Adaptive link adaptation for wireless communications
A wireless communication system is presented in which subframe-specific link adaptation is performed. A mobile device can transmit a signal that informs a base station whether a particular subframe was received successfully. Additionally the mobile device can calculate channel state information (CSI) for a subframe and report the CSI to a base station. The reported CSI may or may not include an indicator for informing the base station about from which type of subframe the CSI was derived. The base station can receive the signal, the CSI and/or the indicator. Based on what information the base station has received, it performs subframe-specific BLER filtering and subframe-specific link adaptation scheduling and MCS adjustments.
1. A method for performing link adaptation in a wireless communication system that includes a base station and at least one wireless device comprising:
receiving at the base station a signal from the wireless device that is indicative of and responsive to a specific subframe type that was previously transmitted from the base station to the wireless device, wherein the specific subframe type is selected from one or more special subframes, wherein the special subframes serve as switching points between DL to UL transmission;
performing subframe-type-specific block error rate (BLER) filtering based at least on the specific subframe type;
performing subframe-type-specific outer-loop link adaptation (LA) based at least on the subframe-type-specific BLER filtering; and
transmitting from the base station to the wireless device subframe-type-specific scheduling and modulation and coding scheme (MCS) information based at least on the subframe-type-specific outer-loop LA.
2. The method of claim 1 , wherein the signal includes ACK / NACK data for the specific subframe type.
3. The method of claim 1 , wherein the signal includes channel state information for the specific subframe type.
4. The method of claim 1 , wherein performing subframe-type-specific outer-loop LA includes:
adjusting a subframe-type-specific step size of a subframe-type-specific MCS differently for different types of subframes.
5. The method of claim 4 , wherein adjusting a subframe-type-specific step size includes:
for a first type of subframe, when the subframe-type-specific BLER filtering is above a subframe-type-specific BLER target, the subframe-type-specific step size is bigger than when the same condition is met for a second type of subframe, and
for the first type of subframe, when the subframe-type-specific BLER filtering is below the subframe-type-specific BLER target, the subframe-type-specific step size is smaller than when the same condition is met for the second type of subframe.
6. The method of claim 1 , wherein performing subframe-type-specific outer-loop LA includes:
receiving at the base station a channel quality signal from the wireless device;
calculating a Doppler frequency based at least on the channel quality signal; and
performing the subframe-type-specific BLER filtering and the subframe-type-specific outer-loop LA to include a Doppler-dependency.
7. The method of claim 6 , wherein performing the Doppler-dependent subframe-type-specific BLER filtering and the subframe-type-specific outer-loop LA include:
if the filtered BLER is greater than a BLER target, then the higher the Doppler frequency the bigger a step size for adjusting the MCS lower, and
if the filtered BLER is not greater than a BLER target, then the higher the Doppler frequency the smaller the step size for adjusting the MCS higher.
8. An apparatus for performing link adaptation in a wireless communication system that includes a base station and at least one wireless device comprising:
one or more processors coupled with memory, wherein the one or more processors are configured to:
receive at the base station a signal from the wireless device that is indicative of and responsive to a specific subframe type that was previously transmitted from the base station to the wireless device, wherein the specific subframe type is selected from one or more special subframes, wherein the special subframes serve as switching points between DL to UL transmission;
perform subframe-type-specific block error rate (BLER) filtering based at least on the specific subframe type;
perform subframe-type-specific outer-loop link adaptation (LA) based at least on the subframe-type-specific BLER filtering; and
transmit from the base station to the wireless device subframe-type-specific scheduling and modulation and coding scheme (MCS) information based at least on the subframe-type-specific outer-loop LA.
9. The apparatus of claim 8 , wherein the signal includes ACK / NACK data for the specific subframe type.
10. The apparatus of claim 8 , wherein the signal includes channel state information for the specific subframe type.
11. The apparatus of claim 8 , wherein performing subframe-type-specific outer-loop LA includes:
adjusting a subframe-type-specific step size of a subframe-type-specific MCS differently for different types of subframes, wherein:
for a first type of subframe, when the subframe-type-specific BLER filtering is above a subframe-type-specific BLER target, the subframe-type-specific step size is bigger than when the same condition is met for a second type of subframe, and
for the first type of subframe, when the subframe-type-specific BLER filtering is below the subframe-type-specific BLER target, the subframe-type-specific step size is smaller than when the same condition is met for the second type of subframe.
12. The apparatus of claim 8 , wherein performing subframe-type-specific outer-loop LA includes:
receiving at the base station a channel quality signal from the wireless device;
calculating a Doppler frequency based at least on the channel quality signal; and
performing the subframe-type-specific BLER filtering and the subframe-type-specific outer-loop LA to include a Doppler-dependency, wherein:
if the filtered BLER is greater than a BLER target, then the higher the Doppler frequency the bigger a step size for adjusting the MCS lower, and
if the filtered BLER is not greater than a BLER target, then the higher the Doppler frequency the smaller the step size for adjusting the MCS higher.
13. A computer-program storage apparatus for performing link adaptation in a wireless communication system that includes a base station and at least one wireless device comprising a memory having one or more software modules stored thereon, the one or more software modules being executable by one or more processors and the one or more software modules including:
code for receiving at the base station a signal from the wireless device that is indicative of and responsive to a specific subframe type that was previously transmitted from the base station to the wireless device, wherein the specific subframe type is selected from one or more special subframes, wherein the special subframes serve as switching points between DL to UL transmission;
code for performing subframe-type-specific block error rate (BLER) filtering based at least on the specific subframe type;
code for performing subframe-type-specific outer-loop link adaptation (LA) based at least on the subframe-type-specific BLER filtering; and
code for transmitting from the base station to the wireless device subframe-type-specific scheduling and modulation and coding scheme (MCS) information based at least on the subframe-type-specific outer-loop LA.
14. The apparatus of claim 13 , wherein the signal includes ACK / NACK data for the specific subframe type.
15. The apparatus of claim 13 , wherein the signal includes channel state information for the specific subframe type.
16. The apparatus of claim 13 , wherein performing subframe-type-specific outer-loop LA includes:
code for adjusting a subframe-type-specific step size of a subframe-type-specific MCS differently for different types of subframes, wherein:
for a first type of subframe, when the subframe-type-specific BLER filtering is above a subframe-type-specific BLER target, the subframe-type-specific step size is bigger than when the same condition is met for a second type of subframe, and
for the first type of subframe, when the subframe-type-specific BLER filtering is below the subframe-type-specific BLER target, the subframe-type-specific step size is smaller than when the same condition is met for the second type of subframe.
17. The apparatus of claim 13 , wherein performing subframe-type-specific outer-loop LA includes:
code for receiving at the base station a channel quality signal from the wireless device;
code for calculating a Doppler frequency based at least on the channel quality signal; and
code for performing the subframe-type-specific BLER filtering and the subframe-type-specific outer-loop LA to include a Doppler-dependency, wherein:
if the filtered BLER is greater than a BLER target, then the higher the Doppler frequency the bigger a step size for adjusting the MCS lower, and
if the filtered BLER is not greater than a BLER target, then the higher the Doppler frequency the smaller the step size for adjusting the MCS higher.
18. The method of claim 1 , wherein the one or more special subframes are distinguished by having different numbers of reference signal (RS) symbols.
19. The apparatus of claim 8 , wherein the one or more special subframes are distinguished by having different numbers of reference signal (RS) symbols.
20. The apparatus of claim 13 , wherein the one or more special subframes are distinguished by having different numbers of reference signal (RS) symbols.