32-Gb/s CAP Signals Wireless Delivery at D-Band Over 4.6 Km Based on Photonics-Aided Technology and Envelope Detection

The Carrier-less Amplitude and Phase (CAP) modulation is an advanced modulation technology with the advantages of high spectrum utilization, low cost, and low complexity. In this paper, based on photonics-aided technology and envelope detection, we experimentally demonstrate the wireless transmission of 4.6 km of 8Gbaud CAP-4QAM signal and 1.2 km of 5Gbaud CAP-16QAM signal over D-band at 125GHz, respectively. At the same time, combined with antenna polarization multiplexing technology, the maximum bit rate can reach 32 Gb/s and 40 Gb/s, respectively. Both BERs are below the 25% overhead soft-decision forward error correction (SD-FEC) threshold of 4.2×10 ⁻² . In addition, in the back-end equalization algorithm processing, we compared the time domain (TD) constant module algorithm (CMA), the Decision Directed Least Mean Squares (DDLMS) algorithm of the time domain multiple input multiple output (MIMO) structure, the frequency domain (FD) CMA algorithm, and the FD MIMO-DDLMS algorithm. The results show that the FD MIMO DDLMS algorithm can effectively compensate for the I/Q imbalance problem of CAP signals while maintaining low computational complexity. As far as we know, this is the first experimental demonstration of a rate exceeding 30 Gb/s in a D-band long-distance transmission system with envelope detection, which provides an effective solution for low-cost millimeter wave transmission.