Resource allocation optimization in TFDM-based flexible-rate simplified coherent PON

In this paper, we propose a mathematical model incorporating entropy loading and the solving algorithm to optimize the diversity gain of a flexible-rate time and frequency-division multiplexing (TFDM) simplified coherent passive optical network, where Alamouti coding is adopted at the optical line terminal (OLT), and the cost of optical network unit (ONU) is reduced to a quarter of a full coherent ONU. In addition, the proposed scheme restricts each ONU from receiving only one subcarrier to further reduce the system costs. The results of 100-Gb/s downstream transmission show that the net data rate (NDR) of TFDM is marginally sensitive to the number of subcarriers used, while the bandwidth requirement on the ONU side can be significantly reduced when the number of subcarriers increases. Besides, we show that TFDM maintains the diversity gain and achieves 13.47 Gb/s higher NDR than time-division multiplexing (TDM) under diversified link qualities.