to meet this requirement longer preamble and 16 bit sfd is defined for frames where the payload data rate is lower than the air data rate of the preamble and the sfd as at a given signal to noise ratio the bit error probability differs for the two rates this is the case with the 125 kbps and 1 mbps payload rates for instance the 2 mbps sfd is received with 3 bit error rate probability when for the same frame the 1 mbps payloads can be demodulated with a ber bit error rate of 1 10000 a known technique for tolerating the relatively high bit error probability is to handle a certain number of bit errors forgivingly in the sfd match for the 125 kbps data rate the last decoded four nibbles and the nibbles of pattern u2014 125 must match in at least 3 nibble positions at 1 mbps the match tolerates single bit or maximum 2 noncontiguous 2 bit burst differences in the comparison of the last received 16 bits and pattern u2014 125 simultaneous isolated single bit mismatches at both ends of the pattern constitute a single 2 bit mismatch burst search for the sfd pattern is started once the header data rate has been determined the logic flow of the process is presented in fig9 the method starts in step 610 and first tests in step 620 for a 2 mb s preamble if not found the routine moves to step 630 for checking the 500 kp s preamble and in step 640 for finding the 250 kb s preamble if one of.