Performance Analysis of a Time and Frequency Domain Spread Multicarrier DS-CDMA System Supporting Parallel Transmission

This paper proposes a time and frequency domain spread multicarrier direct sequence code division multiple-access(TF/MC DS-CDMA) system supporting parallel transmission,which first takes the data bit from serial to parallel conversion and then employs both time-domain and frequency-domain spreading.In the case of constant transmission data rate and spread spectrum gain,parallel transmission can increase the symbol time and reduce code chip-rate,which can improve the capability of anti-frequency selective fading and achieve low-rate signal processing.Signals are received by invoking chip waveform matched filter.The detection performance of single-user is analyzed and the bit-error rate(BER) expression over additive white Gaussian noise channels is deduced.The research reveals that the serial to parallel conversion ratio is related to the reduction of code chip-rate and the number of subcarrier,but unrelated to BER.There is no interference between different data bits for the same user,and the multiuser interference(MUI) only exists between different data bits for different users transmitted by the same subcarrier and there will exist no MUI when the time-domain spreading codes assigned to different users are orthogonal.BER will rise along with the increase of users number and reduce along with the increase of spread spectrum gain and signal-to-noise ratio(SNR) per bit.In the condition of the limited bandwidth,the system can be simplified and meet the performance requirements of BER by reasonably setting the serial to parallel conversion ratio and the parameters of time-domain and frequency-domain spread spectrum.