Medium Access Control in LTE-U
In some implementations, a Medium Access Control (MAC) method for LTE in Unlicensed (LTE-U) includes transmitting at least one of a Clear to Send (CTS) message or a Request to Send (RTS) message on an LTE-U Secondary Cell (SCell) carrier. The at least one of the CTS message or the RTS message may include a duration field. The duration field may indicate a transmission time of a transmission on a packet data shared channel on the LTE-U SCell carrier. An evolved NodeB (eNB) transmits a scheduling grant for the transmission on the packet data shared channel on the LTE-U SCell carrier.
1. A method, comprising:
receiving, at an evolved Node B (eNB), a long term evolution (LTE) Scheduling Request (SR) transmitted from a User Equipment (UE) on a long term evolution (LTE) in Unlicensed (LTE-U) secondary cell (SCell) carrier;
in response to receiving the LTE SR at the eNB, determining, at the eNB, to grant resources on the LTE-U SCell carrier for an uplink transmission, wherein the determininq to grant resources on the LTE-U SCell carrier comprises measuring a signal level lower than a threshold;
transmitting, from the eNB, at least one of a Clear to Send (CTS) message or a Request to Send (RTS) message on the LTE-U SCell carrier, wherein the at least one of the CTS message or the RTS message includes a duration field, the duration field indicating a time period until an end of a scheduled transmission time, and wherein the at least one of the CTS message or the RTS message is addressed to a Medium Access Control (MAC) address or a pseudo MAC address associated with the evolved Node B (eNB); and
in response to transmitting the at least one of the CTS message or the RTS message, transmitting, from the eNB and on an LTE primary cell (PCell) carrier, a scheduling grant for a transmission on the LTE-U SCell carrier, wherein the LTE PCell carrier is in a licensed frequency spectrum.
2. The method of claim 1 , wherein the scheduling grant indicates a Physical Uplink Shared Channel (PUSCH) transmission, further comprising:
receiving, from the UE, a PUSCH subframe during the scheduled transmission time.
3. A method, comprising:
receiving, from an eNB and on a long term evolution (LTE) primary cell (PCell) carrier, an UL grant that indicates a permission for a PUSCH transmission on an LTE in Unlicensed (LTE-U) secondary cell (SCell) carrier during one or more subframes, wherein the LTE PCell carrier is in a licensed frequency spectrum;
determining, at a User Equipment (UE), that the LTE-U SCell carrier is available for transmission during the one or more subframes wherein the determining that the LTE-U SCell carrier is available for transmission during the one or more subframes comprises measuring a signal level lower than a threshold; and
in response to determining at the UE that the LTE-U SCell carrier is available for transmission:
transmitting, from the UE, a CTS message on the LTE-U SCell carrier independent of receiving an RTS, wherein the CTS message includes a duration field, the duration field indicating a time period until an end of the one or more subframes, and the CTS message includes a Medium Access Control (MAC) address or a pseudo MAC address associated with the UE; and
transmitting a PUSCH subframe on the LTE-U SCell carrier during the time period indicated by the duration field.
4. The method of claim 3 , wherein the UL grant is received on a Physical Downlink Control Channel (PDCCH).
5. The method of claim 3 , wherein the UL grant is a semi-static UL grant received in an RRC message.
6. The method of claim 3 , wherein LTE Transmission Time Interval (TTI) bundling is used when transmitting more than one subframes.
7. A base station, comprising:
a memory; and
one or more processors communicatively coupled with the memory and configured to:
receive a long term evolution (LTE) Scheduling Request (SR) transmitted from a User Equipment (UE) on a long term evolution (LTE) in Unlicensed (LTE-U) secondary cell (SCell) carrier;
in response to receiving the LTE SR, determine to grant resources on the LTE-U SCell carrier for an uplink transmission, wherein the determination to qrant resources on the LTE-U SCell carrier comprises measuring a signal level lower than a threshold;
transmit at least one of a Clear to Send (CTS) message or a Request to Send (RTS) message on the LTE-U SCell carrier, wherein the at least one of the CTS message or the RTS message includes a duration field, the duration field indicating a time period until an end of a scheduled transmission time, and wherein the at least one of the CTS message or the RTS message is addressed to a Medium Access Control (MAC) address or a pseudo MAC address associated with an evolved Node B (eNB); and
in response to transmitting the at least one of the CTS message or the RTS message, transmit, from the base station and on an LTE primary cell (PCell) carrier, a scheduling grant for a transmission on the LTE-U SCell carrier, wherein the LTE PCell carrier is in a licensed frequency spectrum.
8. The base station of claim 7 , wherein the scheduling grant indicates a Physical Uplink Shared Channel (PUSCH) transmission, and the one or more processors are further configured to:
receive, from the UE, a PUSCH subframe during the scheduled transmission time.
9. A user equipment (UE), comprising:
a memory; and
one or more processors communicatively coupled with the memory and configured to:
receive, from an eNB and on a long term evolution (LTE) primary cell (PCell) carrier, an UL grant that indicates a permission for a PUSCH transmission on an LTE in Unlicensed (LTE-U) secondary cell (SCell) carrier during one or more subframes, wherein the LTE PCell carrier is in a licensed frequency spectrum;
determine, at the UE, that the LTE-U SCell carrier is available for transmission during the one or more subframes, wherein the determination that the LTE-U SCell carrier is available for transmission during the one or more subframes comprises measuring a signal level lower than a threshold; and
in response to determining at the UE that the LTE-U SCell carrier is available for transmission:
transmit from the UE, a CTS message on the LTE-U SCell carrier independent of receiving an RTS, wherein the CTS message includes a duration field, the duration field indicating a time period until an end of the one or more subframes, and the CTS message includes a Medium Access Control (MAC) address or a pseudo MAC address associated with the UE; and
transmit a PUSCH subframe on the LTE-U SCell carrier during the time period indicated by the duration field.
10. The UE of claim 9 , wherein the UL grant is received on a Physical Downlink Control Channel (PDCCH).
11. The UE of claim 9 , wherein the UL grant is a semi-static UL grant received in an RRC message.
12. The UE of claim 9 , wherein LTE Transmission Time Interval (TTI) bundling is used when transmitting more than one subframes.