问题描述：
英语翻译
MC-CDMA inherits the interference rejection capability of CDMA,and the potential of mitigating multipath propagation effects of orthogonal frequency division multiplexing
(OFDM).MC-CDMA with its frequency diversity is an attractive modulation scheme for multi-user high data rate wireless communication system.However on OFDM and MCCDMA sub-channel decomposition cannot be achieved without adding guard band or cyclic prefix,where a copy of the end part of the data symbol block is transmitted.Due to the relationship between circular and linear convolutions in discrete Fourier transform (DFT),
the residual inter symbol interference (ISI) is eliminated by dropping the guard interval part in the receiver.This method needs transmitting extra guard interval signals that introduces
overhead and thus leads to spectral inefficiency and performance degradation.An efficient scheme which not only counters the degrading effects of ISI but also conserves the bandwidth is the application of discrete wavelet packet transform (DWPT) based MCCDMA.In this paper we replace Fourier based complex exponential carriers of MC-CDMA with an orthonormal wavelets packets,such as daubechies,haar,biorthogonal,discrete
meyer and coiflets to compare the performance of MC-CDMA based discrete fourier transform (DFT) and MC-CDMA based discrete wavelet packet transform(DWPT).
Wireless communications using MC-CDMA offer tremendous opportunity to support high data rate and combat the inter-symbol interference (ISI) due to the multipath propagation effects,inherently present in the wireless channel.The use of single carrier modulation scheme may prove to be unfruitful,since the channel induced inter-symbol interference,can easily distort the data carried by a single carrier.Multi-carrier
modulation (MCM) offers the advantage of spreading out a frequency selective fading over many symbols,which effectively randomizes burst errors caused by fading or impulse noise,so that instead of several adjacent symbols being completely destroyed; many symbols are only slightly distorted.However,the quest for better solution in terms of modulation techniques that could accommodate high data rates,continued and an idea of
combining MCM with code division multiple access (CDMA) was born in 1993 [1].It combines the advantages of CDMA such as interference rejection,frequency reuse etc.,with the advantage of OFDM such as robustness against multipath and impulse noise [2].However,the problem of frequency offset is considered one
of the main drawback of MC-CDMA systems [3],[4],resulting from Doppler’s shift which introduced signal distortion and power loss.In recent years discrete Fourier transform based MC-CDMA is being replaced by a wavelet packet waveforms which have the property of localization in both time and frequency domain [5],[6],[7],[8].
MC-CDMA inherits the interference rejection capability of CDMA,and the potential of mitigating multipath propagation effects of orthogonal frequency division multiplexing
(OFDM).MC-CDMA with its frequency diversity is an attractive modulation scheme for multi-user high data rate wireless communication system.However on OFDM and MCCDMA sub-channel decomposition cannot be achieved without adding guard band or cyclic prefix,where a copy of the end part of the data symbol block is transmitted.Due to the relationship between circular and linear convolutions in discrete Fourier transform (DFT),
the residual inter symbol interference (ISI) is eliminated by dropping the guard interval part in the receiver.This method needs transmitting extra guard interval signals that introduces
overhead and thus leads to spectral inefficiency and performance degradation.An efficient scheme which not only counters the degrading effects of ISI but also conserves the bandwidth is the application of discrete wavelet packet transform (DWPT) based MCCDMA.In this paper we replace Fourier based complex exponential carriers of MC-CDMA with an orthonormal wavelets packets,such as daubechies,haar,biorthogonal,discrete
meyer and coiflets to compare the performance of MC-CDMA based discrete fourier transform (DFT) and MC-CDMA based discrete wavelet packet transform(DWPT).
Wireless communications using MC-CDMA offer tremendous opportunity to support high data rate and combat the inter-symbol interference (ISI) due to the multipath propagation effects,inherently present in the wireless channel.The use of single carrier modulation scheme may prove to be unfruitful,since the channel induced inter-symbol interference,can easily distort the data carried by a single carrier.Multi-carrier
modulation (MCM) offers the advantage of spreading out a frequency selective fading over many symbols,which effectively randomizes burst errors caused by fading or impulse noise,so that instead of several adjacent symbols being completely destroyed; many symbols are only slightly distorted.However,the quest for better solution in terms of modulation techniques that could accommodate high data rates,continued and an idea of
combining MCM with code division multiple access (CDMA) was born in 1993 [1].It combines the advantages of CDMA such as interference rejection,frequency reuse etc.,with the advantage of OFDM such as robustness against multipath and impulse noise [2].However,the problem of frequency offset is considered one
of the main drawback of MC-CDMA systems [3],[4],resulting from Doppler’s shift which introduced signal distortion and power loss.In recent years discrete Fourier transform based MC-CDMA is being replaced by a wavelet packet waveforms which have the property of localization in both time and frequency domain [5],[6],[7],[8].
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