WCDMA Base Station Interference Cancellation Control Loop Optimization
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Solution Overview
Problem
Interference cancellation in WCDMA networks introduces significant delays in control loops, affecting data throughput and capacity, particularly for High Speed Downlink Packet Access (HSDPA) signaling, due to increased processing requirements and power adjustments needed for HS-DPCCH channels.
Innovation Solution
Implementing a radio base station architecture that detects HARQ ACK/NACK messages prior to interference cancellation and CQI messages after, while adjusting transmission power to minimize delays and maintain signal quality, using a signal re-generator and cancelling unit to process signals and control data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If interference cancellation is applied to improve system capacity and throughput, then data transmission performance is improved, but delays in control loops increase
Solution Approach 1:
The HS-DPCCH channel is segmented into two separate detection processes: one for ACK/NACK messages detected before interference cancellation, and another for CQI messages detected after interference cancellation. This segmentation allows critical control signals to be extracted early without waiting for the complete interference cancellation process, thereby reducing control loop delays while still enabling interference cancellation benefits for other channels.
Solution Approach 2:
The ACK/NACK messages are detected in advance before interference cancellation is applied to the received signal. This preliminary detection ensures that critical HARQ feedback is available without delay, allowing the system to maintain fast control loops while subsequently applying interference cancellation to improve overall system capacity and throughput.
2Productivity
If interference cancellation is applied to increase system capacity, then more users can be served, but the complexity of the receiver increases
Solution Approach 1:
The receiver is segmented into multiple processing branches: one branch detects ACK/NACK messages from the original received signal before interference cancellation, while another branch performs interference cancellation and then detects CQI messages. This segmentation distributes the processing complexity across different functional blocks rather than requiring a single complex sequential process, making the overall receiver architecture more manageable and efficient.
3Measurement precision
If HS-DPCCH channel power is increased to maintain signal quality after interference cancellation, then detection accuracy is improved, but cell load increases
Solution Approach 1:
By detecting ACK/NACK messages before interference cancellation is applied, the system obtains these critical control signals when the channel power is still at its original level, ensuring accurate detection without requiring additional power boosting. This preliminary detection eliminates the need to increase HS-DPCCH power solely for ACK/NACK detection, thereby avoiding increased cell load.
Data Source
AI summary
A radio base station for use in a Wideband Code Division Multiple Access network. The radio base station comprises a receiver for receiving radio signals transmitted over the air by users, and a first processor for processing the received signals in order to recover signals for a first group of users, the “cancellers”, and a first set of control signals for a second group of users, the “cancellees”. The radio base station further comprises an interference canceller for performing interference cancellation on the received signals using the recovered signals in order to generate an interference cancelled signal, a second processor for subsequently processing the interference cancelled signal in order to recover a second set of control signals for the cancellees, and a controller for using the control signals to control the transmission of data towards said cancellees.