Transmission of sounding reference signals in communication systems with carrier aggregation
Methods and apparatus are provided for a base station to trigger transmissions of sounding reference signals (SRS) from one or multiple user equipments (UEs) on one or multiple cells and for a UE to determine a power, a time instance, and other parameters for SRS transmissions in response to the triggering. A SRS transmission can be on a cell where a UE is not configured to transmit data or control information.
1. A user equipment (UE) comprising:
a receiver configured to receive a first downlink control information (DCI) format and a second DCI format, wherein:
the first DCI format includes a first block of bits that provides only one of:
a transmit power control (TPC) command value for adjusting only a sounding reference signal (SRS) transmission power on a first cell, or
an SRS request value for either triggering or not triggering a SRS transmission on the first cell and the TPC command value for adjusting only the SRS transmission power on the first cell, and
the second DCI format includes a second block of bits that provides a TPC command value for adjusting both a SRS transmission power and a physical uplink shared channel (PUSCH) transmission power on a second cell; and
a transmitter configured to:
in response to the received first DCI format including the SRS request value triggering the SRS transmission on the first cell, transmit a SRS on the first cell,
wherein the UE is configured not to transmit any PUSCH on the first cell, and
wherein the UE is configured not to process any DCI format scheduling a PUSCH transmission on the first cell.
2. The UE of claim 1 , wherein the receiver is further configured to receive a configuration indicating whether the first block of bits provides only the TPC command value or both the SRS request value and the TPC command value.
3. The UE of claim 1 , wherein the receiver is further configured to receive a configuration indicating that the first block of bits is applicable for the SRS transmission on the first cell and the second block of bits is applicable for SRS transmission on the second cell.
4. The UE of claim 1 , wherein the transmitter is further configured to transmit the SRS from a subset of antenna ports of a set of antenna ports, wherein the subset of antenna ports is indicated by the SRS request value.
5. The UE of claim 1 , wherein:
a size of the first DCI format is equal to a size of the second DCI format that includes only second TPC commands, and
the TPC command from the second TPC commands adjusts the PUSCH transmission power on the second cell.
6. The UE of claim 1 , wherein a SRS transmission power P SRS,c (i) in decibels per milliwatt (dBm) in time instance i and on cell c is:
P SRS,c ( i )=min{ P CMAX,c ( i ),10 log 10 ( M SRS,c )+ P O_SRS,c ( m )+α SRS,c ·PL c +f c ( i )} dBm,
min{x, y} is a minimum function resulting the smaller of numbers x, y,
log 10 (x) is a logarithm function with base 10 resulting a logarithm with base 10 for number x,
P CMAX,c (i) is a transmission power in time instance i configured by higher layers for cell c,
M SRS,c is a SRS transmission bandwidth in time instance i and on cell c,
P O_SRS,c (m) is configured by higher layers for cell c, m=0 when the SRS transmission is configured by higher layers, and m=1 when the SRS transmission is configured by the DCI format,
PL c is a path loss value measured on cell c,
α SRS,c is configured by higher layers for SRS transmission on cell c, and
f c (i) is a transmission power control adjustment state, determined from TPC commands in the DCI format, for SRS transmission in time instance i and on cell c.
7. The UE of claim 6 , wherein:
f c ( O )=Δ P rampup,c +δ SRS,c ,
Δ P rampup,c =min[{max(0, P CMAX, c −(10 log 10 ( M SRS,c )+ P O_SRS,c ( m )+α SRS,c ·PL c ))}Δ P rampupreqsted,c ]
max{x, y} is a maximum function resulting the larger of numbers x, y,
M SRS,c is a SRS bandwidth at a time instance of a first SRS transmission on cell c,
ΔP rampuprequested,c is a total power ramp-up power from a first to a last random access preamble transmission on cell c and is configured by higher layers, and
δ SRS,c is a value of the TPC command in the DCI format.
8. The UE of claim 6 , wherein a power headroom (PH) report for SRS transmission in time instance i and on cell c is determined as PH c (i)=P CMAX,c (i)−{10 log 10 (M SRS,c (i))+P O_SRS,c (m)+α SRS,c ·PL c +f c (i)}.
9. A base station comprising:
a transmitter configured to transmit, to a user equipment (UE), a first downlink control information (DCI) format and a second DCI format, wherein:
the first DCI format includes a first block of bits that provides only one of:
a transmit power control (TPC) command value for adjusting only a sounding reference signal (SRS) transmission power on a first cell, or
an SRS request value for either triggering or not triggering a SRS transmission on the first cell and the TPC command value for adjusting only the SRS transmission power on the first cell, and
the second DCI format includes a second block of bits that provides a TPC command value for adjusting both a SRS transmission power and a physical uplink shared channel (PUSCH) transmission power on a second cell; and
a receiver configured to, in response to the transmitted first DCI format including the SRS request value triggering the SRS transmission on the first cell, receive, from the UE, a SRS on the first cell,
wherein the UE is configured not to transmit any PUSCH on the first cell, and
wherein the UE is configured not to process any DCI format scheduling a PUSCH transmission on the first cell.
