Non-coherent secondary synchronization signal detecting method, device and corresponding computer program

1. A method for identifying a cell and a sub-frame by detecting a part of a secondary synchronization signal of a dedicated synchronization channel, said part of a secondary synchronization signal including a time-domain sequence of N OFDM symbols, N being a positive integer, wherein the method comprises:

for each OFDM symbol among said sequence of N OFDM symbols:

a step of obtaining a set of metrics for each OFDM symbol, each metric of said set of metrics being associated with a predetermined combination of a cell identifier and a sub-frame alignment;

for each metric of said set of metrics:

a step of counting a number of times the metric exceeds a first predetermined threshold, delivering a summed value M indicating the number, and

a step of applying a M among N criterion to said summed value M, delivering a M/N ratio value; and

a step of analyzing said M/N ratio values, in order to identify the cell and the sub-frame, corresponding to the cell identifier and the subframe alignment, associated to a particular ratio value among said M/N ratio values.

2. The method according to claim 1

wherein said metric corresponds to a Carrier-to-Interference Ratio based on a ratio of said secondary synchronization signal power to interference and noise power.

3. The method according to claim 1 , wherein said step of obtaining a metric of said part of a secondary synchronization signal involves a fast sequence transform based on a Hadamard transform.

4. The method according to claim 3 , wherein every OFDM symbol of said sequence of N OFDM symbols is associated to a frequency-domain sequence of 31 even and 31 odd resource elements, each resource element corresponding to one complex-valued modulation of said OFDM symbol and wherein said metric is a result of a calculation among at least one subset of said resource elements, and

wherein said step of obtaining said set of metrics comprises, for a current metric corresponding to a current OFDM symbol and the predetermined combination comprising the cell identifier and the subframe alignment:

a step of obtaining a first value depending on said 31 even resource elements,

a step of obtaining a second value depending on said 31 odd resource elements, and

a step of obtaining said current metric in view of said first and second values.

5. The method according to claim 4 , wherein said first value, for every cyclic shift m applied to said even resource elements, is the m th of the cyclic-correlation and sum operation performed using said Hadamard transform of a basic m-sequence,

and wherein said step of obtaining a second value involves 8 scrambling sequences based on said Hadamard transform, applied on said 31 odd resource elements.

6. The method according to claim 3 , wherein every OFDM symbol of said sequence of N OFDM symbols is associated to a frequency-domain sequence of 31 even and 31 odd resource elements, each resource element corresponding to one complex-valued modulation of said OFDM symbol and

wherein said metric is a result of a calculation among at least one subset of said resource elements, and wherein said step of obtaining said set of metrics comprises, for a current metric corresponding to a current OFDM symbol and the predetermined combination comprising the cell identifier and the subframe alignment:

a step for obtaining a first value depending on said 31 even resource elements,

a step of obtaining said current metric in view of said first value.

7. A device for identifying a cell and a subframe by detecting a part of a secondary synchronization signal of a dedicated synchronization channel, said part of secondary synchronization signal consisting of a time-domain sequence of OFDM symbols, wherein said device comprises:

a processing unit; and

a memory having program instructions stored thereon, which configure the processing unit to perform acts of:

obtaining a set of metrics for each OFDM symbol among said sequence of N OFDM symbols, each metric of said set of metrics being associated with a predetermined combination consisting of a cell identifier and a subframe alignment (CID/SF),

performing the following steps for each metric of said set of metrics:

a step of counting a number of times the metric associated with a predetermined combination of a cell identifier and a sub-frame alignment exceeds a first predetermined threshold, delivering a summed value M indicating the number, and

a step of applying a M among N criterion to said summed value M, delivering a M/N ratio value; and

analyzing said M/N ratio values, in order to identify the cell and the sub-frame, corresponding to the cell identifier and the sub-frame alignment, associated to a particular ratio value among said M/N ratio values.

8. A computer program product stored on a non-transitory computer readable medium, wherein the product includes instructions of program code for implementing a method of identifying a cell and a sub-frame by detecting a part of a secondary synchronization signal of a dedicated synchronization channel, when the instructions are run on a computer, wherein said part of a secondary synchronization signal includes a time-domain sequence of N OFDM symbols, N being a positive integer, and wherein the method comprises:

for each OFDM symbol among said sequence of N OFDM symbols:

a step of obtaining a set of metrics for each OFDM symbol, each metric of said set of metrics being associated with a predetermined combination of a cell identifier and a sub-frame alignment;

for each metric of said set of metrics:

a step of counting a number of times the metric exceeds a first predetermined threshold, delivering a summed value M indicating the number, and

a step of applying a M among N criterion to said summed value M, delivering a M/N ratio value; and

a step of analyzing said M/N ratio values, in order to identify the cell and the sub-frame, corresponding to the cell identifier and the subframe alignment, associated to a particular ratio value among said M/N ratio values.