Abstract In the current passive optical networks (PONs), we address the challenge of dealing with asymmetric channel conditions and asymmetric data rates in order to meet the traffic demand of optical network unit (ONU) to ONU (O2O) communications. A joint network-coding (NC) and power domain non-orthogonal multiple access (NOMA) approach (NC-NOMA) is discussed. The novelty of this NC-NOMA scheme lies in the way the inter-ONUs communicates with an optical line terminal (OLT) at different modulation formats. Specifically, in the uplink communications, at each ONU side, multiple data streams from different ONUs are superimposed into one single symbol. Meanwhile, NOMA is considered by adjusting the optical transmission power of ONUs such that the OLT can decode the signals from different ONUs based on successive interference cancellation (SIC). At the OLT side, the adding zeros approach at the specific positions of the shorter bit sequence is introduced. In the downlink communications, the ONUs obtain their own data by decoding the received messages. By applying NC-NOMA, the ONU with better channel condition only needs to demodulate the fictitious symbols with a low order modulation format instead of demodulating the symbols with a high order modulation format. The simulation results show NC-NOMA with hierarchical adding zeros approach outperforms NC-NOMA with traditional zero padding approach in terms of having lower average end-to-end BER of ONUs without having additional complexity.

中文翻译：

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用于提高非正交多址 (NOMA)-PON 中 BER 性能的网络编码方法的实现

摘要 在当前的无源光网络 (PON) 中，我们解决了处理非对称信道条件和非对称数据速率的挑战，以满足光网络单元 (ONU) 到 ONU (O2O) 通信的流量需求。讨论了联合网络编码 (NC) 和功率域非正交多址 (NOMA) 方法 (NC-NOMA)。这种 NC-NOMA 方案的新颖之处在于 ONU 间以不同调制格式与光线路终端 (OLT) 通信的方式。具体地，在上行通信中，在每个ONU侧，来自不同ONU的多个数据流叠加为一个符号。同时，通过调整ONU的光传输功率考虑NOMA，使得OLT可以基于连续干扰消除（SIC）对来自不同ONU的信号进行解码。在OLT侧，引入了在较短比特序列的特定位置处加零的方法。在下行通信中，ONU通过对接收到的消息进行解码来获得自己的数据。通过应用NC-NOMA，信道条件较好的ONU只需要解调低阶调制格式的虚构符号，而不用解调高阶调制格式的符号。仿真结果表明，在没有额外复杂性的情况下，采用分层加零方法的 NC-NOMA 在降低 ONU 的平均端到端 BER 方面优于采用传统零填充方法的 NC-NOMA。通过应用NC-NOMA，信道条件较好的ONU只需要解调低阶调制格式的虚构符号，而不用解调高阶调制格式的符号。仿真结果表明，在没有额外复杂性的情况下，采用分层加零方法的 NC-NOMA 在降低 ONU 的平均端到端 BER 方面优于采用传统零填充方法的 NC-NOMA。通过应用NC-NOMA，信道条件较好的ONU只需要解调低阶调制格式的虚构符号，而不用解调高阶调制格式的符号。仿真结果表明，在没有额外复杂性的情况下，采用分层加零方法的 NC-NOMA 在降低 ONU 的平均端到端 BER 方面优于采用传统零填充方法的 NC-NOMA。