Method and apparatus for performing random access based on delay determined by network
A method for performing random access is provided. The method is performed for random access procedure based on a lower bound of back-off time and an upper bound of back-off time. Based on the proposed method, subsequent transmission of a random access preamble is determined by control information included in a random access response. The control information explicitly or implicitly indicates an upper bound and a lower bound of a back-off time value. An exact back-off time is selected from a uniform distribution between the lower bound and the upper bound.
1. A method of performing a random access procedure in a wireless communication system using a number of orthogonal frequency division multiplexing (OFDM) symbols, the method performed by a user equipment (UE) and comprising:
transmitting a first random access preamble to a base station (BS);
receiving, in response to the first random access preamble, back-off interval information included in a random access response from the BS;
determining a lower bound of a back-off time value and an upper bound of the back-off time value based on the back-off interval information; and
transmitting a second random access preamble to the BS,
wherein the transmission of the second random access preamble is delayed according to the back-off time value which is selected between the lower bound of the back-off time value and the upper bound of the back-off time value,
wherein the lower bound of the back-off time value is non-zero,
wherein the back-off time value is randomly selected according to a uniform distribution between the lower bound of the back-off time value and the upper bound of the back-off time value,
wherein the back-off interval information is included in a media access control (MAC) protocol data unit (PDU) of the random access response, and
wherein an indication field is included in a first sub-header of a MAC header, and the indication field indicates whether the lower bound of the back-off time value is determined by a multiplication of a predetermined fraction and the back-off interval information of the back-off time value which is determined based on the upper bound of the back-off time value.
2. The method of claim 1 , wherein the first sub-header including the indication field and a back-off index value field consists of eight (8) bits, the back-off index value field indicates the upper bound of the back-off time value, the indication field consists of two (2) bits, and the back-off index value field directly following the indication field consists of three (3) bits.
3. The method of claim 1 , wherein the first sub-header including the indication field and a back-off index value field consists of eight (8) bits, the back-off index value field indicates the upper bound of the back-off time value, the indication field consists of three (3) bits, and the back-off index value field directly following the indication field consists of two (2) bits.
4. The method of claim 1 , wherein a second sub-header directly following the first sub-header is included in a MAC header of the MAC PDU.
5. The method of claim 4 , wherein the lower bound and the upper bound of the back-off time value are determined according to a first information field included in the first sub-header and a second information field included in the second sub-header.
6. A user equipment (UE) in a wireless communication system using a number of orthogonal frequency division multiplexing (OFDM) symbols, the UE comprising:
a processor configured to:
transmit a first random access preamble to a base station (BS);
receive, in response to the first random access preamble, back-off interval information included in a random access response from the BS;
determine a lower bound of a back-off time value and an upper bound of the back-off time value based on the back-off interval information; and
transmit a second random access preamble to the BS,
wherein the transmission of the second random access preamble is delayed according to the back-off time value which is selected between the lower bound of the back-off time value and the upper bound of the back-off time value,
wherein the lower bound of the back-off time value is non-zero,
wherein the back-off time value is randomly selected according to a uniform distribution between the lower bound of the back-off time value and the upper bound of the back-off time value,
wherein the back-off interval information is included in a media access control (MAC) protocol data unit (PDU) of the random access response, and
wherein an indication field is included in a first sub-header of a MAC header, and the indication field indicates whether the lower bound of the back-off time is determined by a multiplication of a predetermined fraction and the back-off interval information of the back-off time which is determined based on the upper bound of the back-off time value.
7. The user equipment of claim 6 , wherein the first sub-header including the indication field and a back-off index value field consists of eight (8) bits, the back-off index value field indicates the upper bound of the back-off time value, the indication field consists of two (2) bits, and the back-off index value field directly following the indication field consists of three (3) bits.
8. The user equipment of claim 6 , wherein the first sub-header including the indication field and a back-off index value field consists of eight (8) bits, the back-off index value field indicates the upper bound of the back-off time value, the indication field consists of three (3) bits, and the back-off index value field directly following the indication field consists of two (2) bits.
9. The user equipment of claim 6 , wherein a second sub-header directly following the first sub-header is included in a MAC header of the MAC PDU.
10. The user equipment of claim 9 , wherein the lower bound and the upper bound of the back-off time value are determined according to a first information field included in the first sub-header and a second information field included in the second sub-header.