Uplink MIMO Scheduling for HARQ Retransmissions
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Solution Overview
Problem
Current wireless communication systems, particularly in UMTS networks, face challenges in increasing the throughput and spectral efficiency for uplink transmissions, as they are limited to single stream transmissions across dual antennas, hindering the implementation of dual transport blocks in the same carrier frequency during the same transmission time interval.
Innovation Solution
The implementation of uplink MIMO transmissions that dynamically switch between single stream and dual stream modes based on HARQ feedback, allocating power between streams to efficiently transmit retransmissions and new packets, allowing for dual transport blocks to be transmitted in the same carrier frequency during the same transmission time interval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If single stream transmission is used across dual antennas, then device complexity is reduced and ease of operation is improved, but spectral efficiency and throughput are limited
Solution Approach 1:
The system dynamically switches between single stream and dual stream transmission modes based on channel conditions and HARQ feedback. The transmission rank is adjusted adaptively, allowing the system to transition from simple single stream operation to complex dual stream MIMO operation when spectral efficiency gains are beneficial, thereby resolving the contradiction between productivity improvement and device complexity increase
Solution Approach 2:
The system changes the transmission parameter (rank/number of streams) based on received signal strength indicator (RSSI) measurements and HARQ ACK/NACK feedback. When channel conditions are favorable and retransmissions are successful, the system increases the number of transmitted streams to improve spectral efficiency, while falling back to single stream when conditions deteriorate, thus managing the complexity-productivity tradeoff
2Productivity
If dual stream MIMO transmission is implemented, then spectral efficiency and throughput are enhanced, but scheduling complexity increases in the presence of HARQ retransmissions
Solution Approach 1:
The system segments the dual stream transmission into independent HARQ processes for each stream. Each stream can be acknowledged or negatively acknowledged independently, allowing the scheduler to manage retransmissions for each stream separately. This segmentation simplifies the scheduling complexity by treating each stream as an independent transmission channel with its own retransmission buffer and HARQ state
Solution Approach 2:
The system uses an intermediary switching mechanism that routes transmissions based on HARQ feedback state. When a NACK is received for a particular stream, the intermediary switches that stream to single-stream mode for retransmission while maintaining dual-stream mode for successfully received data, thereby managing scheduling complexity through intelligent routing decisions
3Reliability
If power is allocated to maintain both streams during HARQ retransmission, then transmission reliability is improved, but power efficiency deteriorates
Solution Approach 1:
Instead of maintaining full power allocation to both streams during HARQ retransmission, the system applies partial action by allocating power only to the stream that requires retransmission (the one that received NACK). The successfully received stream (ACKed) has its power reduced or eliminated during the retransmission interval, thereby improving power efficiency while maintaining transmission reliability for the failed packet
Solution Approach 2:
The system employs periodic power allocation that alternates between dual-stream power allocation during initial transmissions and single-stream power allocation during retransmissions. This periodic switching of power allocation patterns based on HARQ feedback ensures that power is efficiently utilized only when necessary for each stream, balancing reliability requirements with power efficiency
Data Source
AI summary
Methods and apparatuses are provided for uplink MIMO transmissions in a wireless communication system. In some particular aspects, scheduling of the uplink MIMO transmissions may make a determination between single stream, rank=1 transmissions and dual stream, rank=2 transmissions based on various factors. Further, when switching between single and dual stream transmissions in the presence of HARQ retransmissions of failed packets, the scheduling function may determine to transmit the HARQ retransmissions on a single stream transmission or to transmit the HARQ retransmissions on one stream while transmitting new packets on the other stream.