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On MSE Exit Chart Analysis and Real Time DSP Implementation for Iterative (Turbo) Detection

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Abstract

We investigate the use of the mean square error (MSE) transfer characteristics to examine the convergence behaviour of the iterative (turbo) multiuser detector for coded code-division multiple-access (CDMA) systems. Both MSE and mutual information (MI) based extrinsic information transfer (MSE-EXIT and MI-EXIT) chart techniques reveal the same asymptotic and convergence behaviours. An improved low complexity version of the soft interference cancellation MMSE (SIC-MMSE) detection scheme is also proposed for CDMA systems utilizing BPSK modulation. Herein, under fixed-point data representation and computation constraint a real time DSP implementation (using TMS320C6416) is suggested. EXIT charts reveal that fixed-point implementation is feasible at possibly no performance degradation. Based on the measured number of cycles of different constituent sub-functions of the proposed receiver, a data transmission rate of up to 186 Kb/s can be reached for a 5-users load and a processing gain of 7 in an AWGN channel.

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Notes

  1. The term Conjugate is due to the fact that, \( {{\mathbf{r}}_k}\left( {i/i + 1} \right) \) and its conjugate \( {{\mathbf{r}}_k}{\left( {i/i + 1} \right)^* } \)are used.

  2. Notice that this complexity can further be reduced if we assume that the channel is constant over the processed data block so that \( {{\mathbf{\bar{\Lambda }}}_k} = \frac{1}{M}\sum\limits_{i = 1}^M {{{\mathbf{\Lambda }}_k}(i)} \) is used instead of \( {{\mathbf{\Lambda }}_k}(i) \) and hence one matrix inversion is required per data block of M information bits (ergodicity assumption).

  3. Notice that \( {{\mathbf{\Xi }}_{a,k}}(i) \) is a symmetrical matrix which admits real valued eigen values.

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Acknowledgements

The authors would like to thank the Axiocom Inc. and the National Science and Engineering Council of Canada (NSERC) for its financial support. We are grateful the anonymous reviewers critics as well.

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Authors and Affiliations

  1. Laboratory of Signal and System Integration (LSSI), Department of Electrical and Computer Engineering, Université du Québec à Trois-Rivières, C.P. 500, Trois-Rivières, Québec, Canada, G9A 5H7

    Messaoud Ahmed-Ouameur & Daniel Massicotte

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  1. Messaoud Ahmed-Ouameur
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  2. Daniel Massicotte
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Correspondence to Daniel Massicotte.

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Ahmed-Ouameur, M., Massicotte, D. On MSE Exit Chart Analysis and Real Time DSP Implementation for Iterative (Turbo) Detection. J Sign Process Syst 64, 305–317 (2011). https://doi.org/10.1007/s11265-010-0489-2

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  • DOI: https://doi.org/10.1007/s11265-010-0489-2

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