Proactive Grant Scheduling for Satellite Voice Latency
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Solution Overview
Problem
The longer round-trip Ack/Nack feedback time in low earth orbit satellite systems significantly increases latency for packet-based voice calls, exceeding terrestrial network delays, which affects the quality and efficiency of voice services over satellite links.
Innovation Solution
Implementing a method that includes predicting the number of voice data packets to accumulate until a grant message is received and proactively sending scheduling grants to catch up with outstanding packets, along with periodic proactive grants timed to arrive shortly after voice traffic becomes available, to reduce latency and improve packet delivery efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If satellite link is used for voice packet transmission, then coverage area is extended to remote regions, but round-trip delay increases to 48 msec
Solution Approach 1:
The eNB sends multiple proactive grants in advance to the UE before voice packets are actually generated. These grants are sent at predetermined intervals (e.g., every 10-20 msec) so that when the UE needs to transmit voice packets, the grants are already available, eliminating the need for SR-BSR signaling and reducing latency despite the satellite link's long round-trip time.
Solution Approach 2:
The eNB implements periodic transmission of proactive grants at fixed intervals (e.g., every 10, 20, or 40 msec) regardless of whether the UE has data to send. This periodic scheduling ensures that grants are always available when needed, compensating for the 48 msec satellite round-trip delay and enabling timely voice packet transmission.
2Adaptability or versatility
If normal SR-BSR scheduling is used in satellite system, then standard LTE procedures are followed, but voice packet delay increases to 90-130 msec
Solution Approach 1:
Instead of waiting for the UE to send SR/BSR and for the eNB to respond with grants, the eNB proactively sends multiple grants in advance at predetermined intervals. This preliminary action eliminates the 16+ msec SR-BSR signaling delay and the 40 msec DRX sleep mode latency, reducing overall voice packet delay from 90-130 msec to under 50 msec while maintaining LTE compatibility.
3Reliability
If proactive grants are sent at predetermined intervals, then grant availability is improved, but signaling overhead increases
Solution Approach 1:
The eNB sends a predetermined number of proactive grants (e.g., 3-5 grants) in advance at fixed intervals, which is more than the minimum one grant needed but less than continuous grant transmission. This partial excessive action ensures sufficient grant availability to cover the 48 msec satellite round-trip delay while limiting signaling overhead by not sending grants continuously or in excessive quantities.
Data Source
AI summary
There are provided measures for enhancement of packet based voice call service over satellite link. Such measures exemplarily include receiving, from a communication endpoint, a message indicative of at least one voice data packet to be uploaded via a satellite link, determining a first number of voice data packets based on a second number of voice data packets predicted to accumulate until receipt of a first grant message at said communication endpoint, and transmitting, towards said communication endpoint, said first grant message, said first grant message being indicative of an upload scheduling grant for said first number of voice data packets.