- 學位論文
下鏈路FDD-LTE傳輸系統下聯合式整數頻偏及小區身份非同調偵測
Joint Noncoherent Detection of Integer Carrier Frequency Offset and Cell Index Procedures for the FDD-LTE Downlink Transmission System
摘要
本論文主要是基於3GPP LTE下鏈路傳輸規格下提出一種聯合式整數頻率偏移(IFO)及小區身份(Cell ID)非同調偵測方法，此方法共分為兩步驟搜尋，首先，吾人提出利用主要同步訊號(PSS)本身具有的對稱性質及在相位差上存在的相關性，藉此來降低整數頻率偏移及扇形小區索引(Sector cell index)聯合偵測上的硬體資源使用量，接著分析主要同步訊號在頻域接收端，執行相位差相關性運算後實部及虛部與演算法的關係性，發現只有實部能提供此演算法有利的資訊。第二步驟，吾人提出兩種對小區分群識別碼(Cell ID group)偵測的方法，在非時變通道上，提出利用位於接收端不同次訊框中的次要同步訊號(SSS)來增加資訊的可靠度，接著再利用主要同步訊號來降低偵測時所受到的通道干擾；在時變通道上，提出先偵測出Cell ID group m0，再使用參考訊號(Reference Signal)來提升小區身份的偵測性能；模擬結果顯示，經改良後的整數頻率偏移及扇形小區索引聯合偵測法能有效提升約4dB性能，及降低50%複數乘法器使用量，且能在受到較大分數頻率偏移(FFO)時仍維持改良前的性能；第二部分，在非時變通道上，提出的小區分群識別碼偵測，對CP容忍範圍內的時間偏移(Timing Offset)能完全免疫，且能同時偵測出訊框時序(Frame timing)，最後還可藉由整理出的m0及m1規律表，在得知m0資訊下，能有效降低對於m1的運算量達80%以上；在時變通道上，在偵測出扇形小區索引及Cell ID group m0下，藉由規律表同樣也可大幅降低對於小區身份偵測的運算量達80%以上，且還能對扇形小區索引及小區分群識別碼進行複驗工作。
並列摘要
In this paper, we propose the joint noncoherent detection algorithm of integer frequency offset (IFO) and Cell Identity (CID) for the LTE downlink system. In the algorithm, the proposed scheme is divided into two searching steps. First, we use the symmetry property of the phase difference samples of the primary synchronization signal (PSS) in the algorithm design, and thus the hardware complexity of proposed detection algorithm can be reduced. Second, we analyze the real part and the imaginary part of phase-difference correlation of the PSS, and find that only its real part values provide positive information to the algorithm. Therefore, we apply this critical result to the detection algorithm design further to improve the detection performance. In the second searching step, we presented two methods for detecting Cell ID group. In the scenario of time-invariant channel, we use the secondary synchronization signals (SSS) of two different sub-frames of the LTE downlink to increase the information reliability. Then we use the phase-difference of the PSS for mitigating channel impairments. In the scenario of time-varying channel, we first detect Cell ID group m0 and then use reference signal (RS) to improve the detection performance of the CID. Simulation results first show that our proposed joint detection of IFO and sector cell index can not only reduce the requirements of multipliers up to 50%, but also can improve the detection performance for more than 4 dB. Moreover, in the case of not compensating small scale of fractional frequency offset (FFO), the detection performance can also achieve acceptable detection performance. Simulation results also show that our proposed joint detection of Cell ID group and frame timing algorithm can ignore timing offset in the range of cyclic prefix (CP). Besides, when detecting Cell ID group m0 first, the searching works for detecting Cell ID, for both of time-invariant and time-varying, can reduced up to 80% by using the simplified rule table of the Cell ID group.