Methods of discovery and measurements for small cells in OFDM/OFDMA systems
A method of small cell discovery and RSRP/RSRQ measurements in OFDM/OFDMA systems is proposed. A discovery reference signal (DRS) with low transmission frequency is introduced to support small cell detection within a short time, multiple small cell discovery, and accurate measurement of multiple small cells. The DRS consists of one or multiple reference signal types with the functionalities including timing and frequency synchronization, cell detection, RSRP/RSSI/RSRQ measurements, and interference mitigation. RE muting is configured for the DRS to reduce interference level from data to DRS for discovery and RSRP/RSRQ measurements for small cells.
1. A method, comprising:
allocating a set of resource elements (REs) over multiple time-domain OFDM symbols in a set of time slots by a base station for transmitting a corresponding set of discovery reference signals (DRS); and
transmitting configuration information from the base station to a plurality of UEs, wherein the configuration information comprises information on DRS duration, DRS periodicity, and RE muting patterns of the set of REs for a plurality of cells, wherein the plurality of UEs perform cell discovery based on the DRS, and wherein the configuration information indicates whether the allocating has applied RE muting to each of the resource elements (REs).
2. The method of claim 1 , wherein the DRS comprises at least one of a cell-specific reference signal (CRS), a channel state information reference signal (CSI-RS), and a positioning reference signal (PRS).
3. The method of claim 2 , wherein the DRS further comprises a synchronization signal.
4. The method of claim 1 , wherein the DRS occupies one or more subframes, and wherein the DRS is transmitted with a periodicity that is substantially longer than one radio frame.
5. The method of claim 1 , wherein the set of REs are partitioned into a first subset and a second subset, wherein REs in the first subset that are not used for DRS transmission are partially or all muted, and wherein REs in the second subset are not muted.
6. The method of claim 1 , wherein the RE muting includes data with zero power transmission and data with reduced power transmission.
7. The method of claim 1 , wherein more RE muting is applied for a cell if an average cell loading is high, and wherein less RE muting is applied for the cell if the average cell loading is low.
8. The method of claim 1 , wherein no RE muting is applied in control channels, and wherein no RE muting is applied if collide with other reference signals.
9. The method of claim 1 , wherein RE muting patterns in different cells are assigned through coordination by the base station.
10. The method of claim 1 , wherein RE muting patterns in different cells are assigned through physical cell identification (PCI) of the cells.
11. A method, comprising:
receiving by a user equipment (UE) from a base station a set of discovery reference signals (DRS) on a corresponding set of resource elements (REs) over multiple time-domain orthogonal frequency division multiplexing (OFDM) symbols in a set of time slots
obtaining configuration information of the DRS by the UE, wherein the configuration information comprises information on DRS duration, DRS periodicity, and RE muting patterns of the set of REs for a plurality of cells, and wherein the configuration information indicates whether RE muting has been applied to each of the resource elements (REs); and
performing cell discovery based on the DRS.
12. The method of claim 11 , wherein the DRS comprises at least one of a cell-specific reference signal (CRS), a channel state information reference signal (CSI-RS), and a positioning reference signal (PRS).
13. The method of claim 12 , wherein the DRS further comprises a synchronization signal.
14. The method of claim 11 , wherein the DRS occupies one or more subframes, and wherein the DRS is transmitted with a periodicity that is substantially longer than one radio frame.