| 1. |
- Wehinger, Joachim, et al.
(författare)
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On channel estimators for iterative CDMA multiuser receivers in flat Rayleigh fading
- 2004
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Ingår i: IEEE International Conference on Communications, 2004. - 0780385330 ; , s. 2497-2501
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Konferensbidrag (refereegranskat)abstract
- In this work we compare channel estimation algorithms for use in an iterative CDMA receiver in a block fading environment. The receiver consists of a soft multiuser data estimator, a bank of single user decoders, and a multiuser channel estimator. The multiuser data estimator is implemented as parallel interference canceler with unconditional post-MMSE filtering (PIC-MMSE) and the decoder is a soft-in soft-out MAP decoder. In the channel estimator we make use of dedicated pilot symbols and fed back soft-code symbols which are exploited as additional soft pilot symbols when the iterations proceed. We show that using extrinsic information increases the receiver performance significantly compared to using a posteriori information in the feedback for channel estimation. We introduce a linear MMSE (LMMSE) estimator which takes into account the variances of fed back code symbols and compare it to approximations of the least squares (ALS) estimator and the linear minimum-mean-square error (ALMMSE) estimator. Performance results are illustrated in terms of bit error rate (BER) and average normalized square error (ANSE) of the channel estimators. They show that the newly proposed LMMSE algorithm outperforms the ALS and ALMMSE algorithms.
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| 2. |
- Zemen, Thomas, et al.
(författare)
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Improved channel estimation for iterative receivers
- 2003
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Ingår i: IEEE Global Telecommunications Conference, 2003. GLOBECOM '03.. - 0780379748 ; 1, s. 257-261
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Konferensbidrag (refereegranskat)abstract
- In iterative receiver structures, soft information becomes available after the decoding stage in the first iteration. This information is used to enhance the quality of the channel estimates for the next iteration. Channel estimation plays a crucial role in multi-user detection because the effective identification sequence for each user strongly depends on the channel characteristics. To combine deterministic pilot information with soft information, a generalized estimator based on the linear minimum mean square error (LMMSE) principle is derived. We present the special case of orthogonal frequency division multiplexing (OFDM) based multi-carrier code division multiple access (MC-CDMA) in detail and provide simulation results. The presented channel estimation algorithm can be also applied to direct sequence (DS)-CDMA and multi-input multi-output (MIMO) systems.
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