Y. Li, L. J. Cimini, and N. R. Sollenberger, "Robust channel estimation for ofdm systems with rapid dispersive fading channels," IEEE Transactions on Communications, vol. 46, pp. 902--915, July 1998.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....frequency division multiplexing (OFDM) 1] is an efficient modulation scheme for broadband wireless communications. To obtain high data rates, accurate channel estimation is required. A widely explored approach, minimum mean square error (MMSE) channel estimation using Wiener type filters [2 6], uses training data (pilot symbols) as well as knowledge of the channel s secondorder statistics. The latter requirement can be met by assuming some default channel statistics [5] explicitly estimating the channel statistics [6] or using a robust design approach [2 4] Here, we propose ....

....using Wiener type filters [2 6] uses training data (pilot symbols) as well as knowledge of the channel s secondorder statistics. The latter requirement can be met by assuming some default channel statistics [5] explicitly estimating the channel statistics [6] or using a robust design approach [2 4]. Here, we propose adaptive Wiener filters for time varying channel estimation that are attractive in that they do not require any statistical knowledge and are able to track changes of the channel statistics. We consider both the normalized least mean square (NLMS) and recursive least squares ....

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Y. Li, L. Cimini, and N. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Comm., vol. 46, pp. 902--915, July 1998.

....of the proposed techniques. 1. INTRODUCTION Orthogonal frequency division multiplexing (OFDM) is an attractive modulation technique for high data rate wireless communications [1] A crucial issue in achieving high quality of service in wireless communications is reliable channel estimation [2, 3]. Beyond that, it was recently recognized that channel prediction is useful for various tasks like delay free equalization, adaptive modulation, and power control [4 6] Here, we propose two adaptive, decision directed predictors for time varying channels within a coded OFDM system. The adaptive ....

Y. Li, L. Cimini, and N. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Comm., vol. 46, pp. 902--915, July 1998.

....the channel frequency response. With this regard, it is known that good results are obtained by using an estimation algorithm based on the singular value decomposition (SVD) of the autocorrelation matrix of the channel frequency response, 1] Based on this method a robust estimator was derived [2]. However, as the number of tones of the MC system increases and the channel is more dispersive, both methods can become computationally expensive. We present two reduced complexity channel estimation methods for MC systems. The first one is a reduced complexity implementation of the SVD ....

....is derived when f g[n]g are independent zero mean random variables, which yields [R ] m#n = E 2 g[ X k=0 km g[k] 3 (n;m) E[j g[ j ] # (7) and matrix U coincides with the FFT matrix F M with entries [F M ] #n = p M . As shown by Li et al. [2], by setting U = F M , Delta m = 1, for m = 0# 1#: #r; 1 and Delta m = 0, for m = r#r 1#: #M ; 1, a robust estimator is obtained independently of the channel statistics. This method will be denoted as R SVD. Even in the simplified form (7) the SVD estimator may be expensive for systems ....

Y. G. Li, L. J. Cimini and N. R. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. on Commun., vol. 46, no. 7, pp. 902--915, July 1998.

....i=0 h i (t)e j2 f i 1 A : 2) Usually, jG(f)j 1 is true in the frequency range of interest and thus, the particular choice of G(f) can be neglected. Applying Clarke s model [9] with maximum Doppler frequency f D , the random process H (f; t) is described by its covariance function [10] (J 0 ( zeroth order Bessel function of the first kind) HH (f 0 ; t 0 ) 4 = EfH (f f 0 ; t t 0 )H (f; t)g = J 0 (2 f D t 0 ) L h 1 X i=0 2 i e j2 f 0 i : 3) OFDM Transmission OFDM with D subcarriers spectrally spaced by f and guard interval D g T (T ....

.... in Section II with typical urban (TU) hilly terrain (HT) and equalizer test (EQ) power delay profiles [16] is used for simulation and analytical performance evaluation of the proposed DMD for OFDM.We adopt the OFDM parameters from 6 th International OFDM Workshop (InOWo) 2001, Hamburg 19 5 [10], 3] i.e. there are D = 120 active subcarriers, subcarrier spacing is f = 6250 Hz, and block duration is T f = 200 s including a guard time of 40 s. Focusing on transmit (modulation) diversity, we restrict ourselves to the case of one receive antenna (NR = 1) Diagonal constellations with R ....

Y. Li, L.J. Cimini, and N.R. Sollenberger, "Robust Channel Estimation for OFDM Systems with Rapid Dispersive Fading Channels," IEEE Trans. Com., vol. 46, no. 7, pp. 902--915, July 1998.

....the OFDM signal s cyclic extension were published by Moose [26] Daffara [27] and Sandell [28] Combining adaptive antenna techniques with OFDM transmissions was shown to be advantageous in suppressing co channel interference in cellular communications systems. Li, Cimini, and Sollenberger [29] [31]; Kim, Choi, and Cho [32] Lin, Cimini, and Chuang [33] as well as Mnster et al. 34] have investigated algorithms for multiuser channel estimation and interference suppression. B. Adaptive Multicarrier Modulation Against this background, we propose here channel quality dependent variable rate ....

Y. Li, L. Cimini, and N. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Commun., vol. 46, pp. 902--915, Apr. 1998.

....results. 1 INTRODUCTION The scattering function characterizes the second order statistics of random, linear, time varying channels obeying the usual WSSUS assumption [1, 2] An estimate of the scattering function is required or helpful for (e.g. receiver design [2] 4] channel estimation [5], and performance analysis [6] We propose an unbiased and computationally ecient scattering function estimator which, in contrast to existing estimators (e.g. 7] 9] exploits the underspread property of WSSUS mobile communications channels [2, 10] This allows for nonideal sounding signals, ....

