E. Ertin, U. Mitra, and S. Siwamogsatham, "Maximum-likelihood based multipath channel estimation for code-division multiple-access systems," IEEE Trans. Communications, vol. 49, no. 2, pp. 290-302, Feb. 2001.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....on LMS like iteration for approximate ML solution with training sequence and previously detected symbols is considered. However, relying on the previously detected symbols shows a error propagation, especially at low SNR. Other methods are based on expectation maximization (EM) technique [6] [7], or semi blind ML approach [8] These iterative methods are based on slow fading assumption and often suffer from well known problems such as local convergence and high complexity. In this paper, we present a new channel estimation technique which tracks fast fading. Based on a linear ....

E. Ertin, U. Mitra, and S. Siwamogsatham, "Maximum-likelihood based multipath channel estimation for code-division multiple-access systems," IEEE Trans. Communications, vol. 49, no. 2, pp. 290-302, Feb. 2001.

....block into smaller ones and additional pilot insertion in the subblock to resolve the inherent scalar ambiguity of blind methods. Iterative methods based on maximum likelihood (ML) principle have also proposed. Several authors proposed methods based on expectation maximization (EM) technique [6] [7], or semi blind ML approach [8] These iterative methods are based on the slow fading assumption and often su er from well known problems such as local convergence and high complexity. In [9] the authors proposed an ecient channel estimation method based on LMS like iteration for an approximate ....

E. Ertin, U. Mitra, and S. Siwamogsatham, \Maximum-likelihood based multipath channel estimation for code-division multiple-access systems," IEEE Trans. Communications, vol. 49, no. 2, pp. 290-302, Feb. 2001.

....handshaking protocol, and the estimation of ACK packet TOA is complicated by the near far e#ect. Previous approaches to multiuser channel estimation for DS CDMA include subspace based algorithms [1] 2] 3] Expectation Maximization (EM) methods [4] and MaximumLikelihood (ML) approaches [5] 6] [7]. Here, the Generalized Successive Interference Cancellation (GSIC) algorithm [8] is applied to the DS CDMA TOA channel estimation problem. GSIC can be viewed as the estimation analog of successive interference cancellation algorithms previously applied to multiuser detection in [9] 10] 11] ....

E. Ertin, U. Mitra, and S. Siwamogsatham, "Maximumlikelihood -based multipath channel estimation for code-division multiple-access systems," IEEE Trans. Commun., vol. 49, pp. 290--302, Feb. 2001.

....handshaking protocol, and the estimation of ACK packet TOA is complicated by the near far effect. Previous approaches to multiuser channel estimation for DS CDMA include subspace based algorithms [1] 2] 3] Expectation M0ximization (EM) methods [4] and M0ximumLikelihood (ML) approaches [5] 6] [7]. Here, the Generalized Successive Interference Cancellation (GSIC) algorithm [8] is applied to the DS CDMA TOA channel estimation problem. GSIC can be viewed as the estimation analog of successive inteference cancellation algorithms previously applied to multiuser detection in [9] 10] 11] ....

E. Ertin, U. Mitra, and S. Siwamogsatham, "Maximum- likelihood-based multipath channel estimation for code-division multiple-access systems," IEEE Trans. Commun., vol. 49, pp. 290-302, Feb. 2001.

....[1 ] then estimates the times of arrivals, or equivalently round trip travel times (RTTs) and hence relative ranges. Other synchronization approaches for estimating ranges in CDMA systems include subspace based algorithms [4] 5] 6] expectation maximization [7] and maximumlikelihood methods [8]. Alternatively, relative ranges can be estimated using field strength measurements [9] Finally, the range estimates and known or estimated reference node positions are used to estimate the position on the master node. In positioning systems such as the one described above the most substantial ....

E. Ertin, U. Mitra, and S. Siwamogsatham, "Maximum-likelihood-based multipath channel estimation for code-division multiple-access systems," IEEE Transactions on Communications, vol. 49, pp. 290-302, Feb. 2001.

....accurately using conventional matched filter detectors. Many techniques have been proposed for estimating TOAs and other channel parameters in the multiuser channel environment, including subspace based algorithms [12] 13] 14] expectation maximization [15] maximum likelihood (ML) 16] [17], and generalized successive interference cancellation (GSIC) 18] In this paper, the GSIC algorithm, which is the estimation analog of successive interference cancellation (SIC) for multiuser detection [19] 20] 21] is employed for radiolocation. Another problem in radiolocation is the ....

E. Ertin, U. Mitra, and S. Siwamogsatham, "Maximum-likelihood-based multipath channel estimation for code-division multiple-access systems," IEEE Trans. Commun., vol. 49, pp. 290--302, Feb. 2001.

