)OFDM符號(hào)的平均信號(hào)功。理中，和接受信號(hào)不對(duì)應(yīng)的頻率采樣會(huì)被移除。
【正文】 selected as the uplink transmission scheme for LTE. The basic principle of DFTSOFDM transmission is illustrated in(see Figure 28, “DFTS OFDM signal generation”) . Similar to OFDM modulation, DFTSOFDM relies on blockbased signal generation. In case of DFTSOFDM, a block of M modulation symbols from some modulation alphabet, . QPSK or 16QAM, is first applied to a sizeM DFT. The output of the DFT is then applied to consecutive inputs of a sizeN inverse DFT where N M and where the (NM) unused inputs of the IDFT are set to zero. Also similar to OFDM, a cyclic prefix is inserted for each transmitted block. Figure 28 DFTS OFDM signal generation Comparing (see Figure 28, “DFTS OFDM signal generation” ),with the IFFTbased implementation of OFDM modulation, it is obvious that DFTSOFDM can alternatively be seen as OFDM modulation preceded by a DFT operation. If the DFT size M equals the IDFT size N, the cascaded DFT and IDFT blocks of (see Figure 28, “DFTS OFDM signal generation”), will pletely cancel out each other. However, if M is smaller than N and the remaining inputs to the IDFT are set to zero, the output of the IDFT will be a signal with low power variations, similar to a singlecarrier signal. Besides, by varying the block size M the instantaneous bandwidth of the transmitted signal can be varied, allowing for flexiblebandwidth assignment. The main benefit of DFTSOFDM, pared to a multicarrier transmission scheme such as OFDM, is reduced variations in the instantaneous transmit power, implying the possibility for increased poweramplifier efficiency. The power variations are generally measured by the PeaktoAveragePower Ratio (PAPR), defined as the peak power within one OFDM symbol normalized by the average signal power. The PAPR is significantly lower for DFTSOFDM, pared to OFDM, making thus this transmission technique very useful in the uplink considering the transmit power capabilities of the mobile terminal. The basic principle of DFTSOFDM signal demodulation is illustrated in (see Figure 29,“DFTS OFDM demodulation”) . The operations are basically the reverse of those for the DFTSOFDM signal generation of (see Figure 29, “DFTS OFDM demodulation”) , . sizeN DFT (FFT) processing, removal of the frequency samples not corresponding to the signal to be received, and sizeM Inverse DFT processing. Figure 29 DFTS OFDM demodulation
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