Relay Node Adaptive Relaying NOMA Sum Rate
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Solution Overview
Problem
Non-orthogonal multiple access (NOMA) systems face challenges in achieving reliable and efficient data transmission for 'weak' user equipment (UEs) with poor channel conditions, leading to low achievable rates and increased error probabilities, especially when paired with 'strong' UEs having better channel conditions.
Innovation Solution
A relay-based data transmission approach is employed, using a relay node (RN) to improve performance by applying superposition coding and adaptive transmission power allocation, along with successive interference cancellation (SIC) and superposition coding, to enhance the achievable rates and network reliability for both weak and strong UEs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If NOMA is used to improve sum rate and capacity region, then system throughput increases, but achievable rates for weak UEs deteriorate
Solution Approach 1:
A relay node is introduced as an intermediary between weak UEs and the base station. The relay node receives signals from weak UEs, performs SIC to separate and decode messages, and forwards decoded messages to the base station. This intermediary structure enables weak UEs to achieve reliable communication by bypassing the poor direct channel conditions through the relay path.
Solution Approach 2:
The communication path is segmented into two hops: weak UE to relay node, and relay node to base station. The relay node performs message separation by decoding individual UE messages from the superimposed NOMA signal. This segmentation allows the weak UE's message to be decoded at the relay with sufficient power allocation, then forwarded reliably to the base station without being limited by the weak direct channel.
2Reliability
If adaptive power allocation is applied to improve weak UE performance, then achievable rate for weak UE increases, but system complexity increases
Solution Approach 1:
The base station performs preliminary power allocation before NOMA transmission based on channel state information. The power allocation coefficients are predetermined to ensure that the weak UE's signal component receives sufficient power for reliable decoding at the relay node. This preliminary action simplifies the real-time processing complexity by pre-calculating optimal power distribution.
Solution Approach 2:
The system employs feedback mechanisms where channel state information is reported from UEs to the base station, and decoding results are fed back from the relay node. This feedback enables adaptive adjustment of power allocation coefficients to maintain optimal performance while managing complexity through iterative refinement rather than exhaustive optimization.
3Reliability
If relay node is introduced to improve weak UE reliability, then achievable rate for weak UE increases, but device complexity increases
Solution Approach 1:
The complex SIC processing and message decoding functions are extracted from the base station and implemented at the relay node. The relay node is equipped with dedicated decoding capabilities to separate and decode individual UE messages from the superimposed signal. This extraction distributes computational complexity to the relay, allowing the base station to focus on higher-layer processing while the relay handles physical layer signal separation.
Solution Approach 2:
The relay node performs self-service by autonomously decoding messages from weak UEs and forwarding them to the base station without requiring continuous base station intervention. The relay node maintains local buffering and decoding functionality to independently process incoming NOMA signals, reducing the processing burden on the base station and enabling asynchronous operation.
Data Source
AI summary
A relay-based data transmission approach to improve the reliability and/or the energy efficiency of uplink NOMA. A relay node (RN) is employed to improve the performance of both weak and strong UEs. In some embodiments, superposition coding and NOMA-based transmission are applied at the RN and the UEs, respectively, to improve the achievable rates of the UEs.