L. Chu and U. Mitra, "Performance analysis of an improved MMSE multi-user receiver for mismatched delay channels," IEEE Trans. Commun., vol. 46, no. 10, pp.1369-1380, Oct. 1998.  Home/Search   Document Details and Download   Summary   Related Articles   Check

.... because they double the number of PN codes used, the noise enhancement problem of the decorrelating detector is more severe, and their capacity will not exceed 50 of the spreading factor [17] The QS CDMA MMSE detector [16] the improved MMSE (IMMSE) multiuser detector for asynchronous CDMA [26], and two robustified detectors [18] are based on stochastic delay error modelling. The detectors [16] and [26] achieve robustness by averaging over all possible delay errors, assuming zero mean Gaussian [26] or uniform delay error distribution [16] respectively. In [18] the linear ....

....is more severe, and their capacity will not exceed 50 of the spreading factor [17] The QS CDMA MMSE detector [16] the improved MMSE (IMMSE) multiuser detector for asynchronous CDMA [26] and two robustified detectors [18] are based on stochastic delay error modelling. The detectors [16] and [26] achieve robustness by averaging over all possible delay errors, assuming zero mean Gaussian [26] or uniform delay error distribution [16] respectively. In [18] the linear transformation matrix of the MMSE and decorrelating detector is modified. Although the stochastic approach improves the ....

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L. Chu and U. Mitra, "Performance analysis of an improved MMSEmulti-user receiver for mismatched delay channels," IEEE Trans. Commun., vol. 46, pp. 1369-1380, Oct. 1998.

....estimates the channel array response vectors and detects the information symbol sequences for all active users in the system. 73 We assume that the relative time delays for all the users are known at the receiver. The timing error effects on multi user signal detection are analyzed in [3] [5] [63] 111] and it is found that the timing error is much more serious to multi user signal detector s BER performance than any other channel parameter error. We will study the time error effects on the iterative receiver developed in this section using simulations. 4.4.1 SAGE Based Receiver The ....

....the users are known at the base station receiver. However, in practical applications, we have to estimate these parameters. Previous study showed that the BER performance of multi user receivers degrades significantly due to time delay estimation errors for single antenna single path systems [3] [5] [63] 111] In [5] an improved minimum mean squarederror (IMMSE) multi user receiver is proposed taking into account the timing errors. However, numerical results show that the IMMSE receiver performs worse than the MMSE receiver in terms of bit error rate for small timing errors and still ....

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L. Chu and U. Mitra, "Performance analysis of an improved MMSE multiuser receiver for mismatched delay channels", IEEE Transactions on Communications, vol. 46, no. 10, pp. 1369--1380, Oct. 1998.

....in both [85] and [136] Denote the estimated time delay for user k as k , and the delay error as k = k Gamma k . It can be assumed that the delay estimates of different users are independent. The 15 delay error can be modeled as a zero mean Gaussian random variable with variance k [14]. Analogous to Equation (2.8) define the elements of the estimated correlation matrices as s k (t Gamma k ) s j (t lT Gamma j )dt (2.24) s k (t Gamma k ) s j (t lT Gamma j )dt (2.25) When delay mismatch exists, the matched filter front end is aligned with the ....

....error modeling, and the other is based on deterministic delay error modeling. The research on robust multiuser detection based on stochastic delay error modeling has been focused mainly on the MMSE detector. Modified MMSE multiuser structures that are robust to delay mismatch were proposed in [14] [46] 82] An MMSE receiver for quasi synchronous CDMA is proposed in [46] which averages over all possible delay offsets. The delays are assumed to be uniformly distributed over a small fraction of a chip duration. Performance when the signal to noise ratio (SNR) is low is analyzed. For ....

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L. Chu and U. Mitra, "Performance analysis of an improved MMSE multi-user receiver for mismatched delay channels," IEEE Trans. Commun., vol. 46, no. 10, pp. 1369-1380, Oct. 1998.

....which are optimized under the assumption of perfect parameter estimates. In practice, especially in dynamic channels which are typically experienced in mobile communication systems, perfect estimation can hardly be achieved. Mismatch in parameter estimates might greatly impact detector performance [2, 3]. In this paper, we pursue modification of the second approach to reduce detector sensitivity to parameter mismatch. Due to the nonlinear nature of timing in detector formulation, isolation of the timing estimation is desired to reduce the computational effort. Without any presumptions based on ....

