Uplink Performance in C-RAN via Signal Delay Path Adjustment
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Solution Overview
Problem
The limitation in Coordinated Radio Access Networks (C-RAN) is that the difference in RF signal delay paths between multiple towers and a mobile device cannot exceed the network cyclic prefix, posing practicality issues when the actual distance difference exceeds 1 km, which hampers the effective use of C-RAN features for improving uplink performance.
Innovation Solution
A mobile device identifies the signal delay paths to multiple towers, determines the difference, and if it exceeds the cyclic prefix threshold, transmits two streams of the same signal at different times to ensure both signals arrive within the cyclic prefix, allowing for interference cancellation and decoding, even if the distance difference exceeds 1 km.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the receiver uses multiple towers/sites for uplink CoMP to improve uplink performance, then the uplink performance is improved, but the difference in RF time delay between paths must not exceed the network cyclic prefix which limits the practical applicability when distance difference exceeds 1 km
Solution Approach 1:
The mobile device performs preliminary timing adjustments by transmitting multiple streams of the same signal at different times before the receiver can process them. This preliminary action ensures that even when the distance difference exceeds the cyclic prefix, the signals arrive within the acceptable time window for coordinated processing.
Solution Approach 2:
The patent segments the signal transmission into multiple streams sent at different times. By dividing the transmission into separate time slots, the system can accommodate larger distance differences while still maintaining coherence for interference cancellation and decoding at the receiver.
2Adaptability or versatility
If the network cyclic prefix is increased to accommodate larger distance differences, then the adaptability to larger distances is improved, but the receiver scanning period is extended which may reduce spectral efficiency
Solution Approach 1:
Instead of increasing the cyclic prefix, the mobile device performs preliminary timing adjustments by transmitting multiple streams at different times. This approach achieves the needed adaptability without extending the receiver scanning period, thereby maintaining spectral efficiency.
Solution Approach 2:
The system dynamically adjusts the transmission timing of multiple signal streams based on the actual distance differences to towers. This dynamic timing adjustment allows the system to adapt to varying distances without requiring a fixed, extended cyclic prefix, thus maintaining optimal spectral efficiency.
Data Source
AI summary
The instant application describes a method for identifying, at a mobile device, a first signal delay path to a first tower; identifying, at the mobile device, a second signal delay path to a second tower; determining, at the mobile device, a difference between the first signal delay path and the second signal delay path; determining, at the mobile device, whether the difference between the first signal delay path and the second signal delay path exceeds a threshold; and upon determining the difference between the first signal delay path and the second signal delay path exceeds the threshold, transmit from the mobile device two streams of a same signal to a receiver at a network. The first stream of the two streams of the same signal is transmitted at a first time, and the second stream of the two streams of the same signal is transmitted at a second time.