可变码长的OFCDM系统及其仿真分析

具有二维(2D)扩频方式的正交频分码分复用(OFCDM)系统,既能实现频率分集,又能兼顾时间分集,是未来第4代无线移动通信的高速数据传输系统。在实际扩频通信中,为了用户数足够多,且保证解扩接收的准确,需要的扩频码很长,因此文中在现有OFCDM系统之上,提出一种可变码长的OFCDM(VCL-OFCDM)系统,该系统仅需满足扩频码长度为子载波数的整数倍,使得系统可容纳的用户数增大,不再受子载波数目的限制。通过Matlab仿真表明:在同时具有时间选择性和频率选择性衰落信道中,VCL-OFCDM系统的性能优于1D系统性能;扩频码越长,VCL-OFCDM系统性能越好,当平均误码率为2×10-4,用户数为64时,扩频码为26×212系统比扩频码为26×210系统可多提供大约4.8 dB的信噪比增益。

Variable code length OFCDM system and its simulation analysis

Orthogonal frequency and code division multiplexing（OFCDM） system with 2 dimensional（2D）,both to achieve frequency diversity while maintaining the time diversity,its the future 4th generation wireless mobile communications high-speed data transmission system.In practice of spread spectrum communications,for the enough number of users and the accuracy of despreading received,spread-spectrum code required very long,so based on the existing OFCDM system,proposed a variable-length code OFCDM（VCL-OFCDM） system,which only need to meet the spreading code length,was an integer multiple of the number of subcarriers,so the system can accommodate the increasing number of users,no longer limited by the number of subcarriers.By Matlab simulation shows that： in the time and frequency selective fading channel,VCL-OFCDM system is superior to 1D system performance;at the same time,the longer the spreading code,the better the performance of VCL-OFCDM system,when the average bit error rate is 2×10-4 and the number of users is 64,the spreading code is 26×212 for the system than the spreading code is 26×210 for the system can provide more signal to noise ratio gain of about 4.8 dB.