....in y This research was supported by the Air Force Office of Scientific Research under Grant F49620 96 1 0105. Code Matched Filter (CMF) Code Matched Filter (CMF) Maximum Likelihood Sequence Detection b Front End Processor (FEP) Timing Amplitude Estimator r Figure 1: Receiver diagram [3, 4, 5, 6]. Most of the previous works for asynchronous channels considered single or multi shot type receivers where edge effects, defined as a partial observation of the data at the edge of the observation window, contribute to the degradation of detection performance. For additive white Gaussian noise ....

L.-C. Chu and U. Mitra, "Performance analysis of the improved MMSE multi-user receiver for mismatched delay channels," IEEE Trans. on Communications, vol. 46, pp. 1369--1380, October 1998.

....outer products are presented in [11] V. Synchronization mismatch In this section, we examine methods for compensating for mismatch in timing information. It has been shown that errors in synchronization as small as a fraction of a chip can significantly affect the performance of MMSE receivers [5]. Assume that k = k Delta k . Recall that the fractional part of the delay is captured in the effective channel description c k [n] thus the error we must compensate for is the error in the integer part of the delay. A proposed solution is based on [8] We construct U receivers in ....

L.-C. Chu and U. Mitra, "Performance Analysis of the Improved MMSE Multi-user Receiver for Mismatched Delay Channels," IEEE Trans. on Comm., Vol. 47, No. 1, pp. 1369--1380, Oct. 1998.

....pose a significant challenge to receiver design relative to amplitude estimation errors. For DS CDMA receivers, the problem can be simplified by assuming rectangular chip waveforms since the signals may be represented by a linear combination of finite copies of the symbol waveforms shifted in time [12, 13, 14]. However, in practical systems bandlimited pulse shapes such as square root raised cosine waveforms are typically used [15] Compared to received signals modeled with rectangular pulses, which are piecewise linear in the delays, received signals employing bandlimited pulses in general are ....

....for uncertain timing scenarios considered only a finite observation window of data for data detection. That is, observations contained information from only a few transmitted symbols. For asynchronous communication, such limited window sizes can lead to additional performance loss. For example, in [12], we have considered a linear minimum mean squared error (MMSE) receiver with window size equal to the symbol period. Due to asynchronous transmission, some symbols which overlap in time with the interested symbol would be partially outside the window. Since the partially observed symbols are ....

L.-C. Chu and U. Mitra, "Performance analysis of the improved MMSE multi-user receiver for mismatched delay channels," IEEE Trans. on Communications, vol. 46, pp. 1369--1380, October 1998.

....due to its good performance with a moderate number of observations. In this paper, the study of the modified MUSIC delay estimator is motivated by the need for estimator statistics to drive the construction of delayerror insensitive Minimum Mean Squared Error (MMSE) based receivers proposed in [6]. To properly construct the receivers in [6] both bias and variance information about the delay estimators are necessary. In general, the exact properties of the estimates with finite sample size or low signal to noise ratio (SNR) are intractable. In [7] Parkvall provided an asymptotic per ....

....number of observations. In this paper, the study of the modified MUSIC delay estimator is motivated by the need for estimator statistics to drive the construction of delayerror insensitive Minimum Mean Squared Error (MMSE) based receivers proposed in [6] To properly construct the receivers in [6], both bias and variance information about the delay estimators are necessary. In general, the exact properties of the estimates with finite sample size or low signal to noise ratio (SNR) are intractable. In [7] Parkvall provided an asymptotic per This research was supported by the Air Force ....

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L.-C. Chu and U. Mitra, "Performance analysis of the improved MMSE multi-user receiver for mismatched delay channels, " to appear in IEEE Trans. on Communications, 1998.

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L. Chu and U. Mitra, "Performance analysis of an improved MMSE multi-user receiver for mismatched delay channels," IEEE Trans. Commun., vol. 46, no. 10, pp.1369-1380, Oct. 1998.

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L.-C. Chu and U. Mitra. Performance analysis of the improved MMSE multi-user receiver for mismatched delay channels. IEEE Trans. Comm., 46(10):1369--1380, October 1998.

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