Multicast Retransmission via NACK Feedback in Wireless Systems
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Solution Overview
Problem
Current multicast services in wireless communication systems lack a defined scheme for the base station to determine if mobile stations have received multicast data traffic, leading to inefficient resource utilization and no mechanism for retransmitting data to failed receivers.
Innovation Solution
A method where a base station transmits multicast data traffic through a multicast channel and determines if a Negative Acknowledgement (NACK) message is received from mobile stations, retransmitting the data through a different channel only to stations that failed to receive it, allowing selective retransmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the BS transmits signals using the lowest MCS level to ensure cell boundary reception, then the signals are robust against channel conditions, but resource utilization becomes inefficient
Solution Approach 1:
The patent applies different MCS levels to different groups of MSs based on their channel conditions. MSs with good channel conditions (near the BS) receive transmissions at higher MCS levels, while MSs at the cell boundary receive at lower MCS levels. This local differentiation resolves the contradiction by optimizing resource utilization for near MSs while maintaining reliability for boundary MSs.
Solution Approach 2:
The patent segments the cell into different regions based on channel quality, creating multiple transmission groups. By dividing the MS population into segments with different reception capabilities, the system can apply appropriate MCS levels to each segment, thereby improving overall resource utilization while maintaining reliability for all segments.
2Productivity
If the BS transmits multicast data traffic using a multicast channel, then resource utilization is optimized, but there is no mechanism to determine if MSs have received the data or to retransmit to failed receivers
Solution Approach 1:
The patent introduces a feedback mechanism where MSs send NACK messages to the BS when they fail to receive multicast data traffic successfully. The BS uses this feedback information to identify which MSs need retransmission, thereby maintaining both resource efficiency and reception reliability through informed selective retransmission.
Solution Approach 2:
The patent dynamically switches transmission channels based on reception outcomes. The BS transmits initial multicast data on a multicast channel for efficiency, then dynamically switches to dedicated channels for retransmission to specific MSs that failed to receive data, adaptively optimizing both resource utilization and reliability.
3Reliability
If the BS retransmits multicast data traffic to all MSs, then all receivers can potentially receive the data, but resource utilization becomes inefficient due to unnecessary retransmissions
Solution Approach 1:
The patent extracts only the necessary retransmission information from the feedback messages. Instead of processing feedback from all MSs or retransmitting to all MSs, the system extracts only the identities of MSs that sent NACK messages and retransmits data only to those specific MSs, thereby maintaining reliability while optimizing resource utilization.
Solution Approach 2:
The patent applies partial retransmission action by sending retransmitted data only to the subset of MSs that actually need it (those that sent NACK messages), rather than performing full retransmission to all MSs. This partial action maintains reliability for failed receivers while avoiding wasteful resource consumption.
Data Source
AI summary
A method is provided for providing a multicast service by a base station (BS) in a wireless communication system. The method includes transmitting an Nth data traffic corresponding to a multicast service to a plurality of mobile stations (MSs) through a multicast channel in an Fth frame; determining whether a Negative Acknowledgement (NACK) message indicating a failure to receive the Nth data traffic is received from at least one MS in an (F+1)th frame; and when the NACK message is received, retransmitting the Nth data traffic to an MS, which transmitted the NACK message, through an other channel different from the multicast channel in an (F+2)th frame.