IPC분류정보
국가/구분 |
United States(US) Patent
등록
|
국제특허분류(IPC7판) |
|
출원번호 |
US-0003690
(2007-12-31)
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등록번호 |
US-8218665
(2012-07-10)
|
우선권정보 |
TW-96127173 A (2007-07-26) |
발명자
/ 주소 |
- Chin, Wen-Long
- Chen, Sau-Gee
|
출원인 / 주소 |
- National Chiao Tung University
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대리인 / 주소 |
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인용정보 |
피인용 횟수 :
11 인용 특허 :
2 |
초록
▼
A symbol time synchronization method for OFDM systems is disclosed. The invention presents a joint maximum-likelihood (ML) synchronization method for symbol time offset (STO) in OFDM systems. The method is developed in frequency domain under time-variant multipath channels. By analyzing the received
A symbol time synchronization method for OFDM systems is disclosed. The invention presents a joint maximum-likelihood (ML) synchronization method for symbol time offset (STO) in OFDM systems. The method is developed in frequency domain under time-variant multipath channels. By analyzing the received frequency-domain data, a mathematical model for the joint effects of symbol time offset (STO), carrier frequency offset (CFO) and sampling clock frequency offset (SCFO) is derived. The results are used to formulate a log-likelihood function of two consecutive symbols. The joint estimation's method is robust, because it exhibits high performances in high mobility and time-variant multipath fading channels.
대표청구항
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1. A symbol time synchronization method for OFDM systems, the method comprising: receiving frequency domain data from a plurality of channels, and analyzing said frequency domain data; andprocessing said frequency domain data by using a joint maximum-likelihood estimator, and procedures used to obta
1. A symbol time synchronization method for OFDM systems, the method comprising: receiving frequency domain data from a plurality of channels, and analyzing said frequency domain data; andprocessing said frequency domain data by using a joint maximum-likelihood estimator, and procedures used to obtain the estimator comprise: generating a probability density function from said frequency domain data;establishing a log-likelihood function from said probability density function;doing maximum-likelihood estimation according to said log-likelihood function; andgenerating symbol time offset (STO) from said maximum-likelihood estimation. 2. The symbol time synchronization method for OFDM systems according to claim 1, wherein said frequency domain data are {tilde over (X)}l,k≈Ĥi,kXl,kWN[lNt(kεt−εf)−knΔ]+{circumflex over (N)}i,k, i=1, 2, 3, where l is a symbol index; {tilde over (X)}l,k is a received frequency-domain data on a k-th subcarrier Xl,k is a transmitted frequency-domain data on the k-th subcarrier; Ĥl,k is a channel frequency response on the k-th subcarrier; WN=e−j2πlN; {circumflex over (N)}l,k is a FFT (fast Fourier transform) of AWGN (Additive White Gaussion Noise); N is a FFT size; Ns is a whole symbol length including the cyclic prefix; εt is a SCFO (sampling clock frequency offset); εf is a RCFO (residual carrier frequency offset); and nΔ is a STO (symbol time offset). 3. The symbol time synchronization method for OFDM systems according to claim 2, wherein said frequency domain data is analyzed by a frequency domain data analyzing equation: E[X~l1,k1X~l2,k2*]={σH^k2σX2+σN^k2,l1=l2k1=k2=kσH^k′2σX2WN-Ns(kɛt-ɛf),l2=l1+1k1=k2=k,k∈P0,otherwise,,whereσH^k′2andσH^k2arecross-correlationandauto-correlationoftimeaveragedchanneltime-variantfrequencyresponses;σx2isavarianceofthetransmittedfrequencydomaindata;σN^k2isavarianceoftheAWGN;andPisapilotset. 4. The symbol time synchronization method for OFDM systems according to claim 1, wherein said log-likelihood function is Λ(nΔ,ɛf,ɛt)=log(∏k∈Pf(X~l,k,X~l+1,k)×∏k∉Pf(X~l,k)f(X~l+1,k)). 5. The symbol time synchronization method for OFDM systems according to claim 4, wherein said log-likelihood function under optimal residual carrier frequency offset (RCFO) and sampling clock frequency offset (SCFO) may be simply expressed in Λ(nΔ,ɛf,ML,ɛt,ML)=∑k∈P(c2,kγ(nΔ)-c3,kΦ(nΔ))-∑kc4,kΦ(nΔ),wherec2,k=ρk/(σH^k2σX2+σN^k2)(1-ρk2);c3,k=ρkc2,k;c4,k=c2,k(1-ρk2)/ρk;γ(nΔ)isdefinedasX~l,k+X~l+1,k*;andΦ(nΔ)isdefinedas12(X~l,k2+X~l+1,k2). 6. The symbol time synchronization method for OFDM systems according to claim 5, wherein said generating symbol time offset (STO) from n^Δ,ML=argmaxnΔ[∑k∈P(c2,kγ(nΔ)-c3,kΦ(nΔ))-∑kc4,kΦ(nΔ)]. 7. The symbol time synchronization method for OFDM systems according to claim 6, further comprising using a single averaged value ρ for all ρk, said single averaged value ρ may be ρ=∑kX~l,kX~l+1,k*/∑kX~l,k2∑kX~l+1,k2. 8. The symbol time synchronization method for OFDM systems according to claim 7, wherein said maximum-likelihood estimation is simplified as: n^Δ,ML=argmaxnΔ[∑k∈P(ργ(nΔ)-Φ(nΔ))-∑k∉P(1-ρ2)Φ(nΔ)].
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