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Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

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<strong>MC</strong>-CDMA 8910 010 −110 −2BER10 −310 −4QPSK8-PSK16-QAMQPSK, <strong>OFDM</strong>8-PSK, <strong>OFDM</strong>16-QAM, <strong>OFDM</strong>10 −50 2 4 6 8 10 12 14E b /N 0 in dBFigure 2-18 FEC coded BER versus SNR for <strong>MC</strong>-CDMA with different symbol mappingschemes: fully loaded system; channel code rate R = 2/3; Rayleigh fadingFigure 2-19 represents the most important results regarding spectral/power efficiencyin a cellular system, which are in favor of <strong>MC</strong>-CDMA schemes. These curves lead to thefollowing conclusions:– For a given coverage, the transmitted data rate can be augmented by at least 40 %compared to <strong>MC</strong>-TDMA or <strong>OFDM</strong>A.– Alternately, for a given data rate, about 2.5 dB can be gained in SNR. The 2.5 dBextension in power will give a higher coverage for an <strong>MC</strong>-CDMA system, or batterylive extension.2.1.10.3 Synchronous UplinkThe parameters used for the synchronous uplink are the same as for the downlink presentedin the previous section. Orthogonal spreading codes outperform other codes suchas Gold codes in the synchronous <strong>MC</strong>-CDMA uplink scenario, which motivates thechoice of Walsh–Hadamard codes also in the uplink. Each user has an uncorrelatedRayleigh fading channel. Due to the loss of orthogonality of the spreading codes at thereceiver antenna, MRC is the optimum single-user detection technique in the uplink (see

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