A method of automatically tuning subcarriers of a superchannel transmission, wherein the superchannel is a Dense Wavelength Division Multiplexing, DWDM, superchannel, the method comprising: determining at a receiver a received parameter of transmission quality of one or more of the plurality of subcarriers, and tuning (42, 46, 72) a frequency of the one or more subcarrier, and a frequency spacing of subcarriers (16, 17), based on the determined parameter of the transmission quality wherein the tuning comprises: translating the frequencies of the plurality of subcarriers in a slot of the transmission, wherein the translating is in a direction from a subcarrier for which the parameter of transmission quality cannot be determined to a subcarrier providing the parameter of the transmission quality, and determining a frequency change of the subcarrier from a frequency offset determination of the receiver, wherein determining the frequency change of the subcarrier from a frequency offset determination of the receiver comprises determining a first frequency offset from the subcarrier for a local oscillator, changing the frequency of the subcarrier, determining a second frequency offset from the subcarrier for the local oscillator, and determining the frequency change of the subcarrier as a difference between the first and second frequency offsets, and wherein the local oscillator of the receiver varies to track the frequency of the subcarrier only after the frequency offset is determined for that frequency. determining at a receiver a received parameter of transmission quality of one or more of the plurality of subcarriers, and tuning (42, 46, 72) a frequency of the one or more subcarrier, and a frequency spacing of subcarriers (16, 17), based on the determined parameter of the transmission quality wherein the tuning comprises: translating the frequencies of the plurality of subcarriers in a slot of the transmission, wherein the translating is in a direction from a subcarrier for which the parameter of transmission quality cannot be determined to a subcarrier providing the parameter of the transmission quality, and determining a frequency change of the subcarrier from a frequency offset determination of the receiver, wherein determining the frequency change of the subcarrier from a frequency offset determination of the receiver comprises determining a first frequency offset from the subcarrier for a local oscillator, changing the frequency of the subcarrier, determining a second frequency offset from the subcarrier for the local oscillator, and determining the frequency change of the subcarrier as a difference between the first and second frequency offsets, and wherein the local oscillator of the receiver varies to track the frequency of the subcarrier only after the frequency offset is determined for that frequency. translating the frequencies of the plurality of subcarriers in a slot of the transmission, wherein the translating is in a direction from a subcarrier for which the parameter of transmission quality cannot be determined to a subcarrier providing the parameter of the transmission quality, and determining a frequency change of the subcarrier from a frequency offset determination of the receiver, wherein determining the frequency change of the subcarrier from a frequency offset determination of the receiver comprises determining a first frequency offset from the subcarrier for a local oscillator, changing the frequency of the subcarrier, determining a second frequency offset from the subcarrier for the local oscillator, and determining the frequency change of the subcarrier as a difference between the first and second frequency offsets, and wherein the local oscillator of the receiver varies to track the frequency of the subcarrier only after the frequency offset is determined for that frequency.