Reliable Multi-user Uplinks in Fiber-Wireless Integrated Network using Quasi-orthogonal Chirp Spreading OFDM

We experimentally demonstrate a grant-free multiuser upstream with a quasi-orthogonal chirp spreading (QOCS) orthogonal frequency division multiplexing (OFDM) in an intensity-modulation and direct-detection based fiber-wireless convergence over 120-cm wireless and 25-km fiber transmission. By applying the frequency chirp spreading, user subcarriers in a widely-adapted OFDM are re-allocated into the coding channels and occupies the whole available bandwidth. Time and frequency resources can be shared and fully utilized for all active users. Without a time-consuming request-and-grant process, the proposed scheme is suitable for the low-latency and emergency communications. The experimental results reveal a high tolerance of multi-user interference and a less than 3% of error vector magnitude degradation is measured in the most critical scenario that randomly distributed users are totally active and temporally overlapped. Furthermore, a 21.9 dB system power budget is achieved after 25-km fiber transmission. Therefore, our proposed scheme exhibits a high-reliability for the next generation low-latency applications in a fiber-wireless convergence network.