Detecting subframe timing in an OFDM licensed-assisted access signal

A receiver, for detecting the presence and timing of a subframe and/or slot of an Orthogonal Frequency-Division Multiplexing (OFDM) signal comprising subframes and/or slots, each subframe and/or slot consisting of a plurality of OFDM symbols, with at least one OFDM symbol in each subframe and/or slot having a different cyclic prefix (CP) duration from remaining OFDM symbols in the subframe, the receiver comprising:

• radio-frequency circuitry configured to receive and condition a received radio-frequency signal;
• an analog-to-digital converter circuit configured to sample the conditioned radio-frequency signal, thereby generating time-domain samples of the received signal;
• and
• a processing circuit configured to:
• perform an auto-correlation of a first set of the time-domain samples with a second set of the time-domain samples, the second set of time-domain samples being a delayed version of the first set of time-domain samples, where the delay is chosen to correspond to the duration of the OFDM symbol excluding the CP, and where the number of terms used in the summation in the correlation is at least as large as the smallest number of samples in a CP in any of the OFDM symbols within a subframe;
• detect, based on the auto-correlation, first and second correlation peaks meeting one or more predetermined detection criteria;
• determine that the first and second correlation peaks are separated in time by an interval corresponding to an OFDM symbol interval;
• identify, based on the two correlation peaks, one of the correlation peaks as corresponding to an OFDM symbol having a larger cyclic prefix than an adjacent OFDM symbol;
• and
• determine a subframe and/or slot timing for the received signal, based on said identifying.