METHOD AND APPARATUS FOR NETWORK ENERGY SAVING BY TURNING OFF TRANSMIT CHAINS

1 . A method performed by at least one processor of a base station, the method comprising:

sending, in a first state, a first set of one or more probing messages to a UE, the first set of the one or more probing messages including a set of reference signals;

receiving, in response to the first one or more probing messages, a first channel state information (CSI) report from the UEs that includes first CSI derived from measurements of the set of reference signals;

sending, in a second state, a second set of one or more probing messages to the UE, the second set of the one or more probing messages including a subset of the reference signals; and

receiving, in response to the second set of one or more probing messages, a second CSI report that includes second CSI derived from measurement of the subset of the reference signals.

2 . The method according to claim 1 , wherein the first state is a normal state and the second state is an energy saving state.

3 . The method according to claim 2 , wherein in the energy saving state, the base station turns off one or more antennas.

4 . The method according to claim 1 , wherein the first set of the one or more probing messages include an indication of a window having a duration in which the UE measures the subset of reference signals.

5 . The method according to claim 4 , wherein the base station configures the window with a periodic time interval.

6 . The method according to claim 4 , wherein the second CSI report is transmitted from the UE to the base station at a timing outside of the window.

7 . The method according to claim 2 , further comprising:

transmitting, to the UE, a predetermined downlink signal that causes the UE to terminate measuring of the set of reference signals in the normal energy state and initiate measuring of the subset of reference signals in the energy saving state.

8 . The method according to claim 7 , wherein the predetermined downlink signal is a physical downlink control channel (PDCCH) signal.

9 . The method according to claim 7 , wherein the measuring of the subset of reference signals is terminated after a predetermined time interval.

10 . The method according to claim 1 , further comprising classifying, based on the one or more CSI reports, each UE in the one or more UEs into one of a plurality of classification groups.

11 . The method according to claim 10 , wherein the plurality of classification groups include: (i) a first classification group in which each UE assigned to the first classification group does not utilize cell enhancement coverage when the base station is in the energy saving state, and (ii) a second classification group in which each UE assigned to the second classification group utilizes cell enhancement coverage when the base station is in the energy saving state.

12 . The method according to claim 11 , wherein the cell enhancement coverage includes repetition of one or more downlink signals or repetition of one or more uplink signals.

13 . The method according to claim 12 , wherein the one or more downlink signals include one of a physical downlink control channel (PDCCH) signal and a physical downlink shared channel (PDSCH) signal, and wherein the one or more uplink signals include one of a physical uplink shared channel (PUSCH) and a physical uplink control channel (PUCCH) signal.

14 . The method according to claim 2 , further comprising:

transmitting to the UE an, energy saving state indication that includes one or more bits specifying one or more time slots in which the energy saving state is applied.

15 . An apparatus comprising:

at least one memory configured to store computer program code; and

at least one processor configured to access said at least one memory and operate as instructed by the computer program code, the computer program code including:

first sending code configured to cause at least one of said at least one processor to send, in a first state, a first set of one or more probing messages to a UE, the first set of the one or more probing messages including a set of reference signals;

first receiving code configured to cause at least one of said at least one processor to receive, in response to the first one or more probing messages, a first channel state information (CSI) report from the UEs that includes first CSI derived from measurements of the set of reference signals;

second sending code configured to cause at least one of said at least one processor to send, in a second state, a second set of one or more probing messages to the UE, the second set of the one or more probing messages including a subset of the reference signals; and

second receiving, in response to the second set of one or more probing messages, a second CSI report that includes second CSI derived from measurement of the subset of the reference signals.

16 . The apparatus according to claim 15 , wherein the first state is a normal state and the second state is an energy saving state.

17 . The apparatus according to claim 16 , wherein in the energy saving state, the base station turns off one or more antennas.

18 . The apparatus according to claim 15 , wherein the first set of the one or more probing messages include an indication of a window having a duration in which the UE measures the subset of reference signals.

19 . The apparatus according to claim 18 , wherein the base station configures the window with a periodic time interval.

20 . A non-transitory computer readable medium having instructions stored therein, which when executed by a processor in a base station cause the processor to execute a method comprising:

sending, in a first state, a first set of one or more probing messages to a UE, the first set of the one or more probing messages including a set of reference signals;

receiving, in response to the first one or more probing messages, a first channel state information (CSI) report from the UEs that includes first CSI derived from measurements of the set of reference signals;

sending, in a second state, a second set of one or more probing messages to the UE, the second set of the one or more probing messages including a subset of the reference signals; and

receiving, in response to the second set of one or more probing messages, a second CSI report that includes second CSI derived from measurement of the subset of the reference signals.