Handling delay budget in a wireless communication system

1. A method performed by a radio network node, the method comprising:

receiving a data block to be transmitted by the radio network node towards a destination node, wherein the data block is received over an upstream wireless backhaul from an upstream radio network node and the data block is to be transmitted towards the destination node over a downstream wireless backhaul to a downstream radio network node;

receiving from the upstream node control signaling indicating an upstream delay that includes delay incurred up until when the upstream node transmitted the data block to the radio network node;

determining upstream propagation delay that includes propagation delay between the upstream node and the radio network node;

determining a self time delay that is a delay between a receive time when the data block passes a receive reference point in a receive chain of the radio network node and a scheduling time when the data block is available to be scheduled by the radio network node for transmission;

calculating a cumulative time delay as a sum of a least the upstream delay, the upstream propagation delay, and the self time delay;

calculating the remaining delay budget by subtracting the cumulative time delay from the delay budget;

determining, based on the self time delay, a remaining delay budget that indicates a remaining portion of a delay budget for the data block to reach the destination node; and

making a decision about transmission of the data block, based on the remaining delay budget.

2. The method of claim 1 , wherein making the decision for the data block comprises deciding, based on the remaining delay budget, one or more of:

whether to drop the data block;

a modulation and coding scheme with which to schedule the data block for transmission from the radio network node;

which one or more transmission resources to allocate for transmission of the data block;

which of multiple possible routes to the destination node the data block is to be transmitted over;

whether the data block is to be preempted by, or is to preempt, another data block in a transmit buffer of the radio network node; or

a priority or timeliness with which the data block is to be transmitted from the radio network node.

3. The method of claim 1 , further comprising transmitting the data block from the radio network node in accordance with the decision.

4. The method of claim 1 , wherein the decision for the data block is made further based on expected delay that includes delay expected to be incurred after transmitting the data block from the radio network node.

5. The method of claim 4 , wherein the expected delay includes one or more of:

propagation delay expected to be incurred after transmitting the data block from the radio network node; or

time duplexing delay expected to be incurred after transmitting the data block from the radio network node, wherein the time duplexing delay includes delay attributable to wireless backhaul transmissions being duplexed in time with access link transmissions.

6. The method of claim 1 , further comprising receiving control signaling indicating the upstream propagation delay.

7. A method performed by a radio network node, the method comprising:

receiving a data block to be transmitted by the radio network node towards a destination node, wherein the data block is received over an upstream wireless backhaul from an upstream radio network node and the data block is to be transmitted towards the destination node over a downstream wireless backhaul to a downstream radio network node;

receiving from the upstream node control signaling indicating an upstream delay that includes delay incurred between the reference time and a time when the upstream node transmitted the data block to the radio network node;

determining upstream propagation delay that includes propagation delay between the upstream node and the radio network node;

determining a self time delay that is a delay between a receive time when the data block passes a receive reference point in a receive chain of the radio network node and a transmit time when the data block passes a transmit reference point in a transmit chain of the radio network node;

calculating the time delay as a sum of at least the indicated upstream delay, the upstream propagation delay, and the self time delay;

determining, based on the self time delay, a time delay between a reference time and the transmit time;

transmitting the data block from the radio network node towards the destination node; and

transmitting towards the destination node control signaling that indicates the time delay.

8. The method of claim 7 , wherein the control signaling also indicates a delay budget for the data block to reach the destination node.

9. The method of claim 7 , wherein the reference time is a time from which a delay budget for the data block to reach the destination node is measured.

10. The method of claim 7 , wherein the reference time is a receive time when the data block passes a receive reference point in a receive chain of the radio network node.

11. The method of claim 7 , further comprising: receiving control signaling indicating the upstream propagation delay.

12. The method of claim 8 , wherein the data block is a packet, and wherein the delay budget is a packet delay budget (PDB).

13. The method of claim 7 , wherein the data block is a transport block that carries data from one or more packets.

14. The method of claim 7 , further comprising receiving control signaling indicating the delay budget.

15. The method of claim 7 , wherein the radio network node is an integrated access backhaul (IAB) node in a New Radio wireless communication system.

16. A radio network node configured to:

receive a data block to be transmitted by the radio network node towards a destination node, wherein the data block is received over an upstream wireless backhaul from an upstream radio network node and the data block is to be transmitted towards the destination node over a downstream wireless backhaul to a downstream radio network node;

receive from the upstream node control signaling indicating an upstream delay that includes delay incurred between the reference time and a time when the upstream node transmitted the data block to the radio network node;

determine upstream propagation delay that includes propagation delay between the upstream node and the radio network node;

determine a self time delay that is a delay between a receive time when the data block passes a receive reference point in a receive chain of the radio network node and a scheduling time when the data block is available to be scheduled by the radio network node for transmission;

calculate the time delay as a sum of at least the indicated upstream delay, the upstream propagation delay, and the self time delay;

determine, based on the self time delay, a remaining delay budget that indicates a remaining portion of a delay budget for the data block to reach the destination node; and

make a decision about transmission of the data block, based on the remaining delay budget.

17. A radio network node configured to:

receive a data block to be transmitted by the radio network node towards a destination node, wherein the data block is received over an upstream wireless backhaul from an upstream radio network node and the data block is to be transmitted towards the destination node over a downstream wireless backhaul to a downstream radio network node;

receive from the upstream node control signaling indicating an upstream delay that includes delay incurred up until when the upstream node transmitted the data block to the radio network node;

determine upstream propagation delay that includes propagation delay between the upstream node and the radio network node;

determine a self time delay that is a delay between a receive time when the data block passes a receive reference point in a receive chain of the radio network node and a transmit time when the data block passes a transmit reference point in a transmit chain of the radio network node;

calculate a cumulative time delay as a sum of a least the upstream delay, the upstream propagation delay, and the self time delay;

calculate the remaining delay budget by subtracting the cumulative time delay from the delay budget;

determine, based on the self time delay, a time delay between a reference time and the transmit time;

transmit the data block from the radio network node towards the destination node; and

transmit towards the destination node control signaling that indicates the time delay.