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.