A Survey on OFDM-Based Elastic Core Optical Networking <s> b) Adaptive Modulation <s> We show the first experiment of bit and power loading for coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. The data rate of CO-OFDM systems can be dynamically adjusted according to the channel condition. The system performance can be further improved through optimal power loading into each modulation band. <s> BIB001 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> b) Adaptive Modulation <s> Reach estimations for several variable-bitrate OFDM schemes are presented and discussed in the framework of a transparent EU core network scenario. 44% reduction on OE interfaces is found compared to a fixed-bitrate 40Gb/s network. <s> BIB002 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> b) Adaptive Modulation <s> We propose a network model based on format-versatile transceiver for data-rate tunability. We estimate each format's resistance to degradations and dimension a backbone network accordingly, yielding 20% savings on resources compared to single-rate networks. <s> BIB003
Using adaptive modulation technology, as described in Section III-D, a variation of the data rate could be supported by adjusting the modulation format. To increase the transmitted data rate, a higher-level modulation format with more bits per symbol is chosen, under the limitation of the minimum OSNR required to recover the data, while maintaining a constant symbol rate (which corresponds to a constant spectrum width) BIB002 . This technique has been applied to both single-carrier modulation and multi-carrier modulation schemes BIB001 BIB003 . Multi-level modulation such as M-QAM, M-PSK, etc. would be good candidates for the adaptive modulation format, and flexible adjustment of the modulation formats could be implemented by software-defined components. For example, the capacity of a subcarrier using one-bit-per-symbol BPSK modulation is C Gb/s, and thus QPSK with 2 bits per symbol corresponds to 2C, and 16-QAM with 4 bits per symbol corresponds to 4C. Data-rate dynamic adjustment according to the quality of channels was experimentally demonstrated using bit and power loading of optical OFDM subcarriers BIB001 . Reach and transmission performance versus data-rate variation of OFDM transmission was studied in BIB002 . A 25-100 Gb/s PDM-QPSK transceiver with modulation-format versatility was demonstrated in BIB002 .