With the single current method, only signals with positive or negative voltages are transmitted. In this transmission method for baseband systems, the decision threshold is leveled at half the level value (between 0 and 1).
Signals with a level value above the decision threshold correspond to the logical high, below the decision threshold to the logical low. The disadvantage of this method is that disturbances can be interpreted as logical values and that the level of the decision threshold is signal-dependent. With many logical highs it drifts towards higher level values, with many logical lows the decision threshold changes towards lower levels.