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Multi carrier-CDMA

Multi carrier-CDMA. 指導老師 : 黃文傑 姓名 : 吳政修. outline. Advantage of OFDM Disadvantage of OFDM Advantage of DS-CDMA Disadvantage of CDMA What is MC-CDMA Conclusion. Advantage of OFDM. OFDM is robust to frequency-selective fading.

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Multi carrier-CDMA

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  1. Multi carrier-CDMA 指導老師:黃文傑 姓名:吳政修

  2. outline • Advantage of OFDM • Disadvantage of OFDM • Advantage of DS-CDMA • Disadvantage of CDMA • What is MC-CDMA • Conclusion

  3. Advantage of OFDM • OFDM is robust to frequency-selective fading. • It can lower the symbol rate in each subcarrier so that a longer symbol duration makes it easier to quasi-synchronize the transmission.

  4. Disadvantage of OFDM 1.Difficulty in subcarrier synchronization. 2.Sensitivity to frequency offset. 3.Nonlinear amplification. The fact that it is composed of a lot of subcarriers with their overlapping power spectra and exhibits a non-constant nature in its envelope.

  5. DS-CDMA

  6. Advantage of DS-CDMA • DS-CDMA is quite robust to frequency offsets and nonlinear distortion. • It can provide flexibility capacity.

  7. Disadvantage of CDMA • It needs more wideband spectrum than conventional communication. • It will have wrong correlation, self-interference (SI), multiple access interference (MAI) and synchronization problem in high data rate.

  8. What is MC-CDMA • MC-CDMA is the combination of OFDM and CDMA. • The major advantage is that it can lower the symbol rate in each subcarrier so that a longer symbol duration makes it easier to quasisynchronize the transmission. • It is usually used in downlink.

  9. MC-CDMA • MC-CDMA are categorized mainly into two groups. 1.One spreads the original data stream using given spreading code, then modulates a different subcarrier with each chip. 2.Other spreads the s/p converted data streams using the given spreading code , and then modulates a different subcarrier with each of the data stream.

  10. MC-CDMA(1)

  11. MC-CDMA(2)

  12. BER

  13. Conclusion • The bandwidth of MC-CDMA signal spectrum is almost the same as that of a DS-CDMA signal spectrum. • A DS-CDMA system cannot always employ all the received signal energy scattered in the time domain , whereas an MC-CDMA system can effectively combine all the received signal energy scattered in the frequency domain.

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