10. The base station of claim 9 , wherein the transmitter is further configured to transmit a configuration indicating whether the first block of bits provides only the TPC command value or both the SRS request value and the TPC command value.
11. The base station of claim 9 , wherein the transmitter is further configured to transmit a configuration indicating that the first block of bits is applicable for the SRS transmission on the first cell and the second block of bits is applicable for SRS transmission on the second cell.
12. The base station of claim 9 , wherein:
a size of the first DCI format is equal to a size of the second DCI format that includes only second TPC commands, and
the TPC command from the second TPC commands adjusts the PUSCH transmission power on the second cell.
13. A method for operating a user equipment (UE), the method comprising:
receiving a first downlink control information (DCI) format and a second DCI format, wherein:
the first DCI format includes a first block of bits that provides only one of:
a transmit power control (TPC) command value for adjusting only a sounding reference signal (SRS) transmission power on a first cell, or
a SRS request value for either triggering or not triggering a SRS transmission on the first cell and the TPC command value for adjusting only the SRS transmission power on the first cell, and
the second DCI format includes a second block of bits that provides a TPC command value for adjusting both a SRS transmission power and a physical uplink shared channel (PUSCH) transmission power on a second cell; and
in response to the received first DCI format including the SRS request value triggering the SRS transmission on the first cell, transmitting a SRS on the first cell,
wherein the UE is configured not to transmit any PUSCH on the first cell, and
wherein the UE is configured not to process any DCI format scheduling a PUSCH transmission on the first cell.
14. The method of claim 13 , further comprising:
receiving a configuration indicating whether the first block of bits provides only the TPC command value or both the SRS request value and the TPC command value.
15. The method of claim 13 , further comprising:
receiving a configuration indicating that the first block of bits is applicable for the SRS transmission on the first cell and the second block of bits is applicable for SRS transmission on the second cell.
16. The method of claim 13 , wherein:
a size of the first DCI format is equal to a size of the second DCI format that includes only second TPC commands,
the TPC command from the second TPC commands adjusts the PUSCH transmission power on the second cell,
the first DCI format includes cyclic redundancy check (CRC) bits that are scrambled by a first radio network temporary identifier (RNTI), and
the second DCI format includes CRC bits that are scrambled by a second RNTI.
17. The method of claim 13 , further comprising:
transmitting the SRS from a subset of antenna ports of a set of antenna ports, wherein the subset of antenna ports is indicated by the SRS request value.
18. The method of claim 13 , wherein a SRS transmission power P SRS,c (i) in decibels per milliwatt (dBm) in time instance i and on cell c is:
P SRS,c ( i )=min{ P CMAX,c ( i ),10 log 10 ( M SRS,c )+ P O_SRS,c ( m )+α SRS,c ·PL c +f c ( i )} dBm,
min{x, y} is a minimum function resulting the smaller of numbers x, y,
log 10 (x) is a logarithm function with base 10 resulting a logarithm with base 10 for number x,
P CMAX,c (i) is a transmission power in time instance i configured by higher layers for cell c,
M SRS,c is a SRS transmission bandwidth in time instance i and on cell c,
P O_SRS,c (m) is configured by higher layers for cell c, m=0 when the SRS transmission is configured by higher layers, and m=1 when the SRS transmission is triggered by the DCI format,
PL c is a path loss value measured on cell c,
α SRS,c is configured by higher layers for SRS transmission on cell c, and
f c (i) is a transmission power control adjustment state, determined from TPC command values, for SRS transmission in time instance i and on cell c.
19. The method of claim 18 , wherein:
f c ( O )=Δ P rampup,c +δ SRS,c ,
Δ P rampup,c =min[{max(0, P CMAX, c −(10 log 10 ( M SRS,c )+ P O_SRS,c ( m )+α SRS,c ·PL c ))}Δ P rampupreqsted,c ]
max{x, y} is a maximum function resulting the larger of numbers x, y,
M SRS,c is a SRS bandwidth at a time instance of a first SRS transmission on cell c,
ΔP rampuprequested,c is a total power ramp-up power from a first to a last random access preamble transmission on cell c and is configured by higher layers, and
δ SRS,c is a value of the TPC command value in the DCI format.
20. The method of claim 18 , wherein a power headroom (PH) report for SRS transmission in time instance i and on cell c is determined as PH c (i)=P CMAX,c (i)−{10 log 10 (M SRS,c (i))+P O_SRS,c (m)+α SRS,c ·PL c +f c (i)}.