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Joint synchronization and parameter estimation in OFDM signaling
Sara Karami,Hossein Bahramgiri 한국전자통신연구원 2023 ETRI Journal Vol.45 No.2
Challenges in cognitive radio and tactical communications include recognizing anonymously received signals and estimating parameters in a blind or semiblind manner. In this paper, we examine this issue for orthogonal frequency division multiplexing (OFDM) signaling. There are several parameters in OFDM signaling, and the blind receiver must extract and consider the synchronization issue. We assume that the blind receiver is aware of modulation type, OFDM, and not aware of chip duration and the length of cyclic prefix. First, we present new criteria based on kurtosis to estimate these parameters and compare their performance at different levels of additive white Gaussian noise with methods based on correlation, kurtosis, maximum likelihood, and matched filter. Then, we perform synchronization and estimate the start time based on these criteria and several new criteria in two steps: fine and coarse synchronization. Finally, in a more practical setup, we present the idea of jointly estimating the mentioned parameters and the signal start time as coarse synchronization. We compare different criteria and show that one of the pro posed criteria has the highest efficiency.
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순환상관(Cyclic Correlation)을 이용한 OFDM 시스템에서의 블라인드 동기 알고리즘
박병준,고은석,강창언,홍대식,Park Byungjoon,Ko Eunseok,Kang Changeon,Hong Daesik 한국통신학회 2005 韓國通信學會論文誌 Vol.30 No.1C
본 논문에서는 OFDM 시스템의 시간 오차와 주파수 오차를 추정하는 방안을 제시하고 있다. 제안한 동기 알고리즘은 수신 신호의 순환상괸(cyclic correlation)을 이용하며, 이 순환상관에는 시간과 주파수 오차 정보가 모두 나타나게 된다. 따라서 제안하는 추정 알고리즘은 여분의 학습심볼(training symbol)를 필요로 하지 않으며, 채널의 정보를 사용하지 않는다. 제안한 추정 방법은 평균자승오차(mean square error) 성능에서 잡음이나 채널의 특성에 상관없이 거의 일정한 성능을 가지며, 실험 결과는 이러한 특징을 뒷받침 해주고 있다. 좀 더 정확한 추정을 위해서, 순환 상관을 평균을 취하는 방법이 적용되었다. 이 경우, 평균을 취하는 방법은 평균을 취하지 않는 방법보다 훨씬 더 정확한 추정을 가능하게 한다. In this paper, blind synchronization algorithm is developed for estimating jointly timing and frequency offset of OFDM system. The proposed estimator exploits the second-order cyclostationarity of received signals, and then uses the information of symbol timing and carrier frequency offset appeared in the cyclic correlation. As a bling estimator, the information of impulse response of channel and training symbols are not required. The performance of the proposed method is consistent in spite of channel conditions in mean squre error sense, and simulation results prove it. For more accurate estimaion, the method that averages cyclic correlation is applied. In this case, the performance of averaging method is better.
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Quan Liu,Yong Lu,Gang Hu,Shaohe Lv,Xiaodong Wang,Xingming Zhou 한국통신학회 2018 Journal of communications and networks Vol.20 No.6
Due to dynamic channel availability in cognitive radionetworks (CRNs), rendezvous problem is known as the mostchallenging issue in the design of media access control (MAC)protocol, which is a key step for secondary users (SUs) to startcommunication. With the concept of blind rendezvous, numerouschannel-hopping sequence (CHS) based rendezvous schemeshave been proposed to solve this problem in these years. Currently,little attention is paid to the design of a carrier sensing multipleaccess/collision avoidance (CSMA/CA) MAC based on theserendezvous schemes and also the rendezvous de-synchronizationproblem brought by multiple rendezvous networking paradigminto MAC design. To this end, we propose a cooperative channelhoppingbased CSMA/CA MAC (named CoCH-CSMA/CA MAC)which works on the top of existing CHS based rendezvous schemes. Resulting from the rendezvous de-synchronization problem, a newtype of collision, named false collision, is identified. As a SU cannotdiscern the false collision by itself, we design a cooperative controlfeedback scheme which employs correlation-based signal detectionto reduce the coordination overhead of cooperation and helps SUsto avoid backoff misbehavior. Moreover, we analyze the behavior ofour MAC protocol and its advantage. Extensive simulations provethat the cooperative control feedback scheme can effectively alleviatethe impact of rendezvous de-synchronization problem on backoffmisbehavior and improve network performance.
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