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Multi-carrier CDMA

Multi-carrier CDMA . Outline. Introduction System Model Types Applications References . Introduction . Introduction . OFDM benefits: Robustness against multipath propagation channels Low-complex technique Bandwidth-efficient technique CDMA benefis Enables multiple access

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Multi-carrier CDMA

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  1. Multi-carrier CDMA

  2. Outline • Introduction • System Model • Types • Applications • References

  3. Introduction

  4. Introduction • OFDM benefits: • Robustness against multipath propagation channels • Low-complex technique • Bandwidth-efficient technique • CDMA benefis • Enables multiple access • Provide frequency diversity • Mitigates multipath interference

  5. OFDM Signal in Frequency Domain

  6. Simple Transmitter Structure Data Stream

  7. Transmitter Structure

  8. Receiver Structure • Main advantage of the MC-CDMA • receiver employ all the received signal energy • Receiver stages • Coherently detection with DFT • Despreading • Using combining techniques (EGC, MRC, …) • Single-user detection: prefiltering method • Multi-user detection (MUD) • Linear: MMSE, • Nonlinear: PIC, SIC • Turbo MUD

  9. Advanced Variations • MIMO-MC-CDMA • Prefiltering • CSI at tx • Single user detection • Space-time codes (CSI at rx) • Layered space-time • Beamforming • Smart antenna • Low data rate in low number of users • Lower complexity • Transmit array vs. Receive array • Outdoor application • BD-MC-CDMA • Transmitters select carriers (frequency bands) which are under good condition according to feedback information from the receivers and can decrease transmission power for each receiver.

  10. Applications • Beyond 3G and 4G • High data rates: 100 Mbps for DL 20 Mbps for UL • High spectral efficiency in multi-cell environment • Open issues: • slot/frame acquisition, • channel estimation: MIMO and UL, • UL synchronization • Competition with evolution of existing DS-CDMA systems, OFDMA and solution from NTTDoCoMo VSF-OFCDM (variable spreading factor Orthogonal Frequency and Code Division Multiplexing) for the DL.

  11. Applications • Power Line Communications (PLC) • Cellular system: resistance to inter-cell interference • High data rates (100 Mbps) • Compliant with authorized spectrum mask • Competition with OFDMA • Cognitive radio • Adaptive to unused frequency bands

  12. MC-CDMA vs. OFDMA • OFDMA • Assignment of one or several sub-carriers to each user • User-data symbols are allocated directly to channel resources and therefore offers no diversity without channel coding • MC-CDMA • Transmits in parallel chips of a spread data symbol on different sub-carriers • Spreads the user data symbol energy over all channel resources and therefore offers diversity. • Trade-off between the negative impact of MAI and the positive effect of frequency diversity

  13. MC-CDMA vs. OFDMA • Single user scenario: • Comparison depends on coding rates, constellation size and receiver structure • MC-CDMA outperforms COFDM for small constellation (QPSK) • Cellular environment: • Resource allocation for OFDMA system • MC-CDMA can outperform OFDMA in the case of varying resource loads • OFDMA performance in the peripheral cell area surpasses the MC-CDMA

  14. References • [1] T. Sälzer, ”Design of a multi-carrier CDMA downlink with different transmit antenna array strategies,” in VTC-Fall 2005. • [2] Z. Li, M. Vehkaperä, D. Tujkovic, M. Juntti, M. Latva-aho, and S. Hara, “Performance evaluation of space-frequency coded MIMO MC-CDMA system,” in Proc. IST Mobile & Wireless Telecommun. Summit (IST), Aveiro, Portugal, June 15–18, 2004. • [3] S.Hara, R.Prasad, “Overview of Multi-Carrier CDMA,”IEEE 4th International Symposium on Spread Spectrum Techniques and Applications Proceedings 1996, Vol. 1, pp. 22-25, Sep. 1996. • [4] H. Tao, N. Arumugam, and G. H. Krishna, “Performance of space-time coded MC-CDMA over time and frequency selective fading channel,” in Proc. IEEE Conf. Mobile and Wireless Networks (MWCN), Stockholm, Sweden, Sept. 9–11, 2002, pp. 419–423. • [5] Z. Li, M. Vehkaperä, D. Tujkovic, M. Juntti, “Receiver Design for Spatially Layered Downlink MC-CDMA System,”IEEE Trans. Commun., vol.54, pp.1471-1477, May 2005.

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