Downlink Superposition Coding for Rate Fairness
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Solution Overview
Problem
Current downlink multiple access technologies, such as NOMA, face challenges in ensuring fair transmit rates and correct message detection across terminals with varying channel conditions, leading to error propagation and reduced performance due to interference and channel fading disparities.
Innovation Solution
A downlink multiple access method where a base station transmits a superposition of codewords for first and second information to terminals, with specific transmit rate conditions ensuring correct decoding, allowing flexible adjustment of rates and fairness by partitioning messages into first and second information components based on channel conditions and interference considerations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If NOMA technology is used to increase sum rate, then the transmit rate of UE under better channel condition is improved, but the transmit rate fairness for UE under worse channel condition deteriorates
Solution Approach 1:
The message for each terminal is segmented into two parts: common information (first information) and private information (second information). The common information is encoded into a first codeword that can be decoded by all terminals, while the private information is encoded into a second codeword specific to each terminal. This segmentation allows terminals with worse channel conditions to reliably decode at least the common information, improving fairness, while terminals with better conditions can decode both common and private information, maintaining high sum rate.
Solution Approach 2:
Different decoding strategies are applied to different parts of the message based on local channel conditions. The first codeword (common information) is designed with higher redundancy and lower code rate to ensure reliable decoding for all terminals regardless of channel quality. The second codeword (private information) uses higher code rates optimized for terminals with better channel conditions. This local quality differentiation resolves the contradiction between fairness and sum rate.
2Reliability
If a UE under worse channel condition is detected first in NOMA, then correct decoding can be achieved, but the transmit rate is reduced due to treating better condition UE signal as noise
Solution Approach 1:
By segmenting the message into common and private information with separate codewords, the patent eliminates the need for strict detection sequencing. Terminals can decode the first codeword (common information) regardless of channel quality, and then optionally decode the second codeword (private information) if channel conditions permit. This segmentation removes the fundamental cause of the contradiction by allowing parallel decoding of different information types.
Solution Approach 2:
The patent introduces dynamic adaptability in the decoding process. Terminals with worse channel conditions can dynamically choose to decode only the first codeword, while terminals with better conditions can dynamically decode both codewords. The base station dynamically adjusts the code rates and power allocation for the two codewords based on overall channel conditions, resolving the rigid trade-off in traditional NOMA.
3Reliability
If code rate is reduced to ensure correct message detection under interference, then reliability is improved, but transmit rate is reduced
Solution Approach 1:
The message is segmented into two codewords with different code rates optimized for their respective purposes. The first codeword (common information) uses a lower code rate to ensure reliable decoding under all channel conditions, while the second codeword (private information) uses a higher code rate to maximize transmit rate when conditions permit. This segmentation allows the system to achieve both reliability and high transmit rate simultaneously.
Solution Approach 2:
The patent changes the code rate parameter differently for the two codewords. The first codeword uses a conservative code rate that ensures decoding reliability even when treating the second codeword as noise. The second codeword uses an aggressive code rate that maximizes spectral efficiency when channel conditions are good. This parameter differentiation resolves the contradiction between reliability and transmit rate.
Data Source
AI summary
A method and devices are provided. The method includes transmitting, by a first base station, a superposition of a codeword of first information and a codeword of second information to N terminals, where the first information and the second information correspond to each terminal of the N terminals, and N is a positive integer; and a codeword of first information corresponding to the rth terminal is obtained according to a transmit rate and a transmit power for the codeword of the first information corresponding to the rth terminal, a codeword of second information corresponding to the rth terminal is obtained according to a transmit rate and a transmit power for the codeword of the second information corresponding to the rth terminal, the transmit rate for the codeword of the first information corresponding to the rth terminal meets a first condition.