US Patent 7283011 Method for performing dual phase pulse modulation

A modulation method, referred to as dual phase pulse modulation (DPPM), represents digital data as a series of high and low pulses whose widths represent groups of M data bits, with both the high and low pulses representing successive M-bit groups. Each of the 2M possible data values for a group of M data bits uniquely corresponds to one of 2M distinct pulse widths. This modulation method is essentially clockless, with data being decoded from a signal by detecting each pulse's width with respect to the last transition. Power consumption is reduced by having M data bits represented for each pulse transition, and by using both the high and low pulses to represent data.