A suboptimal detector for time frequency packing

A soft-output symbol detector (500) for detecting one or more symbol streams from a received signal (101) representing multiple time-frequency packed linearly modulated signals (101a). The detector (600) comprises one or more processors (601) configured to: process the received signal (101) to compute a proper joint probability mass function (102); form a factor graph (103) by performing an exact factorisation of the joint probability mass function (102); compute marginals (104a) of the joint probability mass function (102) by performing a message-passing algorithm on nodes (103a, 103b) of the factor graph (103); and detect the symbol stream (s) (105a) in dependence on the computed marginals (104a). Detecting the symbol stream (s) (105a) in dependence on the computed marginals (104a) enables the detection to be based on the exact factorisation of the proper joint probably mass function (102) of the received signal (101).