multi-carrier cdma. outline introduction system model types applications references
TRANSCRIPT
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Multi-carrier CDMA
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Outline
Introduction System Model Types Applications References
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Introduction
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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
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OFDM Signal in Frequency Domain
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Simple Transmitter Structure
1kC )2cos( 1tf
)2cos( 2tf
)2cos( tfN
2kC
kNC
Copier
1kc 2kc)(tck
Data Stream
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Transmitter Structure
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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
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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.
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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.
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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
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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
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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
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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.