....drawback of such algorithms is the computational requirement of the signal or noise subspace estimation process, and the limitation on the number of users that can be handled. Recently, a number of channel estimation algorithms based on the maximum likelihood technique (ML) 13] have emerged [14, 15, 16, 17, 18, 19]. The ML technique is an attractive alternative as the ML based algorithms have been shown to be computationally efficient and can handle a large number of users. It has been also shown [17, 18, 20] in the single path case, that the application of the ML technique in the presence of a number of ....

....of channel estimators as well as linear detectors. Several forms of the ML technique have been proposed in literature. These algorithms work in different situations, such as single path and single sensor [14, 16] or single path and multiple sensors [15, 17, 18] or single sensor and multiple paths [19]. Out of these, 16, 17, 18] fall under a distinct class which can be easily separated from our proposed algorithm. All these three algorithms model all the interfering users as colored noise, thus reducing the size of the spreading code matrix and training sequence vector and hence the required ....

E. Ertin, U. Mitra, , and S. Siwamogsatham. Maximum-likelihood based multipath channel estimation for code-division-multiple-access systems. IEEE Trans. Communications - submitted, 1998.

....unknown coefficients [3] and no a priori information about the channels is exploited. We refer to this approach as unstructured channel estimation. More recently, a priori knowledge of the structure of the overall use channel impulse responses has been exploited in order to improve estimation [6, 7, 8, 9, 10, 11]. In some works, the special feature of rectangular chipshaping pulses is exploited to estimate directly the channel physical parameters (delays and path gains) In this way, a minimal number of unknowns needs to be estimated. On the other hand, these methods do not generalize easily to arbitrary ....

E. Ertin, U. Mitra, S. Siwamogsatham, "Maximum-Likelihood based multipath channel estimation for code-division multiple-access systems," submitted to the IEEE Trans. on Commun., June 1998.

....structured correlation matrix is presented in [11] which yields a closed form solution for Hermitian Toeplitz correlation matrix estimations. However, in our particular case, the correlation matrix R does not exhibit a Toeplitz structure. The importance of a good estimate of R is clearly seen in [4], where suboptimal channel estimators are constructed. These estimators are a function of an estimate of R; it is observed that performance degradation is a function of the fidelity of the estimate of R rather than the form of the channel estimators developed. It can be shown that in the flat ....

....Gaussian noise (AWGN) with covariance matrix oe 2 I N , where oe 2 is the noise variance and I N is the N Theta N identity matrix. The fading process fl kl (m) is a complex Gaussian random process which satisfies 1 The more accurate, more realistic three bit scenario can also be handled [4]. But for notational clarity, it is not handled here. An Improved Blind Adaptive MMSE Receiver 6 Effl k 1 l 1 (m)fl k2 l 2 (m)g = ffi(k 1 Gamma k 2 )ffi(l 1 Gamma l 2 ) In other words, the fading parameters are independent for different users and different paths. The partial spreading ....

E. Ertin, U. Mitra, and S. Siwamogsatham. Maximum-Likelihood Based Multipath Channel Estimation for Code-Division Multiple-Access Systems. IEEE Trans. Comm., 49(2):290--302, February 2001.

....acquisition and estimation algorithms have been developed for single path asynchronous DS CDMA systems [11, 12] blind timing acquisition in a multipath fading channel is still an open problem. Multipath acquisition and estimation has been considered in the context of training based algorithms in [13]. We note that in [5, 9] a brief discussion about timing initialization in multipath fading channels is provided, but the algorithms incur a computational complexity as high as O(N 4 ) where N is the spreading gain, which will render the implementation of these algorithms highly costly and thus ....

E. Ertin, U. Mitra, and S. Siwamogsatham. Maximum-likelihood based multipath channel estimation for Code-Division Multiple-Access systems. IEEE Transactions on Communications. in press.

....and estimation algorithms have been developed for single path asynchronous DS CDMA systems 1 [9, 10] blind timing acquisition in a multipath fading channel is still an open problem. Multipath acquisition and estimation has been considered in the context of training based algorithms in [11]. We note that in [5, 8] a brief discussion about timing initialization in multipath fading channels is provided, but the algorithms incur a computational complexity as high as O(N 4 ) where N is the spreading gain, which will render the implementation of these algorithms highly costly and thus ....

E. Ertin, U. Mitra, and S. Siwamogsatham. Maximum-Likelihood Based Multipath Channel Estimation for Code-Division Multiple-Access Systems. IEEE Transactions on Communications, 2000. accepted for publication.

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