Y. Li, L. Cimini, and N. Sollenberger, \Robust channel estimation for OFDM systems with rapid dispersive fading channels, " IEEE Trans. Comm., vol. 46, pp. 902-915, July 1998.

....improved properties regarding intersymbol interference (ISI) and interchannel interference (ICI) 5, 6] Here, we propose an OFDM BFDM receiver for random time varying channels that employs decision directed linear channel prediction. Regular transmission of pilot symbols for channel estimation [7, 8] is not required. This paper is organized as follows. Section 2 reviews coded OFDM BFDM communication over time varying channels. The structure of the novel receiver is described in Section 3. The design of the channel predictor is discussed in Sections 4 and 5. Finally, simulation results are ....

.... OFDM system with predictive equalization: a) prediction MSE, b) symbol MSE, and (c) bit error rate for a slow channel ( 0 = 10 Hz) d) f) the same for a fast channel ( 0 = 50 Hz) dictor, and the measured prediction MSE of a trivial predictor reproducing the previous channel estimate [7]. The substantial di erence between measured and theoretical results at low SNR is due to error propagation. For reasonable SNR values, our predictor performs signi cantly better than the trivial predictor. A similar behavior is observed in Figs. 5 (b) and (c) These gures compare the symbol MSE ....

Y. Li, L. Cimini, and N. Sollenberger, \Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Comm., vol. 46, pp. 902-915, July 1998.

....the value of M . Conversely, setting an upper bound on M is equivalent to limiting the maximum value of ffl.Toovercome this limitation, it is thus necessary to devise methods able to compensate for the unknown multiplicative noise effects are well motivated. Statistical methods were proposed in [4] to counteract rapid channel variability in OFDM systems, assuming that the correlation function of the time varying channel transfer This work was supported by NSP Wireless initiative grant no. 99 79443 function is separable. More recently, an equalization technique for OFDM transmissions over ....

Y. Li, L. J. Cimini, N.R. Sollenberger, "Robust Channel Estimation for OFDM Systems with Rapid DispersiveFading Channels", IEEE Trans. on Commun., Vol. 46, No. 7, pp. 902-915, July 1998.

....[18] Mitigation of fading effects in OFDM was addressed in [12] and [21] where a blind equalization technique in a flat fading environment was proposed. Assuming access to a training sequence, a minimum mean square error (MMSE) equalizer that is robust to channel variations was designed in [13] under a certain separability condition on the channel transfer function. In [10] an equalization algorithm for TV multipath channels was developed, where the time variation is approximated linearly within the block, and the channel is estimated using a pilot signal. In the second part of this ....

Y. Li, L. J. Cimini, and N. R. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Commun., vol. 46, pp. 902--915, July 1998.

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Y. (G.) Li, L. J. Cimini, Jr., and N. R. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. on Comm., vol. 46, pp. 902-915, July 1998.

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Y. Li, L. J. Cimini, Jr., and N. R. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. on Comm., vol. 46, pp. 902-915, July 1998.

....form, where the delay is only a small fraction of an OFDM symbol. This causes the fading to become more randomized between OFDM tones than without the delay diversity. The required channel state information for coherent detection and maximal ratio combining can be obtained by a robust estimator [13]. Space time coding transmitter diversity impairs the system s interference suppression ability because it generates multiple signals that appear independent to adaptive antenna arrays. Hence, adaptive antenna arrays [14] 15] are more effective for cochannel interference suppression for delay ....

....results in the next section, this transmitter diversity approach is especially useful for channels with flat or small delay spread. From (2) the received signal at each antenna can be regarded as the transmitted signal passed through a fading channel . Hence, both a robust channel estimator [13] and adaptive antenna arrays [14] 15] can be used here for minimum mean square error diversity combining (MMSE DC) and coherent detection. B. Permutation Approach Permutation transmitter diversity for an OFDM system is shown in Fig. 1(b) The modulated signal and its permutation are ....

[Article contains additional citation context not shown here]

Y. Li, L. J. Cimini, Jr, and N. R. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Commun., vol. 46, pp. 902--915, July 1998.

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Y. Li, L. J. Cimini, and N. R. Sollenberger, "Robust channel estimation for ofdm systems with rapid dispersive fading channels," IEEE Transactions on Communications, vol. 46, pp. 902--915, July 1998.

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Y. Li, L.J. Cimini, and N.R. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels", IEEE, Tr. on Comm. vol. 46, pp. 902-915, July 1998.

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Y. Li, L. J. Cimini, and N. R. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Commun., vol. 46, pp. 902--915, July 1998.

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Y. Li, L. J. Cimini Jr., and N. R. Sollengerger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Commun., vol.46, pp.902-915, Jul. 1998.

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Y. Li, L. J. Cimini, and N. R. Sollenberger, "Robust channel estimation for ofdm systems with rapid dispersive fading channels," IEEE Transactions on Communications, vol. 46, pp. 902--915, July 1998.

No context found.

Y. Li, L. J. Cimini Jr., and N. R. Sollengerger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Commun., vol.46, pp.902-915, Jul. 1998.

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Y. G. Li, L. J. Cimini, and N. R. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Commun., vol. 46, pp. 902--914, July 1998.

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Y. Li, L. J. Cimini, and N. R. Sollenberger, "Robust channel estimation for OFDM systems with rapid dispersive fading channels," IEEE Trans. Commun., vol. 46, pp. 902--915, Apr. 1998.

No context found.

Y.(G.) Li, L.J. Cimini, Jr., and N.R. Sollenberger, "Robust channel estimation for OFDM system with rapid dispersive fading channels," IEEE Trans. Commun., vol.46, no.7, pp.902--915, July1998.

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