Communication system

1. Communication apparatus for communicating with a mobile communication device in a communication system which uses a plurality of radio frames wherein each radio frame is subdivided in the time domain into a plurality of subframes, said communication apparatus comprising:

a memory storing instructions; and

one or more processors configured to execute the instructions to:

operate a communication cell;

generate discovery signals and configure a periodicity at which said communication apparatus should transmit said discovery signals and, when configuring said periodicity, to select as said periodicity, any of a plurality of possible periodicities, each of said plurality of possible periodicities comprising a plurality of radio frames; and

transmit said discovery signals at said configured periodicity,

wherein said discovery signals are transmitted for a duration that is shorter than said configured periodicity,

said duration comprises a plurality of consecutive subframes that include a predetermined subframe for transmitting a synchronisation signal, and

said discovery signals include a pair of a primary synchronisation signal (PSS) and a secondary synchronisation signal (SSS) that are transmitted in said predetermined subframe, and additional signals for performing Reference Signal Received Quality (RSRQ) measurement and/or Reference Signal Received Power (RSRP) measurement that are transmitted in more subframes than said predetermined subframe, said more subframes included in said plurality of consecutive subframes.

2. Communications apparatus according to claim 1 wherein a range of said possible periodicities extends beyond 50 radio frames.

3. Communications apparatus according to claim 1 , wherein: said base station is operable to operate said cell as one cell of a cluster of cells each cell of which shares a common cell identifier; said processor is further configured to generate is operable to encode an identifier for said one cell into at least one of said pair of said primary synchronisation signal (PSS) and said secondary synchronisation signal (SSS) and said additional signals; and wherein said identifier for said one cell is unique at least within said cluster of cells.

4. Communications apparatus according to claim 3 wherein said processor is further configured to generate is operable to encode at least one of the following: said common cell identifier (or ‘cluster identifier’) into at least one of said pair of said primary synchronisation signal (PSS) and said secondary synchronisation signal (SSS) and said identifier for said one cell into said additional signals; and said common cell identifier (or ‘cluster identifier’) into said pair of said primary synchronisation signal (PSS) and said secondary synchronisation signal (SSS) by encoding a cell group identifier into a first of said pair of said primary synchronisation signal (PSS) and said secondary synchronisation signal (SSS) and a physical layer cell identity (PCI), identifying the cell within a cell group represented by the cell group identifier, into a second of said pair of said primary synchronisation signal (PSS) and said secondary synchronisation signal (SSS).

5. Communications apparatus according to claim 4 wherein said identifier for said one cell, said cell group identifier, and said PCI together provide a global identifier for said one cell.

6. Communications apparatus according to claim 3 wherein said processor is further configured to generate is operable to encode said identifier for said one cell, as a global identifier for said one cell that does not depend on the common cell identifier, into at least one of said pair of said primary synchronisation signal (PSS) and said secondary synchronisation signal (SSS) and additional signals.

7. A method performed by communication apparatus for communicating in a communication system which uses a plurality of radio frames wherein each radio frame is subdivided in the time domain into a plurality of subframes, said method comprising:

operating a communication cell;

generating discovery signals;

configuring a periodicity at which said communication apparatus should transmit said discovery signals wherein, when configuring said periodicity, said periodicity is selected from a plurality of possible periodicities, each of said plurality of possible periodicities comprising a plurality of radio frames; and

transmitting said discovery signals at said configured periodicity,

wherein said discovery signals are transmitted for a duration that is shorter than said configured periodicity,

said duration comprises a plurality of consecutive subframes that include a predetermined subframe for transmitting a synchronisation signal, and

said discovery signals include a pair of a primary synchronisation signal (PSS) and a secondary synchronisation signal (SSS) that are transmitted in said predetermined subframe, and additional signals for performing Reference Signal Received Quality (RSRQ) measurement and/or Reference Signal Received Power (RSRP) measurement that are transmitted in more subframes that the predetermined subframe, said more subframes included in the plurality of consecutive subframes.

8. A computer program product comprising instructions operable to program a programmable processor to perform a method according to claim 7 .