Ungleicher Fehlerschutz mittels Bit-Loading in OFDM und DMT für SISO- und MIMO-Systeme
Zusammenfassung der Projektergebnisse
The project managed to provide a comprehensive treatment of UEP bit-loading for multicarrier modulation (OFDM, Orthogonal Frequency Division Multiplex; DMT, Discrete MultiTone), modifying almost all current algorithms to allow for UEP properties and adding a completely new one that allows very fast convergence to the desired bit load within only 1 or 2 iterations. At the start of the project, only one UEP algorithm was available. Additionally, aspects of bit-loading in multicarrier MIMO (Multiple-Input Multiple- Output) systems were studied, extending it to multi-user aspects, e.g., using hierarchical modulation for user separation as an additional option to FDMA. Rate/performance forecasts were investigated using the SNR (signal-to-noise ratio) instead of the SINR (signal-plus-interference-to-noise ratio) to more easily adapt systems. In MIMO and Multi-User applications, channel uncertainties were considered, how performance deteriorates, when bit loading and precoding steps are based on outdated channel-state information. Furthermore different spatial equalization options were studied to counteract misaligned precoding. User rates of multi-user systems were adapted according to capacities following the chain rule of information theory varying distance ratios of hierarchical modulation schemes. Finally, LDPC coding schemes were adapted to hierarchical modulation as an example of a UEP modulation scheme, showing some effects on the weight distribution of the optimized codes. However, overall, hierarchical modulation was found to be inefficient together with UEP modulation, since the UEP hierarchical modulation leads to less dense and inefficient packings, deteriorating the average performance of the overall system. In the last phase some still interesting aspects could only be treated for a special case, namely the combination of UEP coding and UEP modulation. We had to limit ourselves to LDPC codes for hierarchical modulation. A general treatment is still an objective that we see interesting and may consider for a new project or extension. Nevertheless, we would like to collect some new ideas and draw conclusions from the investigated example, before applying for a new study phase. In the last phase of the project, we already emphasized possibilities for security applications in the sense of a wiretap channel, defining different secrecy classes. When writing the proposal, we were already aware that we can, at best, do first steps into this direction and the reviewers also concluded that the topic will require much more time for a sufficient treatment. We are currently developing very new ideas together with MIMO channels, which are expected to build a sufficient basis for a new project. As part of an industrial R&D proposal, we recently saw some topics to be investigated, where our solutions could actually give quite some guidance. Due to non-disclosure conditions as a reviewer, we are unfortunately not allowed to provide more details. However, it should be pointed out that manufacturers and standards bodies are now starting to look into hierarchical and UEP modulation methods together with UEP coding. The use of the SNR instead of the SINR or using other simplified methods are also discussed and similar approaches are actually also used/discussed in LTE.
Projektbezogene Publikationen (Auswahl)
- “Prioritized Multiuser Transmission Using Virtual Diagonalization and Weighted Sum-MSE,” 15th International OFDM Workshop 2010, Hamburg, Germany, Sept. 1-2, 2010
K. Hassan and W. Henkel
- “UEP Concepts in Modulation and Coding,” Hindawi, Advances in Multimedia, Vol. 2010, Article ID 416797, 14 pages, 2010
W. Henkel, K. Hassan, N. von Deetzen, S. Sandberg, L. Sassatelli, and D. Declercq
(Siehe online unter https://dx.doi.org/10.1155/2010/416797) - Unequal Error Protection Adaptive Modulation in Multicarrier Systems, PhD Thesis, Nov. 5, 2011, Shaker Verlag, Aachen, 2011
K. Hassan
- “Dynamic User Scheduling in Non-Orthogonal Multiuser MIMO-OFDM,” 16th International OFDM Workshop 2011, Hamburg, Germany, Aug. 31-Sept. 1, 2011
K. Hassan, A. Filip, and W. Henkel
- “Adaptive Multiuser MIMO-OFDM QoS-Based Scheduler Using Virtual Channel State Information,” First IEEE International Conference on Communications in China (ICCC 12), Beijing, China, Aug. 15-18, 2012
K. Hassan, A. Filip, and W. Henkel
- “Prioritized Adaptive Modulation for MIMO-OFDM Using Pre-Ordered SIC,” 2012 IEEE 76th Vehicular Technology Conference (VTC2012-Fall), Québec City, Canada, Sept. 3-6, 2012
K. Hassan, K. Saaifan, and W. Henkel
- “Hierarchical Modulation to Support Low-Density Parity-Check Code Design?,” SCC 2013, Munich, Jan. 21-24, 2013
A. Filip and W. Henkel
