Cold-start Of Optical Coherent Receiver With Decision-aided Maximum Likelihood Carrier Phase Estimation

The current IM/DD optical communication systems will be unable to meet the demand forgreater capacity of data transmission in the future. Under this background, coherent opticalcommunications once booming twenty years ago draw the industry’s concern again. Carrier phaseestimation, the kernel technology in the coherent optical communication systems, has always been aresearch hot spot. Among all the carrier phase estimation techniques, decision-aided maximumlikelihood (DAML), a kind of phase estimation algorithm based on totally linearization, can ensurecoherent detection of high-speed optical signal in the real-time system. The DAML receiver hasbecome one of coherent reception modes that the optical communication field considering puttinginto practice in the near future. However, the issues may encounter in the start-up procedure of theDAMLreceiver have never been studied, which mainly reflected in the following aspects:1、In the carrier phase estimation process of a DAML receiver, sending information andestimated results of the symbols several symbols before the current one need to be tracked. Thelegacy way to start up the DAML receiver is to use data-aided estimation. A training sequenceknown to the receiving end must be sent out in the start-up process. However, when there is morethan one receiver in the systems, the transmitter cannot determine the time to send out the trainingsequence because of the inconsistency of the start-up time of each receiver.2、In order to ensure the DAML receiver work in a burst mode communication system, atraining sequence must be sent out according to the original design before the transmission of usefuldata symbols in each block. This is not realistic.Considering the above issues, start of the DAML receiver is studied in this paper. After asystematic and in-depth analysis of the carrier phase estimation process in various types of opticalcoherent receivers, a scheme for cold-start of the DAML receiver is proposed. Simulations are doneto confirm the feasibility of this scheme. Then, considering the effect of the block length of thepower law nonlinear algorithm and the memory length of the DAML algorithm on the performanceof the receiver, we further optimize this scheme. Finally, we analyze the possibility for the receiverto start up at a relatively low speed with this scheme.