Multiuser Detection for WDM Long-Haul Fiber-Optic Communication Systems

光纤链路具有每秒传输太比特的潜力。长途链路，如越洋和洲际数据中继线，已经证明需要这样高的数据吞吐量。系统设计人员能够使用称为密集波分复用（WDM）的技术来提供高数据吞吐量，其中多个较低速率的信号通过使用多个波长的光被组合到单个光纤。长距离WDM光纤信道的性能受到线性色散和非线性串扰的限制。非线性效应在不同波长信道处接收的信号之间产生相关性。在这项研究中，多用户检测方案，利用这种依赖性和联合解调多个信道的开发。在过去的二十年里，多用户检测在射频多用户通信中引起了极大的关注。它们在对抗系统中其他用户干扰的有害影响方面非常强大。在这样做的时候，他们允许每个用户的信道容量从单用户通信的可能增加。同样的优点被怀疑坚持在应用这些检测器的WDM光纤系统。光纤系统的物理模型的许多方面不同于RF模型。由于光纤的非线性和光电探测器的处理，干扰和主要噪声是信号相关的，给出了接收信号的非常不同的统计描述。此外，调制和信号检测只作用于信号的强度，禁止使用的信号相位在任何一端，因此，多用户检测器开发的RF通信不能直接用于光纤problem.In本研究中，最佳和次优检测器，如最大似然，线性，二次和判决反馈检测器设计，以适应光纤系统。特别注意每种设计的硬件要求，以确保它可以以每秒10甚至40千兆比特的速度实现，这是这些类型系统所需的。在相邻信道的小群组上的小同时检测器的系统允许最显著的非线性串扰被消除，而不需要过高的计算复杂性。探测器还必须对分辨率非常粗糙的数据进行操作。这些检测器的性能可以使用最小距离的变量，误差概率的界限，渐近多用户效率的计算和仿真来测量。 通过使用这些技术，系统设计者将能够将光纤放大器之间的跨距长度增加到目前可能的100 km以上，通过将信道间隔减小到低于目前的20 GHz限制来增加信道密度，并将每个信道的服务质量提高到低于10- 12的差错率。

Fiber-optic links have the potential of terabit per second transmission. Long-haul links, such as transoceanic and transcontinental data-trunks, have demonstrated a need for such high data throughput. System designers are able to provide the high data throughput using a technique known as dense wavelength division multiplexing (WDM), where multiple lower rate signals are combined unto a single fiber by using several wavelengths of light. Long-haul WDMfiber channels are performance limited by linear dispersion and nonlinear crosstalk. The nonlinear effects create a correlation between the signals received at different wavelength channels. In this research multiuser detection schemes to exploit this dependence and jointly demodulate multiple channels are developed. Multiuser detection has attracted enormous attention in RF multiuser communications in the last twenty years. They are powerful at combating the harmful effects of interference from other users in the system. In so doing they allow the channel capacity per user toincrease from that possible in single-user communications. The same advantages are suspected to persist in applying these detectors to WDM fiber systems. Many aspects of the physical model of the fiber system differ from the RF model. Because of the fiber nonlinearities and the photodetector processing, the interference and dominant noise are signal dependent, giving a very different statistical description of the received signal. Moreover, the modulation and the signal detection act only on the intensity of the signal, prohibiting the use of the signal phase at either end.Therefore, multiuser detectors developed for RF communications cannot be used directly for the fiber problem.In this research, optimal and suboptimal detectors such as maximum likelihood, linear, quadratic, and decision feedback detectors are designed to suit fiber-optic systems. Special attention is placed on the hardware requirements of each design to ensure that it can be implemented at 10 or even 40 gigabits per second, as required for these types of systems. A system of small simultaneous detectors over small groups of adjacent channels allows the most significant nonlinear crosstalk to be cancelled without requiring a prohibitive computational complexity. Detectors must alsooperate on data with very coarse resolution. The performance of these detectors can be measured using variants of minimum distance, bounds on the error probability, calculations of the asymptotic multiuser efficiency, and simulation. By using these techniques, system designers will be able to increase the span length between fiber amplifiers to more than the 100 km currently possible, increase the channel density by decreasing the channel spacing to below the current20 GHz limit, and improve the quality of service of each channel to below an error-rate of 10- 12 .