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Physical Layer Simulator for WiMAX

This paper presents a physical layer simulator for WiMAX, focusing on the OFDMA technique and various channel coding techniques. The simulation results show the performance of different modulation schemes and the impact of turbo coding.

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Physical Layer Simulator for WiMAX

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  1. International Symposium on Electronics and Telecommunications ETC 2010Ninth EditionA physical layer simulator for WiMAX Marius Oltean, Maria Kovaci, Alexandru Isar, Jamal Mountassir, Petru Lazăr

  2. Outline • Introduction • PHY layer in WiMAX • PHY layer simulator • Simulation results • Conclusions

  3. Introduction • WiMAX: a powerful candidate for 4th generation of mobile communication systems, based on IEEE 802.16e. • MAC layer is oriented on the QoS. • PHY layer relies on OFDMA technique. • DL/UL separation by FDD and TDD techniques.

  4. PHY layer • OFDM symbol: • OFDM/OFDMA implementations are based on the IFFT and FFT techniques. • Two types of permutation are used: PUSC and FUSC. • AMC: reduces the complexity and is well suited for the channels that change slowly in time

  5. MAC layer • for DL FUSC and PUSC, the pilot tones are allocated first. The remaining data subcarriers are divided into subchannels that are used exclusively for data • For UL PUSC, the set of used subcarriers is first partitioned into subchannels and then the pilot subcarriers are allocated from within each subchannel. Fig. 1: WiMAX radio frame (TDD).

  6. DL-PUSC Fig. 2 : Segment 0 composition and pilot subcarriers for DL-PUSC 512.

  7. Channel Coding Techniques • Convolutional coding; • Turbo-coding; • LDPC coding; • Convolutional turbo-coding (CTC) Fig 3. Logical resources for DL-PUSC

  8. PHY Layer Simulator Fig 4. The block scheme of the WiMAX simulator

  9. Simulation Results • computation of BER and BLER statistics; • QPSK, 16QAM; • AWGN channel.

  10. UL-PUSC 512 • QPSK is better than 16 QAM but the communication is slower. Fig. 5: BER performance: UL-PUSC 512.

  11. DL- FUSC 512 The strength of the turbo-codes leads to very good BER results. Consequently: at 2dB the BER is already below 0.0001. For BER=0.001, the gain of QPSK versus 16QAM is approximately 3.5 dB. Fig. 6: BER performance for DL- FUSC 512.

  12. CONCLUSIONS Better understanding of the signal processing steps at the PHY layer of IEEE 802.16e specifications. Performance evaluation in different scenarios A realistic model take into account the time variability and the frequency selectivity.

  13. FURTHER WORK The future improvements will cover some"gaps“ in our simulator. The decoder for 64QAM is not yet implemented. The implemented permutation types may be extended to the adjacent case too since presentlyonly the distributed permutations are simulated.

  14. References [1] J. Yun and M. Kavehrad, ”PHY/MAC Cross-Layer issues in Mobile WiMAX.”, Bechtel Telecommunications Technical Jan. 2006, pp. 45-56. [2] H. Yaghoobi, "Scalable OFDMA Physical Layer in IEEE 802.16 Wireless MAN", Intel Technology Journal, Vol.1, Issue3,2004, pp. 201-212. [3] H. Balta, D. Bosneagu, M. Kovaci, M. Oltean "A Study of the Permutation Schemes Used in the Mobile WIMAX", Acta Technica Napocensis – Electronics and Telecommunications, Volum 29,Nr.3/2008, pp.17-20. [4] WiMAX Forum Applications Working Group, "System design and AWGN Results", 2008. [5] C. Douillard, and C. Berrou, ”Turbo Codes with Rate-m/(m+1) Constituent Convolutional Codes”, IEEE Transactions on Communications, Vol. 53, No. 10, Oct. 2005, pp.1630-1638. [6] J. Vogt and A. Finger, “Improving the max-log-MAP turbo decoder”, Electron. Lett., vol. 36, no. 23, pp. 1937–1939, Nov.2000. [7] H. Balta, C. Douillard, and M. Kovaci, “The Minimum Likelihood APP Based Early Stopping Criterion for Multi-Binary Turbo Codes”, Proc. of. Symposium of Electronics and Telecommunications – ETc 2006, Timisoara, Sept. 2006, pp.199- 203.

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