Siming Liu

Special cascade LMS equalization scheme suitable for 60-GHz RoF transmission system.

We design a specific cascade least mean square (LMS) equalizer and to the best of our knowledge, it is the first time this kind of equalizer has been employed for 60-GHz millimeter-wave (mm-wave) radio over fiber (RoF) system. The proposed cascade LMS equalizer consists of two sub-equalizers which are designated for optical and wireless channel compensations, respectively. We control the linear and nonlinear factors originated from optical link and wireless link separately. The cascade equalization scheme can keep the nonlinear distortions of the RoF system in a low degree. We theoretically and experimentally investigate the parameters of the two sub-equalizers to reach their best performances. The experiment results show that the cascade equalization scheme has a faster convergence speed. It needs a training sequence with a length of 10000 to reach its stable status, which is only half as long as the traditional LMS equalizer needs. With the utility of a proposed equalizer, the 60-GHz RoF system can successfully transmit 5-Gbps BPSK signal over 10-km fiber and 1.2-m wireless link under forward error correction (FEC) limit 10-3. An improvement of 4dBm and 1dBm in power sensitivity at BER 10-3 over traditional LMS equalizer can be observed when the signals are transmitted through Back-to-Back (BTB) and 10-km fiber 1.2-m wireless links, respectively.

Bit-based support vector machine nonlinear detector for millimeter-wave radio-over-fiber mobile fronthaul systems

An effective bit-based support vector machine (SVM) is proposed as a non-parameter nonlinear mitigation approach in the millimeter-wave radio-over-fiber (RoF) mobile fronthaul (MFH) system for various modulation formats. First, we analyze the impairments originated from nonlinearities in the millimeter-wave RoF system. Then we introduce the operation principle of the bit-based SVM detector. As a classifier, the SVM can create nonlinear decision boundaries by kernel function to mitigate the distortions caused by both linear and nonlinear noise. In our design, SVM can learn and capture the link characteristics from only a few training data without requiring the prior estimation of the system link. The bit-based SVM only needs log2M SVMs to detect the signal of M-order modulation format. Experimental results have been obtained to verify the feasibility of the proposed method. The sensitivities are improved by 1.2-dB for 16-QAM, 1.3-dB for 64-QAM, 1.8-dB for 16-APSK and 1.3-dB for 32-APSK at BER = 1E-3 with SVM detector, respectively. The proposed bit-based SVM gains a large improvement in the nonlinear system tolerance and outperforms the system employing k-means algorithm.

A 60-GHz RoF System With Blind VSS-DD-LMS Equalizer for Optical-Wireless Transmission

We experimentally demonstrate a 60-GHz radio over fiber (RoF) system utilizing a blind equalizer to improve the bit error rate performance. We propose a blind variable step-size decision-directed least mean square (VSS-DD-LMS) equalization algorithm with fast convergence speed. To the best of our knowledge, this is the first to apply a variable step size LMS blind equalizer in a 60-GHz RoF system. Using this algorithm, higher convergence speed and fewer iterations can be achieved simultaneously. Comparisons of our proposed algorithm with other existing algorithms in the designed RoF system are reported. The optimal value of the tap number is also investigated. A 5-Gb/s BPSK signal is successfully transmitted through a 10-km fiber and 1.2-m wireless link using our proposed blind VSS-DD-LMS equalizer under a forward error correction limit of 10-3.