一种并行传输的时频域扩频多载波DS-CDMA系统性能分析

提出了一种并行传输的时频域扩频多载波DS-CDMA系统，它先将传输数据进行串并转换而后经过时域和频域两次扩频。在不改变传输数据速率和扩频增益的情况下，并行传输可以增大符号时间和降低码片速率，从而提高信号的抗频率选择性衰落的能力和实现低速率信号处理。采用码片匹配滤波的方式对信号进行接收，分析了高斯信道下的单用户检测性能并推导了误比特率表达式。研究表明，在此系统中串并转换比与码片速率的降低和子载波个数成正比，而与误比特率无关；不存在比特间干扰；多用户干扰只存在于同一子载波传输的不同用户的数据比特之间，且可通过采用正交时域扩频码来消除；误比特率随用户数量的增加而增加，而随每比特信噪比和扩频增益的增加而降低；在带宽受限的情况下，可通过合理设置串并装换比、时域和频域扩频增益参数来简化系统实现，满足误比特率的性能需求。

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.