Transport block size determination for two stage control
Methods, systems, and devices for wireless communications are described. In some systems, two devices may communicate over a sidelink and support a mutually understood transport block (TB) size (TBS) determination procedure associated with a data channel including a control message. A first device may encode and transmit information on the data channel, including the control message and a data message. A second device may receive and decode the information on the data channel. The first device and the second device may determine a TBS for encoding and decoding the data channel, respectively, based on determining an estimated resource element (RE) overhead for the control message and determining an approximate TBS based on the estimated RE overhead.
1. A method for wireless communications at a first user equipment (UE), comprising:
transmitting, to a second UE, a first stage control message via a sidelink control channel;
encoding a data message according to a transport block size that is based at least in part on an estimated resource element overhead associated with a second stage control message, wherein the estimated resource element overhead is different from an actual resource element overhead for the second stage control message, and wherein the estimated resource element overhead is calculated based at least in part on a quantity of information bits for the second stage control message, a quantity of error correction bits for the second stage control message, and a predetermined value associated with the second stage control message; and
transmitting, to the second UE, the encoded data message and the second stage control message via a sidelink shared channel.
2. The method of claim 1 , wherein the second stage control message schedules a transmission of the encoded data message.
3. The method of claim 1 , wherein the estimated resource element overhead is defined per physical resource block or per channel.
4. The method of claim 1 , wherein the transport block size comprises a first transport block size and the method further comprises:
determining a second resource element overhead based at least in part on one or both of the actual resource element overhead for the second stage control message or an overhead value indicated in the second stage control message; and
determining a second transport block size based at least in part on the second resource element overhead.
5. The method of claim 4 , wherein determining the second transport block size further comprises:
determining a number of available resource elements for the sidelink shared channel; and
subtracting the second resource element overhead from the number of available resource elements to obtain an updated number of available resource elements for the sidelink shared channel, wherein the second transport block size is determined based at least in part on the updated number of available resource elements.
6. The method of claim 1 , wherein the first stage control message indicates the estimated resource element overhead.
7. The method of claim 1 , wherein encoding the data message further comprises:
determining a number of modulation symbols for the second stage control message based at least in part on the transport block size, wherein the data message is encoded according to the number of modulation symbols.
8. A method for wireless communications at a second user equipment (UE), comprising:
receiving, from a first UE, a first stage control message via a sidelink control channel;
receiving, from the first UE, an encoded data message and a second stage control message via a sidelink shared channel; and
decoding the encoded data message according to a transport block size that is based at least in part on an estimated resource element overhead associated with the second stage control message, wherein the estimated resource element overhead is different from an actual resource element overhead for the second stage control message, and wherein the estimated resource element overhead is calculated based at least in part on a quantity of information bits for the second stage control message, a quantity of error correction bits for the second stage control message, and a predetermined value associated with the second stage control message.
9. The method of claim 8 , wherein the encoded data message is decoded based at least in part on information decoded from the second stage control message.
10. The method of claim 8 , wherein the estimated resource element overhead is defined per physical resource block or per channel.
11. The method of claim 8 , wherein the transport block size comprises a first transport block size and the method further comprises:
determining a second resource element overhead based at least in part on one or both of the actual resource element overhead for the second stage control message or an overhead value indicated in the second stage control message; and
determining a second transport block size based at least in part on the second resource element overhead.
12. The method of claim 11 , wherein determining the second transport block size further comprises:
determining a number of available resource elements for the sidelink shared channel; and
subtracting the second resource element overhead from the number of available resource elements to obtain an updated number of available resource elements for the sidelink shared channel, wherein the second transport block size is determined based at least in part on the updated number of available resource elements.
13. The method of claim 8 , wherein the first stage control message indicates the estimated resource element overhead.
14. The method of claim 8 , wherein decoding the encoded data message further comprises:
determining a number of modulation symbols for the second stage control message based at least in part on the transport block size, wherein the encoded data message is decoded according to the number of modulation symbols.
15. A first user equipment (UE), comprising:
one or more memories storing processor-executable code; and
one or more processors coupled with the one or more memories and configured to execute the code to cause the first UE to:
transmit, to a second UE, a first stage control message via a sidelink control channel;
encode a data message according to a transport block size that is based at least in part on an estimated resource element overhead associated with a second stage control message, wherein the estimated resource element overhead is different from an actual resource element overhead for the second stage control message, and wherein the estimated resource element overhead is calculated based at least in part on a quantity of information bits for the second stage control message, a quantity of error correction bits for the second stage control message, and a predetermined value associated with the second stage control message; and
transmit, to a second UE, the encoded data message and the second stage control message via a sidelink shared channel.
16. The first UE of claim 15 , wherein the second stage control message schedules a transmission of the encoded data message.
17. The first UE of claim 15 , wherein the estimated resource element overhead is defined per physical resource block or per channel.
18. The first UE of claim 15 , wherein the first stage control message indicates the estimated resource element overhead.
19. A second user equipment (UE), comprising:
one or more memories storing processor-executable code; and
one or more processors coupled with the one or more memories and configured to execute the code to cause the second UE to:
receive, from a first UE, a first stage control message via a sidelink control channel;
receive, from the first UE, an encoded data message and a second stage control message via a sidelink shared channel; and
decode the encoded data message according to a transport block size that is based at least in part on an estimated resource element overhead associated with the second stage control message, wherein the estimated resource element overhead is different from an actual resource element overhead for the second stage control message, and wherein the estimated resource element overhead is calculated based at least in part on a quantity of information bits for the second stage control message, a quantity of error correction bits for the second stage control message, and a predetermined value associated with the second stage control message.
20. The second UE of claim 19 , wherein the encoded data message is decoded based at least in part on information decoded from the second stage control message.
21. The second UE of claim 19 , wherein the estimated resource element overhead is defined per physical resource block or per channel.
22. The second UE of claim 19 , wherein the first stage control message indicates the estimated resource element overhead.