1-Bit Outdated Feedback Sum Rate Scaling in SISO Broadcast Channels
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Solution Overview
Problem
Wireless communication systems face challenges in achieving optimal ergodic sum-rate due to large feedback requirements and feedback delay, which degrades channel state information (CSI) accuracy, especially in multiuser diversity scenarios where instantaneous CSI is necessary for optimal scheduling.
Innovation Solution
A method utilizing one-bit outdated feedback, where users compare their fading power to a predetermined threshold and feed back a single bit, allowing the base station to randomly select users for transmission, maintaining a log log K growth rate in sum-rate capacity similar to full CSI feedback schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If full CSI feedback is used for optimal scheduling, then ergodic sum-rate capacity scales as log log K, but feedback load becomes large and feedback delay causes CSI to become outdated
Solution Approach 1:
The patent extracts only the essential information needed for scheduling decisions by using 1-bit feedback instead of full CSI. Each user feeds back only a single bit indicating whether their channel power exceeds a threshold, extracting the critical decision-making information while discarding unnecessary detail about exact channel conditions.
Solution Approach 2:
The patent applies partial action by using a simplified 1-bit feedback mechanism that provides sufficient information for scheduling without requiring complete CSI. The threshold-based approach provides just enough feedback to identify candidates for transmission, avoiding the excessive feedback burden of full CSI while maintaining acceptable scheduling performance.
2Ease of operation
If full CSI feedback is used, then optimal scheduling is achieved, but feedback delay makes the CSI outdated and degrades system sum-rate
Solution Approach 1:
The patent applies preliminary action by having users prepare and feed back their channel power information in advance relative to the scheduling decision. The 1-bit feedback is sent before the actual transmission occurs, allowing the base station to make scheduling decisions based on the most recent available information without waiting for continuous updates.
Solution Approach 2:
The patent treats feedback information as disposable and fleeting, using a simple 1-bit indicator that may become outdated quickly but is sufficient for immediate scheduling decisions. Rather than maintaining persistent, accurate CSI, the system uses inexpensive, short-lived feedback bits that are updated periodically or on-demand.
3Quantity of substance
If 1-bit feedback scheme is used to reduce feedback load, then feedback requirements are reduced, but multiuser diversity gain is significantly degraded
Solution Approach 1:
The patent changes the parameter of feedback precision from full CSI to 1-bit quantized feedback. By adjusting the feedback representation to a coarser granularity (binary threshold indication rather than continuous channel power values), the system reduces feedback load while maintaining enough information to capture user channel conditions for scheduling purposes.
Data Source
AI summary
A single-input single-output (SISO) downlink channel with K users is analyzed in the presence of Rayleigh flat fading. A limited channel state information (CSI) feedback scheme is included, where only an outdated 1-bit feedback per user is available at the base station for each fading block. A closed-form expression for the achievable ergodic sum-rate of the 1-bit feedback scheme is presented for any number of users, as a function of the fading temporal correlation coefficient, the threshold of the 1-bit CSI quantizer and the SNR. The sum-rate scales with increasing number of users as log log K, which is the same scaling law achieved by the optimal non-delayed full CSI feedback scheme.