System frame number detection

A method comprising causing, at least in part, actions that result in:

• receiving at least one first signal comprising an indication of at least one bit of a first System Frame Number, SFN;
• determining, based at least in part on the received at least one first signal, at least one value of a reliability metric for the at least one bit of the first SFN;
• receiving at least one second signal comprising an indication of at least one bit of a second SFN different than the first SFN;
• and,
• determining, based at least in part on the received at least one second signal and the determined at least one value of the reliability metric for the at least one bit of the first SFN, at least one value of a reliability metric for the at least one bit of the second SFN,
• wherein determining the at least one value of a reliability metric for the at least one bit of the second SFN of the at least one second signal comprises:
• calculating at least one Log Likelihood Ratio, LLR, for the at least one bit of the second SFN of the at least one second signal, and wherein calculating the at least one LLR for the at least one bit of the second SFN of the at least one second signal is based at least in part on a calculated LLR for the at least one bit of the first SFN of the at least one first signal.

A non-transitory computer readable medium comprising program instructions that, when executed by a processor, cause an apparatus to perform at least the following:

• receiving at least one first signal comprising an indication of at least one bit of a first System Frame Number, SFN;
• determining, based at least in part on the received at least one first signal, at least one value of a reliability metric for the at least one bit of the first SFN;
• receiving at least one second signal comprising an indication of at least one bit of a second SFN different than the first SFN;
• and,
• determining, based at least in part on the received at least one second signal and the determined at least one value of the reliability metric for the at least one bit of the first SFN, at least one value of a reliability metric for the at least one bit of the second SFN,
• wherein determining the at least one value of a reliability metric for the at least one bit of the second SFN of the at least one second signal comprises:
• calculating at least one Log Likelihood Ratio, LLR, for the at least one bit of the second SFN of the at least one second signal, and wherein calculating the at least one LLR for the at least one bit of the second SFN of the at least one second signal is based at least in part on a calculated LLR for the at least one bit of the first SFN of the at least one first signal.