Aalto University Schools of Technology - electronic academic dissertations - http://otalib.aalto.fi/fi/kokoelmat_tiedonhaku/e-julkaisut/vaitoskirjat/
Aalto

Iterative Receivers and Multichannel Equalisation for Time Division Multiple Access Systems

Markku Pukkila

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S1 at Helsinki University of Technology (Espoo, Finland) on the 10th of October, 2003, at 12 o'clock noon.

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Abstract

The thesis introduces receiver algorithms improving the performance of TDMA mobile radio systems. Particularly, we consider receivers utilising side information, which can be obtained from the error control coding or by having a priori knowledge of interference sources. Iterative methods can be applied in the former case and interference suppression techniques in the latter.

Convolutional coding adds redundant information into the signal and thereby protects messages transmitted over a radio channel. In the coded systems the receiver is usually comprised of separate channel estimation, detection and channel decoding tasks due to complexity restrictions. This suboptimal solution suffers from performance degradation compared to the optimal solution achieved by optimising the joint probability of information bits, transmitted symbols and channel impulse response. Conventional receiver utilises estimated channel state information in the detection and detected symbols in the channel decoding to finally obtain information bits. However, the channel decoder provides also extrinsic information on the bit probabilities, which is independent of the received information at the equaliser input. Therefore it is beneficial to re-perform channel estimation and detection using this new extrinsic information together with the original input signal.

We apply iterative receiver techniques mainly to Enhanced General Packet Radio System (EGPRS) using GMSK modulation for iterative channel estimation and 8-PSK modulation for iterative detection scheme. Typical gain for iterative detection is around 2 dB and for iterative channel estimation around 1 dB. Furthermore, we suggest two iteration rounds as a reasonable complexity/performance trade-off. To obtain further complexity reduction we introduce the soft trellis decoding technique that reduces the decoder complexity significantly in the iterative schemes.

Cochannel interference (CCI) originates from the nearby cells that are reusing the same transmission frequency. In this thesis we consider CCI suppression by joint detection (JD) technique, which detects simultaneously desired and interfering signals. Because of the complexity limitations we only consider JD for two binary modulated signals. Therefore it is important to find the dominant interfering signal (DI) to achieve the best performance. In the presence of one strong DI, the JD provides major improvement in the receiver performance.

The JD requires joint channel estimation (JCE) for the two signals. However, the JCE makes the implementation of the JD more difficult, since it requires synchronised network and unique training sequences with low cross-correlation for the two signals.

This thesis consists of an overview and of the following 9 publications:

  1. Nefedov N., Pukkila M., Visoz R. and Berthet A., Iterative receiver concept for TDMA packet data systems. European Transactions on Telecommunications, accepted as a regular paper for publication in January 2003. © 2003 by authors and © 2003 Associazione Elettrotecnica ed Elettronica Italiana (AEI), John Wiley & Sons Ltd. By permission.
  2. Nefedov N., Pukkila M., Visoz R. and Berthet A., 2003. Iterative data detection and channel estimation for advanced TDMA systems. IEEE Transactions on Communications 51, No. 2, pages 141-144. © 2003 IEEE. By permission.
  3. Pukkila M., 2000. Turbo equalisation for the enhanced GPRS system. Proceedings of the 11th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications. London, UK, September 2000, pages 893-897. © 2000 IEEE. By permission.
  4. Nefedov N. and Pukkila M., 2000. Iterative channel estimation for GPRS. Proceedings of the 11th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications. London, UK, September 2000, pages 999-1003. © 2000 IEEE. By permission.
  5. Nefedov N. and Pukkila M., 2000. Turbo equalization and iterative (turbo) estimation techniques for packet data transmission. Proceedings of the 2nd International Symposium on Turbo Codes. Brest, France, September 2000, pages 423-426. © 2000 ENST Bretagne. By permission.
  6. Pukkila M. and Olivier J. C., 2001. Turbo equalization with low complexity decoder. Proceedings of the 54th IEEE Vehicular Technology Conference. Atlantic City, NJ, October 2001, Vol. 2, pages 1048-1052. © 2001 IEEE. By permission.
  7. Pukkila M., Heikkilä M. J. and Ranta P. A., 2001. Space-time trellis coding with turbo equalisation for the EGPRS system. Proceedings of the 12th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications. San Diego, CA, September-October 2001, Vol. 1, pages 129-133. © 2001 IEEE. By permission.
  8. Ranta P. A. and Pukkila M., 1999. Interference suppression by joint demodulation of cochannel signals. Zvonar Z., Jung P. and Kammerlander K. (Eds.), GSM: Evolution Towards 3rd Generation Systems. Kluwer Academic Publishers, Dordrecht, Netherlands, 1999, pages 153-186. © 1999 Kluwer Academic Publishers. By permission.
  9. Pukkila M. and Ranta P. A., 1997. Channel estimator for multiple co-channel demodulation in TDMA mobile systems. Proceedings of the 2nd European Personal Mobile Communications Conference, pages 327-333. © 1997 VDE Verlag. By permission.

Keywords: equalisation, channel estimation, turbo equalisation, iterative receivers, joint detection, interference cancellation, TDMA, GSM, EDGE

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© 2003 Helsinki University of Technology

Last update 2011-05-26