SPC03-3: A MIMO-MLSE Receiver for Electronic Dispersion Compensation of Multimode Optical Fibers

In this paper we propose a multiple-input, multiple-output (MIMO) maximum-likelihood sequence estimation (MLSE) receiver for electronic dispersion compensation (EDC) of multimode optical fibers at 10 Gb/s data rate. As the primary example of the effectiveness of the techniques introduced here we present a receiver for the emergent 10 GBASE-LRM standard for 10 Gb/s Ethernet over multimode optical fibers [1]. We show that an MLSE receiver provides an advantage of at least 2 dB over other receivers, such as the decision-feedback equalizer (DFE), on 99% of the local area network (LAN) multimode fiber population, as modeled by a database proposed by the IEEE 802.3aq Task Force [2]. The paper deals with both theoretical and practical aspects of the architecture. To enable the complete integration of this receiver as a single chip in current 90 nm CMOS technology, we propose the parallel-processing digital implementation of a feedforward equalizer (FFE) and a Viterbi decoder together with an interleaved front-end analog to digital converter (ADC). The MIMO structure jointly compensates for fundamental channel impairments such as multimode dispersion, and implementation-related effects such as the limitations of the analog front end (AFE), particularly the one known as fixed-pattern noise (FPN) [3]. As a result of the high speed operation, FPN has a major impact on performance. We show that, without compensation, FPN could result in a degradation of 7.86 dB. With the compensation proposed here, the latter is reduced to 0.23 dB.