An optical receiver, comprising: an optical-to-electrical converter adapted to: mix a modulated optical signal with an optical reference signal to generate a plurality of mixed optical signals; and convert the plurality of mixed optical signals into a corresponding plurality of digital electrical signals (162 1 -162 4), wherein: the plurality of digital electrical signals (162 1 -162 4) comprises a first in-phase digital signal and a first quadrature-phase digital signal that have a first set of signal samples corresponding to a data frame; the data frame comprises: a first plurality of pilot-symbol blocks (PS S), wherein each pilot-symbol block comprises a respective plurality of pilot symbols and a respective guard interval; and a first set of one or more payload-symbol blocks (DS n), wherein each payload-symbol block (DS n) comprises a respective plurality of constellation symbols from a first sequence of constellation symbols; and at least one payload-symbol block (DS n) and another block are concatenated without a guard interval between them, wherein the other block is either a pilot-symbol block (PSs) or a payload-symbol block (DS n); and a digital signal processor adapted to process the first set of signal samples to recover data encoded in the first sequence of constellation symbols. an optical-to-electrical converter adapted to: mix a modulated optical signal with an optical reference signal to generate a plurality of mixed optical signals; and convert the plurality of mixed optical signals into a corresponding plurality of digital electrical signals (162 1 -162 4), wherein: the plurality of digital electrical signals (162 1 -162 4) comprises a first in-phase digital signal and a first quadrature-phase digital signal that have a first set of signal samples corresponding to a data frame; the data frame comprises: a first plurality of pilot-symbol blocks (PS S), wherein each pilot-symbol block comprises a respective plurality of pilot symbols and a respective guard interval; and a first set of one or more payload-symbol blocks (DS n), wherein each payload-symbol block (DS n) comprises a respective plurality of constellation symbols from a first sequence of constellation symbols; and at least one payload-symbol block (DS n) and another block are concatenated without a guard interval between them, wherein the other block is either a pilot-symbol block (PSs) or a payload-symbol block (DS n); and mix a modulated optical signal with an optical reference signal to generate a plurality of mixed optical signals; and convert the plurality of mixed optical signals into a corresponding plurality of digital electrical signals (162 1 -162 4), wherein: the plurality of digital electrical signals (162 1 -162 4) comprises a first in-phase digital signal and a first quadrature-phase digital signal that have a first set of signal samples corresponding to a data frame; the data frame comprises: a first plurality of pilot-symbol blocks (PS S), wherein each pilot-symbol block comprises a respective plurality of pilot symbols and a respective guard interval; and a first set of one or more payload-symbol blocks (DS n), wherein each payload-symbol block (DS n) comprises a respective plurality of constellation symbols from a first sequence of constellation symbols; and at least one payload-symbol block (DS n) and another block are concatenated without a guard interval between them, wherein the other block is either a pilot-symbol block (PSs) or a payload-symbol block (DS n); and the plurality of digital electrical signals (162 1 -162 4) comprises a first in-phase digital signal and a first quadrature-phase digital signal that have a first set of signal samples corresponding to a data frame; the data frame comprises: a first plurality of pilot-symbol blocks (PS S), wherein each pilot-symbol block comprises a respective plurality of pilot symbols and a respective guard interval; and a first set of one or more payload-symbol blocks (DS n), wherein each payload-symbol block (DS n) comprises a respective plurality of constellation symbols from a first sequence of constellation symbols; and a first plurality of pilot-symbol blocks (PS S), wherein each pilot-symbol block comprises a respective plurality of pilot symbols and a respective guard interval; and a first set of one or more payload-symbol blocks (DS n), wherein each payload-symbol block (DS n) comprises a respective plurality of constellation symbols from a first sequence of constellation symbols; and at least one payload-symbol block (DS n) and another block are concatenated without a guard interval between them, wherein the other block is either a pilot-symbol block (PSs) or a payload-symbol block (DS n); and a digital signal processor adapted to process the first set of signal samples to recover data encoded in the first sequence of constellation symbols.