Target Base Station Packet Reordering During Wireless Handover
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Solution Overview
Problem
During handover in wireless communication systems, packets often arrive out of order at the target base station due to the packet-switched nature of the interface, leading to potential loss of synchronization and failure of user equipment (UE) to recover the packets.
Innovation Solution
The target base station determines whether each packet can be sent in order to the UE by comparing sequence numbers and discards packets that cannot be sent in order, or re-orders packets within a designated window, or processes out-of-order packets by incrementing the hyper-frame number and re-assigning sequence numbers to maintain synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If packets are forwarded from source base station to target base station during handover, then data transmission continuity is maintained, but packets may arrive out of order causing loss of synchronization
Solution Approach 1:
The target base station performs preliminary actions by starting a timer and buffering packets upon receiving the first out-of-order packet, before the synchronization loss actually occurs. This proactive buffering prevents the out-of-order packet from causing immediate desynchronization at the UE.
Solution Approach 2:
The target base station acts as an intermediary between the source base station and the UE. It receives out-of-order packets from the source, reorders them using the timer mechanism, and forwards them in the correct sequence to the UE, thus mediating the synchronization issue.
2Reliability
If out-of-order packets are buffered and re-ordered at target base station, then synchronization is maintained, but transmission delay increases
Solution Approach 1:
The system dynamically adjusts the buffering duration based on the timer expiration. The timer is started upon receiving the first out-of-order packet and expires after a predetermined time period. This dynamic timing mechanism allows the system to buffer only as long as necessary to maintain synchronization, rather than using a fixed extended buffer period.
Solution Approach 2:
The system changes the parameter of packet handling from immediate forwarding to timer-based delayed forwarding. By introducing a time parameter (predetermined time period), the system can control the trade-off between synchronization reliability and transmission delay, releasing buffered packets after the timer expires.
3Productivity
If packets are sent out of order to save transmission time, then transmission speed increases, but UE cannot recover packets causing data loss
Solution Approach 1:
The target base station provides self-service by automatically detecting out-of-order packets through sequence number comparison and autonomously buffering and reordering them using the timer mechanism, without requiring intervention from the UE or source base station.
Solution Approach 2:
The system uses feedback from sequence number comparison to determine whether packets are in order. When an out-of-order packet is detected (sequence number not consecutive), this feedback triggers the timer-starting and buffering action, creating a feedback loop that maintains packet recovery capability.
4Productivity
If radio resources are used to transmit out-of-order packets, then resource utilization increases, but synchronization is lost and packets must be retransmitted
Solution Approach 1:
The target base station takes preliminary anti-action by buffering out-of-order packets before they can cause synchronization loss and subsequent retransmissions. By preventing the synchronization issue in advance, the system avoids the greater waste of retransmitting packets that would have been lost anyway.
Solution Approach 2:
The system converts the potentially harmful effect of out-of-order packet arrival into a beneficial outcome. Instead of letting out-of-order packets cause synchronization loss, the timer mechanism transforms them into buffered packets that can be reordered and transmitted correctly, turning a problem into an opportunity for reliable delivery.
Data Source
AI summary
Techniques for sending packets and maintaining synchronization during handover is described. A user equipment (UE) may be handed over from a source base station to a target base station. The source base station may forward packets for the UE to the target base station, which may receive the packets out of order. In one design, the target base station may determine whether each packet can be sent in order to the UE, send the packet if it can be sent in order, and discard the packet otherwise. In another design, the target base station may re-order packets received within a re-ordering window and may send the re-ordered packets to the UE. In yet another design, the target base station may process each packet received out of order as if the packet is in order, e.g., by incrementing a hyper-frame number (HFN) or re-assigning the packet with a later sequence number.