OFDM Burst Frequency Synchronization by Single Carrier ... - ICE

this estimate even for the AWGN channel, eg. [10]Var(2 d fTscoa ) =14SL 2 W (E S=N 0 ) + 18S 2 L W (E S =N 0 ) 2L W = S(B ; 1)(M +1) (7)is too high for OFDM systems. However, the estimator has a relatively large acquisition range.Due to the high variance, a second frequency estimation stage is used, which computes the residualfrequency estimate based on two CAZAC blocks separated by an OFDM block. This frequencyestimate is then used to correct the residual frequency error within this OFDM block. It is possibleto space training segments by more than one OFDM block, in this case, however, both fading(channel dynamics) and phase jitter of analog components severely degrade the estimate. For thene frequency error estimator, henceXfT d s (k) ne = 1 2BS;12 arg r k+l rk+l;kl=2Sk = 2(B ; 1)S + L: (8)The range of correctable frequency osets is limited by the fact that the absolute value of the carrierphase change during k samples should not exceed as otherwise ambiguities of the estimatecannot be resolved. Hence, the frequency oset remaining after coarse frequency correction has tofullljfT s j12(2(B ; 1)S + L : (9)in order to avoid ambiguities. Similar ambiguities occur eg. in [6]. For a static channel, theestimation accuracy also is much better, mainly because the time interval between the samplesused for estimating the phase dierence is much larger. Using the second stage alone, the varianceof the estimate on the AWGN channel is given byVar(d2fTsne ) =2(10)(2(B ; 1)S + L) 2 S EsN 0because due to the non{overlapping of the delay product terms of the estimator in fact a phaseestimation is carried out taking into account the noise power of two samples. As indicated, on adynamic channel, a large k may cause variance oors.4